Water Hammer

Discussion in 'Plumbers' Talk' started by Andrew88, Apr 17, 2019.

  1. Andrew88

    Andrew88 New Member

    I have water hammer on my mains cold supply and it’s driving me mad. The hammer is noticeable where the supply enters the house in the cellar. The pipes have all been clipped. It is most noticeable when quick close valves shut such as the washer and the dishwasher. It was slightly noticeable when other taps were shut off before any changes made to the pipe work.

    I have tried draining the system and this alleviates it but as soon as all the upstairs taps are used and the air expelled then the issue returns.

    I have had the stop cock replaced and I asked my plumber to install a water hammer arrestor. This has been installed just after the stop cock and is a metal bell style expansion vessel. I have also installed a Sioux Chief mini restor on my cold water feed on the washer (as this was the main culprit)

    The issue is still present and actually seems worse. The pipes no longer shake violently but there is a loud thud that comes from the newly installed expansion vessel in the cellar and this causes slight movement of the pipes. This thud is quite loud and echoes throughout the house. This thud occurs when ANY tap is turned off now (unless turned off incredibly slowly). The mini restor has made no difference to the issue when the washer is filling as the noise is coming from the cellar.

    I’m a plumbing novice but it almost seems as though the vessel in the cellar can’t cope with the pressure and that’s what causes the loud thud.

    Any other suggestions. I’m totally tearing my hair out.

    Oh and I don’t have a water meter.

  2. spirits are real 2016

    spirits are real 2016 Active Member

    yes I fixed the same problem by changing the float in the WC it was causing water hammer you could try turning down the stop tap from the main street if you can access it that might help.
  3. KIAB

    KIAB Well-Known Member

    Also the float on cold water tank in loft is another one that can cause noise.
  4. Severntrent

    Severntrent Active Member

    Why from the main street, tweaking down the stopcock before the expansion vessel may help but its a fine balance of slowing the flow through the supply pipes and not restricting it to much so that fill times of toilets,baths, water tanks become unacceptable.
  5. Andrew88

    Andrew88 New Member

    Thanks for taking the time to reply. I’ve tried that before and it still hammered but going to give it another go and see if it helps. I fortunately don’t have any hammer when the toilet fills and I don’t have a header tank in the loft.
  6. Joe the Plumber

    Joe the Plumber Active Member

    For what it's worth, I've had the same problem at home and now have three water hammer arrestors in line just after my stop tap (fortunately in the garage).
    They reduced the noise, but it's still there. Having drained all my mains pipework and turned it back on, the noise went when there was still some air trapped
    in the upstairs pipes, but as soon as they were full, it came back.

    It began when I had to re-pipe my old leaking 20 thread mains supply from underground to above ground through the garage. I'm pretty sure it's resonance in
    the pipework (all very well clipped) that the surrounding earth would have damped out in the old pipes, but I can't prove it.

    It went away when a small-ish housing development was being gobbed up (oops, sorry, built...), down the street from us, presumably as they were using lots
    of water so reducing the local supply pressure, but came back once that was finished.

    I also have a customer with the same problem and they have a long run of incoming pipe (all very well clipped) in their cellar. Again, three arrestors helped,
    but it's still a nuisance.

    However, why it can suddenly start when there've been no alterations done to a mains supply is something I'm interested to find out about. Sorry I can't provide
    you with more of an answer.
  7. Andrew88

    Andrew88 New Member

    Thanks for the reply. It’s interesting that three arrestors in line helped. I’ve seen that bigger arrestors can be bought but they seem really expensive and are often located in the US so they aren’t really an option. Which arrestors are you using?

    The flow and pressure in the house is quite good and I think that high pressure may also play a part. My plumber said it’s good pressure but not ridiculously high.

    It makes me wonder if something has changed as when I moved in it certainly wasn’t this bad. The only plumbing alterations that I’ve made is removing the pipe that went to the outside tap from a T that was under the kitchen sink. As the outside pipe burst. I did this with a view to getting the pipe replaced at some point but I’ve just never got around to arranging the replacement. It could be that this leg of pipe was holding some air absorbing some of the expansion?

    Now it’s the expansion vessel / arrestor in the cellar that the noise is coming from though it doesn’t seem that any other changes past that point would make any difference.

    The only positive is that the pipes are no longer violently shaking in the cellar which was a concern due to them leaking as a result.
  8. Tricky Dicky

    Tricky Dicky Active Member

    Although you said that that the toilet refilling does not cause water hammer, try either isolating its incoming water supply or monitor the float when a tap is turned off.
    I had a similar problem, at my last house, the hammer echoed throughout the house, (especially under the bath panel). Whenever a tap was turned off the float in the WC started to vibrate/oscillate. A new float valve remedied the problem. Took ages to discover the fault.
  9. ecoplumbing

    ecoplumbing Active Member

    Is the incoming supply very high pressure? Might be worth doing a pressure test and fitting a pressure reducing valve after the stop tap . Had a property where the mains pressure was 7bar and it caused all sorts of problems. Fitted a prv and set at 3 bar which made a world of difference.
  10. Andrew88

    Andrew88 New Member

    I’ll have a look!
  11. Andrew88

    Andrew88 New Member

    How’s it best to test the pressure? Any recommendations? Cheers
  12. Heat

    Heat Well-Known Member

    Pressure gauge that connects to your outside tap.
    Not any point in you buying a gauge just for one test. Get a plumber to test it for you.
    Although the gauge complete with 3/4” hose connection (to connect to an outside tap) is fairly inexpensive
    Last edited: Apr 17, 2019
  13. Andrew88

    Andrew88 New Member

    Found one cheap . Going to test the pressure. Outside tap is disconnected but I can try it on the hose connector for the washer. What is an ideal pressure?

    Sorry as you can tell I’m a bit of a novice.
    Last edited: Apr 17, 2019
  14. Heat

    Heat Well-Known Member

    Andrew88 likes this.
  15. Severntrent

    Severntrent Active Member

    Pressure will be usually highest in the night when population have gone to bed, lower in daytime when water usage is higher
    Andrew88 likes this.
  16. Joe the Plumber

    Joe the Plumber Active Member

    I used these arrestors, left at their as-supplied pressure:


    I fitted them into these:


    It's worth noting that if you want to experiment with the pressure in them, you'll need a bicycle pump and you must turn off the mains
    water and open a tap to remove all pressure from your pipework before you start. If you don't, all you'll do is let all the pressure out
    and struggle to put any back in.
    Andrew88 likes this.
  17. Andrew88

    Andrew88 New Member

    Ok so I’ve tested the pressure today and it’s 50psi or about 3 and a ½ bar. So I wouldn’t expect that a PRV would make much difference. I was hoping that it was going to be higher.
  18. Andrew88

    Andrew88 New Member

    Well that’s a new one. Trolling Screwfix forums. You must be very lonely.
  19. Severntrent

    Severntrent Active Member

    In theory it shouldn't matter where the surge arrestor is located but I've always wondered whether its better placed at the top end of the system as opposed to the bottom end, Unfortunately its a question of where you would place it i.e. toilet end, bathroom taps, washer etc etc. Unless you have several strategically place it may have no effect whatsoever but if its driving you mad??? Obviously the bigger the better on a surge arrestor but then its down to cost!!!
    Andrew88 likes this.
  20. Andrew88

    Andrew88 New Member

    Yea. I’m gonna potentially look at getting another one placed in line with the existing one as that’s where the noise is emanating from. I think it just the existing one can’t cope when there is a spike in pressure.

    I was hoping that I could put it down to high pressure but 3.5bar seems reasonable so I think I can rule out a PRV.

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