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Pipe and Tube Pressure Loss Tables

Thursday, May 23rd, 2013

Pressure Loss Tables

Here are some old-fashioned pressure loss tables you can use to calculate the friction loss in your mainline. This is the old-school, low tech method.

How To Use a Pipe Pressure Loss Table:

(PSI = pounds per square inch = lbs./sq.in.)

  • Select the proper table for the type of pipe, i.e.; SCH 40 PVC, SCH 40 Steel, Polyethylene, copper, etc.
  • Locate the proper column on the table for the pipe size.
  • Read down the column to the row for the flow rate (GPM) in the pipe section. You will find a PSI loss value (given as PSI/100).
  • Multiply the PSI loss value shown by the total length of the pipe section, then divide the product by 100. (PSI loss on these tables is given in PSI per 100 feet of pipe.)
  • Pressure loss values in yellow are over 5 feet per second. This is a high velocity, but considered acceptable for short distances (less than 50 feet of pipe length.)
  • Pressure losses greater than those shown on the chart can cause permanent and expensive damage to your plumbing. You must use a lower flow (GPM) in the pipe.

PSI Loss Value x Length of Pipe / 100 = PSI loss in pipe

Example: 1″ size, type SCH 40 PVC mainline. The length of the mainline pipe is 23 feet. The water flow rate through the mainline is 18 GPM. Using a pipe pressure loss table we find that the PSI loss for 1″ SCH 40 PVC at a flow rate of 18 GPM is 8.12 PSI per 100′. Therefore:   8.12 x 23 / 100 = 1.87 PSI – to simplify, you can round up the value to 2 PSI loss

(Note: PSI loss charts vary somewhat from each other. Other charts may result in an answer slightly different from the one in this example.)

PRESSURE LOSS TABLE FOR SCH 40 PVC PIPE

FLOW GPM 3/4″ 1″ 1 1/4″ 1 1/2″ 2″ 2 1/2″ 3″
1 0.13 0.04 0.01 —— —— —— ——
2 0.45 0.14 0.04 —— —— —— ——
3 0.95 0.30 0.08 —— —— —— ——
4 1.62 0.50 0.14 0.07 —— —— ——
5 2.45 0.76 0.20 0.10 —— —— ——
6 3.44 1.06 0.28 0.13 —— —— ——
7 4.57 1.42 0.38 0.18 —— —— ——
8 5.85 1.81 0.48 0.23 —— —— ——
9 7.28 2.25 0.60 0.28 0.09 —— ——
10 8.85 2.74 0.72 0.34 0.11 —— ——
11 10.56 3.26 0.86 0.41 0.12 —— ——
12 —— 3.84 1.01 0.48 0.14 —— ——
13 —— 4.45 1.17 0.56 0.17 —— ——
14 —— 5.10 1.35 0.64 0.19 —— ——
FLOW GPM 3/4″ 1″ 1 1/4″ 1 1/2″ 2″ 2 1/2″ 3″
15 —— 5.80 1.53 0.72 0.22 0.09 ——
16 —— 6.53 1.72 0.82 0.25 0.11 ——
18 —— 8.12 2.14 1.01 0.30 0.13 ——
20 —— —— 2.60 1.23 0.37 0.16 ——
22 —— —— 3.10 1.47 0.44 0.19 ——
24 —— —— 3.65 1.72 0.51 0.21 0.08
26 —— —— 4.23 2.00 0.60 0.25 0.09
28 —— —— 4.85 2.29 0.68 0.29 0.10
30 —— —— 5.51 2.60 0.78 0.33 0.12
35 —— —— —— 3.46 1.03 0.44 0.15
40 —— —— —— 4.43 1.32 0.54 0.20
45 —— —— —— —— 1.64 0.69 0.24
50 —— —— —— —— 1.99 0.84 0.30
55 —— —— —— —— 2.37 1.00 0.35
60 —— —— —— —— 2.79 1.18 0.41
FLOW GPM 3/4″ 1″ 1 1/4″ 1 1/2″ 2″ 2 1/2″ 3″
65 —— —— —— —— 3.23 1.36 0.48
70 —— —— —— —— 3.71 1.56 0.55
75 —— —— —— —— —— 1.78 0.62
80 —— —— —— —— —— 2.00 0.70
85 —— —— —— —— —— 2.24 0.78
90 —— —— —— —— —— 2.49 0.87
95 —— —— —— —— —— 2.75 0.96
100 —— —— —— —— —— 3.02 1.05
110 —— —— —— —— —— —— 1.26
120 —— —— —— —— —— —— 1.47
130 —— —— —— —— —— —— 1.71
140 —— —— —— —— —— —— 1.96
150 —— —— —— —— —— —— 2.23
160 —— —— —— —— —— —— 2.51
FLOW GPM 3/4″ 1″ 1 1/4″ 1 1/2″ 2″ 2 1/2″ 3″

Pressure losses shown in yellow reflect flow velocity between 5 and 7 feet/second. Use care utilizing flow velocities in this range. Water hammer damage can result from a combination of high pressure
and high velocity. Pressure losses shown are in PSI per 100 feet of pipe length.

PRESSURE LOSS TABLE, POLYETHYLENE PIPE

For SDR-7,  SDR-9,  SDR 11.5,  and SDR 15  (all have the same inside diameter)
Flow in GPM 3/4″ 1″ 1 1/4″ 1 1/2″ 2″
1  GPM 0.12 0.04 0.01 0.00 0.00
2  GPM 0.45 0.14 0.04 0.02 0.01
3  GPM 0.95 0.29 0.08 0.04 0.01
4  GPM 1.62 0.50 0.13 0.06 0.02
5  GPM 2.44 0.76 0.20 0.09 0.03
6  GPM 3.43 1.06 0.28 0.13 0.04
7  GPM 4.56 1.41 0.37 0.18 0.05
8  GPM 5.84 1.80 0.47 0.22 0.07
9  GPM 7.26 2.24 0.59 0.28 0.08
10  GPM 8.82 2.73 0.72 0.34 0.10
3/4″ 1″ 1 1/4″ 1 1/2″ 2″
11  GPM 10.53 3.25 0.86 0.40 0.12
12  GPM 12.37 3.82 1.01 0.48 0.14
13  GPM 13.34 4.43 1.17 0.55 0.16
14  GPM 16.45 5.08 1.34 0.63 0.19
15  GPM 18.70 5.78 1.52 0.72 0.21
16  GPM 21.07 6.51 1.71 0.81 0.24
17  GPM 23.57 7.28 1.92 0.91 0.27
18  GPM 26.21 8.10 2.13 1.01 0.30
19  GPM 28.97 8.95 2.36 1.11 0.33
20  GPM 31.85 9.84 2.59 1.22 0.36
3/4″ 1″ 1 1/4″ 1 1/2″ 2″
22  GPM 38.00 11.74 3.09 1.46 0.43
24  GPM 44.65 13.79 3.63 1.72 0.51
26  GPM 51.78 16.00 4.21 1.99 0.59
28  GPM 59.40 18.35 4.83 2.28 0.68
30  GPM 67.50 20.85 5.49 2.59 0.77
32  GPM 76.06 23.5 6.19 2.92 0.87
34  GPM 26.29 6.92 3.27 0.97
36  GPM 29.22 7.69 3.63 1.08
38  GPM 32.30 8.50 4.02 1.19
40  GPM 35.52 9.35 4.42 1.31
3/4″ 1″ 1 1/4″ 1 1/2″ 2″
42  GPM 38.88 10.24 4.83 1.43
44  GPM 42.43 11.16 5.27 1.56
46  GPM 46.01 12.12 5.72 1.70
48  GPM 49.79 13.11 6.19 1.84
50  GPM 53.70 14.14 6.68 1.98
55  GPM 16.87 7.97 2.36
60  GPM 19.82 9.36 2.77
65  GPM 22.98 10.86 3.22
70  GPM 26.36 12.45 3.69
75 GPM 29.96 14.15 4.19

Pressure losses shown in yellow reflect flow velocity between 5 and 7 feet/second. Use care utilizing flow velocities in this range. Water hammer damage can result from a combination of high pressure and high velocity. Pressure losses shown are in PSI per 100 feet of pipe length.

COPPER PIPE AND TUBE

Pressure Loss Table, Type K Copper Pipe or Tubing

Type K copper pipe has the thickest wall and highest pressure ratings of the common copper tubing types. In order of wall thickness, common copper tubing types are Type M (thinnest), Type L, and Type K (thickest). Type L is commonly used for household plumbing. If you don’t know what Type the pipe is, assume it is Type K.

Flow in GPM 1/2″ 3/4″ 1″ 1 1/4″
1  GPM 1.20 0.23 0.05 0.02
2  GPM 4.33 0.77 0.18 0.06
3  GPM 9.17 1.65 0.38 0.13
4  GPM 15.67 2.78 0.68 0.22
5  GPM 4.21 1.02 0.33
6  GPM 5.90 1.44 0.46
7  GPM 7.84 1.90 0.61
8  GPM 10.03 2.46 0.78
9  GPM 12.48 3.03 0.97
10  GPM 15.15 3.68 1.18
11  GPM 4.40 1.41
12  GPM 5.17 1.66
13  GPM 6.00 1.93
14  GPM 6.88 2.21
15  GPM 7.81 2.51
16  GPM 8.42 2.83
17  GPM 9.42 3.16
18  GPM 3.52
19  GPM 3.89
20  GPM 4.28
22  GPM 5.10
24  GPM 5.99
26 GPM 6.95

Pressure losses shown in yellow reflect flow velocity between 5 and 7 feet/second. Use care utilizing flow velocities in this range. Water hammer damage can result from a combination of high pressure and high velocity. Pressure losses shown are in PSI per 100 feet of pipe length.

PRESSURE LOSS TABLE, TYPE L COPPER PIPE OR TUBING

Type L copper tube is the type most commonly used for household plumbing. In order of wall thickness, common copper tubing types are Type M (thinnest), Type L, and Type K (thickest). If you don’t know what Type the pipe is, assume it is Type K.
Flow in GPM 1/2″ 3/4″ 1″ 1 1/4″
1  GPM 0.95 0.16 0.04 0.02
2  GPM 3.44 0.57 0.15 0.06
3  GPM 7.29 1.20 0.33 0.12
4  GPM 12.41 2.05 0.56 0.20
5  GPM 18.77 3.09 0.85 0.30
6  GPM 4.34 1.18 0.43
7  GPM 5.77 1.58 0.57
8  GPM 7.39 2.02 0.72
9  GPM 9.19 2.51 0.90
10  GPM 11.17 3.05 1.10
11  GPM 3.64 1.31
12  GPM 4.28 1.54
13  GPM 4.96 1.78
14  GPM 5.69 2.04
15  GPM 6.46 2.32
16  GPM 7.28 2.62
17  GPM 8.15 2.93
18  GPM 9.06 3.25
19  GPM 3.60
20  GPM 3.96
22  GPM 4.72
24  GPM 5.55
26 GPM 6.43

Pressure losses shown in yellow reflect flow velocity between 5 and 7 feet/second. Use care utilizing flow velocities in this range. Water hammer damage can result from a combination of high pressure and high velocity. Pressure losses shown are in PSI per 100 feet of pipe length.

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Rainbird Anti-Siphon Valve Leaks, Won’t Fully Close

Monday, May 20th, 2013

Rainbird’s residential series valves have a small internal filter which can become clogged with grit, even with reasonably clean water supplies.  When this filter becomes clogged the valve will no longer fully close when operated automatically.  Here’s how to clean the filters.

(more…)

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How to Remove PVC Cement From Your Hands

Thursday, May 16th, 2013

There are several hand cleaner products made for removing PVC cement/glue from your hands.  Most combine a solvent with an abrasive grit and a hand moistening lotion into a single product.  The ones I have used work very well.  They are typically sold at irrigation supply stores.  For some reason I have never seen them sold at the home improvement stores where homeowners tend to buy irrigation supplies.

For the “weekend warrior” who just needs to get the cement/glue off infrequently, acetone will remove it quickly.  Be sure to immediately wash any skin you apply acetone to thoroughly with soap and water after getting the glue off.  Do not leave acetone on your skin!

caution  Repeated skin exposure to acetone may cause serious health issues, so it should not be used by pros who need to remove glue from their hands often.  Be sure to read and follow all precautions on the acetone can.

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How to Remove Paint from PVC Pipe

Thursday, May 16th, 2013

PVC pipe that is exposed to sunlight should be painted to prevent sunlight from destroying the plastic.  But what if you need to repair the PVC pipe later?  You can’t glue pipe that has paint on it.  In fact, you need to remove all of that paint from the area to be glued, even a small amount may cause leaks in the glued joint.

Using a small brush “paint” acetone onto the area of pipe where you want to remove the paint.  (PVC primer will also work as a replacement for acetone, but the purple color makes it hard to make sure all the paint is off.)  Allow the acetone to soak in for a few seconds then scrape off the paint with a knife blade or other metal edged tool like a putty knife.  If some of the paint doesn’t easily come off re-coat the paint with more acetone.  Once most of the paint is off, apply another coat of acetone.  This time use a paper towel to wipe off the remaining paint.  You may need to wipe down the PVC pipe 2-3 times with fresh paper towels to get a nice clean white surface.  Now you can glue your joint using the normal method for gluing PVC pipe as described on the cement/glue can.  The acetone will leave the pipe surface feeling sticky, that’s OK, you don’t need to wait for it to dry before you glue the joint.  The primary ingredient in the purple PVC primer that is used to clean and prepare PVC pipe for gluing is acetone.

caution  Use caution when working with acetone.  Read and follow the warnings on the can.  Repeated skin exposure to acetone may be harmful to your health.

 

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Should the Pipe be the Same Size as the Sprinkler Inlet?

Wednesday, May 1st, 2013

Q.  I was wondering if the size of the water pipe makes a difference in the performance of the sprinkler head — 3/4 inch or 1 inch ??    I have the option of supplying my sprinklers with either a 3/4 inch or a 1 inch water supply line.

A. Yes, the pipe size does make a difference.  The industry “rule of thumb” is that the pipe should never be smaller than the sprinkler inlet, although there is no technical reason for that.  There could be situations where a smaller pipe will work just fine.  But they are not common.  The truth is that in most cases the appropriate pipe size is one to two pipe sizes larger than the inlet.  I’ve seen some sprinkler systems where the pipe needed to be several times larger than the sprinkler inlet, although those situation are very rare.  To confuse things more, some sprinklers have two different size inlets.  In the case of two inlet sizes I would typically use a pipe the same size or LARGER than the largest inlet.

The Right Way:

Sprinklers require water pressure to operate.  Every sprinkler has an optimum water pressure that makes it work best.  Water pressure is lost as the water moves through pipes, valves, fittings etc.  This is called “friction loss” in the irrigation industry (although the pressure loss comes from more than just friction.)   So the size of pipe you use to supply the sprinkler head with water must not only supply the right amount of water, it must also not reduce the pressure below the amount needed to operate the sprinkler efficiently.
Unfortunately there is not a standard “use this size pipe with this size/brand/model sprinkler head” solution.  The right pipe size may vary with every irrigation system.  Figuring out what size to use is not an easy task.  My free tutorial on Sprinkler System Design takes you through the process step-by-step.  While it seems simple enough to stick a sprinkler on the end of a pipe, in truth, irrigation systems require a considerable amount of careful design calculations to work correctly and efficiently.  (That “efficient” part is really important, a sprinkler system designed wrong can easily use 2-3 times more water than one designed right.)  The first couple of pages of the tutorial give a more detailed explanation of what is involved in irrigation design and answer a lot of the “why?” questions that people have at this stage.  Then the tutorial will take you step-by-step through how to figure out what size pipe it should be.  If you are installing a new irrigation system, then the tutorial is the way to go.  Unfortunately once you have the system installed is not the best time to discover you should have had a better design up front!  I’m always telling people that delaying the process for 2-3 weeks to struggle through doing a good design may seem like too much work.  But when you have it installed and you realize you wasted hundreds, maybe thousands of dollars on a system that doesn’t work…  wow!   I get lots of email from people who are not happy when they realize that it often costs more to fix a poorly designed sprinkler system than they paid for it!!!  Please don’t be another one of them.  Better to spend another few weeks watering by hand and take the time to create a good design.

Method for Calculating the Size for a Pipe:

If you want to skip straight to the step of determining a sprinkler system pipe size, you can look at  How to Calculate a Lateral Pipe Size.  This page has a spreadsheet and instructions you can use that will figure out the pressure loss in a length of pipe.  You are jumping to the end of a tutorial when you do this, so you may need to go back a few pages in the tutorial to get the background information you need.  You are going to need to know the type of pipe you are using so you can get the right spreadsheet.  You will also need to find out the GPM of your sprinkler head (see the manufacturer’s website for this) and how much pressure loss (“PSI Loss” column on the spreadsheet) is allowable in your pipe.  Finding this PSI Loss value is going to be the hard part since you are jumping to the end of process.  You will probably need to make an educated guess (assuming you don’t want to just go back to the beginning of the tutorial and do it the right way.)  If you need to guess at the PSI Loss value, I would suggest a maximum value of 0.5 PSI Loss.  That’s 1/2 of a PSI in each pipe section.  Remember that is an educated guess and there is no way I guarantee it will work!  You are taking a risk to shortcut the process.

Risky but Expensive Simple Solution that Usually Works:

If you really don’t want to deal with looking stuff up and doing calculations, one solid rule in irrigation design is that a pipe can never be “too large”.  (For a detailed discussion of why, see why a smaller pipe will not increase pressure.)  So if you are in doubt, you always use a larger pipe size.   You could hook up a 1/2″ sprinkler to a 10″ pipe and the sprinkler would work just fine.  The 10″ pipe would not be kind to your budget, however.

You can use this “larger is never worse” rule to your advantage.  If you really don’t want to deal with calculating the right size, one way to solve the problem is to use a ridiculously over-size pipe.  Ie; if the sprinkler has a 1″ inlet use a 1.5″ pipe  and you will probably be safe.  Of course this may well be overkill as well, but if you don’t want to do all the calculations, then you pay the price of a larger pipe and go with over-kill.  Remember you do this solely at your own risk!

 

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Watering a very narrow 30″ wide lawn strip

Saturday, March 9th, 2013

Q. I need to water a 2.5′ wide by 21′ long grass strip in the middle of my driveway. What is a good method for this narrow an area? My home is located in Southern California.

A. Irrigating lawn in areas less than 4′ wide is very hard and results in a lot of wasted water. It is illegal to install a grass area less than 4 to 6 feet wide in many cities, especially in California and other western States, including ALL of Arizona and most of Nevada (the minimum width varies from town to town.) Enforcement is typically limited to new development, but if you get a permit from the city for the work you may get nailed on this issue.

Using Sprinklers

If you do use sprinklers there is going to be a lot of water waste from over-spray onto the concrete. It will likely run down your driveway and when (not if) the next big drought cycle hits and they start with the “water police” thing you will likely have to stop watering your strip or risk a “fix it” ticket.

If you do use sprinklers you will reduce the radius of each sprinkler to your 30″ width and then you reduce the distance between sprinklers by a similar %. I recommend using side-strip sprays rather than the center-strip type as you will have a lot less over-spray on to the concrete with them. The side strip side are installed down both sides of the strip. Center spray types are installed down the center of the strip. Using center strips type will require half as many sprinklers, but the cost of this initial savings is lousy performance, poor efficiency, and lots of wasted water (it is common when using center strips that 50% or more of the water applied will be wasted.) So let’s say you decide to use 4′ x 12′ pattern side-strip spray nozzles in 4″ pop-up bodies. Since your area is only 30″ wide you would need to reduce the spray width from 48″ to 30″. That would be 62% of 48″ ( 30″ / 48″ = 0.625). So you would also need to reduce the 12′ distance down to 62% also, which is 7.5′ (12′ x 0.62 = 7.44′). So in your 30″ x 21′ area you would space the heads 7′ apart on both sides. After installing the system you would reduce the radius of each head as best you can using the radius reduction screw. It is unlikely you will be able to avoid some over-spray onto the walk as noted earlier. If you decide to use center strip nozzles the procedure and spacing would be the same, there would only be one row of heads, however, installed right down the center of the strip. With center strips you will have to allow more water to overspray onto the cement driveway, if you don’t you will get dry yellow edges. If you want a better explanation of why see this page on sprinkler spacing.

Using Subsurface Drip

Your other option is to use subsurface drip. This is what I would do. In this case I would use three drip tubes running the length of the grass strip. Place one down the middle and the other two should be 4″ in from the edge of the driveway concrete on each side. Use dripperline with 1 gph emitters spaced 12″ apart. Netafim, Rainbird, and Toro all make subsurface dripperline. Make sure the dripperline is a model that the manufacturer claims in their literature is for subsurface installation. Subsurface dripperline uses a different type of emitter designed to keep out dirt and roots. Read my drip guidelines for info on filters and pressure regulators you will need. The salesperson at the irrigation store may tell you that you only need two tubes, which normally would be correct, they typically are spaced 18″ apart, not 12″. There are a couple of reasons I am suggesting 3 tubes rather than 2. First is to get the total flow up because the area is so small and most automatic solenoid valves don’t work very good at really low flows. Another reason is that the concrete on both sides absorbs and radiates a lot of heat, and this is going to make your little lawn strip dry out fast. That’s also why I suggest the dripperlines at the edges of the area be 4″ from the concrete, otherwise the lawn edges right up against the concrete tend to dry up and turn yellow. You are going to need to be careful in selecting your valve, the dripperlines in your 21′ long area are so short that the total flow using 1gph emitters is only going to be 1 GPM; (3 tubes, 20′ long with 1gph emitters every foot. So 20′ x 3 tubes = 60′ of tube. 60′ of tube x 1gph/ft = 60 gph. 1 gpm = 60 gph.) A lot of automatic valves will not work at flows that low. Make sure the rated flow range in the literature for the valve goes that low.

To install your drip system remove the top 5″ of soil from your planter. Now till the soil another 4″ deep. Tamp down the soil to lightly compact it and get rid of air voids. A 8″x8″ hand tamper tool is good for this, you can buy one at any decent garden shop or home improvement store. Now place your dripperline tubes down on top of the soil and use steel erosion control staples to hold the tubes in place. Put a stake every 36″. You can buy the stakes at the irrigation store, they all carry them. The metal stakes work much better than the plastic ones made for drip tube. The stakes are very important, they will rust into the soil and hold the tubes in place. Without them the empty tubes will float to the surface during the winter when the soil becomes saturated during rain storms.

Now put down the final 3″ of soil over the top of the tubes, tamp it down and install your sod (which should be about 1″ thick and should bring the sod surface up even with the top of the concrete.) You will need to lightly hand water the sod for a week or two to keep it cool and moist. It needs time to grow roots down to where the subsurface water from the dripperline is. Slowly back off the hand watering after a couple of weeks. Watch the sod’s color to see how well it is rooting in. If the sod is still in need of top-watering by hand it will turn a dull “flat green” color. When you first install it, the sod will be that dull flat green color because it is stressed from the cutting,shipping and installation. It’s easier to see the color if you stand back and look at it from a distance. Right after you install the sod take a minute to look carefully at it and notice the stressed dull color. Then also note the brighter green color it changes to after you water it the first time it. Now you know what stressed sod looks like and what to look for over the next few weeks. If it is hot or the warm winds are blowing when you install the sod you may need to hand water it more often. Usually watering a couple of times a day is sufficient until the sod is established.

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Creating Water-Proof Irrigation Wire Connections

Tuesday, January 8th, 2013

Water-proofing your irrigation system’s wire splices is one of the most critical tasks in any installation or repair that involves wire splices.  The splices need to be completely water-proof.  Taping them up with electrical tape will NOT work for this!  The electrical tape will allow water into the splice as it becomes old, brittle, and the adhesive on it dries out.  If you don’t water-proof your splices it WILL cause your valve to fail!  Don’t save a buck on a wire splice and ruin a $20 valve! I’ll explain in detail why waterproofing is so important later, first let’s get down to the details on how to make a good waterproof wire splice.

General Things That you Need to Know about all splices!

Caution:  The methods described below are intended for low-voltage wires of 24VAC or less, such as those used in typical irrigation system controls.  They should not be used for higher voltages.

DO NOT BURY SPLICES directly in the ground.  Put a box around them to protect them and to help you find the later.  A small plastic utility box works fine.  Glue a large steel washer to the bottom of the box lid using epoxy.  This will allow you to find the box with a metal detector if grass grows over it.  Splices are the most likely place a wire will short out in the future, so a box makes the splices easier to find and repair.

2-wire irrigation systems:  These are a newer type of system that uses only 2-wires to control all the valves.  The irrigation controller sends a signal through the valves to a decoder at each valve.  The decoder then allows power to the valve solenoid only when told to by the controller.  These types of systems depend on electrical “signals” sent from the controller through the wire to the decoder.  Any voltage leak at a splice can severely impact the signal and cause the system to malfunction.  For this reason splices for 2-wire systems need to be made much more carefully.  Many of the 2-wire manufacturers have specific splice methods they require be used in order to protect your warranty.  Be sure to use these if required!

Not sure if your system is 2-wire?  As i write this in 2013, 2-wire systems are seldom used on residential systems, but they are also gaining popularity and will probably start showing up soon, first on larger systems.  The controller case normally will be clearly labeled as “2-wire”.  A 2-wire system will also have a “decoder unit” installed on the wires at each valve.  Standard irrigation control systems have two wires going to each valve.  But in a standard system one of the wires goes to a single valve and only that valve.  So if you have 4 valves there will be 5 wires (1 common shared by all the valves, + 1 individual wire to each of 4 valves = 5 wires.)  On a 2-wire system with 54 valves there would be only 2 wires and each valve would have a decoder unit installed on it.  The presence of a decoder to be installed at each valve is the best way to tell if it is 2-wire.

The best way to make the splice is to use special water-proof splice connectors that you can buy at any hardware store.  These are made for sealing outdoor wire connections and work very well.  There are many different styles and types available.

Water-Proof Twist On Connectors – “Nut” Style or “Wing” Style

Most of the connectors currently used by pros consist of an twist on type wire connector that is filled with a water sealing grease.  Sometimes these are called water-proof “nut” or “wing type” connectors.   These are inexpensive and very simple to use. Here are general instructions for use since a lot of these inexpensive connectors are sold without instructions.  If instructions came with the connectors please use those instructions, as they are intended for the actual connectors you bought!

