20.3: The Function of a PRV’s Bypass Check Valve
- Page ID
- 117100
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Even though a pressure reducing valve is normally open, reverse flow through it isn’t always reliable. Under certain conditions, especially in fast-cycling circuits, pressure pulses can appear at the outlet. If these pulses are higher than the valve’s set pressure, the valve may suddenly snap shut—even when you don’t want it to. This unintended closure can block return flow, potentially causing system malfunctions or unwanted actuator behavior.
To prevent this, many systems include a bypass check valve. This check valve is connected in parallel with the pressure reducing valve and allows fluid to flow freely in the reverse direction, bypassing the PRV altogether.
There are two common ways to include this check function:
- Externally – By plumbing a standalone check valve around the PRV.
- Internally – By using a pressure reducing valve that has a built-in (integral) check valve, which is more compact and efficient.
The integral check valve allows reverse flow without affecting the pressure-reducing function during normal forward flow. This is especially useful in circuits where actuators need to return quickly or where pressure pulses are unavoidable.
The schematic symbol for a pressure reducing valve with an internal check valve includes a check valve drawn in parallel with the main valve symbol. This visual cue tells you that the valve can control pressure in one direction and allow unrestricted flow in the other.