Plumbing – Do pressure reducing valves also function as check/one-way valves

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If installing a pressure reducing valve, is there any sense in installing a one-way check valve in series, or would it be redundant? (i.e. does the PRV also act as a one-way valve?)

Best Answer

First, no, they don't function as a check valve. They limit inflow by dynamically changing the valve opening so that when less pressure is on the out side, the valve opens up fully, and too much pressure on the out side causes the valve to shut. In a no pressure situation (where water could go backwards), it won't be impeded at all.

Assuming that this is for your residential plumbing, you generally wouldn't install a check valve, because you want to be able to drain the system at the shut-off if you ever need to do any modifications.