  1. For every 3 connections you need buy 5 connectors.  Why?   Because you will probably make several bad splices, and you will have to remove those connectors and toss them in the trash.  They can’t be reused because when you remove them a lot of the sealer comes out with the wire.   (If you look close most connectors actually say “do not reuse” or similar language on them.)
  2. Start by stripping the insulation off the end of the wires to expose the bare metal wire.  Do not strip off too much insulation, the exposed  bare wire should be about 1/2 the length of the connector body.   You can splice 3 wires together easily using a single connector.  It’s OK to put 4 or 5 wires in a connector, but be warned that it gets a lot more difficult getting the wires to stay in the connector when you use more than 3 wires.
  3. Place the bare ends in one hand and using your other hand, align the wires side-by-side, so the ends of the bare sections are lined up together.  Those ends need to all go into the connector together at the same time, so hold the wires tight and don’t let them slip out of position.  Do not try to insert an additional wire into a wire connector that already has wires spliced together in it.  You need to remove all the wires and redo the splice to add more wires.
  4. Push the connector down over the bare ends of the wire.  Twist the connector clockwise to screw it on.  Hold the wires firmly in position as you twist the connector over them.  The connector has threads, a spring, or barbs inside it that will grab the wires and cinch them together tightly as you twist it on.  Stop twisting when you feel substantial resistance.
  5. Hold the connector in one hand and tug on each of the wires with the other to make sure the wires are secure and will not pull out.  If a wire feels loose or pulls out, disassemble the entire splice and try again.   Use a new connector as some of the sealer will probably be lost when you remove the connector, and it needs all the sealer for a good seal.   If the wires still pull out after another try you are probably using the wrong size connector.
  6. Finally make a visual inspection of the splice.  The insulation on the wire should be fully inserted into the sealer gel or grease.  No bare wire should be visible.  That’s all there is to using twist on wire connectors, they are very quick and easy.

The connector size is important when using twist on connectors!   Be sure you buy and use the correct size connector for the wire sizes you are splicing. The package will list the various wire size combinations that the connector works on.  The connector colors indicate the connector’s size and most are standardized.  Here are some general guidelines.  Warning: There are some brands that do not follow these color guidelines so double check the instructions on the package!

Connectors for #18 wire.  Most residential irrigation systems use #18 size wire, this is the size of most of the multi-wire underground irrigation cables sold in hardware stores.   Unfortunately the colors for these connectors are not standardized.  Most I have seen are dark blue or black.  Make sure it says it will connect 2- #18 wires.

Connectors for #14 & #12 wire.  Larger irrigation systems and commercial irrigation often use individual #14 wires.  Sometimes #12 will be used for irrigation systems with very long distances between the controller and the valve.  Most often these connectors are yellow.   Note: Most of the yellow connectors I have seen will NOT connect a single #14 wire to a typical valve solenoid wire.  For this you will probably need the smaller #18 wire connectors above.

Twist-On Waterproof Wire Connectors. Wing Style on left (blue), Nut Style on Right (black).

 

 

 

Mechanical Clip Style Non-Stripping Connectors

Clip style is a catch-all name I use for the various types of connectors that use a mechanical clamping system to grab and bite into the wire.  Typically with this type of connector you push the wire into a round slot on the connector, and then squeeze some type of clamp that bites into the wire to hold it in place.  Some require pliers to squeeze the clamp into the wires.   The most popular of these types of connectors for irrigation use is the Blazing Snaploc BVS Series wire connectors and the 3M Scotchlok 314 series connectors.  These connectors are more expensive but make a very secure connection almost always on the first attempt.  You won’t need to buy nearly as many extras for bad splices.

 

Container Type Connectors

These connectors are a two piece, two step system.  You connect the wires together using either a standard twist type wire connector, a crimp sleeve, or even soldering the wires together.  Then you shove the splice into a container filled with a water-proofing grease or jell and snap a retainer lid closed to hold the splice inside the container.

A variation on this type of connector is the original waterproofing method used back when I started in the business.   You mixed a 2-part epoxy resin in a small plastic envelope and then shoved the splice into the envelope so it was covered in resin.  The resin was allowed to harden creating a solid water-proof seal.  Unfortunately the resin was a carcinogen.   I don’t think these are sold any longer.

 

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Pump Cycles On Briefly When Irrigation is Off

Thursday, November 1st, 2012

Q.  My irrigation pump runs fine when the system is operating, but after it turns off it cycles on for 5 seconds every 10 minutes or so.

A.  If you are using a pressure switch and pressure tank to turn the pump on and off my first guess would be that you have a water leak in your irrigation system.  The water leaks out, which cause the water pressure to drop, then the pump kicks on and recharges the pressure.  Then the pump shuts off again.  That would cause exactly this symptom.

Knowing the problem is the easy part.  Finding the leak, that could be harder to do.  It could be a zone valve that isn’t turning off all the way or it could be a leaky pipe.  You can narrow the search area a little,  the leak will be someplace in the pressurized part of the system, that is, between the pump and the zone control valves.  Start by looking for obvious dripping, then look for someplace that seems wetter than it should.  If it is a leaky zone valve then the water will be leaking through the valve into the sprinkler zone pipes and will dribble out at the lowest sprinkler head.  So look at the sprinkler heads.  There will be a small “swampy” area around the lowest sprinkler head that is controlled by that valve.

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How to Find Buried Pipes, Wires, and Valves

Wednesday, September 19th, 2012

If you have an underground sprinkler system (drip systems too), somewhere out in your yard there are buried pipes, wires, and maybe even valves.  But where are they?  Sometimes they are above ground, so all you need to do is look around a bit.  If not, then they aren’t visible because they are buried.  (Big sigh.)  You have perhaps the toughest problem there is in the irrigation repair business.  There are no easy and inexpensive ways to find a valve (or pipe, or wire, the methods for finding them are basically the same.)   But I can offer some tips to help.

Before we get going on how to find a valve let me make a couple of comments about what to do when you do find it.

Digging it Up

Once you find the valve you will probably need to dig it up.  If you’re lucky it will be in a valve box and the box will not have been filled with dirt by some gopher.  If there is a box be prepared to find critters inside the box when you open it!  Use a shovel to pry the lid off from a safer distance.  If the valve is not in a box, you need to be really careful when digging.  Electric solenoid valves have wires attached to them that are very easy to cut with a shovel and very hard to repair once cut.  Also if you hit the solenoid with a shovel you will probably break it and possibly break the valve as well.  Even the valve body is easily cut as well as the pipe.  So go slow and easy.  Dig around the valve using a hand trowel.  Better yet (I know this makes a mess!) you can use the stream from a garden hose with a patio cleaning nozzle on it to dig and use the water blast to loosen the dirt around the valve and wires.  A plastic drink cup (ie; a McDonald’s cup) works good scoop out the muddy water and is unlikely to damage the valve.

If you cut or even nick the insulation off a wire, splice it back together using a water-proof splice kit made for underground wire splices.  It is really important that the bare metal not be exposed to soil or water.  Electrical tape will NOT work as a splice water-proofer!  Use a special water-proof splice connector you can buy at any hardware store for ALL your irrigation wire splices and connections.   Even ones above ground!  If any water leaks into the splice it will corrode the wire.  Even if the wire is not corroded through the corrosion can block enough electric current to make the valve not open.  If the wire breaks or corrodes it will be a major pain to find where the problem area in the wire is.  You will probably have to replace all of the wire.  You do not want to have to do that!  Water-proof those splices.  Got it?

 

Be Prepared to Replace the Valve

There is a pretty good chance that if you can’t find the valve you will need to replace or repair it when you do.  That’s just how the odds stack up.  If the system is in such bad shape that you can’t find the valves, usually the valves are in bad shape also.  At the least, the solenoid on the valve is probably dead or close to it.  So prepare yourself now for that expense and effort.

 

Box It!

Once you find your valve, put a valve box around it!  Irrigation valves are often marketed as “direct-burial”, but as you now know (or will soon discover), finding one that has been buried directly in the dirt is very difficult.  It doesn’t need to be a big fancy box, they make nice little inexpensive ones that work fine.  Even a used 1 gallon plastic plant container flipped upside down will make a decent temporary valve box until you can afford something better.  It just isn’t a good idea to bury a solenoid valve directly in dirt.  Besides the problem of finding it later, burying it can also make it fail faster.  Plus you are a lot more likely to damage a valve buried in dirt when you dig it up for repairs.  And all valves are going to need to be repaired someday!  So put those underground valves in boxes, and while you’re at it, put 4″ of gravel under the box!  The gravel keeps gophers from digging into the box from underneath and filling the box with dirt.  You might also want to measure and write down where the box is located as measured from a couple of fixed locations, such as a house wall or fence.  That helps you find it if grass grows over the top of it… if you don’t lose the measurements!

Ok, time to get to work.

 

How to Find a Buried Valve

1. Start by trying to figure out what the most likely place is where the valve would be installed.  To do this you need to try to “get inside the head” of whomever originally installed the system.   This helps cut down the “search area”. Do you know where other valves are in the yard?  Are they each inside the area they water? If so, the others are probably inside the area they water also.  Are they grouped together?  Then the others may be nearby.  Maybe there is a pattern to the placement of the valves, all on one side of the yard perhaps, or all in a row?   If you don’t know where any of the valves are, you still know a pipe takes water to them.  Find where that pipe connects to your water supply.  Now try to figure out which way the pipe goes from there.  Sometimes if you look real close you can see a slight indentation in the soil where the trench for the pipe was dug.  Another tip, the grass is often just slightly greener where the trench was dug.  For lawns, if you mow the grass short and look across the surface you can often see slight “troughs” where the trenches were dug and the soil has settled.

If you have the original plans for the sprinkler system they may help you find the valves, pipes and wire locations.  If this is a commercial irrigation system the local building inspector or planning department may have a copy of the plans.  However, even if you do have the plans, chances are the valves aren’t located where the plans show them.  So I wouldn’t waste too much time looking for plans.  In 35 years of practice and thousands of irrigation systems, I seldom saw the contractors install the valves exactly where they were shown on my plans.  Even when I required my contractors to label and dimension the valve locations, I often discovered they just made up the dimensions!!   At best a plan might give you a hint as to where to look.

2. If the valve you are looking for is an electric valve that actually still works, try turning the valve on and see if you can hear the solenoid buzzing or water whizzing through the valve. Try using a mechanic’s stethoscope placed on the ground to listen.  Or cut the bottom out of a paper cup, place it upside down on the ground, and put your ear over the top.  Do this late at night or in early morning to reduce background noise and make it easier to hear. Note; if the neighbors see you they will think you’ve lost your mind!

3. Try a metal detector if you own or can borrow one.  I’ve honestly never tried this, but some people tell me it works, and it seems logical.  Most valves have at least a little metal in them, although the cheapest ones have very little.  The solenoid on an automatic valve has a bit of metal in it also.  If you have, or can borrow, a metal detector you may be able to locate the valve or the wires with it.   If the valve or wire are buried deep, a low cost metal detector will probably not find them. In my opinion the chances of success using a metal detector probably are not good enough to make it worth the expense of buying one. But if you have one or can borrow one, why not try it? I’d love to get your feedback on use of a metal detector if you try it!

4. Use a valve chatterer. This won’t work if the wires to the valve are cut or broken. So if you’re trying to find an automatic valve that won’t open, a chatterer is not likely going to help.  A chatterer is a electrical device you put on the valve wire that makes the valve rapidly turn on and off.  The result is that some brands of solenoid make a loud clicking or chattering sound that will give away it’s location.  Unfortunately some valve brands don’t make much noise at all. And the deeper the valve is buried, the harder it will be to hear it chatter. Most irrigation pro’s have valve testers that include a chatter function along with other testing tools.  These are handy tool for diagnosing valve electrical problems, but tend to be priced beyond what is justifiable for a homeowner to buy.  (See ads for typical chattering devices at right. Also see my review of the Armada Pro48, which is the one I use.)  To use a chatterer you disconnect the valve’s wires from the controller/timer and hook them up to the chatterer device. Turn the chatterer on and the valve should rapidly open and close and create a noise.  Just like with listening for the water running through the pipe, you will have to go out in the yard and listen for the chattering, and it will help if it is during a quiet time of the day.

Make your own chatterer.  All you will need is three 9-volt batteries and a friend with dexterous fingers.  Someone who texts a lot on their phone is perfect!  Start by making a valve actuator. Here’s how to make one out of three 9-volt batteries.  To chatter the valve simply attach one of the valve wires to one terminal of your home-made actuator and tap the other wire against the other terminal of the actuator.  Tap the wire at one second intervals. It doesn’t matter which wire goes to which terminal. The valve should turn on and off with each tap and make a clicking sound.  I don’t recommend tapping the wires on the controller/timer terminals to chatter the valves. If you slip up while trying to tap the wires against the terminals and short circuit the wires you can damage the controller/timer.  Destroying an expensive controller will ruin your day!

5. Water Dowsing,  aka; water witching.  This is a method of finding a water filled pipe by walking slowly while holding a branched stick or a couple of bent wires in your hands.  I won’t try to explain how to do it, you can look it up if you want to try it.  I’ve never witnessed it done successfully firsthand.  But I have met several people over the years who have either seen it done successfully or done it themselves successfully.  This includes people I trust, so I’m not in doubt of their claims.  Now did they see or do what they thought they did?  The answer to that thorny question I will leave to you to decide!

OK, the science behind dowsing is very shaky- at best.  Most explanations I have heard are that those with the talent are able to read subtle signs on the ground surface that indicate the location of water or the pipe.  They then subconsciously transfer that information to the movements of the sticks, like a Ouija Game.  Everyone I know who claims dowsing works or that they have the ability to do it IS an expert who has worked in the industry many years.  I can tell you that with 35 years of experience I can often look at an irrigated area and tell you where the pipes are with reasonable accuracy.  No sticks needed.  Just lots of experience looking at irrigation systems, and hints like those I’ve already covered, dips in the ground surface where trenches have settled, areas that are greener than others, etc.    At any rate, I don’t want to get into any arguments over dowsing.  I present it as an option that many believe works.  If you can find someone with the talent, they may, or may not, be able to help you find the pipes, valves, or wires (yes, some dowsers claim they can find wires too!)

6. Use a wire locator (aka; wire tracer) device. This is how the pros do it, but if you notice the cost of a wire locator (ads on right), you will probably find that if you are a homeowner it is not within your budget! Some tool rental places, especially those that cater to professional contractors, have wire tracers they rent.  (Sprinkler Warehouse rents wire tracers using overnight shipment.) You use a wire tracer to follow the path of the wires to the valve, starting at the controller/timer. Again, if the wire is broken you may not be able to follow it (although the better units can even jump the signal over small wire breaks.  However, it will find the location of the break so you can repair the break in the wire.  Then you can continue tracing the wire to the valve– or the next break in the wire! )  Also be aware that it takes a bit of practice to use a wire tracer, but it can be mastered in a few hours.  The way it works is that you attach a signal generator attached to the valve wire.  Then you use a receiver that senses the signal.  The receiver beeps when you are near the wire.    A word of warning on wire tracers. You need a tracer with a signal generator that is powerful enough for the sensor to be able to pick up the signal through 24″of dirt depth. While most residential irrigation wires are not installed that deep, they are supposed to be!  The wire tracers made for use by electricians to find wires in house walls are not powerful enough to detect buried wires, even if they are only a few inches deep. I have one made for detecting wires in walls, that also lists irrigation systems as a suitable use, and it will NOT detect wires buried even 1″ below ground!!!  So before you spend money, make sure the device is suitable for wires that are buried underground.

Hey, do you know someone who works as a line-person for a phone or cable company?  They may have access to a wire locator since they often use them for repairs.  Maybe this weekend they might trade a few minutes of their time for a couple of beers?  hmmmm?

Now for the “this is a lot of work” solutions!  Start with a trip to the store to stock up on Advil and Ben-Gay.
7. Probing for valve boxes.  Before you try digging, first try a shallow probe for valve boxes. If valve boxes were placed over the valves when the system was installed, they are probably just below the surface. Often the only reason you can’t see them is that grass grew over the top of them. A pitch fork is ideal for probing for the boxes, just gently stab the ground until you hear the clunk of a fork tine hitting the plastic box top. If you don’t have a pitch fork a metal yard rake works for some people (others can’t get the motion right to plant the rake tines through the grass), a stick with a long nail-spike on the end of it works good to probe the ground, and last resort is to use a screwdriver on your hands and knees (ouch!)  Again, use logic to figure out the best place to start probing.

8. Probe or dig to find the pipes. (My back is hurting just from writing about it.)  If no valve boxes were used, then you will need to probe deeper. Now, just to warn you, it is highly likely you will cut or break a pipe or wire while you are doing this.  So just be prepared for that as a cost of the process of finding the valve.  OK.  Fortunately installers who don’t use valve boxes also tend to not bury the pipe and valves very deep, cause they’re lazy and cheap.  Normally the pipe from the water supply to the valve is buried deeper than the pipe from the valve to the sprinkler heads. (This pipe is called the “mainline” and is supposed to be at least 18 inches deep!) Plus the wires normally are thrown in the same trench with that mainline pipe going to the valves, and you don’t want to cut or nick a wire with a screwdriver blade.  So it’s best to start at a sprinkler head and work backwards toward the valve.  Use a long blade screwdriver to gently probe for the pipe around the sprinkler.  Try to pick a sprinkler head you think might be close to the valve. If you can turn on the sprinklers, the one closest to the valve will often come on slightly quicker than the others, and have more pressure, so it will have a more “powerful” sound and forceful spray when it is operating. Be gentle when probing, don’t break or pierce the pipe! Once you find the pipe keep probing and follow it back to the valve.  If the ground is really dry and hard, you might want to water it to soften it up first. As you follow the pipe consider marking the pipe locations on the grass or dirt using some of that special marking spray paint or the little sprinler flags they sell at irrigation supply stores.  Marking the pipe location will help you track where you found pipes (ie; this could be a multi-day project!)  Tip;  draw yourself a diagram of the sprinkler pipe locations for future use as you find out where the pipes are!

What if you can’t find the pipes with a screwdriver? Well, in that case it’s time for a shovel. Have fun digging up the yard! :(

 

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How to make an Organic Pre-filter for a Pond or Stream Irrigation Water Supply

Wednesday, September 19th, 2012

Pre-filters are used when pumping water from a pond, or a slow moving stream or river.  These instructions are based on a 20 GPM water supply, if you need more water you will need to use a larger pipe and hole, or manifold multiple pipes together. This is a very basic outline of what is required, you will obviously need to adapt it to your situation.

Dig a 3 foot deep 10 foot long hole in the stream or pond bed .  Next make a intake manifold, it is just a piece of 2″ SCH 40 PVC pipe with a cap on one end and your intake pipe connected to the other end.  You then drill one hundred each, 3/8″ diameter holes in the manifold pipe to allow the water to flow into the manifold.  Put a plastic liner on the bottom of your hole.  Now put 6″ of 3/4″ diameter gravel in the hole.  Then lay the intake manifold in the hole on the gravel and pack another 12″ deep layer of 3/4″ gravel around and over it. On top of that you place another 18″ deep layer of 3/8″ gravel.

The gravel acts as a “pre-filter”.  As the water moves slowly down through the gravel layers to the intake manifold the sand and much of the algae gets trapped in the gravel.  This is generally enough to protect the pump.  You still need a filter after the pump and it still might need to have a auto-flush mechanism.

To slow down a fast moving small creek to allow pumping water from it the classic method is to create a small, low, dam using sand bags.  Not only is the use of sand bags easy, it is also temporary and the sand bags can be removed seasonally if desired.

Remember that in most countries there are lots of rules and regulations that apply to disturbing stream beds.  In the USA, at a minimum, you should contact the US Fish and Game Department and EPA for advise.  There are probably also State and Local regulations as well.  The fines for violating rules or regulations can be very extreme!  Make sure you get a ll required permits.

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Pressure Loss in Sprinkler Risers

Saturday, September 8th, 2012

Q.  How do I calculate sprinkler risers losses in a sprinkler zone where the risers are extra long, 3 ft or more above ground?  I have 10 risers in a zone for my proposed sprinkler irrigation system.

A.  If you are using my Sprinkler System Design Tutorial and a standard riser of the recommended size, then you don’t need to worry about pressure lose in the riser, the tutorial has friction loss for the risers built-in to the formulas it uses.  So you can ignore the riser pressure loss.  Some standard risers are shown on the page on Sprinkler Risers in the Irrigation Installation Tutorial.  The recommended size for a riser?  In most cases it should be the same size as the threaded inlet on the sprinkler.  But please actually read that page on risers, as there are some exceptions to that rule for certain types of standard risers!

Non-Standard Risers:

OK, I realize that didn’t answer your question, you are asking about a non-standard riser that uses a long pipe to hold the sprinkler high above the ground.  In that case you must calculate what the friction loss will be in the longer-than-normal riser pipe. (In this case that would be the 3 ft long pipe you described in your question above.)  To do that you simply use the same friction loss spreadsheets that you use to calculate the friction loss in any other pipe.  Just use this link to get the proper spreadsheet from my website for the type of pipe you are using.  Then open the spreadsheet and on the first line enter the pipe size, GPM of the sprinkler you will install on the riser, and the length of the riser.  Enter an error factor of 1.4 rather than the default 1.1.  This is because even your “longer” riser is shorter than the typical pipe length that the default error factor is based on.  Now read the friction loss.  That’s it, you have the friction loss for your non-standard riser!  Don’t worry about the fittings like ells and couplings that are part of the riser, that is part of what the error factor is compensating for.

When adding the riser friction loss into the total friction loss calculations for your whole sprinkler system, just add in the loss for a single riser.  Use the friction loss value for the riser that has the highest friction loss.  (This is most likely the one with the highest GPM sprinkler, or it may be the longest riser if you have different riser lengths.  You may have to calculate the friction loss for several different risers to figure out which of them has the highest loss.)  Why do you add in the friction loss for only one sprinkler, rather than the combined loss for all of them?  Because as a single drop of  water goes through the sprinkler system it only goes through one sprinkler, not all of the sprinklers.  You have to think about the water as a collection of millions of drops, not as one solid body.  So the pressure loss is what a single drop would experience as it travels through the system.  As a drop of water enters the sprinkler system it travels through a water meter, lots of pipe, a valve or two, then it finally blows out through a single sprinkler onto  the landscape.  The pressure loss  calculation for the whole sprinkler system is determined by what the worst case pressure loss values would be for a single drop of water traveling through the sprinkler system.

OK, so you calculated the friction loss, but what if it is a really high value, or maybe the calculator complained about the velocity being to high.  In this case you need to use a larger size pipe for your riser.  For the velocity in a riser you can go all the way up to the 7 ft/sec maximum without too much risk.  Velocities in the marginal “use caution” zone are generally OK for risers.  High velocity in a riser will seldom cause a water hammer problem, unless you are using a special type of sprinkler that has a solenoid valve built in to it.  Those sprinklers are called “valve-in-head sprinklers”, they are very expensive, and are mostly used for golf course greens.

 

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Where to Get Answers to Specific Irrigation Questions

Friday, July 20th, 2012

Contact Information

For Comments & Feedback:

I welcome your feedback on the websites. If you find a bad link, an inappropriate link, or you have suggestions for the tutorials, I would love to hear from you! I do read and appreciate all input regarding my websites. Consider this my “thank-you” in advance.

If you want to send a complement, you can email me, or you can post comments on my Facebook Page. Please do not ask irrigation questions on my Facebook page as I will just delete them. See below for irrigation questions.

Errors: If you find an error in the website please give me the address (URL) of the page you found it on if you can. With several websites and hundreds of pages of content it really helps me in locating the error. Thank you very much for your assistance!

Email comment or feedback.

To Request a Link:

See The Irrigation Industry Directory and look for the Submit tab.

 

Irrigation & Landscape Questions:

Here are a few suggestions for getting answers to your questions. PLEASE DO NOT TELEPHONE ME WITH QUESTIONS.

Step One:

The best place to start if you have a question is with a search of my website by entering a search phrase below. The answers to most common questions are here.  The answers to most of the harder questions are also here if you dig deep enough.  You may have to read a couple of pages to get enough background to understand the solution.  Each time I get a unique question I post the question and answer on this website, so after thousands of questions, most are answered here!  (Note: I have several websites and this search engine searches all of them, so you may see some weird results regarding hotels and my family vacations!)

Google
Custom Search

(This search feature is provided by Google and is subject to Google’s privacy policy.)

Step Two:

ARE YOU DESIGNING A NEW IRRIGATION SYSTEM?  If so, have you read through my tutorials on How to Design a Sprinkler System or How To Design a Drip System?  It may seem obvious, but I get a lot of questions from people who are totally lost but haven’t tried, to be blunt, reading the instructions!  A lot of people who write me for help are trying to wing it on the design or think they can just randomly put some sprinklers around the yard.  That just doesn’t work out very good unless you have money to burn.  Irrigation systems have to be designed right or they become huge money pits.

I wrote these tutorials many years ago and have refined them continuously since then.  Thousands of people have used them, and I have hundreds of letters of thanks from folks like you, saying how great their new irrigation systems are.  I offer these tutorials to you to use totally free, and I would love for you to use them.  A lot of colleges use them for text books on irrigation.  But they are still simple enough for the average 6th grader to use (several wrote me to say they have!)  Please save yourself a lot of regret and try them out.  I get a lot of letters each year from people saying “I wish I had followed your advice and used your tutorial.”

Step Three:

Some various sources for quick help:

If you really want free help, try a local store or nursery. For irrigation questions go to a store that specializes in irrigation equipment. I haven’t found that the employees at hardware and home-center stores are knowledgeable about irrigation. I often check out the irrigation department of those stores to look for new products, and I overhear a LOT of bad advice being given by their employees. About 80% of what I overhear is at least marginally bad advice. Some of the advice I hear is not just bad, it is just flat wrong! There are some shining exceptions, of course, and if you work at one of those stores I’m sure that you are one of them! But the bottom line is that you are better off going to a professional irrigation specialty store if you need irrigation advice, and even then use care.

Step Four:

Ask me!  Yes, there is a small cost, explained in the “fine print” section below, so read it before you ask!   I will generally answer if I’m not busy with other things.  I answer about 98% of questions asked.  Often I will include the URL of an article and ask you to also read it.  (I’m lazy and don’t want to rewrite background information you need to understand difficult issues!!)

