How to Calculate Residual Pressure in a Sprinkler System

If your sprinkler system isn't working up to par, residual pressure could be part of the problem. Residual pressure is measured in psi and is a result of a drop in pressure when the sprinkler is operational. If you want to measure residual pressure in your sprinkler system, a pressure gauge -- an instrument that measures psi -- can give you the information you need to troubleshoot your sprinkler system.

Pressure gauge
Adjustable wrench

Instructions

- 1
  Turn off the sprinkler's water supply.
- 2
  Turn off the sprinkler heads. Exactly how you do this depends on your sprinkler system. In general, lawn sprinkler heads can be turned off by adjusting a screw on the sprinkler head with a screwdriver. For indoor sprinkling systems, you may be able to shut the system off from the controller.
- 3
  Locate a point on the sprinkler system where you can attach the gauge to the main water pipe that feeds into your sprinkler.
- 4
  Attach the gauge to the main water pipe that feeds your sprinkler system. Each gauge will be slightly different. In general, if you have a pressure gauge with a quick connect fitting, simply screw the quick connect plug onto the pipe.
- 5
  Turn the water supply on without activating the sprinkler system.
- 6
  Take an initial psi reading. This is your static water pressure.
- 7
  Turn on the sprinkler system and then watch the pressure gauge for a drop in pressure. The reading is your residual water pressure. For example, say your initial reading was 40 psi. Once you turned on the sprinkler system, the reading drops to 30 psi. The residual water pressure for your sprinkler system is therefore 30 psi.

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