A sprinkler system is a lot like a car in the fact that it has many separate moving components that need to work harmoniously to help produce the end result. A very common and a very important part that can go bad are the electric valves. There should be a separate valve for each zone of the sprinkler system and when one goes bad you will have to replace it.
Just as a car requires regular maintenance, so does a sprinkler system. This always gets me, I have people whom it truly upsets to spend $165 to replace a valve that sometimes are as old as 25 years, but they’ll buy or lease a new fully loaded car every three years…hmmmm? Even with regular maintenance, there isn’t much that can be done to prevent the valves from going bad, they just wear out. Usually the first thing to fail is the solenoid, which depending on age of the valve may be replaced without having to remove the entire valve.
Replacing the solenoid may be easy once you have located the correct valve as well as diagnosed the problem. The solenoid is on the top of the valve with two wires coming out of it. You will want to make sure to shut off the water source prior to replacing the solenoid, then make sure to clear the valve of all dirt and debris around and underneath it. You will want to make sure that you remove all water from the valve box, this is important so that you do not get any dirt or debris in the solenoid, which may cause the solenoid to not sit in the valve correctly and the valve very well may become stuck open.
Once you are ready , simply turn the solenoid counter-clockwise until it is removed from the valve. Put the new solenoid in place and turn clockwise gently until it is snug, DO NOT OVER TIGHTEN. An over-tight solenoid can strip the valve permanently damaging it and cause it to remain open. Too loose and the valve will stay on also. Now that you have installed the new solenoid, you are ready to re-wire.
Now one at a time, cut one wire from the old solenoid and connect one wire from the new one. Then clip the second wire from the old solenoid and connect the second from the new one. Make sure that one lead is on the common or negative wire (usually white), and the other wire is connected to the hot wire.
The next thing that usually goes bad is the valve’s diaphragm. This is a rubber piece with a spring which controls the opening and closing of the valve. There are only 2 things that can happen when the diaphragm goes bad: The valve is stuck shut and will not open, or the diaphragm is stuck open and the valve will not shut down completely or at all.
In most situations, the whole valve will need to be replaced by digging it up and cutting the PVC. This is usually done when I run into an older model electric valve that I cannot obtain replacement parts for, or, the valve body is actually cracked or damage for whatever reason. Most of the time you can replace just the bad valve, but if the valves were plumbed in too closely together you may have to replace more than one. I have been on jobs where there is only 1 valve bad, however six valves needed to be replaced due to the fact that whomever installed it plumbed them so close together, that it was impossible to only replace one. Usually this is better for the customer anyway, because once one goes bad, it is only a matter of time before the other ones start going bad.
The actual plumbing may vary from situation to situation, but the main points are to get the flow of the valve correctly. All reputable brand valves have an arrow on them showing you which direction that the water flows through them. Just remember it sounds fairly easy, and for some it very well may be, but if you are in doubt, call a licensed sprinkler professional.