Pump questions: I can’t tell you what size or brand of pump to buy. I simply don’t have enough knowledge of pump brands and models. I suggest you read my pump tutorial, figure out the GPM and PSI you need, then talk to a professional pump dealer.

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Protecting Pump against No Flow Damage if a Valve Fails

Thursday, May 3rd, 2012

Q. I am currently in the process of converting my entire lawn irrigation system into an electronically controlled system using a control and relay setup for the pumps. I currently have two centrifugal pumps that pump water from a pond about 150 yards away. The system has seventeen zones and I have already ordered all the valves needed as well as the controller and pump relay and am in the process of installing it all. I am concerned with the fact that if one of the valves fail to open then I may have a problem with too much pressure and would like to know what kind of setup you suggest in order to overcome this. I researched pressure relieve valves and such but I feel that a flow sensor combined with a high pressure sensor to turn the pumps off would be the safest route in order to minimize damage to the pumps. How could this be done to cut pumps off if there is too much pressure or no flow at all?

A. They make flow sensors that use paddle wheels, they can actually measure the flow rate in the pipes in GPM or cu ft/min. They are a great way to go for this. They require that you have a fancy irrigation controller that can work with them, so you may need to return your controller and upgrade it. The irrigation controller measures the flow and compares it to the pre-programmed flow that should be present in the system for the valve that is currently open. The controller then makes a decision based on that flow. If the flow is too low or too high it can shut down the pumps or close a master valve that shuts off the water to the entire system.

The sensor needs to be installed in a tee on a straight length of pipe. The length of the straight pipe should be 5x the pipe diameter before the sensor and 5x after it. This is to reduce water turbulence in the pipe caused by turns, the turbulence can cause inaccurate pressure readings.

You can also use a pressure sensor and pump logic controller to turn off the pumps at high pressure or very low pressure. You should be able to get what you need at a specialty pump supplier. The sensor is a bit different from the typical pressure switch. A standard switch turns the pump on at low pressure and off at high pressure. The logic controller is basically used as a detector and timer. The timer would only turn off the pump if the high pressure was present for maybe 4 minutes or so. It is normal to have a pressure spike as the system changes from one valve to another, you don’t want the pump to shut off during the switch of valve zones. You also need a delay to allow the pump to start up, since there will be no pressure until it gets going (so the switch would never allow the pump to start!) The pressure sensor also needs to be on a straight pipe section like the flow sensor.

If you wnat to use a pressure sensor you should also do a quick test to make sure your pumps are capable of producing a high enough pressure to detect. Some pumps don’t produce very much increased pressure, even at no flow. So you need to make sure your pump will, if it doesn’t you need to use a different method of detecting no flow, like a flow sensor. Run the pump as normal with the smallest valve circuit open and check the pressure. Now shut off the valve and watch the pressure (don’t let it run for more than 3-4 minutes without flow! Don’t want to overheat the pump.) Ideally you want to see a pressure increase of 5 or more psi. The more pressure increase you have the less likely you are to get a false alarm caused by a small pressure spike.

If the pump doesn’t produce enough pressure to measure the increase at no flow you will need to use a flow switch to detect flow. A flow switch is nothing more than a paddle that sticks down into the pipe. When the water is flowing it presses against the paddle and the switch opens/closes (depending on how you have it set.) It’s very simple. Unfortunately flow switches also break pretty easy, so they have to be frequently replaced. That’s why I don’t use them as my first choice.

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Sprinkler Coverage, Nozzle Selection, & Sprinkler Spacings

Thursday, January 12th, 2012

Step #3 of the
Landscape Sprinkler System Design Tutorial

Previous Page of Tutorial - - Sprinkler Design Tutorial Index - - Next Page of Tutorial

This is important, read it carefully!

Sprinkler Coverage:

The area watered by each sprinkler must overlap substantially the area watered by the adjacent sprinkler. This overlap may seem like a waste at first, but it is a very important necessity. Without this overlap it would be impossible to design sprinkler systems that provided uniform water coverage.

Have Doubts?  See for yourself, it only takes a couple of minutes to prove! Grab a piece of paper and draw circles on it so that all areas of the paper are inside a circle, but no circles overlap. You can’t do it, can you?

Important!
Sprinklers are intentionally designed to require 100% overlap of watered areas. That means each sprinkler throws water ALL the way to the next sprinkler in each direction. READ THAT AGAIN!

That’s right, 100% overlap of watered areas is REQUIRED or you will get dry spots! This is known in the industry as “head-to-head coverage or head-to-head spacing”.  A lot of those free design guides you find in stores and on the Internet get this wrong.  They don’t show enough overlap!  The writers of those brochures think you are going to look at the overlap and buy the brand of sprinkler that shows the least sprinkler heads.  So they try to make it look like you can use less sprinklers with their brand.  After you’ve bought the sprinklers if you have dry spots, well hey, it’s YOUR problem now!  You’ll probably just buy a few more of their sprinklers to get rid of the dry spots. In fact, it will probably take more sprinklers to fix the dry spots than it would have to do it right the first time. $$$ Ching, ching!

Diagram of head-to-head irrigation sprinkler coverage

Lawn sprinklers spaced head-to-head

Rule: Sprinkler Radius = distance between sprinklers

 

One more time: The water from any single sprinkler should actually get the sprinklers on each side of it wet!

Now that I’ve told you that you SHOULD use head to head spacing I’m going to backtrack a bit and tell you that you can space a few of the sprinklers slightly farther apart as needed to work around odd shaped areas. I still recommend that you keep at least 80% of the sprinklers at head-to-head spacing! Take the sprinkler head watering DIAMETER and multiply it by 0.6 to get the absolute maximum distance that should ever occur between any two adjacent sprinklers. (Remember most manufacturer’s give you the radius of the sprinkler, you need to multiply by 2 to get the diameter.) For example, 15′ radius spray heads should never be more than 18′ apart (30′ diameter x 0.6 = 18′). Note that we rounded to the nearest foot. If the sprinkler system is in a windy area I suggest the majority of the sprinklers be spaced at 45% of the diameter (that’s closer than head to head!), as winds over 10 mph really mess up the sprinkler patterns.

(Optional reading for those who need explanations.) Back when I designed my first sprinkler system in High School I wondered why they wanted so much overlap of the sprinklers. It seemed to me to be nothing more than a ploy to sell more sprinkler heads! I was smarter than that, so I stretched them out to save my folks some money! The result was big dry spots, and my parents wound up replacing the sprinkler system a few years later. (They never said anything about it to me, I just noticed the new sprinklers a few years later on a visit home from college.) Ouch! Not a good start for a future irrigation expert! Now that I’m a bit wiser and more knowledgeable I realize there is a good reason behind the head-to-head coverage. Unfortunately, it’s rather hard to explain. The perfect sprinkler would put out a pattern of water that is heaviest right next to the sprinkler, then uniformly declines out to the radius. So the farther you move away from the sprinkler, the less water falls on any given patch of ground. When we test sprinklers for water coverage we set up a series of cups between the sprinklers to collect the water that falls. That way we can see how much water falls at various distances from the sprinkler. In the diagram below you can see what happens when there are various distances between the sprinklers.

Sprinkler coverage at various spacings

Close to 100% sprinkler overlap is important for good water application uniformity

In example “A” the sprinklers are just barely overlapping and much more water is falling in the cups next to the sprinkler heads. But the middle 3 cups are only getting ½ the water of the cups next to the sprinkler. If you watered long enough to keep the middle green, the areas around the sprinklers would turn to mud! In example “B” we see that moving the sprinklers closer together has evened up the amount of water a bit more. However the areas near the heads are still getting 25% more water than the other areas. Not enough to cause mud, but you would definitely see rings of greener grass around the sprinklers! Example “C” shows almost head-to-head spacing. The cups are almost all uniformly full! So don’t stretch the distance between sprinklers.

What if you need a smaller radius than the sprinklers available?

Almost all sprinklers have a radius adjustment device on them so that you can reduce the radius of the water throw. This is one way you can adjust for narrower areas. Keep in mind that for most sprinklers you can’t reduce the radius by more than 50% without causing problems. The other solution for smaller areas is to use nozzles made to spray less far, or that spray a special pattern. An example of a special pattern would be the nozzles that spray a 4′ x 30′ rectangular pattern. These are commonly used in long, narrow areas.

 Remember if you reduce the radius of the sprinkler you must reduce the distance between sprinklers by the same distance! Keep the coverage head-to-head!
Calculating the GPM for sprinklers when you reduce the radius is easy:

For spray heads you just use the manufacturer’s chart.  When you use the radius adjustment on a spray you are simply reducing the water pressure by closing a small valve in the nozzle.  As the pressure drops, so does the radius.  Just look at the manufacturer’s chart for the radius you plan to reduce the sprinkler down to.  Then read the GPM for that radius!  For example, your designing for 30 PSI.  The radius at 30 PSI of the sprinkler you selected is 15 feet with 1.85 GPM according to the manufacturer’s chart.  But you want the radius to be 14 feet.  Looking at the manufacturer’s chart you see that the radius of the same sprinkler is 14′ at 25 PSI with 1.65 GPM.  So the GPM of that sprinkler if you reduce the radius to 14′ will be 1.65 GPM.  That’s because when turn the radius adjustment screw to reduce the radius to 14′ what you REALLY did was reduce the pressure to 25 PSI!

For rotor heads the GPM stays the same no matter how much you reduce the radius!  That’s because reducing the radius on a rotor doesn’t change the amount of water coming out of the nozzle.  To change the radius a small screw extends into the stream of water coming out of the nozzle.  The tip of the screw deflects the water which “screws it up” (pun intended) so it doesn’t go as far.  This creates another problem, however, which is that it really messes up the uniformity of the water.  So when you use the radius adjustment on rotors, you tend to get dry spots.  This is one reason I strongly suggest that you use a smaller nozzle if possible rather than using the radius adjustment screw on the sprinkler.  The other reason is that when you reduce the radius you really should also reduce the GPM of the sprinkler.  Otherwise there will be a lot more water under the sprinkler with the reduced radius. Bottom line- use the radius adjustment screw on rotors only when nothing else will work.

 Warning for rotors only:
When designing systems with rotors do NOT rely on the manufacturer’s stated radius for design. They get those distances by testing the rotors inside a building with no wind. The real world is harsher! If the gallonage of the rotor is less than 6 GPM the maximum spacing should never be more than 35′ between rotor type sprinklers.

Stryker’s Rule: the spacing in feet between rotors can never exceed the operating pressure in PSI at the sprinkler inlet (So a rotor with a 30 PSI operating pressure = 30 foot maximum spacing between rotors.  Yes, I know the package says you can space them farther apart.)

Ignore the rule above and you will be very sorry!

 

Sprinkler Precipitation Rate and GPM

The precipitation rate is the amount of water the sprinkler throws onto the area it waters, measured in inches per hour. (Inches per hour is how deep, in inches, the water would be after one hour if it didn’t soak into the ground or run-off.) Precipitation rate must be considered when selecting your sprinkler heads to eliminate water application uniformity problems (dry spots).

Spray Heads: Almost all sprinkler manufacturers make their spray heads so that you can mix and match nozzle patterns and the precipitation rates will still match for all the heads. This is referred to as “matched precipitation rates”. Look for this feature when selecting your sprinklers. Important: do not mix different brands of spray heads and nozzles together on the same valve circuit without checking to see that they have the same performance specifications. Just because the nozzle will screw into the sprinkler body doesn’t mean it’s designed to work with that sprinkler!

Rotors: Rotor-type heads aren’t quite as easy. You must select the appropriate nozzle size for each rotor in order to match the precipitation rates. A simple illustration will help explain. Rotor heads move back and forth across the area to be watered. The rotation speed is the same regardless of whether the rotor is adjusted to water a 1/4 circle or a full circle. So the stream from a 1/4 circle head will pass over the same area 4 times in the same amount of time that it takes for a full circle head to make one pass over the area it waters. With the same size nozzle in both, a 1/4 circle rotor will put down 4 times as much water on the area under the pattern as a full circle rotor will. (Remember that after every quarter turn the 1/4 circle rotor reverses direction and covers the same area again!) To match the precipitation rates between these sprinklers, the quarter circle rotor must have a nozzle that puts out 1/4 the amount of water that the full circle nozzle puts out! A half circle rotor must have a nozzle that puts out 1/2 the water of a full circle. This is why when you buy a rotor-type sprinkler head they often include a handful of different size nozzles with it. Wait, there’s more (don’t panic yet, there is a simple solution forthcoming)!

If you have rotors that are adjusted for different radii you will need to adjust the nozzle size to compensate for the radius change also! For example if most of the rotors are set for a 30 foot radius, but one is adjusted down to 20 ft., the 20 ft. one will need a nozzle 1/2 the size. (Remember: when you reduce the RADIUS by 1/3 you reduce the AREA by a little more than half.)

 Avoid using rotors with nozzle flows that are less than 2.5 GPM, except in corners (quarter circle patterns). Flows under 2.5 GPM give very poor coverage due to the tiny water stream. Even a slight breeze will distort the watering pattern and give you dry spots. I strongly suggest that you stick to using nozzles as close as possible to the GPM of those in the cheat chart below.

O.K. Now that you understand the principles, let’s simplify this a bit by using a cheat chart…

Unless you really know what you’re doing (in which case you wouldn’t be reading this tutorial), you should stick with the nozzles on this chart:

Jess Stryker’s

Quick & Dirty Guide for Rotor Nozzle Selection

1. Find the section of the chart with your desired spacing.
2. Find the pattern (1/2, full circle,etc.) of the sprinkler.
3. The chart tells you the GPM the nozzle must have.
4. Use a nozzle size that comes close to matching both the PSI – GPM combination.
5. Ignore the radius given by the manufacturer.
6. Be sure to read the notes below the chart!


For 20-29′ spacing between sprinklers-
1/4 circle . . . 30 PSI – 0.8 GPM
1/2 circle . . . 30 PSI – 1.6 GPM
3/4 circle . . . 30 PSI – 2.4 GPM
full circle . . 30 PSI at 3.2 GPM
Important: see notes below!

For 30-39′ spacing between sprinklers-
1/4 circle . . . 40 PSI – 1.5 GPM
1/2 circle . . . 40 PSI – 3.0 GPM
3/4 circle . . . 40 PSI – 4.5 GPM
full circle . . 40 PSI – 6.0 GPM

For 40-55′ spacing between sprinklers-
1/4 circle . . .55 PSI – 3.0 GPM
1/2 circle . . . 55 PSI – 5.5 GPM
3/4 circle . . . 55 PSI – 8.0 GPM
full circle . . 55 PSI – 11.0 GPM

Important Notes:

It is critical that the water pressure (PSI) at the sprinkler be as high, or higher, than the distance between the sprinklers in feet (per Stryker’s Rule). For example, if you space the sprinklers 45′ apart, you must have at least 45 PSI of pressure at the sprinkler inlet. That’s the pressure at the sprinkler inlet, not the total pressure available. Remember, you will lose pressure in the pipes and valves, so the pressure at the sprinkler inlet will be lower than your available pressure! Go back to the tutorial pressure loss pages to figure out how much pressure will be lost in your sprinkler system.

Select the nozzle size closest to these GPMs without regard to the radius the manufacturer gives. For example, if you are looking at a 25′ radius, the chart above says to use a 1.6 GPM nozzle for a half-circle rotor. But you happen to notice that the rotor manufacturer’s literature says that at 25 PSI, a 1.6 GPM nozzle has a radius of 32 feet. So why am I telling you to space it at 25′? When the manufacturer tested the rotor on their test range (inside a large building with no wind) they measured a few drops of water 32′ from the rotor. When you install it out in your yard it will not perform as well. You may still get a few drops of water 30′ or even 32′ from the head, but not enough to grow anything. You need to trust me on this one! Remember, if the sprinkler sprays too far, most rotors have a radius reduction screw that will allow you to very easily reduce the radius. But, if the rotor does not spray far enough there is nothing you can do about it without a major expense! Best to play it safe.

You may want to make additional adjustments to nozzle sizes after installation to compensate for your specific conditions. Most rotors now come with a “nozzle tree” that contains most of the different nozzles for the rotor, so you can change the nozzle sizes if you need to. Some manufacturer’s don’t offer nozzles sizes larger than 3.0 GPM for their economy-priced heads (providing those extra nozzles would probably cost them at least another nickel in costs!). You may need to upgrade to the next better model line if you have a large yard! The larger size nozzles for 40′ spacing are not available with most of the “mini-rotor” models sold for residential use. You will need to upgrade to the next model. Also, sometimes other nozzle sizes are available separately from the manufacturer, for example low angle nozzles. You will probably need to get these from a store that specializes in irrigation sales, rather than a hardware or home store. Look in the yellow pages under “Irrigation” or “Sprinklers”, or try one of the online stores listed in the tutorial links pages.

There is a conflict between the nozzles recommended for the 20-29′ spacing range of the chart and my previous advice to “avoid using rotors with nozzle flows that are less than 2.5 GPM”. This is because the Nozzle Selection Guide assumes you will be mixing 20-29′ radius rotors together on the same valve with 30′ plus radius rotors. To keep from having enormous nozzles on the larger radius rotors I am recommending that you use smaller nozzles than I would otherwise consider for the smaller radius rotors. This is essentially a compromise. Sometimes it is not practical to obtain perfection! If all or a majority of your rotors will be spaced at 20-29′ apart, then you should probably use larger nozzles than I recommend in the chart. In other words, use those listed in the chart for 30-39′ spacing for the 20-29′ spacing. This will help avoid problems caused by the wind blowing the spray out of the irrigated area. However, if your sprinkler system will be located in an area with little or no wind you can go ahead and use the smaller nozzles in the chart. What is little or no wind? Go outside in the evening or early morning when you will likely be irrigating. If you can feel the wind blowing even gently against your face, I would consider that enough wind to need the larger nozzles.

If you calculate the precipitation rates you will notice that the shorter spacings result in a higher precipitation rate than the larger spacings. This is because the smaller heads with lower GPM rates are more susceptible to wind and evaporation, and thus it is assumed less of the water is actually reaching the ground. The higher precipitation rate compensates for this.

 

Windy Locations

If you are designing a sprinkler system for an area where the wind blows a lot you should look at the Irrigation and Wind FAQ.

Select Your Sprinklers

If you haven’t started shopping for sprinklers yet, now’s the time to start checking out what’s available.  Check out which sprinklers are available and look them over.  Write down a list of the heads you think will work well for your irrigation system on your Design Data Form. Be sure to list the PSI and GPM for each head as given in the manufacturer’s literature, along with the maximum spacing between heads.

 

 One last warning!!!

Do not blow-off my advice on sprinkler spacing in order to save a few bucks on sprinkler heads! Right now you may be feeling pretty smug about how much money you saved by stretching the sprinkler spacing. But next summer you’re going to look pretty stupid to the neighbors, standing out there with a hose watering the yellow spots your new sprinklers don’t cover!  I have a collection of “wish I’d listened to you” letters from people who didn’t take this advice. I get a few more of these every year, and these are just the brave folks willing to confess they messed up. They all say you should listen to me on this!

Later on you will need to know the flow rate for each sprinkler you use, so it might be helpful to make some notes on the back of your Design Data Form showing the nozzle size and GPM you will need for each different sprinkler you plan to use. Otherwise you’ll wind up having to look the information up over, and over, and over…

 

 

Draw the Sprinkler Heads on Your Plan

You’re now ready to pencil in the sprinkler head locations on your drawing. Hallelujah! I know it seems like it took a long time to get here, but to do a good job we needed to cover a lot of background information! Use a pencil to draw in the sprinkler heads so you can easily make adjustments to the locations later. Many people find it helpful to use a compass to draw a light pencil line showing the radius of water throw for each head.

Remember these tips:

  • Keep the distance as uniform as possible between heads. To the extent possible a sprinkler should be equal distance from the adjacent sprinkler in each direction (forming a triangle if possible). Changes in spacing between adjacent sprinklers should be made as a gradual transition when possible.
  • Try to position heads so that if you were to draw a straight line between adjacent heads they would form an equilateral triangle (each side of triangle is same length). This is called “triangular spacing” and creates more even water coverage than “square spacing” (ie; lines between 4 heads form a square). That said, you will often be unable to form a triangle so don’t panic if you can’t.
  • Don’t stretch the spacings, use “head to head” spacing. Using too many sprinkler heads is seldom a problem, using too few sprinklers heads is ALWAYS a disaster!
  • Start by drawing a sprinkler in each corner. Next, draw sprinklers around the perimeter of the irrigated area, watching that they are not too far apart (one more time, better too many than too few!). Adjust the locations to make the spacing between sprinklers as even as possible. After the perimeters are done, then draw the sprinklers in the interior area.
  • If the sprinklers need to overlap so that the spray from one head goes over and beyond the next that’s OK. While you don’t want to over-water, it is always easier to correct an over watered area than a under watered one. For example, you can use the radius adjustments on the sprinklers to cut down the water in the over-irrigated areas. If need be you can even remove or relocate a sprinkler later. It’s much easier to remove one than to add one!
  • Sprinklers that are placed closer than 6 feet apart need some special consideration. Standard spray-type sprinklers don’t work well if the radius is adjusted below 6 feet. (The opening the water goes through is so tiny that the normal expansion of the plastic or metal on a warm evening can close off the water flow!) If the area is long and narrow (4′ wide or less), use the strip pattern nozzles. I prefer the so called “side-strip” type that you place along the edge of the area, they have better patterns than the center strip nozzles. End-strip nozzles have notoriously bad patterns, they shouldn’t be more than 10′ from the next head! When using standard spray sprinklers (like quarter, half, and full circles) in areas where the radius must be adjusted to less than 6 feet use a “pressure compensating device” to reduce the radius. The pressure compensating device is normally installed under the nozzle where it reduces the flow and pressure through the nozzle. The good news is that by using a under sized pressure compensating device you can also reduce the nozzle radius! Unlike the adjustment screw on the nozzle these devices work well regardless of the temperature. However, you will need to select the proper size pressure compensating device for each nozzle. It is possible that every nozzle will need a different size! To select the right device you use a special chart provided by the pressure compensating device’s manufacturer. The chart will tell you exactly which device you must use with each different nozzle in order to get the radius you want. Most major sprinkler manufacturer’s make pressure compensating devices for their spray sprinklers, and the charts you need can be found in their catalogs. You may need to go to a commercial sprinkler supplier to find them.

Study the example drawing below.

Sprinkler spacings -Draw the sprinkler head locations on your plan

Sprinkler spacing for optimal head-to-head water coverage

Again, notice that the radius of each sprinkler’s spray goes all the way to the next sprinkler! This is critical.

Note that in the example above only the lawn area outlined with a green curving edge is being watered. The area between the lawn (green line) and the edge of the property (brown line) would most likely be planted with shrubs and irrigated separately from the lawn. In most cases a drip system would be considered for watering the shrubs as it is less expensive and more efficient. See the separate guidelines for designing drip irrigation systems.

Bonus landscape design tip: Creating a border of shrubs around the perimeter of your yard is, in most cases, a good landscape design practice. A shrub border helps to reduce the visual impact of the fence (assuming that like most residential properties you have a fence.) Shrubs also typically use less than half the water of lawn areas of the same size, saving money spent for water. Once a month you need to weed and trim shrub areas, as opposed to the lawn that needs to be mowed every other week at the least in summer. A border using shrubs of various sizes, textures and colors can add greatly to the attractiveness of your yard. Place smaller shrubs near the lawn, with larger growing varieties behind them next to the fence.

 

 

Sprinkler Layout for Narrow Planters:

Sample sprinkler head layout for narrow planters

Sample sprinkler head layout for narrow planters using strip nozzles

This example shows the typical placement for sprinkler heads in a narrow planter. In this example, special spray sprinkler nozzles called “end-strips” and “side-strips” are used. These nozzles spray a long, but narrow, pattern. A typical pattern is 4′ x 30′ (4′ out and 15′ in either direction from the head). There are also spray nozzles called “center-strips” which don’t work as well. Be careful when using end-strips. They tend to have a weak coverage area on either side of the nozzle (the yellow area in the drawing above). Avoid using 2 end-strips facing each other in a lawn area. If possible always install a side-strip in the middle between 2 end-strips. The sprinkler layout above is for lawn. In a shrub area you can eliminate the sprinklers on one side as long as the width of the planter is 4 feet or less- so you can install the sprinklers on one side only. Shrubs don’t need as even a watering pattern. Lawns require heads on both sides. Note the triangular arrangement of the sprinklers, which gives more even coverage. Yes, it takes an extra head to create the triangle pattern, and you need to space the heads a little closer together than the normal maximum on one side to create the “triangle pattern”, but it’s worth the cost.

For narrow strips wider than 5′ you would use regular half circle heads on both sides. The distance between the sprinkler heads should not be more than 1 foot greater than the width of the planter. In other words, if the planter is 8 feet wide you would install half circle heads on both sides of the planter, not more than 9 feet apart from each other. As with the example above, it is best if you arrange the sprinklers in a triangular pattern.

 

Sprinkler GPM

As we saw previously, the flow rate in gallons per minute (GPM) of each sprinkler head is determined by the nozzle installed in the head. It is necessary to know the GPM for each head in order to determine which heads will be connected to each valve and in order to determine the size of each pipe in the sprinkler system.

You will probably need to dig up the sprinkler manufacturer’s literature again. In the literature the manufacturer shows different GPM and radius information for each sprinkler nozzle based on the operating pressure (PSI). Now we can use that information to find the GPM for each sprinkler head. First, determine what the SPACING is between each head and the others around it. Next, look for the radius closest to that spacing and use the corresponding GPM as the flow for the head.

Write down on your plan the GPM for each sprinkler next to the sprinkler symbol.

Hint: You will find the GPM and radius data for many of the popular sprinklers in the product reviews .

Example: You note that a spray type head on your plan is a 1/2 circle pattern and the distance to the 3 closest adjacent heads are 13 feet, 12 ft., and 14 ft.. So the spacing for this head is 14 ft. (the highest of the 3). Looking at the manufacturer’s literature you note that a radius of 14 ft. for the 1/2 circle nozzle in this sprinkler requires a pressure of 25 PSI and a flow of 1.65 GPM. Write down the flow of 1.65 GPM next to the sprinkler head on your drawing. You then repeat this procedure for each sprinkler head on your drawing.

