This house, 30 years old, has two water feeds, one for a drinking water tap and one that drives through a water softener, in the garage, into the house indirect system. Twice this year the house has been shaken by drumming - sounds, and feels, like a helicopter just overhead! I've managed to stop it by opening the drinking water tap for about 10 seconds. What's causing it and what's the remedy?
TIA
PA
Water hammer, can be started by a rapid shut-off of a tap or e.g. washing machine solenoid valve.
Peter Able presented the following explanation :
You have a tap or valve, where the tap washer is vibration at a resonant frequency. You need to find out which tap or valve is partially open at the time you hear the noise and then fix it.
Our kitchen hot tap does it when left near fully open, waiting for the hot to appear. The noise begins, as the hot appears, which is handy - I just swing the spout around to the washing up bowl and turn it on full.
Thanks Andy. This happens when nothing is happening in the house's plumbing - not even a cistern refilling after a flush. Plus it can't be relieved by opening any tap but the drinking water feed tap. Nor by flushing any cistern. I've been down this paths.
It is audible outside the house at, roughly, where the water supply - both direct and indirect - enters the house.
PA
Thanks, Harry. The resonant frequency is about 10Hz. That is too low, isn't it? The drinking water feed has a stopcock and then a tap. I've played with both. The stopcock has no effect, the tap kills the vibration after about 10s of full on.
PA
Could be started by a pressure wave coming in from the street, once it sets up a oscillation e.g. involving a cistern float, it can then continue by itself.
Can you set it off if you try?
You said two separate water feeds, is that literally two pipes coming in from the street, or just that the drinking water tap is tee'ed off before the piework continues to the softener, then splits to feed tge rest of the house from there?
As others have suggested, try sligtly closing down your stopcock(s).
You probably need to install a shock arrestor such as
- or maybe a larger one - to absorb the pressure fluctuations and stop the noise.
The noise is caused by a standing wave which can be triggered by a tap suddenly shutting, or sometimes by a tap that's slightly open such that the small flow acts a bit like the mouthpiece of a woodwind instrument, and the vibrations are amplified by the pipework.
The arrestor adds some resilience into the system which reduces the resonant frequency to below the audible range.
Thanks, Roger. I guess that a damper may stop this - but I'm left wondering what has caused this after 33 years of no issues; and where I'd put it. There's only about 2m of the drinking water feed in the house. The rest is underground.
When the effect starts again, I'll check to see if the water softener inlet and output pipes and the road-side meter vibrates !
PA
We had the same trouble a couple of years ago - did all the usual things without being able to track it down to anything in our house. Decided it started coincident with some plumbing work in the adjoining house where a downstairs loo was added - probably with sharp shut-off taps and valves. Our mains water pressure is quite high so I fitted a regulator and a shock arrester just after the internal stopcock. This improved the hammering but did not completely eliminate it. A couple of weeks later the plumber re-appeared next door and the noise has never come back - guess they were suffering too.
Picture here - was just a straight pipe on the left (stainless steel).
Thanks, Geo. I think that must be the situation here, too. Sod's Law, it hasn't happened since - but when it does I'll be searching outside.
Our water softener must damp the house - but the drinking water feed comes off the main before it feeds the softener. The amount of energy going into the vibration points directly away from the house - and it was audible outside the house.
PA
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