Low Pressure In One Of My Zones
Most people don't realize they have low pressure on one of their zones unless they either frequently inspect their system while it's running or notice dead spots in their yard. Having low pressure could mean a few things. The most likely reason would be a leak somewhere in that zone.
What To Look For?
The first thing you should do is check to see if the low pressure is just in that zone or if it's in the entire system. If it's just certain zones, then you can try walking the area where the zone is and see if you notice any places that may be holding water where a leak might be. Another thing you can do is to see if you certain heads have more pressure than other. For example, if one head has higher pressure, but the next one doesn't, then there could be a leak in the pipe between the two heads. Another place to look is around the sprinkler heads. Sprinkler heads are prone to being hit with mowers or other traffic and can snap at the base. When this happens, the sprinkler heads look normal, but are actually leaking out of the base below the ground.
Can't Find The Leak?
If you didn't have any luck finding the leak, the next step would be to locate the valve in the ground that controls that zone. It can be difficult to locate these sprinkler valves because over time they covered with grass. If you can't find it, you will need to contact an irrigation company to come out and locate it with a valve locator. After you locate the valve, you need to manually turn that valve by turning either the solenoid or bleed screw. This should allow the valve to open up and let water through to that sprinkler zone. If you can hear a whistling or something that sounds like it's restricting the water flow in that valve, then you might have a bad diaphragm or some type of blockage inside the valve. Some times you can open the bleed screw for a minute and then close it and it can unblock the valve if that's the problem.
Conclusion
Finding a leak isn't always easy unless it's what we call a "gusher", but with time and knowledge, you can pinpoint the area to start looking. Always be cautions when digging because the sprinkler wires may around the same area.