Add sprinkler GPMs on your plan.

Note sprinkler GPM on your plan

Write the GPM of each sprinkler on the plan next to the sprinkler

 

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Hydro-Zones, Valve Zones, & Sprinkler Pipe Layout

Thursday, January 12th, 2012

Step #4 of the
Landscape Sprinkler System Design Tutorial

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Hydro-Zones:

The next step in designing your irrigation system is to identify the individual hydro-zones that exist in the area to be irrigated. Different areas of your yard have different water needs. Each of these areas is called a “hydro-zone”. You need to irrigate them separately from one another to keep from drowning some plants while others are dying of thirst. For example, a grass lawn will almost always need more water than a shrub bed. Plants in the shade of a house need less water than those in direct sun. Tropical plants need more water than desert plants. Remember that over-watering plants can be as harmful to them as underwatering. Many plant diseases are the direct result of over-watering, particularly fungus and molds.

  Using a pencil lightly outline the different hydro-zones in your yard on your plan. Some hints:

  • Lawns and shrubs should NEVER be in the same hydro-zone, so start by creating two hydro-zones, lawns and shrubs.
  • Shady and sunny areas should not be in the same hydro-zone. The shadiest areas are typically in the shadow of buildings where little or no direct sunlight reaches all day long. Go out and walk around your yard. Look for places where the soil stays moist when compared with the rest of the yard. Separate the sunny and shady areas of the lawn area into different hydro-zones. Do the same for the shrubs areas.
  • Plants with different water requirements should not be in the same hydrozone. Show a separate hydro-zone for any grouping of plants that need more or less water than the others. If you’re not familiar with the water needs of various shrubs look them up in a good garden encyclopedia. You can also tell a lot just by observation. Do some plants in your yard seem to wilt easier than others? On large projects you may also have different soil types in various parts of the irrigated area. These may also need separate hydro-zones. This is very common for golf courses and parks.
  • Never combine spray heads, rotors, or drip irrigation in the same hydro-zone. The water application rates are different for each of these, which will cause either dry or wet spots. For example, rotors often apply water at half the rate as spray heads. So if you were to combine spray heads and rotors on the same valve, and then turned on the water long enough to apply just the right amount of water in the spray head area, the area with rotors will only get half the water it needs.

 

The irrigation for each of these hydro-zones will need to be controlled by its own valve. This way the watering times can be individually adjusted for the specific needs of each hydro-zone. Nothing gets over or under watered. Over and under-watering is a major factor in promoting plant disease, and it wastes water. In some small yards it may not be practical to create separate hydro-zones for all the different water needs. This is an individual decision that you will need to make. Another option is to relocate or replace plants that don’t fit in well with others in the area. I often adjust the outlines of lawn areas to avoid small areas I know will have a different hydro-zone than the rest of the lawn, such as in the shade of a building, or under a large tree.

 

Drip Irrigation Systems:

If you use drip irrigation for your shrubs you can much more easily mix plants with varying water uses together. The best way to do this is to install two separate drip systems in the same area, one irrigating just the high water users and one just the low water users. Another cheaper, but less effective, way is to install more emitters at the plants which need more water. The disadvantage of this second method is that most water loving plants don’t just want more water, they want it more frequently, which is not possible when everything is on the same system. Irrigating too frequently is a major cause of plant disease so be warned!

 

Valve Zones:

Previously you wrote down your “design flow” on your Design Data Form. As you remember that was the maximum amount of water available for the irrigation system measured in gallons per minute (GPM). Hopefully you also noted on your plan the flow (GPM) for each sprinkler head. Now you need to divide the irrigation system into valve zones that do not exceed that amount of water. Remember that the valve zones can’t cross over the boundaries of the hydro-zones you drew previously. (Hydro-zones can’t overlap valve zones.) Here’s an easy way to do this:

  1. Add together the GPM for all the sprinklers in a hydro-zone.
  2. If the total GPM of all the sprinklers in the hydro-zone exceeds the design flow GPM, you will need to divide the hydro-zone into more than one valve zone.
  3. The total GPM for each valve zone should never exceed the design flow GPM.
  4. Drip irrigation and sprinkler irrigation may NOT be mixed together in a single valve zone. Fixed spray type sprinklers may NOT be mixed with rotor type sprinklers in the same valve zone. You need to create separate valve zones for each of these.

Repeat this procedure for each hydro-zone.

Lightly circle on your plan the heads that are in each valve zone as shown below.

 

Now identify the location where your valves will be installed. If the valves will be above ground pick somewhere they will be hidden, like behind shrubs. Usually they are placed near the water source but there is no reason they need to be. Remember that if you plan to use anti-siphon type valves they must be installed at an elevation 6″ HIGHER than the highest sprinkler head, so they will probably need to be on the uphill side of the irrigated area. The valves do not need to be grouped together in the same location, you can place them where most convenient. Placing the valves in small groups of 2 or more, close to the areas they will water, can often save money by reducing the amount of pipe needed.

 

Draw in a valve symbol on your drawing for each valve zone. This will represent the valve that turns on and off the sprinklers in that valve zone. See the illustration on the next page of the tutorial for a typical valve symbol.

 

 

Sprinkler Pipe Layout

Now that you have the valve zones shown on your drawing it’s easy to add the pipes going to the sprinklers. Start with one of the valves and draw a line to the closest sprinkler in the corresponding valve zone. Then draw a line to the next sprinkler in the valve zone, and the next, etc. Some helpful tips:

  • For small residential sprinkler systems try using a different color pencil for the pipes in each valve zone. This will make your plan easier to understand.
  • Where possible you can minimize the amount of trenching by placing pipes together in the same trench. Show these pipes side-by-side on your plan.
  • Run the pipes as efficiently as possible. In most cases this will be the shortest possible route between each sprinkler, but this is where you need to just look at your plan and think about it a bit. You may find it easier to run one pipe down the center of an area and spur off of it to each sprinkler. Or it may be easier to split the piping with one pipe going to half the sprinklers and the other going to the other half. Some may want to minimize the number of trenches, even if it means using a less direct route for the pipe so two pipes can share a trench. There is no set routing pattern that you must use for the pipe. If for some odd reason you need to route the pipe all the way around the yard to get to a sprinkler only a few feet away from where you started that’s O.K. Try several different layouts until you find one that YOU like, that fits YOUR needs.

Proper Pipe Connection Alignments

  • Show no more than 2 pipes connecting to a sprinkler head– one coming into the sprinkler, and one going out. If you need to branch off from the sprinkler with a 3rd pipe, show the 3rd pipe branching off of the 1st pipe just before it goes into the sprinkler. There is no part made that will allow 3 pipes to connect together at a sprinkler head location. Study the sample drawing below for examples.
  • Try to avoid running pipes within 5 or 6 feet of existing trees. The roots will make it hard to dig trenches for the pipe. With really big trees I try to keep the trenches out from under the canopy of the tree. If I need a sprinkler in that area I run the pipe around the perimeter then go straight in toward the trunk to the sprinkler head. Of course, this may not always be possible. Sometimes you will just have to go through an area with tree roots.

Splitting flows or splitting hairs? You may have heard that the flow from each valve should always be split just after the valve, with one pipe going to half the sprinklers and the other pipe going to the other half. The reasoning is that this “balances” the system. Good designers can balance the flows without resorting to this old method. You are well on your way to becoming a good irrigation designer, so you can forget about such amateurish methods! Route the pipe however you want to route it!

Draw pipes between sprinklers

Draw the lateral pipes between the sprinklers and the valves. If you haven’t drawn the mainline pipe from the valves to the water source, draw it now also.

Determine Flows in Pipes:

In order to determine the pipe size we need to know the flow rate (GPM) of the water in the pipe. Calculating the water flow in each section of pipe is extremely easy, but many people have problems with it. They try to make it too complicated. Just observe the layout of the sprinklers and ask yourself which sprinklers are DOWNSTREAM of this pipe section. It’s simple logic, the water must flow through this pipe to reach the sprinklers downstream. Add the total GPM of those sprinklers together and you have the GPM that will be flowing through the pipe.

    1. Start at the valve. The first section of pipe goes from the valve to the first sprinkler head. All the water for every sprinkler operated by this valve must flow through this section of pipe to get from the valve to the sprinklers, right? So the flow in GPM for this section of pipe is the total of the GPM of all the sprinklers operated by the valve added together.
    2. The remaining sections are just as easy. The total flow through each section of pipe is the same as the total GPM of all the sprinklers downstream from that pipe section. Add together the individual GPMs for each of those sprinklers to get the flow through the pipe section. Don’t make it harder than it is! If you have a short spur pipe leading off to a single head, then only the water going to that head will pass through the spur pipe! So the flow for the spur pipe is the same as the GPM of that single head. Carefully study the sample design below.

Using a pencil, write the flow for each pipe section down on your drawing next to the pipe.

Show flow in each pipe section.

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Sprinkler System Design: Automation, Costs, Contractors, more…

Sunday, December 11th, 2011

Finished!
Landscape Sprinkler System Design Tutorial

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Well, if you are working through the Sprinkler Design Tutorial, you’re now pretty much finished with your irrigation design. Here’s a few reminders and additional items to consider.

Automatic controllers: For automatic systems you will need a controller (often called a “timer”) with one “station” for each valve. If you have both lawn and shrub areas you should make sure the controller has 2 or more “programs”. Multiple programs are somewhat like having several “timers” in the same controller. This allows you the flexibility to run the lawn and shrub irrigation on different days. Study the different models and features available on various controllers. They range from simple timers to extremely complex computerized units that can monitor all the functions of your entire home!  I suggest you take a look at the article on Smart Controllers if you are interested in the latest innovation for saving you time and water.

Isolation valves: It’s a good idea to install a manual shut-off valve at the point where your irrigation system connects to the water supply. I know I already covered this, but not doing it is a big regret that I hear often.  An isolation valve allows you to shut down the irrigation for control valve repairs without shutting off the water to your house.  You will have to repair a control valve at some time.  I recommend using a “ball valve” for the isolation valve, as ball valves are the most reliable and reasonably priced shut off valves.   Most inexpensive “Gate valves” will leak.

Wires for valves: For wires going to the automatic valves use wire made specially to be buried. Most people use a special direct burial cable made for irrigation systems. The cable contains 3, or more, separate, 18 gauge wires. On commercial systems the standard wire used is “#14-1 AWG-UF” which is a single strand, direct burial type wire. One white color “common” wire goes from the controller to every valve, and one individual “lead” wire of a color other than white goes to each valve from the controller. Be sure to read the Irrigation Installation Tutorial.  Also there is a sketch of typical irrigation system wiring that should help you understand the wiring.

Details: To further help you there is a collection of installation details. These simple sketches will help you figure out how to assemble your irrigation system. These installation detail drawings are normally included as a part of the design drawings for an irrigation system.

Filters: I recommend you install a screen-type water filter upstream of the valves.  Drip systems should always have a filter! This helps reduce maintenance problems caused by small bits of sand which are found in almost all water systems. These small sand grains can make the automatic valves malfunction and also clog sprinkler heads over time.  A $50.00 filter may seem expensive, but it is a lot cheaper than a $100 valve repair job or replacing a dead lawn.  I recommend a “150 mesh screen” in the filter. The filter can be installed underground in a box if you don’t want it visually cluttering up your landscape. On the other hand, it is nice to have it in a more convenient above-ground location for maintenance. Remember, you need to clean the filter screens at least once a year if not more often! For tons more information on filtration see the Irrigation Water Filtration Tutorial.

Cold Winter Precautions:  Unless your irrigation system is in an area where it never freezes you should insulate the backflow preventer and any other above ground equipment. Backflow preventers are very expensive, you don’t want an unexpected freeze to catch you off-guard. A few years back that happened here in California and thousands of backflow preventers had to be replaced because the water froze in them and they split open! I usually use foam insulation tape to wrap the backflow preventers and above ground valves, then wrap the insulation with a layer or two of 10mil black plastic tape to protect it. There are also some pretty neat backflow preventer blankets (essentially a big insulated bag), that are made to fit over the backflow preventer like a big coat. They work good, I use them. (I have a small one in my truck that I use to keep cans of soda cool when I’m on the road. It also makes a great pillow!) If the backflow preventer has air vents or a water blow-off outlet it is extremely important that they not be blocked by insulation! There should be instructions that come with your backflow preventer.

Winterization:  In areas where freezing weather occurs you need to take precautions to protect your irrigation system from freezing. There is a whole tutorial on winterizing your sprinkler system in areas where it really freezes hard. It covers the various methods used, advantages and disadvantages of each, and what you will need to install as part of your new sprinkler system for each method.

Pumps: Thinking you might need an alternative water source for your sprinklers such as from a pond or lake? Check out the Irrigation Pumping Systems Tutorial.

How much will it cost?

That’s hard to say. I priced out the materials for the little sample irrigation system at the top of this page at $375.00. That included reasonably good quality sprinkler heads, “funny pipe” type risers, Cl 200 PVC pipe, anti-siphon valves, and a very inexpensive $50.00 controller. That comes to about $0.25 per square foot of irrigated area. You may need to add extra for a better backflow preventer and better controller. I would suggest in most cases that you estimate at $0.25 per square foot plus the controller and backflow preventer cost.

Professional Installers:

Installation generally costs about 1.5 times the cost of the materials.  Installation costs can vary wildly, be sure to get 3 bids.  If any bid is significantly lower than the others I would be extremely suspicious and use extreme caution before hiring that cheap contractor.  Never pay a deposit up front unless you are willing to risk losing that money.  If the contractor needs up front money insist that he deliver  materials equal to the deposit value to your house prior to payment.  Remember if the contractor needs money up front to buy supplies that means the suppliers won’t sell to him on credit.  Suppliers sell to almost everyone on 30-day interest free credit, so if they don’t trust him/her to pay them that should be a huge warning to you!  The irrigation installation business is very easy and cheap to get started in, and as a result it has a huge number of contractors are under-financed, then under-bid to get work, can’t complete the work, and fail.  Understand that property laws in the USA allow the supplier to place a lien on your home for the value of any materials the contractor buys for your sprinkler system, but does not pay for.  It does not matter if you paid the contractor already for those materials.  The supplier can still make you pay for them again.  That is the law.  Be smart, protect yourself!!!

Installation

Now you’ll probably want to move on to the tutorial on to the Sprinkler System Installation Tutorial.  It covers in more detail the various irrigation parts you will use, like sprinkler risers. It also teaches you to “talk sprinklers” (so you can sound like you know more than you do!), helps you make a list of the materials you will need to buy, provides some helpful forms you can print out, explains which tools can make your day or break your back, and a few other tips and tricks! Be sure you read it before you buy anything or start digging!!! (Just when you thought you were finished!)

End of Tutorial

 

Tutorial Credits:
(As you will note, I’ve enlisted some assistance from my family members!)

Written by Jess Stryker, Landscape Architect, unless noted otherwise

Constructive Criticism:

  • Julie Stryker, the love of my life!
  • Nathan Stryker, my son.
  • Dan Fahndrich of Farwest Gardens, Inc.
  • The many tutorial users who have asked questions and pointed out unclear topics.
  • And even a few jerks who have kept me (sorta) humble!!!

HTML Coding and page design:

  • Jess Stryker & Nathan Stryker
  • WordPress
  • NoteTab Pro by Eric G.V. Fookes, www.notetab.com

Graphics:

  • Jess Stryker
  • Nathan Stryker
  • Steve Brinkman

Other individual credits are listed on the pages of the tutorial.

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Why Not Use 1/2″ Pipe or Tube for Irrigation

Saturday, December 3rd, 2011

Well, if you have been reading my tutorials, I guess it’s pretty obvious that I’m not recommending you use 1/2″ pipe. I have a number of reasons for this.

  • 1/2″ PVC pipe is generally not available in most areas except in SCH 40 type.
  • The water capacity of 1/2″ pipe or tube is very low.
  • 1/2″ PVC pipe is hard to glue together without using too much glue. The glue piles up on the inside of the pipe when you insert it into the fitting and blocks the water flow. Too much glue also weakens the wall of the pipe and a leak develops after a few years.
  • Using 1/2″ pipe means you have to have another size of spare pipe and fittings on hand for repairs.
  • But the biggest reason is that 1/2″ pipe leaves no flexibility for future changes or additions to your sprinkler system. If you ever need to add another sprinkler to the pipe you’re screwed.

My conclusion: The small amount of money saved by using 1/2″ pipe just isn’t worth the hassle and risk.

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Irrigation Lateral Sprinkler Pipe Size

Monday, November 28th, 2011

Step #5 of the
Landscape Sprinkler System Design Tutorial

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Friction Loss:
As water moves through a pipe it loses pressure due to a phenomenon commonly called “friction loss”. Much of this loss is caused by turbulence, but we call it friction loss for simplicity. The amount of friction loss is determined by the type of pipe, the diameter of the pipe, the amount of water flowing through the pipe, and the length of the pipe. A complex formula (called the Williams/Hazen Formula) predicts the amount of pressure that will be lost due to friction loss.  The water also loses pressure each time it passes through a valve, a backflow preventer, or anything else it encounters on it’s way to the sprinkler head. Even a bend in the pipe causes pressure loss!  Don’t panic over the formula, we’ll use a pipe sizing chart or a friction loss calculator!

You need lots of pressure at those sprinkler heads!
The sprinkler head needs a minimum amount of water pressure to work properly. The manufacturer’s performance charts tell you how much pressure is required to achieve a specific radius for the water.  As the pressure increases so does the flow (GPM) and the radius of the throw. So in order to assure that there is enough pressure to make the sprinklers operate as they should, we need to calculate the pressure losses between the water source and the sprinkler head.  If the pressure loss is found to be too great, then we must reduce.  The easiest way to do that is to use a larger size pipe.

 

DETERMINING THE SPRINKLER PIPE SIZE

There are several methods used to determine pipe sizes of sprinkler system lateral pipes.  I’m going to explain two methods.  One method is faster but less accurate, the other is very accurate but takes more time.

Chart Method:

Pros: The fastest and easiest method.  Requires a single, simple calculation and uses a chart to determine the sizes.
Cons:  The learning curve to use it is a bit more difficult to understand.  It uses an averaging system to arrive at pipe sizes.
See step-by-step tutorial for the Chart Method

Trial & Error:

Pros:  Very accurate, calculates the pressure loss in each pipe section using a spreadsheet.  Easier to understand.
Cons:  Time consuming, need to enter data into the spreadsheet, uses trial and error to establish pipe sizes.
See step-by-step tutorial for the Trial & Error method

Which method should you use?  For a beginner with a small irrigation system probably the Trial & Error system will be easier.  Below are overviews of each method for experienced designers to use.  Unless you are experienced you should probably read the full tutorial for the method you select.

Overview: CHART METHOD FOR LATERAL IRRIGATION PIPE SIZING

See Determining Sprinkler Pipe Size Using a Pipe Sizing Chart for detailed step-by-step instructions.

Calculate the PSI/100 value:

( ____ PSI x 100) / ____ Feet Total Length = PSI/100

____ PSI.  Insert the maximum PSI loss for the valve circuit laterals into the formula where it says “____PSI.”

____ Feet.  Insert the distance from the valve to the farthest sprinkler on the valve circuit  in the space labeled “____ Feet Total Length” in the formula.

Remember that the maximum total pressure loss between the valve and the last sprinkler may NOT exceed 20% of the sprinkler head operating pressure.

The Pipe Size Table or Chart:

Sprinkler Pipe Sizing Chart for Laterals
PSI/100 = Desired PSI Loss in Lateral x 100 / Total length of Lateral

PSI/100

0.2

0.5

0.8

1.0

1.5

2.0

3.0

4.0

5.0

6.0

SIZE

2.2

3.3

4.4

5.0

6.2

7.1

8.5

10

11

13

¾”

3.8

6.3

8.1

9.2

11

13

17

20

22

24

1″

7.1

12

15

18

22

25

31

36

37

37

1¼”

11

16

22

24

31

35

44

48

49

49

1½

18

30

40

44

57

65

76

76

76

76

2″

28

46

60

67

83

96

114

114

114

114

2½”

46

75

100

112

140

162

165

170

170

170

3″

87

140

185

208

250

280

280

280

280

280

4″

255

410

540

600

600

600

600

600

600

600

6″

 Flows shown red are over 5 feet/second. Use caution!

Instructions:

    1. Find your PSI/100 value in the top blue row.
    2. Read down the column to the value equal to, or higher than, the GPM in the pipe section.
    3. Read across to the pipe size for that section in the right column.
    4. Repeat steps 2 & 3 for next pipe section.

This table uses an averaging formula based on the assumption that all flows for any given size of pipe will not be at the maximum GPM for that size of pipe. In rare cases the PSI loss for the entire lateral may exceed the desired loss by up to 10%. This table assumes the use of Cl 200 PVC pipe, adjustments to the pipe sizes are required for other pipe types, such as poly or SCH 40 PVC.

Pipe Sizing Chart, Copyright 1979, Jess Stryker, All rights reserved.

Notes about the Pipe Sizing Chart:

  • Warning:  The sprinkler pipe sizing chart is based on using Cl 200 PVC pipe.   It also works for Class 125 (not recommended) and Class 160 (hard to find).
  • Schedule 40 PVC: If you plan to use Schedule 40 PVC pipe (“SCH 40″) for the laterals you need to make an adjustment before using the chart. Reduce the PSI/100 value you just calculated for the valve circuits to 1/2 the original values.
  • Polyethylene, Polybutylene: After you obtain your pipe size from the chart you need to increase it by one size to get the proper size for poly pipe. In other words, if the chart says ¾” PVC pipe, then you should use 1″ poly pipe. 1″ would become 1¼”, 1¼” becomes 1½”, 1½” becomes 2″, etc.
  • Where’s the 1/2″ pipe?  See “why not 1/2″?”

CONFUSING?  DON’T PANIC:   For detailed instructions see the page Irrigation Pipe Sizing Chart for Laterals.


 

Overview: TRIAL & ERROR METHOD TO DETERMINE LATERAL PIPE SIZE

See Calculating Sprinkler System Pipe Size Using a Spreadsheet for detailed step-by-step instructions.

This method involves trying various pipe sizes until a good combination is found.  A spreadsheet does the calculations.

You will need a spreadsheet friction loss calculator:  Friction Loss Calculator Spreadsheets

Remember that the maximum total pressure loss between the valve and the last sprinkler may NOT exceed 20% of the sprinkler head operating pressure.

Use the spreadsheet friction loss calculator to determine the pressure loss:

  1. Download and open the Friction Loss Calculator.
  2. There is a line on the spreadsheet for each section of pipe.
  3. Start with the pipe section after the control valve and work out to the farthest sprinkler.
  4. Select 3/4″ pipe for the pipe or tube size. (See “why not 1/2″?”)
  5. Enter the GPM for the section of pipe.
  6. Enter the length of the section of pipe.
  7. Use an error factor of 1.1
  8. Go to the next line down and repeat steps 4-7 for the next pipe section.
  9. The spreadsheet calculator will tell you the velocity and PSI Loss for each pipe section.
  10. At the bottom of the calculator it will tell you the pressure loss total of all sections combined.
  11. Change the pipe size if the velocity or total pressure loss is too high.

You must calculate the pressure loss for each of the possible water paths in the valve circuit.

Here is an example of the possible water paths for a valve circuit, shown in red, blue, and magenta.

Start with the water route that is the longest.  In this case that would be the red route.   There are 9 pipe sections in this route labeled 1-9.  Enter the data from this route into the calculator.  Use a larger pipe size if the velocity is not safe.   Check that the friction loss “Total of All Sections” does not exceed your maximum allowable amount.

Write the pipe size for each section on your plan.
Now repeat the process for the blue water route and then the magenta color route.

Confused? For detailed instructions on using the spreadsheets see What Size Pipe for Sprinkler System Laterals?

 

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Calculating Sprinkler System Pipe Size Using a Spreadsheet

Saturday, November 26th, 2011

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THE GROUND RULES

First a tip that just may save your behind!

When in doubt, always use a larger diameter pipe!

It will not harm anything to use a larger pipe size.  Period.  If you are uncertain whether to use a 3/4″ or 1″ pipe, then you should use the 1″.   Using a larger size pipe is ALWAYS the safest choice.

No, I don’t own stock in an irrigation pipe manufacturer and I’m not getting kickbacks for pushing bigger pipe! Unlike clothing, pipe can never be “too large”. Contrary to what might appear to be true, forcing water into a smaller pipe REDUCES the water pressure, and hurts sprinkler performance. This is because the smaller pipe creates more pressure loss due to friction and turbulence as the water flows through it. It’s another of those hard to grasp hydraulic principles! Just remember that when it comes to pipe, bigger is better! I’m always amazed at how many irrigation equipment sales people don’t know this most basic of irrigation rules. I’ve had clients tell me they were told to use a smaller pipe to keep the pressure up by tech support people at some of the major sprinkler manufacturer’s. That’s an industry disgrace!

So one more time to drill it into your head– You don’t decrease the pipe size to keep the pressure up- or down for that matter. That is totally, completely, wrong. The reason we use smaller pipe is to save money. Which of course, is a good reason!  For those who want more specifics on this, there is a very boring scientific explanation at the bottom of this page.

Is it Pipe or Tube?  For the most part I use the term “pipe” rather than “tube” on this page and elsewhere.  Bad habit of mine (note that by reading carefully, you have found one of my faults!)  The difference is the material they are made from.  Steel and PVC plastic are generally called pipe.  Polyethylene, PEX, and copper are usually referred to as tube.  I often screw up and call tube pipe!  :)

 

 

TRIAL & ERROR METHOD TO DETERMINE LATERAL PIPE SIZE USING A SPREADSHEET

 

This method involves trying various pipe sizes until a good combination is found.

Definitions you need to know:

Lateral pipe: all the pipes between the control valve and the sprinkler heads.

Mainline: The pipe that goes from the water source to the control valves.

Control Valve: The valve that turns on and off a group of sprinklers. Most often it is an electric valve operated by a timer.

Valve circuit: a single valve, and all the pipe, fittings and sprinkler heads downstream from it. In other words, all the sprinkler heads that start working when you turn on the valve are part of the same valve circuit.

