Jumping or skipping zones is the most common issue faced by indexing valves.
Sadly, it’s not the indexing valve causing the issue but rather how it integrates with the rest of the irrigation system and how that system is operating. Think of it like this: the indexing valve has one moving part; it’s incredibly simple in its design. If there’s something mechanically wrong with the valve, it will simply hang up and get stuck.
For example, issue number one:
The Faulty Check Valve
Check valves are used on pump-driven systems, and their sole purpose is to maintain the pump’s prime. If the check valve doesn’t close completely, the water will slowly trickle back to the source and leave air pockets in the line.
You will most likely notice this issue after your pump has been off for a reasonable amount of time, and when you crank it up, it takes anywhere from a few seconds to a few minutes to get water.
This will cause an initial burst of water from the pump, pushing the disk down. Unfortunately, due to those pockets in the line, the water flow will decrease to the point where the disk floats back up and rotates. Then, as the pump completes the re-priming process, the volume of water will go full force and push the disk back down, skipping a zone.
There’s an excellent test for this and two methods to accomplish it. The first involves a ball valve. If you have one, turn the pump on and get a zone running. Then, close the ball valve, give it a few seconds, and open it back up. Please don’t close it for an extended period because your pump will eventually burn up.
Just see what zone pops up, close the ball valve, give it 5 seconds or so, and open it back up. Repeat this and see if you can get the valve to go through the entire cycle.
If you don’t have a ball valve, the next best thing is to use your timer/controller with a short interval. Turn it on, see what zone comes up, and cut it off. Give it a few seconds, and do it again. See if the shorter interval helps.
If the ball valve / shorter interval appears to help, the question becomes, “What’s happening during that extra time?”. The answer is almost always that the water is slowly trickling back to the source, and the one device that’s supposed to keep that from occurring is the check valve.
Culprit number two is a lot rarer as most of our business is in the State of Florida, and the state of Florida is pretty flat. This issue occurs when there are lines above the indexing valve in elevation.
When the water flow is stopped, gravity will want to level that water off throughout the system wherever possible. If there are lines above the valve, water will now flow into the indexing valve through the valve outlets.
This will often cause the valve to jump zones, and a check valve should be installed on any outlet going up in elevation from the indexing valve.
It’s Forming a Vacuum
This is rarer and is just as likely to cause a valve to hang up on zones as it is to cause it to jump them.
You go to a restaurant and order a beverage. It arrives with a straw in it. You place your finger on top of that straw and remove it from the beverage. Even though the bottom end of the straw is open, the liquid will remain in the straw due to the vacuum your finger is creating.
An irrigation system can form a vacuum in a very similar fashion. It will usually cause a valve to simply stick on a zone, though it can cause it to jump also. The key to this is what’s called an atmospheric vacuum breaker or air release valve. Most city water systems have these already installed, but they do go bad on occasion.
What these devices do is simply remove the finger from the straw after you power the system down. This allows the valve to advance quicker and function better overall.