RPZ in a Flow or Dynamic State – Relief Valve Discharges Water

/in /by

What would cause the relief valve to discharge water? Water will discharge from the relief valve when the pressure in the zone, the area between the first and second check valve downstream of the relief valve, approaches the supply pressure or inlet pressure.

The zone pressure, which should be lower than supply pressure, will be equal to or approach the supply pressure for several reasons:

  • If the supply pressure is fluctuating (decreasing) – water will discharge from the relief valve intermittently.
  • If the first check valve is fouled open and the device is in a no-flow condition – water will discharge from the relief valve continuously.
  • If the second check valve is fouled open and the device is in a backflow condition – water will discharge from the relief valve intermittently or continuously depending on the type of backflow.

Fluctuating Supply Pressure – Relief Valve Discharging Intermittently

Water will intermittently discharge from the relief valve if the supply pressure is fluctuating down. The supply or inlet pressure fluctuation causes the pressure in the zone to be equal to or approach the supply pressure. If supply pressure changes often, the relief valve will spit and stop, spit and stop often. If a device has a supply pressure of 60 PSI and a zone pressure of 5 PSI less than the supply pressure with the relief valve forced open with a 2 PSI spring, the relief valve will open when the supply pressure falls to 57 PSI. This device has a 3.0 PSI Buffer Value.