GPM:  Gallons per minute, a measure of water flow rate.  Use primarily in the United States.

PSI:  Pounds per square inch, a measure of water pressure.  Use primarily in the United States.

You will need a spreadsheet Friction Loss Calculator.
Here’s a page with calculators for almost every type of pipe: Friction Loss Calculator Spreadsheets
Grab the appropriate spreadsheet for the type pipe you plan to use.

Now you just enter the appropriate data for each section of pipe into the calculator and then read the total pressure loss at the bottom of the spreadsheet. If the pressure loss is too high, then try making one of the lengths of pipe larger. The calculator will also give you the water velocity in each section of pipe, and warn you if the velocity is too high.

Detailed Instructions:

The best way to teach this is probably to walk you through a couple of examples. 

If I may make a suggestion, download the spreadsheet for Cl200 PVC now, and open it up in a separate window.  Then think about each step, enter the values I show into the spreadsheet, and actually try to duplicate what I do in the examples below.  Something about actually doing this helps engage people’s brains.  People tell me they read it twice and still don’t get it when they just read it, but as soon as they actually TRY it, then it suddenly makes sense.  It’s called learning by doing, and it is considered the best teaching method.  This process is simple, HOWEVER, it is not obvious and sounds illogical to those not trained in hydraulics.

 

A Simple Example:

Example Plan

The sketch above is an example of a very simple valve circuit with 5 sprinkler heads. In this example the sprinklers are 15′ apart and each sprinkler uses 3.7 GPM of water. The red numbers on the sketch are the total water flow for each pipe section in GPM.
Let’s assume we want to use Cl200 PVC pipe and we want a maximum total of 4 PSI of pressure loss in our lateral pipes.

If you are working through the Sprinkler Design Tutorial the maximum total pressure loss is entered on your Design Data Form in the Pressure Loss Table section.  There you will see a figure you entered called “_____ PSI – Laterals”.   That is the maximum PSI loss for the laterals, use that number here.  If in doubt, 3 PSI is a reasonably safe value for most sprinkler systems.

If you don’t understand how to calculate the water flow in each section (the red numbers) you should take a look at the Sprinkler Pipe Layout page.
Remember that the maximum total pressure loss between the valve and the last sprinkler may NOT exceed 20% of the sprinkler head operating pressure.
Example: 20 PSI sprinkler operating pressure. 20 x 0.20 = 4 PSI maximum pressure loss in circuit laterals.
If you don’t understand pressure losses in irrigation, see Pressure Loss & Selecting Your Sprinkler Equipment.
For advice on types of pipe (Cl200, poly, etc.) see Irrigation System Lateral Pipes.

To use the spreadsheet friction loss calculator to determine the pressure loss:

  1. Download and open the Friction Loss Calculator.
  2. There is a line on the spreadsheet for each section of pipe. So for this example you will enter data for 5 pipe sections.
  3. Start with the pipe section closest to the valve as section #1, and work out to the farthest sprinkler head.
  4. Start by selecting 3/4″ pipe for the pipe or tube size for all the sections. (See “why not 1/2″?”)
  5. Enter the GPM for the section of pipe.
  6. Enter the length of the section of pipe.
  7. Use an error factor of 1.1
  8. Go to the next line down and repeat steps 4-7 for the next pipe section.
  9. The spreadsheet calculator will tell you the velocity and PSI Loss for each pipe section.
  10. At the bottom of the calculator it will tell you the pressure loss total of all sections combined.

Here’s what the spreadsheet calculator looks like after we enter the data requested for each of the pipe sections using the example in the sketch above.

 

Note that the “Total of all Sections” shown at the bottom exceeds the 4 PSI maximum limit we set for pressure loss. Also notice that the velocity in two of the sections (highlighted in red) exceeds the safe level. The marginally high velocity highlighted in yellow is considered acceptable by most experts, since these are lateral pipes. (The marginal velocity level would not be as acceptable in mainlines.) Start by fixing the velocity problems.  To decrease the velocity in those sections we will need to increase the pipe size.  So let’s increase the pipe size for the two sections highlighted with red to 1″. Here’s what it looks like after the change:

 

Now the velocities are all within acceptable levels. Also note that increasing the pipe sizes reduced the pressure loss “Total of All Sections” shown at the bottom to 2.9 PSI, which is well below our maximum level of 4 PSI. That’s good, no more changes are needed.    It is not possible for the pressure loss to be “too low.” As long as it is under the maximum it is fantastic.  So what would happen if the pressure loss was still too high? If there was still too much pressure loss we would need to try increasing the size of some of the pipes to lower the friction loss.

So we now have pipe sizes that will work for each section of pipe in our lateral. I’m often asked at this point if it would be OK to make some of the pipes 1/2″ since the pressure loss is so low? The answer is yes, but you might not want to do it.   See my explanation of the problems associated with the use of 1/2″ pipe.

 

A More Complex Example:

Now lets look at a more complex valve circuit. (Please note that this circuit is much larger than that found on a typical residential irrigation system. It would require much more water than most residences have available and is just used to show you an example of a much more complex layout.)  As with the previous example we will assume that our maximum pressure loss value for the valve circuit is 4 PSI.

This valve circuit involves numerous paths the water may take. This makes the calculation a bit more complex, as a separate calculation is needed for each possible route that the water might take through the laterals on it’s way to the last sprinkler at the end of a pipe. If you look at the example above you will notice there are 3 sprinklers that are at the end of pipes, each sprinkler at the end of a pipe represents a different route the water can take. So this circuit has 3 and will therefore require 3 separate pressure loss calculations.  The next drawing shows the possible water routes in magenta, blue, and red colors.

It may help to think of each path as the shortest route that a single drop of water could take to go from the valve to the last sprinkler on a pipe branch.  For some people it helps to think of it as a road map and your looking for the shortest route to each of the dead ends at the end of the roads.

Start your calculations with the water route that is the longest. In this case that would be the route highlighted in red. There are 9 pipe sections in this route, I have labeled them 1-9 for clarity. Just as before, enter the data from this route into the calculator, and make all the pipe 3/4″ size.   Here’s what the spreadsheet looks like:

As you can see there are a number of pipe sections highlighted red due to unsafe velocity.  Change those pipe sections to larger pipe sizes until all the velocities are within safe levels.

Here’s the resulting spreadsheet calculator with the smallest possible pipe sizes.  However, notice the Total of All Sections is 4.4 PSI, which is more than our 4 PSI maximum:

So we need to make some of the pipe sections larger in order to reduce the pressure loss (or friction loss.)  Start by increasing the size of one of the the smaller pipe sections.  Changing a 3/4″ pipe to a 1″ size is a lot less expensive than changing a 1″ pipe to 1 1/4″.  So for the example lets change section 7 from 3/4″ to 1″.  Doing that drops the Total of all Sections value to 3.77 in our example, below the 4 PSI maximum we set earlier.  So now everything is good, these sizes will work for the “red” highlighted water route.

Now we add the pipe sizes from the spreadsheet to our circuit drawing (note that the pipe sizes for the red highlighted sections have been added on the next drawing below.)

Now we relabel our sections to follow the blue highlighted route.

Using the blue highlighted water route, repeat the same process used for the red one. Enter the GPM and pipe lengths for each section in the spreadsheet. This time we already know the sizes for sections 1-6, they were entered into the spreadsheet when we did the red section.  So we just enter those for the new blue sections 7 and 8, again using 3/4″ size pipe.   And it looks like this on the spreadsheet calculator:

Using 3/4″ pipe size for our two new sections works good.  The velocity is safe and the Total of All Sections is 3.29 PSI, so the pressure loss for this route is also within the 4 PSI maximum we set.  Write the size of the two new sections on the drawing and the blue water route is done.

Now all that remains is to do are the calculations for the magenta highlighted water route. That is done the same way, entering the data into the spreadsheet calculator for each pipe section. Start with 3/4″ then change to larger sizes until the velocity is safe.  Then check that the total of all Sections is less than 4 PSI as before.  Here’s the data entered into the spreadsheet calculator:

Now all that remains is to insert our lateral pipe sizes from the spreadsheet calculators into the drawing of the valve circuit.

All done! So the pressure loss for the entire circuit is the same as that for the highest water route.  In this case the red route was highest at 3.77 PSI.  So the pressure loss for the lateral circuit shown here is 3.77 PSI.

Often I get asked at this point why the “Total of all Sections” pressure losses for all 3 routes wasn’t added together?  The pressure loss for the red route was 3.77 PSI, for the blue section it was 3.29 PSI, and for the magenta route it was 3.02 PSI.  So the confusion is that it seems like there should be a total loss of 10.08 PSI!  Nope, the pressure loss for the entire lateral is 3.77 PSI, the loss of the highest route.  To understand this think of a single drop of water again.  It can only travel on one route from the valve to the farthest sprinkler.  It is not going to go backwards and try another route!  So the pressure loss for the entire valve circuit is equal to the pressure loss from the valve to the farthest sprinkler.

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Irrigation Pipe Sizing Chart for Laterals

Saturday, November 26th, 2011

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(Sometimes called a Pipe Sizing Table.)

This method is based on the assumption that you are using Cl 200 PVC pipe for the lateral pipes.  With minor adjustments this method will also work reasonably well for SCH 40 PVC pipe or polyethylene irrigation tube.  For other types of pipe or tube you will need to use the Trial & Error method to determine the pipe sizes.

While the Pipe Sizing Chart method described here seems rather complex when you read it the first time, it is actually extremely fast and easy once you figure it out.  You will start with a simple calculation to obtain a “PSI/100″ value.  Then you will use that value in the Pipe Sizing Chart to figure out the maximum flow for various sizes of pipe.  You will only do this once for each sprinkler system.  Once you have that schedule you will fly through inserting pipe sizes into your plan.  Most designers who “design in their heads” are using this method or a close variation of it.   It is the method I use when designing my systems.

Definitions:

Lateral pipe:  The pipes between the control valve and the sprinkler heads are called “laterals”.

Mainline:  The pipes that go from the water source to the control valves are called “mainlines”.

Control Valve:  The control valve is the valve used to turn on and off a group of sprinklers.  Often it is an electric solenoid valve operated by a timer.

Valve circuit:  A valve circuit consists of  a single control valve, and all the fittings, pipes, and sprinkler heads that it turns on.

GPM:  Gallons per minute, a measure of water flow rate.  Use primarily in the United States.

PSI:  Pounds per square inch, a measure of water pressure.  Use primarily in the United States.

 

BASIC RULES TO KEEP IN MIND

When in doubt, always use a larger diameter pipe!

You may always use a larger size pipe.  No, I don’t own stock in a irrigation pipe manufacturer.  But using a larger size of pipe will not cause any harm to how well your sprinkler system works.  Using a larger pipe will NOT noticeably reduce the water pressure.  (Yes, I did condition that statement with a “noticeably”.)  The only damage done by using a larger size of pipe is to your pocketbook.  Larger pipe generally costs more.  But from a irrigation system performance perspective you will NEVER hurt anything by using a larger size pipe.  Now I realize that somewhere out there, somewhere will tell you this is not true.  They are going to tell you that you need a smaller pipe to squeeze the water and create more pressure.  They are totally wrong of course, but as you read this you are probably uncertain who is right, since they will claim I am wrong!  Ask them to provide you with a scientific, documented explanation of why they are right.  I will also provide both a basic and a very scientific explanation with references for you.  Here’s mine: Using A Smaller Pipe to Increase Water Pressure.  OK, sorry, I’ll climb down off my soapbox now.

Is it Pipe or Tube?  I tend to call everything pipe.  Habit, since here in La La Land (Los Angeles, California) we use mostly PVC pipe for irrigation.  However some types of “pipe” are technically defined as “tube”.    The difference is the material they are constructed of.  Steel and PVC plastic are generally called pipe.  Polyethylene, PEX, and copper are usually called tube or tubing.  If I say pipe where I should say tube, please accept my apologies.

 

CALCULATING THE PSI/100 VALUE:

The PSI/100 value is a value used in the Pipe Sizing Chart (we’ll get to the chart in a moment.)  The PSI/100 value determines which column of the chart you will use when finding the pipe sizes.   A simple calculation will give you the PSI/100 value.

The PSI/100 formula:

( ____ PSI x 100) / ____ Feet Total Length = PSI/100

For those who prefer variables, this is the same formula written using variables:    (LPSI * 100) / FTL = PSI/100

Here are the values to insert in the blank spots (“____” ), or variables, in the formula:

____ PSI.  (LPSI)  Insert the maximum PSI loss for all laterals on the valve circuit into the formula where it says “____PSI.”  .

If you are working through the Sprinkler Design Tutorial look on your Design Data Form for the Pressure Loss Table. There you will see a figure you entered called “_____ PSI – Laterals”.   That is the maximum PSI loss for the laterals, use that number here.  If in doubt, 3 PSI is a reasonably safe value for most sprinkler systems.  If you don’t understand pressure losses in irrigation, see the Pressure Loss & Selecting Your Sprinkler Equipment and Lateral Pressure Loss pages.  Remember that the maximum total pressure loss between the valve and the last sprinkler may NOT exceed 20% of the sprinkler head operating pressure.  Example:  20 PSI sprinkler operating pressure.  20 x 0.20 = 4 PSI maximum pressure loss in circuit laterals.

 ____ Feet Total Length.  (FTL)   Insert the distance from the control valve to the farthest sprinkler  in the space labeled “____ Feet Total Length” in the formula.

For this value you need to figure out the total length of pipe (in feet) that the water needs to travel through in order to get from the valve to the farthest sprinkler.   Measure only the pipe sections that the water would pass through on the way from the control valve to that farthest sprinkler.  Don’t add in the length of any side spurs going off to other heads that aren’t on the longest route.  In the example below, the route from the control valve to the farthest sprinkler that you would measure the distance of is shown in red.  Totaling each of the pipe sections along that route results in 118′.  So 118 feet would be the ___ feet value you would use in the PSI/100 formula.

Example of A Typical Valve Circuit


Now use the PSI/100 formula above to calculate the PSI/100 value.  ( ____ PSI x 100) / ____ Feet Total Length = PSI/100

Write down the PSI/100 value.  ____________ 

Example: Let’s say the value “____ PSI – Laterals” is 4 PSI. Let’s also assume that the total length of the lateral as measured above is 118 feet. Those values inserted in the formula would look like this:  (4 PSI x 100) / 118 feet     Now do the math.  4 times 100 = 400.  Then 400 divided by 118 = 3.389    Round that number to 3.4.    Therefore when using this example your PSI/100 value to use in the Pipe Sizing Chart would be 3.4 PSI/100 .

You can repeat this procedure for each valve circuit. But the usual method is–

It is possible to use the same PSI/100 value for all the valve circuits. That’s how most professionals (myself included) do it. The only catch is that you must use the “worst case” PSI/100 value. In other words you need to figure out which of the valve circuits on your entire sprinkler system has the longest “Feet Total Length” between the valve and last sprinkler.   Then use that valve circuit to calculate your worst case PSI/100 for the entire sprinkler system.  The advantage of using the same PSI/100 value for everything is uniformity of design and, obviously, doing only one PSI/100 calculation for the entire sprinkler system saves time.  For example, a pipe with five half circle spray heads downstream would always be the same size pipe. This is much less confusing for the installer, which is the main reason we do it this way.

 

Pipe Sections and GPM:

Each section of lateral pipe may be a different size. For example, the first section of pipe leading away from the valve might be 1 1/4″. The next two sections might be 1″, and the rest of the sections might be 3/4″. The pipe size to each section is based on the actual GPM flow passing through that section of pipe, so you will need to know what the GPM flow is for each section.  If you have been working through the Sprinkler Design Tutorial you have already figured this out and written these GPM values down on your plan in an earlier step.  If not, you will need to take a few minutes to do this now.  See the page on Sprinkler Pipe Layout for instructions on figuring out the GPM for each pipe section.

 

THE PIPE SIZING TABLE or CHART:

before you use the chart…

Warning:  The sprinkler pipe sizing table /chart is based on using Cl 200 PVC pipe.  For other pipe types you will need to make an adjustment if you want to use the chart.

Schedule 40 PVC: If you plan to use Schedule 40 PVC pipe (“SCH 40″) for the laterals you need to make an adjustment before using the chart below, because SCH 40 PVC pipe has a much less water capacity than other PVC pipes. Reduce the PSI/100 value you just calculated for the valve circuits to 1/2 the original values.

Example for SCH 40 PVC pipe: In the example above you calculated a value of 3.4 PSI/100. But you have decided to use SCH 40 PVC pipe for the laterals, rather than Cl 200 PVC pipe. So you will need to reduce the PSI/100 value by half. 3.4 x 0.5 = 1.7 PSI/100. So your new value is 1.7 PSI/100. As you will see, this will result in much larger lateral pipes! This is why most people do not use SCH 40 PVC for laterals, and why I recommend you use Class 200 PVC. It makes a big difference in cost!

Class 125, Class 160, or Class 200 PVC pipe: The chart below is based on the use of Class 200 PVC pipe. It also works for Class 125 (not recommended) and Class 160 (hard to find).

Class 100 and 315 PVC pipe: As a general rule, these types of PVC pipe are not used for laterals.

Polyethylene, Polybutylene: Use the chart below. Then, after you obtain your pipe size from the chart you need to increase it by one size to get the proper size for poly pipe. In other words, if the chart says ¾” PVC pipe, then you should use 1″ poly pipe. 1″ would become 1¼”, 1¼” becomes 1½”, 1½” becomes 2″, etc.  Note: PEX pipe is not the same thing as polyethylene irrigation pipe.

PEX: Do not use the chart for PEX pipe.  PEX has extremely limited flow.  Use the Trial & Error Sizing Method for PEX!

To use the chart you will use the PSI/100 value you calculated along with the GPM flow in the pipe section.

 

Sprinkler Pipe Sizing Chart for Laterals

PSI/100  (round down)

0.2

0.5

0.8

1.0

1.5

2.0

3.0

4.0

5.0

6.0

SIZE

2.2

3.3

4.4

5.0

6.2

7.1

8.5

10

11

13

¾”

3.8

6.3

8.1

9.2

11

13

17

20

22

24

1″

7.1

12

15

18

22

25

31

36

37

37

1¼”

11

16

22

24

31

35

44

48

49

49

1½

18

30

40

44

57

65

76

76

76

76

2″

28

46

60

67

83

96

114

114

114

114

2½”

46

75

100

112

140

162

165

170

170

170

3″

87

140

185

208

250

280

280

280

280

280

4″

255

410

540

600

600

600

600

600

600

600

6″

Flows shown in red are over 5 feet/second.
Sprinkler Pipe Sizing Chart, Copyright 1979, Jess Stryker, All rights reserved.
Permission is granted for reuse for any purpose and in any media, provided the copyright notice is maintained.

Sprinkler Pipe Sizing Table /Chart Instructions:

  1. Start with the pipe section farthest from the valve (connecting to the last sprinkler head.)
  2. Find the PSI/100 value in the top row (blue text, directly under the heading PSI/100.)
  3. Read down that column and find a value equal to, or higher than, the GPM in the pipe section.
  4. Now read across to the right column to find the pipe size to use for the pipe section.
  5. Repeat steps 3-5 for the other pipe sections in the lateral valve circuit.

Notes:

  • Flows over 5 ft/second are considered marginal (shown in red on chart.)  Most experts believe that flows up to 7 ft/sec are acceptable for laterals.  However flows over 7 ft/sec velocity are not considered safe, so they are not shown on the chart.
  • This table uses an averaging formula based on the assumption that all flows for any given size of pipe will not be at the maximum GPM for that size of pipe. In rare cases the PSI loss for the entire lateral may exceed the desired loss by up to 10%.
  • This table assumes the use of Cl 200 PVC pipe, adjustments to the pipe sizes are required for other pipe types, such as poly or SCH 40 PVC.
  • No 1/2″ pipe?  See my explanation of why I don’t use half-inch size pipe.

 

Example Using the Pipe Sizing Chart:

 Example Sketch of a Sprinkler System

In the example above the flows for each pipe section are noted in gray text with an arrow pointing at the pipe section.  The red pipe circuit has the longest distance between the control valve and the farthest sprinkler head.  So for our example let’s use the red pipe circuit.

First we need to calculate the PSI/100 value.

We start with the maximum pressure loss we want in our lateral pipes.  For this example we will use 4 PSI.
Now we measure the total pipe distance from the valve to the farthest head.  I showed this route using a bold red line.  It is 96 feet from the control valve to the farthest head when following this bold red route.
Now the PSI/100 formula with the values from this example inserted:  ( _4_ PSI x 100) / _96_ Feet Total Length = _4.2_ PSI/100

Now we start using the chart to find the pipe sizes.

Our PSI/100 value is 4.2, so we look on the chart.  Rounding down we see that 4.0 is the closest PSI/100 value on the chart, so we use the 4.0 column.
Now read down the 4.0 column.  The numbers will tell us the maximum flow for each pipe size.
So the first number we see is 10.  That would mean 10 GPM.  Reading across to the right we see that 10 GPM is the maximum flow for 3/4″ size pipe.
Continuing in the 4.0 column, the next number is 20.  Again we read across and see that 20 GPM will be the maximum flow for 1″ pipe.
Reading down one more line we see that 36 GPM is the maximum flow for 1 1/4″ pipe.  And we can continue this on down the chart.
So now we can create a simple pipe size schedule to use for our plan, based on the values we took from the pipe sizing chart:

Up to 10 GPM = 3/4″ size pipe
Up to 20 GPM = 1″ size pipe
Up to 36 GPM = 1 1/4″ size pipe
Up to 48 GPM = 1 1/2″ size pipe
Up to 76 GPM = 2″ size pipe

Now  go back and look at the flow for each section of pipe on your plan.  Then based on the GPM flow, insert the pipe size from the schedule you made.

So the section with a flow of 2.5 GPM will be 3/4″ pipe.
The section with 1.3 GPM will also be 3/4″ pipe.
The section with 3.8 GPM will be 3/4″ pipe.
The section with 6.4 GPM will be 3/4″ pipe.
The section with 1.3 GPM will be 3/4″ pipe.
The section with 2.6 GPM will be 3/4″ pipe.
The section with 9.0 GPM will be 3/4″ pipe.
The section with 11.5 GPM will be 1″ pipe.

I’ve inserted these pipe sizes on the example sketch above.

See how fast and easy that is?  Once you have the initial PSI/100 calculations done you can use the pipe sizing chart to create a custom pipe schedule for your plan.  Then it is really fast to simply look at the flow in a pipe section, look it up on the schedule, and write in the pipe size!  You can see why pros use this method, it allows them to fly through a large design with hundreds of sprinklers.

 

 COMMON PROBLEMS AND QUESTIONS REGARDING USING THE PIPE SIZING CHART

Is your PSI/100 value off the chart? If your PSI/100 value is 6.0 or higher you should use the 6.0 column. At 6.0 you have reached the maximum safe capacity of the pipe sizes used on the chart.

Is the pipe size larger than the valve size? It is fairly normal for the first pipe after the valve to be one size larger than the valve. So you may have a 1″ mainline going into a 3/4″ valve and then have a 1″ lateral pipe coming out of the 3/4″ valve.  This is very common, and is not a problem at all.  So don’t worry if the pipe size you get from the chart is larger – or smaller – than the valve size.

Write the pipe size down next to the pipe on your plan. Repeat for each pipe section.  Repeat for each valve circuit.

 

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Using A Smaller Pipe to Increase Water Pressure

Saturday, November 26th, 2011

There is a very persistent misconception in the lawn sprinkler industry that using progressively smaller pipe sizes in a sprinkler system will help keep the water pressure high.   The argument is that as the water moves through the pipes past the sprinklers, the pipe must get smaller in order to squeeze the water so that the pressure stays high enough to operate the sprinklers.  Unfortunately, it’s not true.  It would be nice if it was, because we could eliminate pumps.  Plus think of all the money you would save on pipe.  The smaller the pipe you used, the better your system would work!  So why not use 1/4″ or even 1/8″ tube for the pipes?  That would really pump up the pressure!  Sounds a little silly when you look at it that way, right?  OK, enough with the sarcasm.  I’ll explain this whole mess.

Squeezing the water into a smaller pipe will not increase the water pressure!

Part of the reason this misconception persists is that it does seem logical.  The example most often given to support this idea is what happens when holding your thumb over the end of a hose.  As you press your thumb over the opening, making it smaller, you can feel the water pressure against your thumb increase.  Pushing your thumb even tighter against the end of the hose, makes the opening even smaller, and you feel the pressure increase even more.  That would seem to prove that decreasing the opening size is increasing the water pressure.  So logically, using a smaller pipe would also increase the water pressure.

Unfortunately there is a lot more happening with this “thumb over the hose end” example than you realize.   As water moves through a hose or pipe there is a lot of resistance caused by the hose or pipe surfaces.   The water moves through the hose at the maximum speed it can while still overcoming this friction.  When the water reaches the end of the hose it has close to zero pressure left as it exits.  So if you have, say, 50 PSI of water pressure at the hose faucet, the  water will move as fast as it can through the hose, such that it will use up almost all that 50 PSI of pressure by the time it reaches the end of the hose.  If there were 60 PSI of pressure, the water would just move a little faster through the hose so that it used up almost all 60 PSI by the time it exits.  So basically regardless of the pressure, almost all the water pressure is used up by the time the water flows through the hose.  The nature of water is that it will reach the most efficient balance between flow rate and pressure loss that it can.  (Note, I am oversimplifying this to make it digestible for the average person.  If you have a degree in hydraulics you already know all the other related stuff about open vs. closed channels and nozzling effects.)

When you put your thumb over the end of the hose you change the flow dynamics in the hose.  Your thumb restricts the flow of water through the hose.   With your thumb over the end, the water is flowing much slower through the hose, and as a result, there is a lot less pressure loss due to friction.  So with less pressure being lost in the hose, the pressure at the end of the hose where your thumb is increases.  The tighter you squeeze your thumb, the more the flow is reduced, and the greater the pressure you feel will be.  But you haven’t created any NEW pressure.  You have simply traded reduced flow for increased pressure.    You can easily test this yourself.  Take a bucket and time how long it takes to fill it using an open end hose.  Now time how long it takes to fill the same bucket with your thumb firmly pressed over the hose end.  It will take longer to fill, because your thumb has reduced the flow!  The same thing would happen in your sprinkler system if you used smaller pipe to increase the pressure.  The smaller pipe would restrict the flow of water.   The reduced flow would reduce the pressure loss in the pipes, resulting in more pressure.  But of course the sprinklers would not work because they won’t be getting the flow they require!    Sprinklers require both flow and pressure.

