Jess Stryker's Landscape Sprinkler Design Tutorial Step #2  Valves

What Type of Valve to Use:

There are many different kinds of valves available. You will need at least two different types for your irrigation system.

An emergency shut-off valve. This valve should be installed at the closest point possible to your water source, that is, the location where you tap in for the irrigation system. Without this valve you will need to shut-off the water to the entire house when you want to work on the mainline or irrigation valves. The most commonly used valves for this purpose are "gate valves" because they are inexpensive. Unfortunately the cheap gate valves you're likely to use also tend to not close completely and fail after a short period of time. While a gate valve will get you by, I recommend that you use a "ball valve", "disk valve", or "butterfly valve". These cost a bit more but are much more reliable and will last several times longer. So if you pay twice as much for a ball valve it's probably still the best deal! If you do use a gate valve make sure that it is a "wedge" type and buy a good quality one (it will cost as much or more than the ball valve, but it will also work as good). There's nothing worse than trying to work on a system when you can't shut off the water completely.


Control valves. These are the valves that turn on and off the sprinklers. You have two basic styles to choose from.

Globe or angle valve. This valve is available in any size and is commonly installed underground in a box or vault. Since it doesn't incorporate a backflow preventer you must provide one separately. See the section on backflow preventers (its back a few pages). The globe style valve is the most commonly used valve on commercial sprinkler systems.


Anti-siphon valve. Available only in 3/4" and 1" size. This is my recommendation for homeowners. The anti-siphon valve incorporates a backflow preventer into the valve. This saves a considerable amount of money, as backflow preventers are very expensive. The anti-siphon valve MUST be installed above ground and MUST be at least 6" higher than the highest sprinkler head. This means that if you want to use anti-siphon valves you will have to locate the valves at the highest point in your yard, and run a water supply pipe to them from the water source (this water supply is called a "mainline"). The mainline should be buried 18" deep.

Operation Method

The control valves may be manually operated or they can be remotely controlled. Manual control is simple, the valve has a handle you use to turn it on. Remote control valves are either electric or hydraulic, but almost everyone uses electric. The electric valve operates on 24 volt alternating current (vac) and is turned on and off by a timer called an "irrigation controller" or often just "controller". Anti-siphon, globe, and angle valves are all available as automatic valves. Pretty much all valves and controllers are compatible unless the controller is battery or solar operated. (Most controllers have a battery to backup the program in case of a power failure, these are not "battery operated". If it has a plug, you're O.K.) So you can buy a brand
"X" controller and it will work fine with brand "Y" valves. Or you can even use various brands of valves together.

Flow Control

I strongly recommend that if you are going to use automatic valves, you select one that has a manual flow control on it. This is in addition to the manual on and off control on the valve. The flow control bypasses the automatic valve features allowing the valve to be closed by turning a handle just like a standard manual valve. It also allows the valve to be "throttled", that is, left in a partially closed status.

• You can manually force the valve closed if it sticks open. Failure to close automatically is the most common valve problem, so there's a good chance that someday you will use the flow control.
• If your flows are low, it may be necessary to throttle down the flow control to make the valve close reliably.
• Partially closing the flow control will make the valve close faster, which is not something you want to do normally, but sometimes it is necessary. On automatic systems it is common for the next valve to open before the previous one fully closes. The resulting loss of pressure due to two valve circuits being on at the same time can cause the first valve to never close. This is often a problem with systems that use pumps to supply the water.
• You can use the flow control to throttle the flow if your sprinklers are misting or your pressure increases for an unknown reason.
• If a sprinkler breaks and you don't have time to fix it, you can shut off the valve with the flow control and all the other valves will still operate as normal. That way you don't have to mess with the controller program.

