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Knock in the pipes when valve shuts

Discuss Knock in the pipes when valve shuts in the UK Plumbers Forums area at Plumbers Forums

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Hi All,
I hope you are doing well.
I have a problem. Not sure if this was always like that or something is degrading.
Whenever the toilet refills when it finishes there is a knock in the pipes. The same happens when the washing machine finishes taking water.
Is this because there is too tight on one of the elbows and the cold water pipe knocks on the floor joists? The noise is definitely between the ground and first floor where the most pipes go.
Please advise.
 
A couple of years ago I went to a house with the exact same problem. Pipes clanging like mad when things were flushed or taps turned on etc. The culprits were buried in the walls so no easy access to clip them. So, I fitted a shock arrester straight after the main stop tap. Silence resumed in the household plumbing again. The product code is 597801 if bought in Wolseley.
597801_wm.jpg
 
so is this pipes being installed incorrectly or is it that every property should have this arrestor?
It can be a symptom of a failing fill valve but seeing as you have the issue from two appliances it's probably not that. High water velocity can also cause it. Turning your stopcock down a little might stop the bang, just reducing the flow rate a little. Could also be caused by high pressure mains if you have a really good supply so a pressure reducing valve just after the stopcock could do the trick. An alternative is the shock arrestor that's been suggested here.
 
It can be a symptom of a failing fill valve but seeing as you have the issue from two appliances it's probably not that. High water velocity can also cause it. Turning your stopcock down a little might stop the bang, just reducing the flow rate a little. Could also be caused by high pressure mains if you have a really good supply so a pressure reducing valve just after the stopcock could do the trick. An alternative is the shock arrestor that's been suggested here.
It well could be I have opened the stopcock too much.
Thank you, I will give it a try.
 
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