OK, that’s the layman’s explanation.  But there are also some much more complex scientific theory that I have been asked about in relation to this topic.   So here’s some very scientific explanations.

Bernoulli’s Principle, Venturi Effect, & Flying Pigs

Grab your thinking caps for this.  As you well know, Bernoulli’s Principle essentially says (paraphrased) that as the speed of a fluid increases, the pressure of that fluid decreases. If it didn’t, pigs wouldn’t fly.*   Obviously as you force a given amount of water through a smaller size pipe, the velocity of the water must increase for it to get through the smaller pipe.  According to Bernoulli’s Principle that will decrease the water pressure!  This is called the Venturi effect.  By suddenly forcing the water through a narrow passage you can actually create enough of a pressure decrease that it creates suction.  This is how many fertilizer injectors work.  It also is another reason why using a smaller pipe would not increase the pressure– it would actually decrease it!

Another less common argument is the pipe size must be decreased because the flow is decreasing at each sprinkler head location along the pipe route. Thus if the pipe were to remain the same size, the velocity in the pipe would decrease, resulting in an increase in pressure (according to Bernoulli’s Principle again.)  This is actually a good, scientifically based point, and accurate too!  So the argument is that the pipe sizes must become smaller in order to keep the velocity constant and avoid an increase in water pressure. (Are you bored yet?) Unfortunately when used as an argument for using smaller pipe, this one falls flat when you do the actual math.  At a flow of 7 feet per second, which is the maximum recommended safe flow for PVC pipe, the maximum possible pressure increase  due to velocity change would be a whopping 1/3 PSI.  So in theory, using a smaller pipe would eliminate that 1/3 PSI pressure gain.  But using a smaller pipe probably would also increase the pressure loss due to friction, as previously mentioned.   The drop in pressure due to friction loss likely will offset most if not all of any gain that might have occurred due to decrease in velocity.  Even if it didn’t the maximum possible pressure gain of 1/3 PSI is simply not significant and would not be noticed.  So I stand by my statement that the only reason to decrease pipe size is to save money.

*Oh, by the way, Bernoulli’s Principle is why airplane wings create lift, which helps airplanes fly.  Therefore, it is also the reason that people, and yes, even pigs, can fly!

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Spreadsheets for Calculating Pipe Pressure Loss

Monday, October 10th, 2011

Here are some spreadsheets I have created to help you calculate the capacity and water pressure loss through pipes and tubes of various types and sizes. These should be useful for both figuring pressure loss in mainlines and laterals. Each spreadsheet allows for multiple sections of pipe of various sizes and flows. All you do is select the proper spreadsheet for the type of pipe you are going to use, select the pipe size from a drop down list, enter the flow through the pipe in GPM, then enter the length of the pipe in feet. The spreadsheet calculator will then do the math to give you the water velocity in the pipe along with the pressure loss in PSI for that section of pipe. If there are multiple sections of pipe the spreadsheet will also total all of them for the total pressure loss.

Full instructions for using the spreadsheets are included on the spreadsheets.

 

Please read this paragraph before you try to use the spreadsheets.

These spreadsheets use Apache Open Office.   That means you need to have the Open Office program installed on your computer for them to work.  I use Open Office because it is a free, safe program that is available for just about every desktop and laptop computer make and model.  That means just about everyone can use it, and nobody has to make a major software investment just to use the spreadsheets.  If you don’t already have Open Office you will need to install it on your computer before you can use the spreadsheets. You can uninstall it when you are done using it if you want.  Download it free from http://www.openoffice.org .  It does take a while to download Open  Office.  It is a full office productivity suite.  (Check it out, there are some cool apps in it!)

Your browser may try to “open” the spreadsheets if you left click on the links, even if you don’t have Open Office installed.  This is because most computers have some type of minimal spreadsheet reader installed on them, so the reader will try to open these spreadsheets.  If they were just simple spreadsheets they would probably work with the readers.  But they aren’t.   In most cases you will get a corrupted version of the spreadsheet that does not work.  This is because these friction loss calculators use very complex formulas that the “stripped down” spreadsheet readers can’t handle.  You need to install Open Office.   I may have already mentioned this. :-)

Remember, you can un-install Open Office when you are done if you don’t like it.

If you try to open the spreadsheets directly using your Internet browser they will probably open as Read Only and the spreadsheet won’t work.  This is because the browser will not open an executable file directly.  (It is trying to protect you from possible viruses.) 
Solution:  Right click on the link and “Save” the file to your hard drive.  The actual wording varies, so depending on your browser you may select “Save link as..”, “Save Target as…”, etc.   This should save the spreadsheet file to your hard drive.  Then open it directly from your computer without using the browser plug-in.  Tablet and phone users:  you may need to get to a real computer to use the spreadsheets.

If the spreadsheets don’t work for you..

  1. Do you have Open Office installed?  If not, install it.
  2. Are you using Open Office to read the spreadsheet?  Sometimes another spreadsheet program will try to open it instead of Open Office.
  3. Have you tried saving the spreadsheet file to your desktop, starting up Open Office, then opening the spreadsheet with Open Office?
  4. If the spreadsheet says it is “Read Only” you probably are using a non-compatible plug in.  Install & use Open Office.
  5. Just dragging the spreadsheet link to your desktop may not actually save the file.  You need to right click on the link and select Save as…
  6. If you have an older version of Open Office you may need to upgrade it.
  7. Try rebooting.  I’ve experienced a problem where if I try to open one of these spreadsheets in a browser the computer gets messed up and won’t start Open Office.  Rebooting fixed the issue.

SPREADSHEET CALCULATORS FOR PVC PIPE

Do not try to open these spreadsheets by left clicking on the links.  Save the spreadsheets to your hard-drive first.  See the explanation above.

Cl 125 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

Cl 160 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

Cl 200 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

Cl 315 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

SCH 40 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

SCH 80 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

 

SPREADSHEET CALCULATOR FOR POLYETHYLENE TUBE

Do not try to open these spreadsheets by left clicking on the links.  Save the spreadsheets to your hard-drive first.  See the explanation above.

Polyethylene Tube Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

 

SPREADSHEET CALCULATOR FOR PEX TUBE

Do not try to open these spreadsheets by left clicking on the links.  Save the spreadsheets to your hard-drive first.  See the explanation above.

PEX Tube Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

 

SPREADSHEET CALCULATORS FOR COPPER TUBE

Do not try to open these spreadsheets by left clicking on the links.  Save the spreadsheets to your hard-drive first.  See the explanation above.

Type K Copper Tube Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

Type L Copper Tube Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

Type M Copper Tube Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

 

SPREADSHEET CALCULATOR FOR SCH 40 STEEL PIPE

Do not try to open these spreadsheets by left clicking on the links.  Save the spreadsheets to your hard-drive first.  See the explanation above.

SCH 40 Steel Pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.  (also use for galvanized steel)

 

 

 

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How Far from a Fence Should Sprinklers be Installed?

Saturday, July 30th, 2011

Q. How far should the sprinkler line be from a wooden fence? Im gonna run lines next to a wooden fence all around the perimeter of my backyard. Fence is about 8 feet tall.

A. There are several issues here that come to mind.  Most of this applies to walls as well as fences.

Installation:
If your are using a trencher or [plow to install pipe the machine will likely not get closer than 18 inches to the fence.  I would stay even further away, maybe as much as 3 feet.  Both of these machines have a tendency to slip from side-to-side or get out of alignment when operated, especially by a inexperienced non-pro.  You don’t want the machine to go through the fence.

Future maintenance:
One issue here is future maintenance should you need to dig up the pipe for a repair.  You want enough room that you aren’t whacking the shovel handle (or your shoulders) against the fence if you need to dig.  That would mean at least a foot of distance from the fence.  Maintenance of the fence is another issue.  If you spray water on the fence it will shorten the life of the fence, not to mention leaving ugly water stains on it.  It is near impossible to remove water stains from a fence.

Sprinkler Heads and Water Stains on the Fence:
The sprinkler heads should probably be about a foot minimum from the fence.  The closer they are, the more water they will get onto the fence.  The water will
stain the fence and also shorten the fence life.  To keep the water off the fence completely means the sprinklers have to be very far from the fence, typically at a minimum 24″ away for spray type, 36″ for the larger radius rotors.  There are variables that impact that distance they need to be away from the fence.  Different sprinklers have different amounts of accuracy as to the edge of the water pattern.  Impact type rotors often spray a lot of water to the side, outside the normal watered area, thus they need to be very far away.  In fact, with impacts I would say that you are not going to keep the fence from getting wet, period (unless you keep the head farther away than the radius of the impact sprinkler!)  Also wind plays a huge factor in blowing water onto the fence.

Don’t Plant Lawn Next to a Fence!
When I want to keep a fence dry I plant a minimum 3 foot wide strip along the fence with shrubs and water them with drip irrigation (or use shrubs that don’t require irrigation).  That way I can keep sprinkler watered lawn at least 3 feet from the fence so the sprinklers are at least 3 feet away.  If the area is windy I go with 5 feet distance.

Generally it is considered bad landscape design to put a lawn next to a fence, unless it is an extremely attractive fence that you want to be a focal point of the landscape!  Standard practice is to “buffer” the appearance of the fence with a shrub planter along the base of the fence.

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Adding a Booster Pump with a Well Pump

Saturday, July 30th, 2011

Q.  I have a shallow well that was drilled this summer and a centrifugal pump pulling up about 15 gallons/min (HAPPY!).  The problem, it will only produce somewhere around 30psi (sad!).  Am I able to add a booster pump to this setup to produce more psi or should I just forget it and go for a submersible pump?  Obviously the booster pump would save me $…

A. You can add a booster pump but it is tricky.  The flow range of the booster pump needs to match that of the existing well pump.  Using two pumps will probably use considerably more electricity than a single new pump, especially if it is a submersible.  Submersibles are by nature more efficient than a centrifugal pump at the top of the well and now you are adding the friction drag of two pumps rather than one.  I can’t tell you how much the electricity cost difference would be, that’s beyond my knowledge level.  But ongoing electricity cost is certainly something to look at.

Essentially when you couple two pumps together they are going to have to play nice with each other.  You don’t want one to over-power the other and do most all the work while the other just causes drag.  Plus you need to deal with the wiring issues and how you will start the two pumps.  Hopefully they would both stay primed so, in most cases, you could start them both together using the irrigation controller connected to a relay connected to the pumps.  You might need two relays if the pumps exceed the capacity of the relay.

Finally you will need to deal with figuring out if and how you will handle problems such as the malfunction of one of the pumps.  If one burns out the drag created by the burned out pump could very quickly burn out the other.  Hopefully you would quickly notice the problem, since the irrigation system would not work well at all if only one pump was running.  But what if you were on vacation when it happened?

You probably should get a local pump professional who knows his/her stuff and has experience with two pump systems to help you if you use two pumps.

Basically if you want to keep this a simple do-it-yourself project I’m thinking buying a new submersible for your well would be the better way to go.

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Automating a Rain Barrel Irrigation System

Saturday, July 30th, 2011

Q.  Can you suggest an affordable electric valve which can be actuated by a standard irrigation controller to control drip systems which are gravity fed from tanks above ground filled with captured rainwater? The water pressure is less than 1 PSI, though flow rate through valve can be as high as 5 GPM.

A.
Automatic Valves for Rain Barrels:
I can’t think of any standard solenoid irrigation valves that would work with a typical rain barrel.  The standard solenoid valves used for irrigation systems simply need more pressure than you have available from a typical gravity fed rain barrel.  The higher pressure requirement for the valve is a function of the hydraulics that makes the valve operate.  You either need more pressure or you need a different type of automatic valve.  If you want to create more pressure you need to raise the height of the rain barrel.  For every foot you raise the rain barrel you will create 0.433 PSI.  The minimum operating pressure of most irrigation valves is at least 15 PSI, that means the barrel needs to be 34 feet above the height of the valve.  That is simply not practical in most cases!  Now you understand why those water towers you see in some communities are so high!

Yes, they do make motor-operated valves that will work with almost zero water pressure.  I’ll address that later.

Use a Pump for your Rain Barrel!
The best way to accomplish what you want may be by not using a valve at all!  Consider using a small pump placed on your rain barrel outlet hose.  Most irrigation systems do not work very efficiently at the low water pressures typical of rain barrel systems.  Thus a pump is often the best solution as it may provide the added benefit of more water pressure.

Drip Emitter Selection
Most people use drip irrigation with their rain barrels, so that is what I  will assume here.  (If you want to use sprinklers you will probably need a lot more water pressure, and therefore a larger pump.)  I’ve found the best emitters for the very low pressures in a rain barrel fed system are the most simple emitters, such as those commonly called a “flag emitter” or “take-apart emitter”.  Another popular choice for emitters when using a rain barrel is the adjustable flow emitter/bubbler.  These use more water, but are particularly good for watering pots of various sizes as you can adjust the flow needed for each pot.   Stay away from higher cost emitters and those labeled as “pressure compensating” as they tend require higher pressures to operate efficiently.  Keep the tube lengths short, longer tubes need more water pressure to push the water to the end of the tube.  Note: Very low pressure drip systems are going to be less uniform.  That’s just the way it is, you will have to either live with that, or use a pump that creates a pressure of 15 PSI (35 feet of lift) or more.  Most people just elect to be content with the low uniformity.  If you want to test the uniformity of your drip system it is very easy to do, simply build your drip system and attach it to your rain barrel.  Then place a disposable plastic cup under each emitter and run the system for a few minutes.  All the cups should have about the same amount of water in them.  If the water in the cups varies greatly then the uniformity is pretty bad.  If the uniformity is bad enough that you think it will create uneven watering you can do a simple test to see if more pressure will help by hooking your drip system up to a garden hose.  Be careful, the garden hose will provide more pressure than you need, so turn the valve on slowly and don’t turn it on all the way.  Usually the higher pressure from the garden hose will result in more uniformity between the water in the cups.

Selecting and Installing Your Pump
Make sure the pump is rated for enough flow to supply your emitters, and enough lift to get the water needed for your irrigation over the top of the barrel.  Add the flow rate of all the emitters together to determine the flow rate needed for the pump.  for example if you have 15 emitters that are rated at 1gph (gallon per hour) then the pump will need to supply at least 15 gph.  If the barrel is 5 feet tall then the pump will need to lift the water 5 feet.  Some pumps list a PSI output value rather than a foot of lift value.  To convert PSI to feet of lift multiply PSI times 2.31.  So a  pump with a 5 PSI output will lift water 11 feet. (5 x 2.31= 11.55)

If you can find one the right size, a submersible pump is the easiest and best method.  Unfortunately most are made to be fountain pumps or sump pumps and they don’t create enough water pressure.  If you find one that will work for you, attach your irrigation hose to the pump, put the pump in the bottom of the barrel, and run the tube up over the top of the barrel.  You will need a air vent at the high point on the tube near the top of the barrel (above the maximum water level) to prevent water from siphoning out of the barrel through the tube when the pump is not running.  You can buy an air vent from any drip irrigation store.  Or… a very simple and cheap way to create an air vent is to add a drip emitter on the hose at the top of the barrel, so that the water from the emitter drips back into the barrel and is not wasted.  When the pump turns off, this emitter will allow air to flow back into the tube and the air will stop the water from siphoning out.

If you don’t use a submersible pump then the pump will be attached to an outlet at the bottom of the rain barrel.  Make sure the pump is bolted or screwed down to a firm surface or it will jump all over the place when it runs.   The tube from the pump outlet will need to be looped up above the top of the barrel and an air vent (or emitter as described above) installed at the high point to prevent the water from draining out through the pump when the pump is off.

Controlling the Rain Barrel Pump:
The pump can be turned on and off by using a timer.  A simple lamp or other household electricity timer will often work for an extreme low cost option, however lamp timers are pretty limited.  Most timers of this type will only turn on  and off the pump once a day, and do it every day.  Most people don’t need to water daily, so this could waste water.  If you do use a simple timer make sure it is rated for a voltage and amperage that is equal to or higher than the input of your pump.

If you want to use a standard irrigation timer to control the pump you will need to buy a pump relay unit.  Irrigation timers output 24 VAC, most pumps use 120 VAC.  So the pump can’t be connected directly to the irrigation timer.  A relay is used to allow the pump to be turned on by the timer.  You can purchase a pump relay made for irrigation timers at almost any irrigation supply store.  Make sure the relay is rated for the correct voltage and amperage for your pump.   Instructions for installing and wiring the pump relay should be provided with the pump relay.

Multiple Watering Circuits:
Most rain barrels don’t hold enough water to supply more than a single irrigation watering circuit, but in some cases they might.  If you need more than one “valve circuit” you can simply duplicate the pump solution above and use two pumps.  Multiple pumps may be the least expensive solution for as many as 3 or more irrigation circuits.  As an alternative, you can use multiple motorized valves (see below) with or without a pump.   Another alternative is to use a single pump that is sized to provide enough water and pressure for a standard irrigation setup using solenoid valves.  I would suggest that the pump for this would need to create a minimum of 25 PSI in addition to sufficient flow to supply the largest irrigation circuit.  Use a standard irrigation controller that has a “pump start” feature to turn on and off both the valves and the pump.  The pump will require a pump relay to control it as described above for the single pump system.

Motorized rain barrel valves:
They do make mechanical motor-operated ball or butterfly type valves that will open at any pressure.  They are used primarily for non-irrigation purposes.   Before you purchase a motorized valve I suggest you install your irrigation system and test it using a manual valve as described above.  If it works fine without a pump then you can use a motorized valve to control it.

When using a motorized valve make sure the motor operates on 24VAC.  When I first wrote this article, the only motorized valves I was familiar with were very expensive, industrial quality models, costing several hundred dollars.  However, an email from “Randy G.” says he has successfully used the much less expensive motorized ball valves that are made for hydronic heating systems.   I haven’t tested these valves, but I looked over the literature on the Taco valve Randy mentions, and it seems to indicate the valve would work.   Per Randy, “the Taco Sentry series are motorized ball valves…, and can be had for $70 or so at most online stores…  Honeywell, White-Rodgers, and several other companies also sell ones with similar prices.  You can get the Honeywell ones dirt cheap…, but I’ve heard their reliability is lower, so I haven’t tried them – something about oxygen breaking down the rubber over time.  And, of course, make sure you get a motorized ball valve, not a heat motor valve, unless you really want to use lots of power and take several minutes to open or close…”

Randy also suggests “Virtually all modern (heating) zone valves are 24VAC, and thus directly compatible with standard irrigation timers, especially the Taco electronic ones that draw relatively little power, good for cheap electronic timers.”  To find these motorized valves do a search for “hydronic zone valve”.  Be sure to note the connection types for the valves, most are made to connect to PEX pipe or be soldered onto copper.  You may have to install adapters to fit them to your irrigation system pipes or tubes.

Special thanks to Randy for supplying this helpful tip!  If you try these valves for your system I would love to hear your thoughts on them as well.

 

People keep writing to say they are having trouble finding equipment that will work with a rain barrel, particularly pumps, so I’ll add some links below as I discover suitable products.  Disclosure: I get a small commission on sales of these items if you buy them through these links.

The Little Giant 35-OM pump is made for high pressure applications like commercial carpet cleaners, but it produces good pressure at a low flow, a combination that is great for small drip systems.  Amazon doesn’t list the performance chart for this pump so here it is:

40 gph at 70 ft hd
60 gph at 65 ft hd
80 gph at 58 ft hd
100 gph at 54 ft hd
120 gph at 45 ft hd
140 gph at 30 ft hd

gph = gallons per hour.      gph/60=gpm
ft hd = feet of lift.       ft hd x 0.433 = psi (pounds per square inch)

 

 

 

 

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How to Use Pressure and Flow Switches with Irrigation Controls

Thursday, May 26th, 2011

Almost any major maintenance problem in an irrigation system will cause a unusual pressure level or flow level in your irrigation system.  Therefore pressure and/or flow monitoring is a good way to detect problems.  Most of the time the response to a abnormal pressure or flow level would be to shut down the system, or possibly to shut down the current valve zone  and try another one.  Irrigation systems are typically shut down using what is called a master valve.  A master valve is a single valve located at the water source that can shut off all the flow of water into the irrigation system.  For more details see my article on master valves. On systems with a pump you will probably want to shut off the pump.  Sometimes, as with booster pumps, you will need to both shut down the pump and close a master valve.

So what problems might an abnormal pressure or flow indicate? A very low pressure may indicate that perhaps the pump is broken (if you have a pump), an intake screen is clogged, a filter is dirty, a valve failed to open, or a pipe has broken.  Abnormally high pressure could be the result of  a valve not opening when it should, a dirty filter (if the pressure is measured upstream of the filter rather than downstream) or some obstruction in the pipes.  Low flow could indicate a valve failed to open, a filter is dirty, or that a pump isn’t working as it should.  High flow could indicate a broken pipe, a broken sprinkler, or a valve that is stuck open.   In most cases monitoring either flow or pressure is sufficient as opposed to monitoring both.

 

How to Monitor Your Irrigation System

There are a number of different ways to detect and respond to abnormal pressure or flows.  Following are a few or these.  If you would like to suggest other methods, please contact me.  I realize this is not an exhaustive list.

Use a Smart Irrigation Controller that has a Sensor Input and Response Feature:
This is probably the easiest way to add pressure detection and response.   It is also what I consider to be the preferred method, as it is reliable and gives you the most control.  Some high-end irrigation controllers can use an electronic sensor hooked up to the mainline pipe to monitor the water in the irrigation system. Some of these controllers use flow sensors, some use pressure sensors, some can use both types.   These controllers with advanced features are typically sold as Smart Controllers and are expensive compared to ones typically found on a residential irrigation system.  Prices for these controllers typically start around $300.00 and go up into the thousands for ones that handle dozens of stations.  But then you get a lot more with them too.  They are sold through professional irrigation supply stores, both online and locally.

WARNING: Be sure the controller will do exactly what you want BEFORE you purchase it!  Not all controllers marketed as “Smart Controllers” have these sensor input features, many only work with specific types or even models of sensors, and some controllers may not provide the response options you want or need.  You need to research the controller carefully.  Don’t rely on a simple check list of features!  “Sensor input” can mean almost anything, you need details!  I have seen controller feature lists where the unit sounded fantastic and ultra flexible, only to discover after closer examination that the actual response features don’t do what I need or want.   Read the actual owner’s manual (most controller manufacturer’s have them available on their websites) to see what the true capability of the controller is.  Read the sections of the manual on how to hook up the sensor, then there will also be a separate section on how to program the sensor you should look through.  Some controllers allow for time delayed responses, some don’t.  If you have a pump you will almost always need a time delay feature to bypass the sensor when the pump is starting up.  Even those controllers that do allow you to add delay times may not allow as much or little time as you need.  It is critical that you do as much research as possible before you go to the expense and effort of purchasing, installing and programming the controller.

For example, I have a Rainmaster Eagle Smart Controller on my own irrigation system, as well as using it on the majority of the commercial systems I design.  This particular Smart Controller has flow sensing capabilities, but it does not have built-in pressure sensing capability.  It does have a delayed response allowing delays of 1-6 minutes, but only in one minute intervals.  It will also allow the use of one additional simple on/off type sensor (most controllers have a circuit for this type of very simple sensors.  A simple rain switch is an example of this type of sensor.)    It has an audible “chirp” alarm that alerts you that a sensor response has been activated.  While this particular controller meets my needs, it certainly will not meet everyone’s.  Almost every major irrigation company makes a Smart Controller, and each has different features and capabilities.  Be sure you are using up-to-date resources when checking out models.  Smart Controller models are introduced each year, and often the capabilities of existing models change from year to year, so it is hard to keep up with them.

When using a controller with a pressure and/or flow sensor you start by installing the actual sensor on  the mainline pipe.  The method varies with the brand and model of sensor, most are pretty easily installed.  The sensor is wired to a special terminal on the irrigation controller.  Typically the wire used must be a special shielded communications cable, rather than standard irrigation valve wire.  Consider installing communications cable in PVC conduit to protect it, as it is very sensitive to even the smallest nicks from shovels, animals digging it up, or rodents chewing on it.  Most pressure sensors work by sending a reading of the current pressure to the controller every few seconds.  A typical flow sensor has a small paddle that turns as the water flows through the pipe.  Flow sensors normally send a signal based on the amount of flow, for example they might send a signal each time 5 gallons of water has flowed past the sensor.  The controller then interprets that data from the sensor and responds.   In most cases you will pre-decide what the response will be when you set up the controller.  For example; if you have a system with a pump, you could program the controller to shut down the irrigation system if the pressure was below 10 PSI for more then 2 minutes during the set irrigation period.  The 2 minute qualifier (delay) for shut down would allow the pump time to pressurize the system during start up and also avoid “false alarms” caused by brief dips in pressure.

Using a Simple Pressure Switch with a Pump Operated System:
This method is for those with pumps.  What I am describing here is for emergency shut off only.  I’m assuming you already have something set up to turn on or off the pump during normal irrigation operation.  That might be a standard pressure tank with a pressure switch to control it.  Or you may be using the pump start feature on the irrigation controller to actually start and stop the pump using a 120v relay.  The new pressure switch we are talking installing in this case is used only to detect pressures that indicate a problem and turn off the pump.  So if all is hooked up properly, in the event of blockage or no water going into the irrigation system the pressure will drop and the new pressure switch will shut the pump off.

This method requires that your irrigation system is leak free and can hold pressure for days between irrigations.  If the system is not leak free see #4 below.

1. Make sure you have a really good quality spring-loaded check valve on the irrigation mainline pipe.  The check valve goes someplace after the pump, but before the pressure switch.  A good quality check valve is needed to keep the water from leaking backwards out of the system through the pump.  Typically the self-priming feature of the pump is not good enough by itself to do this, you need a separate check valve.

2. You will need to use a pressure switch that works backwards from normal ones used for household water systems, since you want the switch to shut off the pump at low pressure (standard switches used on household water systems turn on the pump at low pressure.)  Some switches can be wired to work either way, others can’t.  Keep in mind that the low end on many common pressure switches in around 25-30 PSI.  That might be a bit higher than you want for a low end shut off, especially if your system will be operating at less than 45 PSI.  You don’t want accidental “false” shut offs since the only way to get the system back on will be to manually start the pump and hold it on until the pressure is back above the shut-off level.

