Domestic water hammer

[AJWParticipant @ajw]

Had to replace a dripping (overnight) cold water tank ball valve. Turned off mains with a valve that's located immediately beneath the tank in our airing cupboard.

Work complete turned mains back on and we were getting a 'thump' when taps turned on and a 'bang' when turned off? Quite violent.

Why?!!

Turned mains off at incoming under sink, drained everything, all taps open, wc systems, all pipes containing mains.

All taps and valves off, turned mains back on and encouraged pipes to fill working its way up to loft – all ok now –

Don't understand how a valve 5 ft away from my original valve change could have caused this.

Anyone had similar?

Alan

[AJWParticipant @ajw]

[Jon LawesParticipant @jonlawes51698]

Maybe you had some air in the pipes which was absorbing it originally which you have now inadvertently purged. I believe you can get a device which reduces this.

Another possibility is the gland on the stopcock is now misbehaving since being disturbed, or had not been opened fully originally to reduce the flow into the system?

All amateur speculation on my part of course.

[mechman48Participant @mechman48]

FWIW; It is possible that the ball valve float in the tank was 'bobbing up & down ' due to water rippling/splashing as it refilled causing the plunger to quickly push/pull the valve itself to open & close rapidly causing the banging.. sharp on/off of water flow which obviously disappeared as it levelled off & settled down.

George.

[Martin KyteParticipant @martinkyte99762]

We always fitted filter units in the water feeds to the electron microscopes to remove vibration from the pumps in the chiller units. They were fitted upside down with no filters so that there was a 'head of air to act as a cushion.

regards Martin

[Les Jones 1Participant @lesjones1]

Are the taps that give the problem fed from the high pressure mains supply that feeds the tank or are they fed from the output of the tank ? Assuming they are fed from the high pressure side it may be that the new ball valve has a snap action cut off rather than the type that gradually shuts off the flow into tank. I think Jon Lawes about air in the pipes acting as a cushion before the ball valve was replaced could be right. If so fitting a Hammer Arrester may solve the problem. (Search Toolstation, Screwfix, or plumbing suppliers for " Hammer Arresters" to find one.)

Les.

Hammer Arresters

[old martParticipant @oldmart]

There may be a pipe that is able to shake and amplify the hammer. Check and stuff a bit of sponge lagging in any flexable areas. The ammount of opening of valves can affect the hammer, and the repaired ballvalve will probably operate slightly differently than it did before.

[Howard LewisParticipant @howardlewis46836]

The original Portsmouth type ball valve, in the toilet, was replaced by a modern diaphragm ball valve, which seems to have some sort of servo action, giving a very sharp cut off. The "thump" is akin to shutting the cold water tap, in the kitchen, very quickly. Thankfully, just one thump rather than a continual succession.

So it may be initiated by the new valve causing rapid shut off.

Howard

[AJWParticipant @ajw]

Interesting! The new valve is a direct replacement for the original and does not cause any thumps or bangs when operating.

Since draining down and refilling the effect is very much less than before and now only audible with tap 'turn offs'

Think I might investigate hammer arresters as we have had this effect in the past and it has been quite violent.

Alan

[duncan webster 1Participant @duncanwebster1]

I fitted a hammer arrestor, for some reason the new dishwasher seems to turn the water on and off very frequently, and the banging kept me awake. Hammer arrestor made precisely no difference. Almost closing the isolation valve has helped, keeps the velocity of water in the pipe low. This not applicable to taps on the sink of course

[AJWParticipant @ajw]

Been looking at hammer arresters and to me they don't look big enough? Duncan's experiences? I think I was imagining something like the size (volume) of a small fire extinguisher. Tempted to make one.

Still have the bang and thump when operating cold taps although it is different – sounds more relaxed!

Alan

[Grindstone CowboyParticipant @grindstonecowboy]

You could always use a C/H expansion vessel. Probably easier than making one.

Rob

[Martin KyteParticipant @martinkyte99762]

Posted by duncan webster on 24/03/2021 19:15:01:

I fitted a hammer arrestor, for some reason the new dishwasher seems to turn the water on and off very frequently, and the banging kept me awake. Hammer arrestor made precisely no difference. Almost closing the isolation valve has helped, keeps the velocity of water in the pipe low. This not applicable to taps on the sink of course

We used these on the microscopes (see post above). Much bigger.

**LINK**

Mount upsidedown half full of air. It's perfectly possible to build one.

regards Martin

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