How to Determine the Cause of Low Pressure on a Zone
The first question to ask, silly as it might sound, is “has it ever worked properly?” Since most systems come on while the owner is asleep it is very common for the system to have a long running but unknown problem. If the answer is “no” you might have a design problem. At this point you get a professional involved.
The next question is “if it did work at one time, has anything changed?” For example, have you added 2 or 3 heads or rotors to that zone? If so the zone may now need more water than is available. Your system only has so many gallons per minute it can provide. Going over the limit will reduce performance and coverage. For example, if you have 30 pounds per square inch of water pressure and 15gpm available on a zone you can run 5 heads spraying a 24’ diameter. If you add just two heads you will drop down to a 20’ circle.
If by chance you have added heads and cannot remove them the next best choice is to look for lower volume nozzles. In the example above the nozzles took 2.7gpm. Another brand only uses 2.2 gpm. This would fit into your design and maintain performance. Because of the lower rate you would have to water that area longer but your coverage would return.
But you haven’t added any heads and pressure on that one zone is down. Let’s start simple. Let’s look for a leak. Turn on the zone. If you know where your valve is, start there. If not, then start at your controller. Slowly walk toward and around the area with the problem. We are looking for bubbling water, soft spots, soggy spots, holes, and, of course, flowing water. If it has been an extremely dry summer look for an area that is suspiciously healthy. Find it? You have a broken pipe. No leak? Keep reading.
If you know where the valve is for that zone then go there next. Some valves have a flow control handle to adjust the flow to the zone. Make sure it is not turned down. Don’t be surprised if your valve does not have one. Some people don’t use them.
If you don’t have a flow control, or if it’s not turned down, then the problem is probably in the valve. For some reason it is not opening completely.
If you don’t know where your valve is, or you do and the flow control is not the problem, I recommend getting a professional involved. The valve may have to be rebuilt or replaced. If you wish to do it yourself it is fairly easy. Take a look at this GUIDE. If this doesn’t fix it you definitely need to get a professional involved.