3. There a problem to be dealt with.  The problem is that valves close slowly, taking as much as a minute or two to close after the controller tells them to.  At the end of the last irrigation cycle a typical controller closes the last valve and immediately shuts off the pump.  But it takes the valve several seconds up to a minute or two to actually close.  During this closing period the system will depressurize.  With no pressure in the system the pump will not restart for the next irrigation cycle, because the low pressure shut-off switch is detecting low pressure and shutting off the power to the pump.  There are two ways to deal with this.

A. You can fool the controller into keeping the pump running after the last valve circuit has finished watering.  Your controller needs to have the capacity for one extra valve on it to do this, so if you have 10 valves you will need a controller with 11 stations.  The last station on your controller needs to not have a valve attached to it.  Program 1 minute of time on that last station.  Now the controller thinks it is operating one last valve, so it keeps the pump running.   That will keep the system pressurized while the final valve closes.  If one minute is not enough time for the final valve to close then add another minute of run time to that last empty station.

B. Some controllers have a built in delay feature that keeps the pump running after the last valve closes.  This feature keeps the pump start circuit energized, which keeps the pump running for a minute or two after the last valve is signaled to close.  This gives the valve time to close before the pump is shut off.   Some less expensive controllers have this feature.  But typically only high-end controllers have this feature, so this method isn’t very practical.  If you are going to buy an expensive controller you might as well forget about using a pressure switch and use a Smart Controller and a sensor to shut the system down, as described in the first section of this article.

4. Often a small leak will cause the system to depressurize between irrigation runs.  This can be a major problem.  The pump will not start if the pressure is low, the low pressure switch is going to shut off the power to it.

If the leak is very small you can install a pressure tank, just like on a typical house water system.  Assuming a small leak, the tank keeps the system pressurized.  But that only works with a very small leak and it can take a huge pressure tank to supply enough water to keep the system pressurized.   If your system has a larger leak you will need to find and repair the leak.  If you can’t get the system leak free, you will need to take a different approach, as described below.

You can use a timer to over-ride the low pressure switch, and allow the system to start even with no pressure.  You will need a “Time Delay Relay”.  The time delay relay needs to be the type that allows the power to flow when energized, then shuts it off after a minute or two of delay.  It needs to have an automatic reset.  You then install the relay on a bypass wire around the low pressure switch.  That way the pump can start even when the pressure switch is “off” due to low pressure.  You will need to work with someone knowledgeable when ordering the time delay relay to be sure you get the correct relay, as they make many different kinds.

Using a Pump Controller with a Sensor:
This is essentially the same method as the Smart Controller method I described earlier.  Only the “smarts” are in the pump controller rather than in the irrigation controller.  Some of the newer digital pump controllers (don’t get confused here, we’re talking about a separate pump controller, not the sprinkler controller) are programmable, they are simply a small computer that operates a relay that starts and stops the pump.  You hook them up to a pressure sensor, also to the irrigation controller, and to any other sensor you want (wind, rain, temperature, light, flow, you name it.)  Then you can program them to do just about anything using that information input.  They can turn off the pump if a low pressure occurs for more than x number of seconds, turn off the pump if a high pressure occurs for x number of seconds, turn on the pump at a given time of day, etc.  Pretty much any input you want can cause the pump to turn on or off.  The capability depends on the brand and model of the pump controller. The downside is it takes electronics know-how to set the thing up and someone tech savvy to program it.  Typically you hook up a laptop to the pump controller to program in the logic, then once it is programmed it runs by itself.  The laptop just gives you an interface that is easier to work with.  I really can’t give you much more details beyond that, this type of pump control is beyond my expertise, I just have seen pump system experts use them to do amazing things.

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Is Bending PVC Pipe OK?

Wednesday, May 18th, 2011

PVC fittings only come in 90 degree and 45 degree angles.  Sometimes you need a smaller bend.  A website reader asked if it is safe to bend PVC pipe and if so, how much can PVC pipe be bend without damaging the pipe?

The answer is that, yes, it is OK to bend PVC pipe, but don’t bend it too sharp or too much.  Each pipe manufacturer has rules on what degree curve you can bend the pipe to based on the type and size of pipe.  You could look that up but it would take a lot of time and even then figuring out how much a 15% bend is out in the yard is not very practical for the average homeowner.  So here is a simpler “rule of thumb” that I basically just made up.  But it seems to work reasonably well, it’s easy to do, and it gives you a nice, visual answer!

To determine how much is the maximum bend you should allow grab one end of a length of the pipe you plan to bend and hold it so the other end is off the ground.  The amount the pipe bends on it’s own is about the maximum amount of bend you should allow.

You can also make any angle you want simply by using two 45 degree ells.  This is easier to demonstrate than to explain.  Get two 45 degree PVC ells.  Lightly push them together onto either end of a very short piece of pipe.  (Don’t glue them for now, this is just a learning experience.  If you do ever use them on a irrigation system then you can glue them!)  Now start twisting them in different directions.  You will see that you can make any angle curve from 0 degree up to 90 degree!  Add another 45 degree ell and you can make even more angles.  Have fun.  It’s cool!

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All Valves Come on and Stay On Continuously

Friday, May 6th, 2011

Q.  I just restarted my sprinkler system after it had been winterized. When I turned on the water to the system, all the valves stations came on at once, as if by-passing the timer unit.  Even when I turn the timer unit Off, the sprinklers keep running.

A.   This is a common problem when restarting after your sprinkler system has been winterized, or after the system has been turned off for an extended period of time.  It also often occurs with brand new solenoid valves that have just been installed.  There are a  couple of possible problems that can cause this, so we’ll look at a couple of solutions.  One of the tricks below should get your irrigation valves opening and closing properly again.

Air Trapped in the Valve:

The valves may have air trapped in them.   A small bubble of air becomes trapped in the tiny water ports of the valve, this stops the water from flowing through the port.  Since the water flowing through the port is what holds the valve diaphragm closed, the valve stays open.

1. Turn on the main water supply.

2. Now go to the individual valves and using the manual open & close control on the valve.  The manual open & close control is either a lever on the valve (most often it is under the valve’s solenoid), or it may be a screw on the top of the valve bonnet.  If it is a screw don’t fully remove it, just open it until water starts squirting out.  Set it to open, wait a few seconds, then set back to closed.  If the valve doesn’t close within a minute, try it again.  It may take several tries to get the air bubble to “burp” itself out.  Try tapping the valve to dislodge the air while the valve is open if needed.  Note: old plastic valves may become brittle and crack when tapped, so if the valve is plastic and old don’t tap on it except as a last resort if the air doesn’t come out.

3. If that doesn’t fix the problem, you can almost always force the air out using the manual flow control on the valves.  Unfortunately, some inexpensive valves do not have a flow control.  The flow control is a handle, similar to what a manual valve has, that is on the top of the valve.  It works just like a regular faucet, turn clockwise to close.  Most flow controls have a hand operated flow control, others have a cross handle that is turned using a tool (pliers will work if you don’t have the special valve opening tool.)  A few valves have a screw for the flow control that requires a screwdriver to turn.  Try completely closing and then reopening the manual flow control on each valve.  That should force the air out and fix the problem.

Valve Needs to be Throttled:

If air in the valve doesn’t seem to be the problem it is possible that your valves don’t have enough pressure differential and they need to be throttled in order for them to close by themselves.

Here’s how to throttle them using the flow control adjustment:

Note: some inexpensive valves do not have a flow control adjustment feature on them.  If that is the case you are not going to be able to do this.  You will need to replace the valve with a better quality valve that has a flow control.

1. Use the manual flow control on each valve to close all of the valves.  Now the main water supply should be on, but none of the valves should be allowing water through.  So no sprinklers are running.
2. Start with just one valve at a time.  Rotate the manual on/off lever to the on position.  Open the manual flow control knob all the way (turn as far as it will go counterclockwise). The valve should come on and sprinklers run.
3.  Next rotate the manual on/off lever under the solenoid to the closed position.  The valve should close (it may take it a minute or two to close) but probably won’t, because that is the problem, they won’t close!   If the sprinklers turn off the valve is working correctly, go to the next valve and start again with step #2.  If the valve does not close by itself, you need to throttle the valve.  Continue to step #4.
4. To throttle the valve you partially close the flow control knob.  Start by turning it one full turn clockwise.  Wait a minute for the valve to close.  If it doesn’t close, turn the handle another half turn clockwise.  Wait again.  If the valve still doesn’t close turn it another half turn.  Keep doing this, at some point the valve should suddenly make a whooshing noise and close.  If the valve is broken it will never close by itself and eventually as you close the flow control more and more the sprinkler radius will start becoming noticeably reduced.  If that happens you need to repair or replace the valve.  But in most cases the valve will close by itself after you have partially closed the flow control.  It might take 4-5 complete turns before this happens.

You shouldn’t see any significant change in the sprinkler performance with the valve flow control in the partially closed position, except that the sprinklers may mist a little less (which is a good thing.)  This is called “throttling the valve” and some valves won’t close by themselves unless they are throttled.  The way a solenoid valve works is that the pressure differential as the water goes through the valve is what the valve uses to power itself into the closed position.  If there isn’t enough pressure differential the valve will not close by itself.   Often there is not enough pressure differential when there aren’t very many sprinklers on the valve circuit. When you throttle the flow control you are simply increasing the pressure diferential.

You can leave the flow control in a partially closed position permanently, it will not hurt the valve.  The valve is designed to allow you to do this.  The sprinklers should still operate well as the amount of water throttled when you partially close the valve is not significant.

For valve repair instructions see  how to fix a solenoid irrigation valve.

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Valves Downstream from Anti-siphon Valve?

Saturday, April 30th, 2011

Q.  I have manual shut-off valves installed downstream from my electronic anti-siphon valves.  I installed them to turn off the water to parts of my yard where I grow annuals and only need to water for a few months out of the year.   I would really appreciate it if you would explain why valves downstream cause the anti-siphon valve backflow prevention to fail.

A.  If there are some sprinklers that are not shut off by the downstream valves (ie; there is always a sprinkler that will be on when the anti-siphon valve is on) then you should be fine.  The key to this is that when the anti-siphon valve is closed the water remaining in the pipe downstream of the anti-siphon valve MUST become depressurized.  Depressurizing normally occurs when you shut off the anti-siphon valve and the remaining water pressure in the downstream pipes is released through a sprinkler.   But if you have a valve downstream of the anti-siphon valve it will trap pressurized water in the pipe between the anti-siphon valve and the downstream valve and not allow it to “depressurize”.  Note that sprinkler heads with built-in check valves will also hold the water pressure in the pipe.  That is why when using anti-siphon valves you should remove the check valve from at least one of the sprinklers on each valve circuit (normally you would remove it from the sprinkler on the circuit with the highest elevation.)  the check valves are easy to remove from the sprinklers, normally you just unscrew the sprinkler cap and lift out the riser assembly.  You will see a rubber washer attached to the bottom of the riser assembly, pull it off.  That rubber washer is the check valve seal, with it removed the check valve won’t work.   Now reassemble the sprinkler.

How an anti-siphon valve works:
The  anti-siphon valve works by use of a little air vent that is located on the downstream side of the actual valve.  Look at the anti-siphon valve you will see there is a large cap directly above the water outlet of the valve, the air vent is under this cap.  If you look closely at the lower perimeter of the cap you will see holes or slits that allow the air to move in and out of the vent.  When the anti-siphon valve is turned off the pressure drops in the pipes downstream from it as the remaining water flows out of the sprinklers.  When the pressure drops the little air vent drops open and lets air into the pipe right behind the valve.   This air goes into the pipe and breaks any siphon effect (“anti-siphon”) so that sprinkler water can’t be drawn backward through the valve into the potable water supply.

(Water from the sprinkler pipes can be siphoned back into the water supply system when pressure is lost in the water supply system.  For example, the water company might depressurize their pipes to make repairs.  It doesn’t happen frequently, but it does happen.  When the pressure drops the flow reverses and water from the sprinkler pipes, along with dirt and other yucky stuff, can be sucked in through the sprinklers and then into the water supply system.  When the pressure returns that dirty sprinkler water may go back into the sprinkler system, but it may just as easily go to your kitchen or bathroom sink.  So why wouldn’t the closed anti-siphon valve stop this from happening?  After all the purpose of a valve is to stop water from flowing through it when it is closed, right?  Yes, of course, if the valve is a manual valve.  But electric solenoid valves are “directional” valves.  What that means is they are designed to stop the flow when the water is flowing in one direction only.  When the water flows backwards they don’t fully close!)

What the downstream valve does:
If you have another shut-off valve after the anti-siphon valve, then the water on the downstream side of the anti-siphon valve will stay pressurized even when the anti-siphon valve is closed.  This water pressure holds the little air vent in the closed position so it can’t let in air, and therefore the siphon effect is not broken.  This means the anti-siphon part of the valve will not work.  Even worse, when the little vent is held closed for days at a time due to the constant downstream pressure, it eventually just sticks in the closed position.  Then even if the pressure drops the anti-siphon won’t work.

My Friend or Irrigation Person Says This is All Just Something  YOU Made Up!
Unfortunately, this wrong practice of installing valves after an anti-siphon valve is pretty common in the irrigation industry.  I’ve been called some pretty ugly names over this issue.  Fortunately for me, you don’t have to take my word for it.  Tell your friend/buddy/pal to read the box the anti-siphon valve came in.  It says right on it “do not install valves downstream” or something similar.  If you don’t have the box or it didn’t come in one, then go to the manufacturer’s website and find the anti-siphon valve installation instructions.  You will find that same warning.  Here’s a sample from Rainbird if you want to check for yourself:  Rainbird Anti-siphon Valve Operation Manual. See the section that starts with the heading “CAUTION”.

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Using a Looped Mainline for Irrigation

Wednesday, April 27th, 2011

Looping your mainline often allows you to use a smaller pipe size for it, so using a loop system can be financially advantageous on a large irrigated area.  A looped mainline also provides maintenance advantages on larger sprinkler systems, and almost all large landscape irrigation systems, like parks and golf courses, utilize a loop mainline layout.  For smaller sprinkler irrigation systems they often provide little or no advantages.   As a general rule if you have less than 10 valve zones you are not going to get much of an advantage from a looped mainline.

What is a Looped Mainline?

The irrigation mainline is the pipe that runs from your water source to the individual valves that turn on a group of sprinklers or a drip irrigation circuit.   When the mainline is looped that simply means that all or part of it creates a continuous loop.  Typically a looped mainline starts with a single pipe coming out from the water source (pump, water meter, etc.) then the single pipe splits into two pipes.  the two pipes loop around the irrigated area and then rejoin each other to create the “loop”.   Zone valves would be located at various points along the loop to supply groups of sprinklers.   Normally you would put a isolation ball valve on each leg of the loop at the “split”, the location where the pipes separate into the loop.  A third isolation ball valve is placed on the far side of the loop, allowing the loop to be divided into sections.  (see the sketch of a looped mainline below)   Additional isolation valves may be added anywhere along the loop if desired, to divide it into more segments.  The isolation valves allow you to shut down sections of the mainline for repairs while the rest of it may still be operational.  For a large irrigation system being able to shut down only a portion of the system for repairs can be very advantageous.   Very large irrigation systems may have multiple loops, sometimes one loop will even be inside of another loop.

Plan View Sketch of a Looped Mainline

Plan View Sketch of a Looped Mainline

How to Design a Looped Mainline

When using a loop you should use the same size pipe for the entire looped portion of the mainline.  (This is not a hard and fast rule, just a strong suggestion unless you really understand hydraulics!)  The pipe leading from the water source to the loop may need to be a larger size than the loop pipe.  It is also OK to have mainline “spurs” off of the loop leading to other valves or faucets.  While unusual, the pipe size of the spurs may also be larger than the size of the loop pipe if they need to be.  Valves for sprinkler zones, faucets, quick coupler valves or any other equipment may be placed anywhere along the loop, as well as on the mainline leading to the loop or even on spurs off of the loop. Normally drinking fountains would be on a separate pipe and not connected to the irrigation system due to the possibility of water contamination from the sprinklers.  See the article on use of backflow preventers for more information on contamination.

Multiple Loops

You can have multiple loops, but I suggest that if you do, you size the pipe using the outside perimeter (largest) loop, as if there were not any cross pipes within the loop (using the method that follows below.)  Then after you have determined what size the outside loop pipes need to be,  use the same pipe size for any smaller loops or cross pipes inside the perimeter loop.  (Technical note: The pipe sizes of inside loops and cross pipes do not necessarily need to be the same size as the outside loop, it is just that using the same pipe size will almost always work.  Using a smaller size pipe may work, but it may not.  So it is  advisable for non-experts to stick with the same size!)

Loop Mainline Calculations

You must calculate both the friction loss AND the velocity for a looped mainline.  We’ll go through the process step-by-step.  You calculate the pressure loss for the non-looped mainline section from the water source to the beginning of the loop in the normal way (as described in the Irrigation Mainline Tutorial), using the pipe size, flow rate, and length of the pipe section.  I suggest that you use one of the  the Friction Loss Calculator Spreadsheets I’ve created, they are easier for non-mathematically oriented folks to use than the old manual calculations using charts.  Choose the proper spreadsheet for the type of pipe or tube.   Then enter the  size, the GPM, and the length of the loop.  Pressure loss for spurs off of the loop are also calculated using this same method.

Pressure Loss in the Loop:

To calculate pressure loss for the looped section we simply will assume that the water flow splits, and 1/2 of the water is going around 1/2 of the loop and the rest of the water is going the other way around.  To do this start by determining the “highest flow GPM” that is found on the looped section.  If you are planning to operate only one valve at a time that would be the flow for the largest zone valve to be installed on the loop section.  If you will be running more than one valve at a time then the “highest flow GPM” will be the combined flow rate for the largest group of valves that will operate at the same time. Once you have the “highest flow GPM” you calculate pressure loss in the pipe using the calculator.  But for the looped portion you will enter 1/2 of that “highest flow GPM” for the flow in the looped pipe and 1/2 of the total loop length (all the way around and back to the beginning) as the length of the pipe.  The calculator result is the pressure loss in PSI for the entire looped section.

Total Pressure Loss for the Mainline:

Just total up the pressure loss for the mainline leading to the loop, the pressure loss for the loop, and if you have any spurs add to your total the pressure loss for the single spur having the largest loss value.  The total of those is the pressure loss for your entire mainline network.

Velocity Problems:

As mentioned, this method of calculating pressure loss uses an averaging system that assumes that half the water goes one direction to the valve, and the other half goes the other direction.  While this is not a perfect method, it works good enough for figuring out the pressure loss.  However, the flow doesn’t really split evenly in both directions.  In reality the flow balances in each direction based on pressure loss, with most of the flow in the loop going the shortest distance to a valve.  So if one of the zone valves is just a few feet from the split point on the loop, almost all the flow will go through that short distance rather than going the long way around and back to the valve.  Also in the event you make a repair you may close those isolation valves mentioned earlier.  This will force all of the flow in a singe direction through one side of the loop.  So we come to the second rule of loops, the pipe size for the looped section must be large enough to handle ALL of the flow in one direction.  If it is not, you may create excessive velocity of flow in a section of pipe which can cause major, and very expensive, problems.  This means you must check the velocity of the flow while assuming all the flow may go in a single direction around the loop.  If the velocity is over 7 feet per second you may create excessive pipe wear and water hammer.  Pipe wear can seriously shorten the life of your system, water hammer is much worse, let’s just say you don’t want it.  (Look it up if you really are curious.)

Calculate the Velocity:

Using the Friction Loss Calculator Spreadsheets mentioned above enter the pipe size, the “highest flow GPM”, and any random value for the length of the loop.    Ignore the pressure loss it gives you, just check the ft/sec velocity result it gives you.  The velocity MUST be less than 7 ft/sec.  If it is not, you will need to use a larger size pipe for the loop.

That’s it!  You should now know how to create a looped mainline.  If it seems confusing try rereading it, it is admittedly a bit confusing after the first reading!  It really is simpler than it first sounds, be patient, grab some coffee, take your time.  Go back and actually work through it one sentence at a time, study the sample sketch of a looped mainline and try sketching your own on paper.    Practice a bit with the Pressure Loss Calculator to see what happens when you change the input values.  It should start to make more sense.

 

 

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Huge Grass Yard with Minimal Water Supply

Sunday, April 24th, 2011

Q.  My pump produces 10 GPM at 45 PSI or 7 GPM at 65 PSI.  Do you think the flow is decent for my yard?   When I had pro’s quote my job (which is why I’m doing it my self as the numbers were huge) they all said I’d need about 40 sprinkler heads.

A.  My gut feeling is that you don’t have enough water capacity from your pump and/or well to irrigate the size of area you have planted in lawn.  (Don’t panic yet, keep reading for some suggestions.)  40 sprinklers would be a lot to try to run off of 7-10 GPM of flow.  But it depends greatly on your climatic location and water needs.  If you only need irrigation for periodic supplemental watering you may be OK.  The rule of thumb is that 10 GPM will water about 1/2 an acre of lawn, assuming you need to water about 3 times a week to keep the grass lush.  So if you need to water only twice a week, then you could water more area with 10 GPM of water flow.  Also, the rule of thumb assumes you only wish to water during the night hours.  You could water more area if you are willing to water 24/7 during the peak hot season.  Keep in mind that if you share the water use with your house that 24/7 watering might not be a good idea as you won’t have any water left over for use in the house.  When your spouse gets in the shower and no water comes out because the sprinklers are using all of it, things are not going to be pretty!

The rule of thumb is that it takes 20 GPM to water an acre of lawn in a hot climate area.  So if you have a larger lawn you may need to think about adding a new pump and/or well.  I really don’t have enough info to say for sure since I don’t know the size of your yard or your climate location.  Take a look at this article which will show you how to calculate how much water you will need for your exact situation:
http://www.irrigationtutorials.com/advice/how-to-estimate-water-useage-required-for-an-irrigation-system/

Options to consider if you don’t have enough water:
An option a lot of people in rural areas use is to create watering zones around the property.  They heavily water the area right around the house, possibly 25′ or so out from the foundation, sufficient to create a really lush green lawn.  Then for the next 25-50′ out they apply just supplemental water, watering maybe once (or twice) a week in hot weather.  This supplemental water area would tend to yellow a bit and show stress during the hottest part of the year.  Then they have a “no irrigation” area at the far reaches of the property that gets no irrigation water at all.

Tips on designing supplemental water areas: The sprinkler system design for a supplemental water area should be the same as for the lush area.  In particular, the distance between the sprinkler heads should be the same for both the lush and supplemental areas.  The only difference is that the supplemental area doesn’t get watered as often.  Don’t try to stretch out the sprinkler spacings to use less heads in the supplemental area, that will result in problematic dry spots that create a splotchy look to the grass.  A splotchy lawn really looks bad.  If you space the heads correctly then you will get a uniform looking lawn in the supplemental area, it will just have a yellower tint to it, and it will not be nearly as noticeably “ugly” as a splotchy lawn.   Also by designing the supplemental area for “full water coverage” you have the future option of turning that area lush by simply adding a new well or bigger pump.  If you skimp on the sprinkler spacing it is really difficult to correct the spacing problem if you ever wanted to make it lush.  You can add more heads, but I can tell you that over my 35 years in the business I have never had a customer who was happy with the results of adding more heads.   Your only real option to fix a system with heads installed too far apart is to rip it all out and start over.  Expensive!!!

Another option: If you don’t have the water supply or money to do all of it right, then install it in phases.  Start with the area around the house.  Then add more sprinkler zones to water the areas farther out from the house each year as you have funds and time.  Add another pump and/or well later when you need the water.   The critical thing is to “do it right” in regards to the sprinkler spacing and resist the temptation to stretch spacings between the heads to stretch the water supply or save money.  The results are always disappointing if you do that.

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Can I Run Two Irrigation Valves at the Same Time?

Tuesday, March 29th, 2011

Q.  Is it possible to have two valves on at the same time or to run two irrigation valves at once?

A. Yes, it is often possible to run two valves at once.  However there are several problems that can occur.

You must have a sufficient water supply for both valves to run at once.  If the performance of the sprinklers suffers and you start seeing dry spots in the landscape, you obviously don’t have enough water.  You may need to do some adjusting of the sprinklers as the water pressure operating them is likely to be less when two valves are on.

Both valves running at the same time may require more water than the pipe supplying them can reasonably handle.  This can result in water hammer, or premature pipe wear/failure, due to high water velocity.

Water Hammer: Listen for a loud water hammer “thump” or “bang” noise when the valves close.  A gentle thump is fine, but if the pipes reverberate from it that is not good.  Run just one valve and listen to the sound when it closes.  Assuming the irrigation is properly designed, that should be the “normal” closing sound.  Now listen to the sound when both valves are closed together to see if it is significantly louder.  If it is significantly louder, that is not good.  You can possibly reduce or eliminate the water hammer problem by closing the valves separately, one at a time.

High Velocity: Premature wear due to velocity is harder to figure out.  It generally isn’t a problem unless the water is really flowing fast through the pipe, like 8 feet per second or higher.  The only way to determine if it is a problem is to do a couple of calculations.  Start with the sprinklers.  On top of each sprinkler is an identifying names and part numbers that tell you the brand, model, and hopefully the nozzle size. Write down that information for each sprinkler, then look up the water use (GPM value) for that sprinkler and nozzle at the sprinkler company’s website.  (You may need to call the company’s help line to assist you, each brand and model is different so I can’t give exact instructions.)  Now add together the GPM values for all the sprinklers that are running at the same time when two valves are turned on.  This will tell you how much water the two valves require when running together.  Next find the size and type of the water pipe that leads to the valves.  (For example it might be a 3/4″ copper tube, or maybe a 1″ PVC pipe.  It may be several different sizes and types of pipe, in which case you would use the smallest pipe size and type.)  Using that information you can calculate the velocity of the flow in the pipe using the Friction Loss Calculator at http://www.irrigationtutorials.com/formulas.htm#sec8.  Just enter the pipe type, size, and GPM into the calculator and it will give you the velocity.

