Choosing the right valve
As irrigation has become more standard on jobs of all kinds across the United States, most grounds maintenance workers have acquired a basic knowledge of valves. What many of us don't know is that a huge variety of valves are available to fit particular jobs.
If you pick the wrong valve for a project, you will have either paid too much or will be returning to the job site for repairs. This article will describe good choices for valves-from small drip systems to golf irrigation-and how to avoid future problems.
Point-of-connection valves Installing a point-of-connection (POC) valve is the first thing you should do when starting an irrigation job. That way, you have to shut off the main water supply to the property only once. Most installations use a gate valve, but ball valves may be acceptable if you have enough room inside a valve box for the handle and think that it may be turned on or off frequently.
Most POC valves are in the "on" position and stay there. They are turned off only if there is a leak or other problem. Make sure this is a brass or cast iron valve larger than 3 inches in size. If you are connecting to copper, use a slip-fitting valve that can be permanently soldered in place for decades of leak-free service.
Anti-siphon, backflow and reduced-pressure valves These valves prevent irrigation water from "backflowing" into a drinking water supply. Determining whether you need one is simple: if you are on city water of any kind, even from a hydrant, these are required. If water is not coming from a drinking water supply, you don't need them.
On residential or small commercial jobs with a POC of 1 inch or less, a brass anti-siphon valve may double as a system shut-off valve. Reduced-pressure or "RPZ" valves perform the same function for big taps, usually larger than 3 inches. They are a complex assembly that includes gate valves, pressure outlets, test cocks, check valves and air gaps. You should install all these valves a minimum of one foot above the highest point on your irrigation system. Many municipalities have strict equipment guidelines-contractors should check local requirements for these valves before installation.
Residential and commercial irrigation valves Rule 1: Avoid cheap plastic valves. As professional installers and managers, why would we install equipment that we know is going to fail? Not all plastic is the same: glass-filled nylon material is far stronger and becoming a standard for contractor-grade valves. Good quality valves of 3/4 to 2 inches from reputable manufacturers will have stronger bodies, more durable rubber diaphragms, stronger springs and better solenoids.
Always select a valve with its own shut-off capability so that repairs can be made without shutting down the whole system. Never install an irrigation valve without a manual bleeder screw. Also avoid electric anti-siphon valves that sit above grade. They are unsightly and will degrade much faster because of exposure to outside elements.
A better installation has one brass anti-siphon valve above grade, followed by a manifold of in-line below-grade electric valves housed in a valve box. Brass valves are generally not required for this scale of installation unless there is a large budget or the usage will be especially heavy.
Municipal, large commercial and golf irrigation valves This is the realm of 1 1/2- to 3-inch valves, brass or glass-reinforced nylon bodied only. When choosing these valves, first consider the quality of the water source. Most residential or commercial jobs use clean city water, but larger jobs may be drawing from ponds, streams or canals. If the water is cloudy with silt or has visible algae, consider using valves that have an internal "scrubber" mechanism. That will prevent fine internal screens and ports from clogging.
On golf courses and other big jobs, filtering water before it reaches sprinklers or valves is common to prevent constant downstream problems. At this level, you may be coming off an irrigation mainline with a riser and will want some sort of isolation capability between the feeder line and your valves.
Bottom inlet angle valves threaded right on the riser may work fine, but this valve does not allow an isolation gate valve to be installed. Whenever this type of valve requires repair or replacement, the entire mainline or system will have to be shut down and drained.
With big valves for big jobs, don't use residential-type sprinkler wire: most applications require a minimum of #14-gauge solid copper core wire for each valve.
Sizing valves Besides using common sense to acquire good quality equipment, the most important aspect you should consider when choosing valves is size. Size is based on flow, so you need to figure out how many sprinklers, bubblers or emitters are going to be on each valve zone. It's important to have an irrigation design on paper so that you can figure out how much flow you have per zone. A basic rule is that you want to split the flows as equally as possibleso that you do not have 5 gallons per minute (gpm) on one valve followed by 15 gpm on the next. The chart below lists the maximum recommended values for sizing electric irrigation valves:
The values above follow a general rule in irrigation design that water velocity should not exceed 5 feet per second in PVC piping systems. The more flow through a valve at any size, the more pressure loss you will encounter. Before sizing your valves, add up all psi friction losses through your valve, piping and irrigation devices so that you know for sure that you'll get the coverage you need.
Valves larger than 3 inches are not recommended for landscape or golf use, except in specialized situations. Larger valves are expensive, complex and need to be specified by an irrigation designer or engineer for each individual location. We have not included 1/2-inch valves because their small size, high psi loss and small price differential from a 3/4-inch valve makes them impractical.
Special features Besides the "scrubber" option mentioned earlier, many special valve features are available. One of the most popular is a pressure-regulating module that allows constant downstream pressure regardless of source line psi. Most sprinklers have an optimum operating range between 30 and 50 psi, so if your line pressure is far above this you will want to regulate it somehow.
Placing a separate pressure regulator after the valve is the preferred method for many installers, but this requires more parts, labor and has more possible leakage points. Drip-irrigation systems require pressure regulation and filtration after the valve, but the entire assembly is usually built as one unit and housed in one valve box.
Hydraulic valves are turned on or off with tubing and water rather than wires and voltage. These valves are to be used only with an entirely hydraulic system, usually on large golf irrigation systems in lightning-prone areas. All other aspects of a hydraulically operated valve are the same except that filtration of the hydraulic tubing to operate the valve is an extra, mandatory step. Because many systems are now using effluent water, the familiar purple color indicating "do not drink" is a feature now being applied to solenoids and valve handles.
Top 5 installation tips Here are some of the most helpful tips for saving time and money when installing valves: * Leave at least 12 inches of slack wire at every valve. * Don't cram valves into a valve box; leave room to repair. * Use Teflon tape instead of paste for fewer leaks. * Install as straight as possible for easy service from the top. * Always use PVC primer for leak-free solvent welds.
Note on quality Every contractor knows that having to return to a job site to fix faulty installations is more time consuming and expensive than doing it right the first time. If you install a valve and it starts dripping slightly, take it out and redo it-it's not going to stop leaking by itself.
The old saying "you get what you pay for" is especially true with irrigation valves that turn on and off thousands of times, year after year. So beware of trying to save a couple bucks when buying valves. Installers that always use good equipment and proper techniques prosper longer than those who don't.
Gary Kaye, CID, is an editor for LandscapeandSprinklers.com (Cincinnati, Ohio) and president of Golf Engineering Associates (Phoenix, Ariz.).
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