Irrigation Tutorials

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Typical Pressure Loss for Water Meters

 

You may or may not have a water meter. If you buy your water from a water company or municipal water district you probably have a meter. If your water comes from a well, lake, or stream you probably don’t have a meter. The water meter measures how much water you use, that way the water company can charge you for the amount you use. Even if you get your water from a water provider you may not have a water meter, I didn’t have one at a couple of the homes I’ve owned (water was provided for a flat monthly fee regardless of how much was used.)  If you do have a meter where should you look for it?  In warm weather climates it will most likely be located near where your water supply taps into the water company’s pipes. This is usually right next to the street curb, or perhaps adjacent to an alley behind your home. In climates with extreme cold weather the meter may be under the house in the crawl space, but in most cases it is inside the basement.  Many newer meters have electronic features for remote reading, they send your water usage information to the water company via wires or radio signals.  Many of these new electronic models are actually flow sensors rather than traditional meters.  See the section on flow sensors below.

Just as a  side note, most water meters measure cubic feet of water.  Cubic feet is the measurement unit that water providers like to use.  A cubic foot of water is equal to 7.48 gallons.  Do not confuse cubic feet with acre feet.  Both are measurements of water quantity, but they are not the same thing.  An acre-foot is a whoping 325,900 gallons! 

Combination mechanical and electronic water meter with a radio transmitter built into the box lid.

Combination mechanical and electronic water meter with a radio transmitter built into the box lid.  You can read water quantity used on the mechanical dial face and it also transmits water use to the water district.

Flow Sensors (optional)

Some people install their own water metering device on the irrigation system main supply pipe so they can monitor just the irrigation water usage.  A flow sensor rather than a water meters is used for this.  The difference between the two is that a typical water meter measures only the amount of water used, flow sensors measure the rate of flow.  This allows them to monitor how much flow the irrigation system is using at any given moment.  The flow sensor typically creates an electronic pulse when a given amount of water has passed through it, for example a cubic foot of water. The flow sensor connects up to the irrigation controller that is used to turn on and off the irrigation system. Some higher-end models of irrigation controllers have the ability to monitor the number of pulses from the sensor and use the data to determine how much water is flowing at the moment, as well as the total amount of water used per irrigation cycle.  Using this information the controller can evaluate the irrigation system performance and respond to it. For example the controller might detect that the flow is higher than normal, indicating a leak in the irrigation system, or maybe a broken sprinkler head. Likewise a flow that is lower than expected might indicate a valve did not open when it was supposed to. The controller then sounds an alarm, or may shut off the water to limit damage from the leak. Flow sensors and controllers that monitor flow are features that are common on many larger irrigation systems, like parks and golf courses. Now, as the price of the equipment is rapidly dropping and water conservation is becoming an issue in more places, homeowners are starting to implement these optional flow sensing features as well.  Controllers that have this monitoring feature are called “Smart Controllers”.  Note that not all Smart Controllers have this monitoring feature.  For more information see the article on Smart Controllers.

If the meter is buried in a box, be careful when you open the box. Over the years I’ve encountered just about every creepy thing one can imagine in those boxes! Turtles, rats, snakes, various dead things. Ants and spiders are most common. It’s not a bad idea to be prepared to jump back, and maybe have a can of bug killer handy when opening a underground box. Once you find the meter you will likely need to clean it off so you can clearly see it. The meter should have a size stamped on it, if not, sometimes the meter size is shown on your water bill.  If all else fails, call your water company and ask them for the meter size, it should be in their water billing information.  The pressure loss (PSI Loss) for water meters is based on the meter size and the flow rate.  If you know the brand of the water meter you can probably find a table on the manufacturer’s website that tells you the pressure loss for the meter size at various rates of flow.  If not, the charts below should be close enough.

The charts below give typical pressure losses for various meter sizes and flow rates. If your meter is a combination of two sizes (like 5/8 x 3/4) use the chart for the smaller size. These dual-size meters are made by taking a small meter and putting a larger size inlet and outlet on it. So it is really the smaller size meter. For flow sensors you will need to contact the sensor manufacturer to find out how much pressure loss to expect in your unit. Flow sensor losses are generally less than those for a standard water meter, so if you can’t find a manufacturer’s flow loss table, in most cases you can safely use the values in the water meter tables below for flow sensors.

pencil Find your meter size below, then use your “Initial Design Flow” (from your Design Data Form) to find the PSI loss. Enter the PSI loss from the table below on the water meter line of the Pressure Loss Table. If you don’t have a water meter just enter 0 on the table.  If you modify the Initial Design Flow later you should come back and change the water meter/flow sensor PSI Loss values as well.  (This will be true of all your PSI Losses in the Pressure Loss Table that are based on flow.  If you change the Design Flow for your system you will need to update the PSI Loss values.  There is a bit of trial and error to the irrigation design method as you attempt to find that “sweet spot” that balances pressure vs. flow to give the optimum performance.)

 5/8″ meter
5 GPM 1 PSI loss
7 GPM 2 PSI loss
9 GPM 3 PSI loss
11 GPM 4.5 PSI loss
13 GPM 6 PSI loss
15 GPM 8.3 PSI loss
Don’t exceed 15 GPM

 

 3/4″ meter
4 GPM 0.5 PSI loss
8 GPM 1 PSI loss
11 GPM 2 PSI loss
14 GPM 3 PSI loss
17 GPM 5 PSI loss
20 GPM 6.5 PSI loss
Don’t exceed 20 GPM

 

1″ meter
8 GPM 0.5 PSI loss
13 GPM 1 PSI loss
19 GPM 2 PSI loss
23 GPM 3 PSI loss
26 GPM 4 PSI loss
29 GPM 5 PSI loss
32 GPM 6 PSI loss
34 GPM 7 PSI loss
Don’t exceed 34 GPM

 

1 1/4″ meter:
(This is not a standard water meter size. If you have one it is probably a 1″ meter modified to have a 1 1/4″ inlet and outlet.  But, then again, it might be a 1 1/2″ modified to 1 1/4″.  Not very helpful? Unless you are reasonably sure by looking at it that it is a 1 1/2″, you should assume it is 1″.)

 

1 1/2″ meter
17 GPM 0.5 PSI loss
22 GPM 1 PSI loss
31 GPM 2 PSI loss
38 GPM 3 PSI loss
45 GPM 4 PSI loss
50 GPM 5 PSI loss
55 GPM 6 PSI loss
60 GPM 7 PSI loss
Don’t exceed 60 GPM

 

2″ meter
36 GPM 1 PSI loss
51 GPM 2 PSI loss
63 GPM 3 PSI loss
72 GPM 4 PSI loss
82 GPM 5 PSI loss
88 GPM 6 PSI loss
100 GPM 8 PSI loss

Contact manufacturer for larger size meters.

That wasn’t hard, was it?  You’re gonna fly through this!

Water meter in basement.

Electronic remote reading water meter in a basement.  The water supply pipe exits the floor, there’s a ball valve with yellow handle, then a pressure regulator, and finally the water meter. (Note wires for remote reading.)

 

Water meter box near curb.

A typical water meter box near curb.

 


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