Water system hammering...

[tiger79]

I recently replaced the Whale Watermaster fresh water pump with an identical new one.  The pump won't turn off when the taps are closed - the pressure builds and there's then a hammering noise from near the calorifier.  At the same time, the relief pipe on the pressure relief valve vibrates in time with the hammering noise.  Does it sound like I need a new PRV?  The one there is original, so 10 years old.  The water pump is 3bar, so if I need a new PRV I guess I should get a 4bar version?

The hammering noise had started with the old water pump, which then refused to prime, which is why I replaced it.

[Yngmar]

Could be the pressure switch on the pump is not working or not set correctly (there's an adjustment screw on it usually). If it doesn't switch off at 3 bar then the PRV is just doing its job.

If the PRV has failed, there would be water coming out of the relief valve, or the pipe if there is one attached (ours had a return pipe to the tank). Easy to check with the quick-connect plumbing.

If so, yes, ours was a 4 bar PRV, 1/2" BSP.

[diverphil]

3 bar seems a high pressure for the pump system to run at, sure flow pumps I've seen are around 20/30 psi that's around 1.5 to 2 bar, i would assume running at higher pressure would cause vibration in the pipework when it pumps up to high pressure as the pump is working harder, the other bit that might cause it would be if the accumulator diaphragm was split, so there would be no cushioning effect for the pulses from the pump.

[tiger79]

3 bar seems a high pressure for the pump system to run at, sure flow pumps I've seen are around 20/30 psi that's around 1.5 to 2 bar, i would assume running at higher pressure would cause vibration in the pipework when it pumps up to high pressure as the pump is working harder, the other bit that might cause it would be if the accumulator diaphragm was split, so there would be no cushioning effect for the pulses from the pump.

The factory-fitted original pump was 3bar.  It's a Whale Watermaster and no accumulator is needed.

[tiger79]

Update - the PRV was faulty and was allowing pressure to escape, which is why the pump wouldn't turn itself off.  Unfortunately, the PRV is totally inaccessible, buried beneath a rats-nest of Whale quick-connect fittings.  I initially thought there was no alternative to biting the bullet and removing the calorifier.  But then I thought I'd try a bit of lateral thinking and I accessed the leak-off pipe from the faulty PRV, cut into it and fitted a new PRV inline.  Works perfectly and saved me a lot of hassle.