Pressure reducing valves - do any work with zero flow?

[Chris Green]

Looking at pressure reducing valves available from Toolststion, Screwfix and such I note that a lot of the reviews say that the pressure builds up when there's no flow. I.e. the pressure reduction reduces the pressure available when running a tap or (more to the point possibly) a shower but when all taps are turned off the outlet pressure builds up to match the inlet pressure.

I need to reduce the pressure to some small waterers (as in things for animals to drink from) which will, if they are working, reduce the flow to zero. Can one get pressure reduction valves for this sort of application?

[Dave Liquorice]

Not on the one I have here. It holds the outlet pressure at the set point pretty well. 2.5 bar IIRC with a supply around 4 to 5 bar. Washing machine and electric shower share the same cold supply, both can be used at the same time without any temperature changes from the shower. There is brief pulse in the shower flow as the W/Mc abruptly open/closes its valve but that is all.

Bear in mind that a PRV is spring biased one way valve. If part of the system freezes the expansion cannot "escape" up the supply, so it finds somewhere else, pushes a joint apart, splits the pipe...

The one way valve action can also "trap" water hammer pressure pulses, which may not be producing an audible bang.

[harry]

It depends on the nature of the valve seat. Metal to metal ones are eroded by the fluid passing through and start to pa ss on zero flow.

Some have plastic or rubber obturating plate that remains tight for longer but usually they don't maintain as accurate a flow.

What usually happens is the safety valve (downstream of the PRV) lifts and lets the excess away. But they too suffer from the same problem of wear on the seat.