Materials

Valves come in both brass and plastic models. Most used today are plastic, but brass is not at all out of the picture. There is no doubt that a brass valve will last longer if installed in the sunlight. From an operational point of view both are reliable, especially for automatic systems. For manual valves my experience is that brass will last much longer. If you use plastic valves above ground you may wish to consider building a cover for them to protect them from sunlight, which can destroy the plastic over time. Two types of plastic material are used for valves. Glass-reinforced nylon is the best, it is tougher, more resistant to impact, and has a higher pressure rating. PVC is used for lower cost valves, it still is as strong as the pipe you're using, although that really depends on how thick the plastic is! I recommend avoiding valves with "solvent weld" connections (the pipe glues directly into the valve.) If the valve fails, they can be difficult to replace. Plus only the cheapest valves come with solvent weld connections, so what does that tell you about the likelihood you will need to remove it some day? Hmmm....

Maintenance

Today's valves are pretty maintenance free. Almost all automatic valve failures result from installation or design problems. Ignore the following and you will hate your valves regardless of what type or brand you buy!

Join the "Hall of Shame"! Simply ignore the following advice, then send me your "I'm an idiot, I wish I'd listened..." sob story. I'll add it to my collection and shed an alligator tear or two for you!

• Dirt in the irrigation pipes. Inside the valve there are very small water passages that lead to and from the solenoid. If a grain of sand or glob of algae gets into these passages it can block them and the valve will fail to open or (more likely) fail to close. It is critical to flush all the dirt out of the pipes before installing the valves. A 150 mesh filter installed at the water source connection can also help keep out sand that comes in with the water supply. You may be surprised to learn that most water companies have considerable amounts of sand in their pipes. When you install a new sprinkler system the higher flows stir up this sand and then it gets into your new system. That's why I tell you in the installation tutorial to flush for so long. You have to get the sand out of both the sprinkler system pipes and the water supply pipes! I can't stress this enough! It's like a cheap low-flow toilet. You have to flush, flush, and flush again!
• Almost all valve solenoid failures are caused by water getting into the solenoid. The water gets into them through the wires. The solenoid wires have multiple strands of wires twisted together with insulation around them. Because they are twisted there are very small gaps between the wires. Water is sucked up through these small passages into the solenoid by capillary action. Thus it is critically important that the wire splices on the valves be completely water proof so that water can't be sucked into the solenoid through the wires. You should water-proof the wire splices right after you test the valves! They only need to get wet once to ruin the solenoid. The Installation Tutorial has more on this.

---

Valve Size and Pressure Losses:

Emergency Shut-Off Valve:

The pressure loss through the emergency shut-off valve is not significant enough to worry with. We will ignore it. The emergency shut-off valve should be the same size as the pipe it is installed on.

Automatic Valves:

WARNING!!! If you use the wrong size automatic valve, the valve may not work!

The pressure loss in an automatic valve is the energy source used by the valve to open and close. If the valve doesn't have enough pressure loss it will not have the energy needed to close by itself. Always size automatic valves based on the flow rate using the manufacturer's chart as a guide. Never assume that the valve should be the same size as the pipe! It is very common for the valve to be a different size than the pipe it is installed on. I have seen some rare cases where a 3/4" valve was the proper size for the flow through a 2" pipe!!! If you absolutely must guess, use the next valve size smaller than the pipe size and assume a pressure loss of 6 PSI. Never guess if your flow is less than 5 GPM, always use a chart! Many automatic valves won't work at all at flows below 5 GPM! 

The size of the automatic valves is determined by the manufacturer's recommended flow range, together with the pressure loss through the valve at the selected flow. You will need to get the valve manufacturer's flow chart for the model of valve you plan to use. This information should be on the valve package. You will also find this information for most popular valve models in the reviews on this website, Click Here. If you still can't find it, try the valve manufacturer's website (click here), or ask for a data sheet on the valve at the store where you buy the valve. (At discount home improvement stores you are likely to get a blank stare from the employee if you ask for a data sheet!) If you can't find this information for the valve you want to use, I strongly suggest you find another valve. After the valve is installed is not a good time to discover it's the wrong size and won't work!

