Re: PRV before pump inlet?
Posted by KevinS on June 08, 2003 at 19:35:33:
In response to Re: PRV before pump inlet?
Just for the forum's record, I plumbed up the pump with the PRV in the attic and it all works fine. The shower can deliver 12/18 l/m (lo/hi) and it appears to work perfectly in either mode. The PRV is a SYR (Reliance) 310C, and it's set at somewhere just over the 0.5 bar minimum. There's no toil on the motor, and no cavitation (though there was air left in the pipes that initially caused me concern!).

After reading a bit more about PRVs, it seems that the low pressure generated by the pump at the inlet is exactly what allows the PRV to cause flow.

: The setting is immaterial, since as soon as the pump starts it will produce a low pressure area between it and the PRV, (that is the only way the pump could move water), so in effect the outlet pressure from the PRV may always be less than the setting.

: : It was my understanding that a PRV can still allow a high flow, but will reduce the pressure (dissipated on the spring). The pump is designed to work as low as 0.1 bar inlet. If I gave it 0.7, wouldn't that be likely to supply within it's tolerances?

: : : You never restrict the flow to the inlet of any pump. Doing so will cause cavitation and damage/destroy the pump.

: : : : I have a 0.2 bar (2M head) cold water supply and a 2.1 bar (maximum) hot water supply. I also have a shower pump/mixer that has an inlet min-max range of 0.1 bar to 1 bar.

: : : : My question is this: is it advisable to use a Pressure Reducing Valve (PRV) to reduce the hot supply pressure to, say 0.5 bar, before the inlet to the pump?

: : : : My worry is that the draw from the pump will fight with the PRV and cause problems, and the shower unit was a bit too expensive to risk without advice!

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