If you decide to use a controller to operate the valves the controller must be a brand that provides sufficient amperage to run two valves at the same time (most do.)  If you want the controller to run the valves at the same time, but start and stop them about one minute apart to reduce water hammer, you will need a controller that allows you to run two separate valve zones at the same time.  Most controllers have a “stacking feature” that prevents them from doing this.  You will need a controller that allows you to turn off the stacking feature.  Most controllers can’t do this.  You will probably need to enlist a knowledgeable controller salesman at a professional irrigation supply store to assist you in finding a controller that will work for this unique situation.

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Can I Pump my Irrigation Water from a River, Creek, or Pond?

Thursday, March 24th, 2011

Q.  We live on a river.  I would love to plant some interesting things on the bank below our home but with the price of water these days I would love to be able to pump some river water up to do the job. Do you think that that is something we could do without spending a fortune?  It would be great to have a soaker system.

A.   First, you must have the right to take water from the creek, river,. pond, etc..   This almost always means you need to talk with the US Fish & Game Department, State regulators, and possibly the Environmental Protection Agency (or equivalent agencies for whatever country you are located in.)  If you take water from a creek or pond or any other natural body of water in the USA without checking on the legal rights and requirements you can get into a lot of hot water, fast.  The fines penalties and restitution costs can be enormous.  So before you do anything, start doing some calling around.  Be safe, not sorry.  If you don’t know who to call, try calling the local County or Parrish Planning Department, they should be familiar with the agencies that regulate water and be able to point you to the right people.

Yes, from a physical standpoint it is not difficult to pump the water.  The cost depends on how fancy you make it.  My parents had a cabin on a river in Oregon.  They simply had a small portable pump that sat on a concrete block and was chained to a tree.  One end of a 15′ garden hose was attached to the pump intake, the other end of the hose had a piece of window screen tied around it to create a home-made filter and keep out small fish and junk.  The end of the hose with the screen filter was tied to a concrete block and dropped into the river.  The pump outlet was attached to a second garden hose, this one was 150 feet long.  A long extension cord went from the pump to the power outlet at the cabin.  They put a sprinkler on the end of the hose, placed the sprinkler where they wanted water, then plugged in the pump.  Simple, cheap.  You could easily semi-automate that by simply plugging the pump’s power cord into a timer to turn it on and off.

A fancier system is certainly possible.  The pump still needs to be portable in most cases.  The pump has to be mounted less than 8 feet above the water level (the closer the better.)  You need a pad of some sort to put the pump on, but it is best if the pump can be easily moved, especially if the water level fluctuates in the creek or floods.   There is also the possibility of using a submersible pump.   A submersible should not sit on the bottom of the stream if there is a lot of mud and silt in the water that would get sucked into the pump.  If you have a floating dock or a pier an alternative is to place the pump on it (or hang it below the dock in the case of a submersible pump.)  Submersible pumps are often strapped to the side of pier pilings.  Be sure to read installation instructions for the pump, many pumps have very specific positioning requirements, some submersibles must be installed inside a special sleeve.

You can get about as fancy as you want- using automatic controls to start and stop the pump and also to open and close multiple irrigation valves.  Many irrigation controllers have built in circuitry that will start and stop the pump for you using a electrical relay.  If you do it yourself, and you need only something similar to my parent’s  small pump  you could probably install a pump  for around $200.00.  The price can go up fast as you get bigger and fancier, $1000.00 is not an out of line figure for a pump system capable of watering an acre or so of yard.  The wiring for the pump automated controls is a bit tricky, so most people would want to have that part done by a electrician.  How much that costs depends on the length of wire needed to reach the pump.  One option to look at when you get to larger irrigation systems is a pre-constructed pump unit.  This consists of the pump and all of the needed controls for it pre-installed and pre-tested on a metal frame.  You just hook up the pipes and wires to it and turn it on.

You may also need a storage tank for the water, especially if you have a small water supply (like a creek.)   That way you could pump a small flow continuously from the creek  to fill the tank.  Once in the tank the irrigation water would either be pumped out of the tank to the irrigation system by a second pump, or if the tank can be located 30′ or so higher than the level of the irrigated area, you could use gravity flow from the tank.  (If you want to use sprinklers the tank would need to be at least 60 feet higher to create enough pressure for a small sprinkler.)  The tank will probably need to be a lot larger than you think.  Typically they are 5,000 gallons or larger.  To find out what size tank you will need you need to determine how much water it will take to irrigate your area.  See How to Estimate Irrigation Water Quantity Needed for instructions on estimating your water requirements.

One last word of warning before you start:  PLAN FIRST, BUY LATER!   Don’t run out and buy an “irrigation pump” first!  Most pumps sold with the description “irrigation pump” are designed to operate a single sprinkler on the end of a hose.  You need to design the irrigation first, then you will now how much water volume AND water pressure the pump will need to produce.  The Sprinkler System Design Tutorial takes you through the process of irrigation system design and finding the right pump size.  It’s at  http://www.irrigationtutorials.com/sprinkler00.htm

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Why not use those huge sprinklers?

Monday, March 21st, 2011

Q.   I don’t understand why I can’t apply the same guidelines from your tutorial and choose 2 or 3 heads with 70 foot spacing?  That would mean a lot less sprinkler heads on my large acreage lawn.  Other than not being able to aim them as selectively, I’m missing the reasons I shouldn’t go this route.  But you caution against it, so I’m sure I’m missing something.

A.  Someplace around 55 foot spacing things start to get all screwy.  They do make sprinklers that will shoot that large radius.  They are pricey, the cost works out about the same per square foot irrigated regardless of the spacing (funny how that happens!)   The problem is there’s just too much wind drift, evaporation, etc. at those wide spacings.  Plus to get water to fly those long distances you need big, heavy water drops with lots of momentum.  Those big drops just beat the crud out of the lawn, and cause compaction of the soil.  Think of what it would be like if a really hard rain storm occurred each time you watered.  Where the huge droplets don’t compact the soil they may erode it.  Golf courses and parks have fought this problem for years.  Most city parks have now settled for 55′ spacing rather than deal with the grief of citizen complaints about dead grass.

The bigger radius heads work better with pasture grasses, where long unmowed grass blades soften the droplet impact and a few dry spots and general “ugliness” aren’t as important.

It also takes lots of water pressure and volume to get that water out there.  70 feet radius means you need 70 PSI and 30 GPM at each sprinkler head.  That means probably 85 PSI or more coming out of the pump.  Most systems with big sprinklers like that run at over 100 PSI of pressure, which means lots more wear and tear on the system, and a shorter life-span.   With those high pressures, design becomes critical, mis-design a single thing and it is unforgiving; water hammer can rip the whole system apart in a big hurry.

Then there is the safety issue.  You ever been hit by a 30 GPM stream of water flying from a nozzle at 70 PSI?   I have, it knocks you on your butt and hurts like hell!  Keep in mind that the really big impact guns used on farms reverse with enough force to kill you if you are struck in the head by the sprinkler arm.   Liability is the biggest reason that parks and golf courses are ditching the big water guns for smaller sprinklers.

Bottom line is that using big radius sprinklers just gets really tricky and the results are ho-hum at best.  It’s not a good solution in the vast majority of situations.  If you do want to mess with it, get professional help with the design.  Most of the sprinklers over 70′ radius are only sold by agricultural irrigation dealers.

Large Radius Sprinklers

Big Irrigation Guns in Florida

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Winterization for Areas with Periodic Freezing

Wednesday, February 16th, 2011

Q.  We typically have hot summers (month long +100 degree weather,) but recently we are also experiencing very cold winters (recently had 0 degree with -17 degree wind chills that froze a lot of pipes in the city.)  Do you have any suggestions that would be useful about winterization for  Southwest USA irrigation, or any particular materials that are specific to this area I should ask for?

A.  This is a situation which occurs all through the southern US, as far inland as Nevada (Reno sees this type of temperature extremes every year), and up the west coast all the way into the Pacific Northwest.   In these areas you see overnight freezing, which is typically followed by above freezing daytime temps.  To make it worse, it is often necessary in these areas to irrigate during the winter months due to drying wind and high daytime temperatures!  In these places we generally don’t winterize irrigation systems by draining the pipes in the winter, as the soil insulates them enough to prevent freezing.  Sometimes we bury pipes much deeper in these places, say 18″, to keep them below the frost level.   Any above ground equipment will need insulation installed on it to prevent freezing during the nights.  So generally I wrap the above ground pipes with foam or fiberglass insulation, extending down underground to below the typical freezing depth.  Where exposed to sunlight I wrap the insulation with a high grade pipe wrap tape that is UV resistant, or with metallic tape.  Without protection foam insulation degrades pretty fast from sunlight exposure.  Do not use standard duct tape, it is not UV resistant and will be a mess within a year or two.  For above ground valves and backflow preventers you can purchase insulating covers that can be placed over them like a big bag, (one brand name that comes to mind is Polar Parka) or you can wrap them in fiberglass pipe insulation wrap.  Just make sure water can drain out of the bottom someplace, in case there is a leak.  Fiberglass insulation must be wrapped with plastic tape or something else waterproof to keep it dry, it will not insulate if it becomes wet. You can also put thermostat controlled electric pipe heaters on the pipes as another option.

The killer problem is when you have hard freezes that last for several days.  Insulation doesn’t work very well during long duration freezes, as the cold has time to penetrate the insulation.   In areas where freezing weather lasts longer than over-night, but you still need to keep the irrigation system operational, it is a good idea to install electric pipe heaters on backflow preventers and above-ground valves.  If you don’t need to irrigate during the winter in hard freeze areas, then you should do a full winterization process that includes draining water from the pipes.  For more details on winterization see the Irrigation System Winterization Tutorial.

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Outlet Pipe Size for Pump- is a Bigger Pipe Better?

Friday, February 4th, 2011

Q.  I’m designing a pump system from a lake and have read and understand your calculation of FT HD needed for pump selection but it seems that the upstream (uphill) pipe diameter would be a factor in the calculation.  I was going to use larger pipe to reduce pipe resistance and valve pressure drop but it seems to me the weight of the additional water (back pressure) would be higher for a  larger diameter pipe than a smaller one.  It must be easier to push water up a 3/4″ column than a 1 1/2 inch column.  You mention nothing about this.  Excluding pipe resistance, does the pipe diameter play a roll in taxing the FT HD required?  Rephrased –  Does a larger diameter column of water have any effect on the static pressure or force required to move it?

A.  The short answer is that the larger pipe would be better because there would be less pressure loss in the pipe.  This is due to less “friction loss” as the water flows through the larger size pipe.  The larger amount of water in the bigger pipe has no impact on the water pressure.   A smaller pipe may create more friction loss however, so it can be worse than a larger pipe.    To find out, you need to calculate the friction loss in the different sizes of outlet pipe based on the flow and pipe size.  See the Friction Loss Calculators to calculate the friction loss in pipes.

More detailed answer:
One of the really hard to grasp principles of hydraulics is the relation of volume of flow, pressure, and the weight of water.  Odd as it seems a larger pipe will actually be easier for the pump.  It’s not the volume of water, but the height it is lifted that matters.  In a way this is a variation on the old saying “which weighs more, a pound of feathers, or a pound of lead?”  Obviously both weigh a pound!  This version could be phrased “which is easier for the pump, 5 GPM in a 1/2″ pipe or 5 GPM in a 2″ pipe?  Neither because 5 GPM is still 5 GPM regardless of the pipe size!  Yes, you would need more power if you were actually lifting more water, also we would need more power to lift the water higher, but neither is not what is happening.  The amount of water nor the height we are lifting hasn’t changed.

The other issue here is flow through a pipe.  This is the issue that actually makes the smaller pipe potentially worse than the larger.  Because the smaller pipe is smaller it is harder to force the water through it.  The resistance of the walls of the smaller pipe causes pressure loss as water flows through.  this is commonly called “friction loss”.  How much friction loss occurs depends on the flow rate and pipe size.  Both higher flows and smaller pipes sizes result in greater friction loss.  This is the only reason a smaller pipe would be worse than the bigger pipe.  How much worse is dependent upon the actual flow rate and pipe size.

As a general rule (ie: not always true, but is most of the time)  the pipe size of the pump outlet is almost always smaller than the size of pipe that will provide optimal flow from the pump.  In other words, if a pump has a 1″ threaded outlet, it is very likely that a 1 1/2″ pipe would be attached to the 1″ outlet for use as the outlet pipe.  Pump manufacturer’s tend to use smaller size inlets and outlets to save money.

More technical answer:
Think about feet of head.  As discussed in the Pump Tutorial, the number of feet of water depth determines the water pressure.  So 80 feet of water depth equals a pressure of 80 ft. hd.  This pressure will be the same regardless of the pipe size.  The water pressure at the bottom of an 80′ high 1/2″  pipe is exactly the same as the water pressure at the bottom of an 80′ high 6″ pipe, even though the 6″ pipe holds a lot more water.  A pump actually works by creating water pressure.  So for the pump there is no difference between pumping into either size pipe, the water pressure required to move the water into the bottom of both pipes is the same.  Now the pressure lost as water moves through the two pipes will be different.  Assuming a high rate of flow, a lot more pressure will be lost due to friction in the smaller pipe.    So for that reason using a larger pipe will be better.  Depending on the flow, however, it may be only very marginally better.  To find out you need to calculate the friction loss in the outlet pipe based on the flow and pipe size.  See the Friction Loss Calculators to calculate the friction loss in pipes or tubes of various types.

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Can I Just Punch Holes in a Tube to Make Drippers?

Thursday, February 3rd, 2011

Q.  I’m installing a drip irrigation system and to save some money, I decided to buy inch wide black tubing.  I used a hot needle to make some small holes every 27 inches apart from each other, but when doing water pressure testing , some holes emit more water than others.  What do you recommend in this case? Is it a bad idea to punch my own holes?  Or is there a way to do this with an even result in each hole?

A.  Just punching holes doesn’t work well, as you discovered.  It’s almost impossible to get the holes uniform in size, and even if you did, variations in the water flow patterns inside the tube would make each hole emit water at a different rate.  The solution is simple.  You need to install barbed drip emitters in the holes.  The drip  emitters are small, plastic, highly-engineered devices that regulate how much water comes out, so that each hole gives a very uniform rate of flow.  A typical emitter (sometimes called a dripper) is about the size of 5 dimes stacked on top of each other.  The emitter has a barbed inlet on one side that pushes into the holes in the tube.  You just snap the barb into a hole punched in the tube.  Then the water drips evenly out of an outlet hole on the other side of the emitter.  You need one emitter for each hole.  Emitters are typically sold in packages of 10, 25, 50, or 100 emitters per package.

Since you already bought tube, cut off a small piece of your tubing that has a hole in it and take it with you to the store.  1″ black tube is probably not made for use with drip systems.  It probably has a thicker wall than standard drip system tubing, so the barbs on some brands of emitters may not be long enough to push all the way into the tube and lock in place.  Most brands should work, but in your case it would be best to test it at the store so you don’t have to make another trip back to the store if the emitters don’t fit.  The emitter’s barb should push all the way in and lock the emitter onto the tube.  It should not easily pull out.

It might be a good idea for you to read the Drip Guidelines at http://www.irrigationtutorials.com/dripguide.htm .   There are a lot more mistakes you can make, and I’d hate to see you waste any more of your time and money.

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How to Estimate Water Useage Required for an Irrigation System

Monday, January 31st, 2011

The amount of water needed for irrigation depends on many different factors.  A reasonably accurate estimate of the amount of irrigation water needed can be made using Eto data for your actual zip code.  “Eto” is the amount of water needed for irrigation, based on scientific research.  You can find the historic Eto for any zip code in the USA at the website www.rainmaster.com/historicET.asp courtesy of the Rainmaster irrigation controller company, who makes very good “Smart” irrigation controllers.   I use one of their Eagle model controllers on my own home.  (Rainmaster get a plug from me as well as a big “thank you” for providing the ETo look up service online.)  Unfortunately the Eto value only tells you how many inches per day are needed, which for most folks is a meaningless value. It makes more sense if you think about rainfall which is often also measured in inches.  If you find you need 0.20 inches of irrigation, then 0.20 inches of rainfall would provide the required water.  But most people in the USA want a value in gallons, which requires you to provide a little more information about your yard.  Then you plug the values into a simple formula, and do a little multiplication and division on any calculator.

Formula to calculate the gallons of irrigation water needed per day:
(Eto x PF x SF x 0.62 ) / IE  =  Gallons of Water per day

Values for the formula:
Eto: Get this from http://www.rainmaster.com/historicET.asp .  Enter your zip code, or a nearby zipcode, and the website will give you the average daily ET value for each month of the year.  Use the highest value or the “suggested reference value”.  Usually they are the same thing.

PF: This is the plant factor.  Different plants need different amounts of water.  Use a value of 1.0 for lawn.  For water loving shrubs use .80, for average water use shrubs use 0.5, for low water use shrubs use 0.3.

SF: This is the area to be irrigated in square feet.  So for a 30 foot x 50 foot lawn you would use 1500.

0.62: A constant value used for conversion.

IE: Irrigation efficiency.  Some irrigation water never gets used by the plant, this value compensates for that.  I suggest using 0.75 as the value for this.  Very well designed sprinkler systems with little run-off that using efficent sprinklers can have efficiencies of 80% (use 0.80).  Drip irrigation systems typically have efficiencies of 90% (use 0.90).

Example:
A 1500 square foot grass lawn in zip code 85232 (Central Arizona)
Start by looking up the Eto for zip code 85232 at the Rainmaster website, which displays a suggested reference value of 0.3 inches per day using June, the driest month of the year in that area.

Now rewrite the formula inserting your values into it:

0.3 (Eto value)  x  1.0 (grass value)  x 1500 (sq ft)  x 0.62 ÷ 0.75 (efficency factor) = gallons of water per day

Now do the math, just punch the values into a calculator and get your answer:
0.3   x   1.0   x   1500   x   0.62   ÷   0.75   =   372 gallons per day



We could figure out the average daily water use for other months of the year also.  Just use the same formula but insert the Eto value from the Rainmaster website for the month you want to get a valve for.

Remember this calculation just gives you an estimated value.  There are many other factors that could make this value higher or lower.  When planning for how much water a system that has not yet been designed or installed will use, it would be very wise to allow for  error by adding 10% or more to the daily water use needed.  It is generally better to have too much water, than to have too little!  Play it safe!

A common related question is “how much water pressure will my irrigation system need?”  The answer depends on a lot of factors, but as a rule of thumb, I would suggest 50 PSI of water pressure as a good starting point for sprinklers, 45 PSI for drip systems.  If you have a large yard and want to put the sprinklers farther than 30 feet apart you will need more pressure.  For example, if you want your sprinklers 45 feet apart you will probably need 65 PSI of water pressure.  To get a real value you will need to create an actual sprinkler system design. See the Landscape Sprinkler Irrigation System Design Tutorial .

Never buy a pump, sprinklers, or any other materials before your sprinkler design is completed!

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Drip tube blows off fittings.

Monday, January 24th, 2011

Q:  The pressure is blowing off the pipes/tubes from the barbed fittings on my drip irrigation system.  This is only happening on hot days (30°C=86°F in the shade).  Pipe temperature could be as high as 45°C=113°F.  Our water pressure varies between 2.5 and 3.1 bar (35 and 45 PSI.)

A:  Drip tube should not blow off the barbs, even on a hot day when the temperature softens the plastic tubing (however the heat does make it easier for them to blow off!)  There are three common reasons the tubes blow off.

1. The most common problem is that the water pressure is too high.  This is probably your problem.  The water pressure should be around 1.3 to 2.0 bars (20 – 30 PSI).   You should install a pressure reducer after your valve to lower the pressure.

2.  The pipe and fittings may not be the same size.  This is one of the pitfalls I warn about in my Drip Guidelines.   16mm and 18mm tube  are both commonly referred to as 1/2 inch in the USA! The fittings for these two are not interchangeable.

3. Pressure spikes can pass through the less expensive pressure reducers often sold for drip systems.  If you have high water pressure this may be the problem.  The solution is to install a high quality brass pressure reducer valves.  These generally are sold in the plumbing department rather than the irrigation department of stores and cost $50.00 or more.

Common sizes are 12 mm (0.455″ or 3/8″), 16mm (0.620″ or 1/2″), 18mm (0.720″ or 1/2″), and 24mm (0.940″ or 3/4″). Do you see the problem? Two sizes are commonly referred to as “1/2 inch” in the USA! The fittings for these two are not interchangeable.

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Drip emitter installation tools.

Monday, January 24th, 2011

Q:  Have you come across tools to insert drippers in tubes or pipes?  Pushing the dripper’s into the tube is leaving my fingers bruised.

A:   You’re right, some of the hole punches are better than others.  I have one that has a nice big grip handle on it that is easy to hold.  But another inexpensive hole punch I have simply has a rounded top that you press with your palm to force the punch into the tube.  It makes your palm sore after just a few uses.  Pressing the emitters into the holes can be a pain too.  Inserting a couple dozen emitters into the holes can leave your finger tips hurting!  Some emitters have irregular, rough, or sharp edges that make it even worse.

Fortunately there are many tools made to help you out.

There are any number of simple hole punches.  Some are small and hard to hold, some have larger handles which makes them a bit easier.  All of these are very simple tools, you hold them in your hand and press a sharp tip through the wall of the tubing, a bit like an ice pick would work.  Actually an ice pick would work to make a hole, however I have found that any type of pointed punch tends to be too aggressive; it punches a hole through one side of the tube and out the other, making two holes!  Then you have to put a goof plug in one of them to plug it up.

Another thing to consider is the shape of the hole punched.  Most punches actually create a round hole about an 1/8″ in diameter.  Some create holes as large as 1/4″ for specific brands of emitters with larger barbs.  It is much easier to get the emitter into a round hole than one made with a pointed tip, such as a nail. When holes are made with a pointed tip the plastic tube tends to stretch as the tip goes through it.  Then the hole closes back up when you pull the tool out, the resulting small hole is hard to get the emitter barb into.  Also a pointed tip is more likely to tear the tubing wall as the tubing stretches around the tool, creating something more similar to a slit than to a round hole.  There is some debate as to if these tears in the tubing will enlarge over time (similar to how a tear in a plastic bag sill get larger if you pull on it.)  I tend to think you are better off with a round tipped punch that punches an actual round hole in the tube, as opposed to a pointed tip.

Note that any punch that you hold with your finger tips, or press a small “knob” with your palm to operate, is going to be hard on your fingers or palm if you install more than a dozen emitters at a time.  These super cheap punches work fine for a few emitters, but beyond that… ouch!

There are more sophisticated hole punch tools, like the Miracle Punch.  It holds the tube firmly in place which aligns the hole properly.  It operates similar to a pair of pliers, which is much easier on your hands.  There is at least one other “pliers type” tool I have seen on the market, however it does not hold the tubing as firmly.

There are a number of devices made to install the emitters.  Most of these are product specific, that is they only work with a particular brand and model of emitter. They generally have a handle on one end and a molded cradle that you place the emitter in on the other.  You place the emitter in the cradle and then press it into a hole you have already punched in the tube using a hole punch.  Some of these device have both the hole punch and emitter insertion cradle as part of the same tool.

Some companies, like Rainbird, make emitters that are “self punching”.  The barb on the emitter is sharp enough to create it’s own hole when pressed hard against the tube.  Rainbird makes a tool that you place the emitter in, then using the tool you press the emitter into the tube.  My experience is that you need this tool to use the self-punching feature of the emitter.  Without it I have not had much success getting the emitters lined up correctly and pressing them in with your fingers is near impossible.  You don’t have to use the tool to insert the Rainbird emitters, it works fine to punch a hole first using a punch and then stick them into the hole.

TIP: Try wearing heavy leather gloves when installing the emitters to reduce hand pain.  Also try putting a couple of pieces of cardboard in your palm between the hole punch and your hand, to help distribute the pressure over a larger area of your palm.

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Book Review by Jess

 

How Roosevelt Spent the
Bail-Out Money in 1937!

This is Timberline Lodge in Northern Oregon. It seems fitting to take a look at it today, as it was built during the depression as a WPA project to create jobs. Today millions of people every year still enjoy this National Historic Landmark. Those bail-out dollars have had a lasting impact!

Timberline Lodge, Government Camp, Oregon.

The Lodge in the photo above is buried under 25 feet of snow! I love exploring old hotels and I'd like to show you some of them. Take a free on-line tour of Timberline Lodge with me. The craftsmanship and art make Timberline Lodge one of a kind.

Timberline Lodge
Online Virtual Tour
Historic-Hotels-Lodges.com

 

 

Sprinklites:

Sprinklites, decorative lights and sprinklers rolled up in one. I wasn't excited about them when I read about them... Now, after having 2 sets of them in my own yard for over 2 years, I still think they are way cool! And way better than those cheap imitations they sell at the warehouse stores. See review.

 

Go back in time!

The photo below is of the Oregon Caves Chateau. It's one-of-a-kind, and one of my favorites. Built in 1934, it is essentially unchanged since it was built. The exterior is shingled with tree bark. A real creek flows through the dining room. Even the furniture is still original! The hotel is owned by the National Park Service and operated by a local non-profit.

The Oregon Caves Chateau
The Oregon Caves Chateau
Online Virtual Tour
Historic-Hotels-Lodges.com

 

Window decals & more

Click on the image for a direct link to where I got this decal for my truck. It was easy to install and looks great!

Automotive Decals and More...

 

My Other Websites:

A man can not live for irrigation alone!

Historic-Hotels-Lodges.com
Free virtual tours of grand hotels. I like exploring old buildings and had a lot of photos of old hotels we stayed at, so I made this website.

Landscape Tutorials
A few landscape related tutorials I've thrown together.

Jess & Julie Stryker's Homepage
Primarily meant for my family and friends, but you're welcome to take a look! Some stories I've written, family photos, pictures of my yard (lower your expectations!), etc.

JessStryker.com
Originally my Landscape Architectural Design business' website. Now that running IrrigationTutorials.com has become my main business, I use it for whatever, mostly photos I've taken in National Parks and other scenic places.

Finding My Way in S.L.
Yes, I'm one of those people who has a "Second Life". For the record, there's nothing wrong with my first life! For some reason I just find the virtual world there fascinating. Enough excuses, it is what it is and I blog about it at findingmywayinsl.com. See the blog to find out what about S.L. interests me most. (Big surprise: it's mostly how-to articles on building stuff... wouldn't you know that's what I'd write?)

 

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