For example, lets say you are going to use an automatic anti-siphon type valve. Your Design Flow is 20 GPM, so for now we will assume the flow through the valve will also be 20 GPM. (If it turns out the flow will be less, you can resize the valve later.) The manufacturer's flow chart would look something like this:

Wontwurk Valve Company, Inc. - Valve Performance Data

	5 GPM	10 GPM	15 GPM	20 GPM	25 GPM
3/4" Anti-Siphon Valve	5.0 PSI	5.5 PSI	6.0 PSI	8.0 PSI	---
1" Anti-Siphon Valve	2.5 PSI	3.5 PSI	3.0 PSI	4.0 PSI	9.0 PSI

Warning: This chart is not real. Do not use these values!

The chart above tells us that the pressure loss for our valve would be 8.0 PSI if we used a 3/4" valve and 4.0 if we used a 1" valve. So we could select either one. The pressure loss information from the chart would be the number that you write into your Pressure Loss Table on the "_____ PSI - Valves" line. So if we decided to use the 3/4" valve, the value would be 8 PSI. But what if after adding all the pressure losses in the loss table, you discover that the losses are too high? In that case you could go back and change to a 1" valve. That would reduce the pressure loss down to 4 PSI, rather than 8. With that said, as a general rule I try to avoid losing more than 6 PSI through a valve. So I would not use a 3/4" valve in the example above if it were my sprinkler system. Why? Valves need pressure drop for them to work correctly, but really high pressure losses are hard on the valve. As the pressure loss through an automatic valve increases, the speed that the valve closes also increases. Thus a high pressure loss can cause the valve to snap closed extremely fast, and that is bad for the entire sprinkler system. Plus the water is moving extremely fast through the valves at those higher pressure loss rates, resulting in more wear on the valve seats. So the valve will fail earlier.

If you looked closely at the chart above you may have noted a couple of interesting items. First, and most obvious, is that no pressure loss is given for a 3/4" valve at 25 GPM. This is because that flow is outside the acceptable range for the valve. You should not use the valve at that high a flow rate. The next item is less obvious, but if you look closely the pressure loss for the 1" size is less at 15 GPM than it is at 10 GPM! This is very common with valves, often water turbulence inside the valve can cause the valve to perform better at higher flows than it does at low flows.

One final note. As you move through the tutorial you will find that even though the valve will handle a certain flow, that flow is often too high for the same size of pipe. So it is very common to have a valve that is one, or even two, sizes smaller than the pipe it is installed in. In fact it is so common that they actually make special pipe fittings (connectors) for this. For example they make a PVC plastic male adapter that glues onto 1" pipe, but has 3/4" threads so you can install a 3/4" valve on a 1" PVC pipe. They also make one that glues onto 1 1/4" pipe but has 1" threads. Because the flow capacity of a given size of poly pipe is less than that of PVC it is even more common to have a smaller valve in a poly pipe.

For Manual Valves:

Manual valves are much more forgiving than automatic valves. You don't need to worry about having enough pressure to allow the valve to close by itself, it uses "elbow grease" to power it! However, you still need to find out what the pressure loss through the valve will be so you can enter it in your Pressure Loss Table. As with the automatic valves, you use a chart provided by the manufacturer for this. Follow the same procedure given above for automatic valves. Unfortunately, pressure loss data for manual valves can be hard to find as many manufacturers don't provide it. As a general rule, allow 2 PSI pressure loss for a globe or angle type manual control valve, 5 PSI if it is an anti-siphon valve.

Manual irrigation control valves should be of the "angle" or "globe" type with replaceable rubber seats. Never use a gate valve as a control valve. It is not made to be regularly opened and shut. Many gate valves will fail after as little as 10 uses! .

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

Glossary    Conversion Formulas    About the Author

Comments?   Questions?   Product Data & Reviews   More Irrigation Tutorials!

www.IrrigationTutorials.com

IrrigationTutorials.com is not affiliated with any irrigation product manufacturer, distributor, or retailer.

By using this tutorial you agree to be bound by the conditions and limitations listed on the disclaimer page.

Jess Stryker's Irrigation Tutorials
Copyright © Jess Stryker, 2001
All rights reserved.