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PostPosted: Thu Jul 27, 2017 2:52 pm 
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i've really annoying water hammer which only happens when i flush the bathroom toilet, i've tried fastening down the pipes were i can but it's made no difference i've tested my mains water pressure and it's 5.5 bar is that to high ,of maybe a different flush mechanism might work can you get one that doesn't shut off so fast.


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PostPosted: Thu Jul 27, 2017 3:04 pm 
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Generally this is a worn diaphragm seal on the inlet feed. If you have an inlet like that in the video it will probably be the cause. You can by the rubber replacement washer quite cheaply. See https://www.youtube.com/watch?v=r2ot2cypULs

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PostPosted: Thu Jul 27, 2017 3:36 pm 
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cheers i will give this a try, what about the water pressure is 5.5 bar ok ?


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PostPosted: Thu Jul 27, 2017 3:42 pm 
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To my knowledge the incoming mains is on average between 2 and 4 bar so 5.5 is a little high. I would have thought that turning your stopcock off a bit should see a reduction and that might solve the issue.
The proper plumbers will be on later and advise you different if necessary :thumbright:

DWD



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PostPosted: Thu Jul 27, 2017 5:18 pm 
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5.5 bar is certainly decent pressure. My house is 3.5 which is fairly typical round here, my brother's house (built 10 years ago) was just over 7 bar. I did put a 3.5 bar pressure reducing valve on his, as I was fitting an unvented water heater that needed a 5 bar pressure relief valve.

Closing a stopcock off a bit has no effect at all on the static water pressure. Unless you turn it off completely of course, in which case it'll go from 5.5 bar to 0!

I had a similar annoying water hammer issue at home that I couldn't trace after I did our bathroom. Same sort of thing, it was most noticeable when valve in the loo cistern closed, although you could also make it happen if you really shut the basin taps off quickly. I knew all the pipework was securely fixed, as it's all my own work right back to the stopcock. It turned out to be the hydraulic block in the combi boiler that hadn't quite been secured properly after I'd had the plate heat exchanger cleaned a couple of years ago. I found it by isolating the cold supply the boiler, which caused the hammer to stop.

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PostPosted: Thu Jul 27, 2017 5:57 pm 
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I thought that restricting the flow at the stop cock might help Chris, I accept it would not reduce the pressure but a slightly reduced flow rate might help???

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PostPosted: Thu Jul 27, 2017 6:23 pm 
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dewaltdisney wrote:
I thought that restricting the flow at the stop cock might help Chris, I accept it would not reduce the pressure but a slightly reduced flow rate might help???

Yep - sorry DWD. Didn't mean to imply that that might not cure it (or at least mask the effect)! I was typing in a hurry as the Mrs had just walked in through the door from work :-)

So what happens when you do that is that, say the running pressure with the cistern fill valve open is 2 bar, when the valve closes instead of jumping back up to 5.5 bar in, say, 1/10th of a second, the reduced flow rate might make it take 2 or 3 10ths of a second to get back up to 5.5. Which might be long enough to reduce the knock without making the reduction in flow too noticeable. I appreciate you probably already know all that DWD -- just explaining for the sake of completeness.

I'd personally want to trace the cause, as something is knocking/vibrating that shouldn't be, but obviously that might involve lifting floorboards or removing boxing-in. In which case, turning down the flow might well be the easier solution!

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PostPosted: Thu Jul 27, 2017 6:34 pm 
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after looking in the toilet cistern i found the fill valve was leaking out of the top it was a fluid master bottom fill, i have just replaced it with a new one and it seems to have stopped but i have had this before if the water is turned off it seems to stop for a while then come back i guess that's because of a bit of air trapped in the pipes , chrrris you are right turning down the stop cock doesn't work i've tried that before.


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PostPosted: Thu Jul 27, 2017 6:42 pm 
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Many (modern) fill valves come with a couple of inserts to prevent the issue, one for high pressure one for low. Fit the wrong insert and you will still have an issue.

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PostPosted: Thu Jul 27, 2017 10:27 pm 
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Another thing to look at is fitting a water hammer arrestor near the valve that causing the problem (assuming it's just one valve). They're basically a tiny expansion vessel and the idea is that the pocket of air in them abosrbs the shockwave in the water as it passes along the pipework. They only really work if it's one particular valve that's causing the problem rather than run of unsecured pipework or something. Might be worth a punt if it is just the toilet fill valve that's the issue though. They're not expensive.

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PostPosted: Fri Jul 28, 2017 7:52 pm 
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well after fitting a new toilet inlet valve all was well until today and it's started again, the strange thing is now its pretty much everything that is causing hammer, hot tap, toilet and dish washer which is odd as its only ever been the toilet that caused it.


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PostPosted: Fri Jul 28, 2017 10:25 pm 
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Two options I can think of then:-

1. Trace the location of the water hammer by isolating different appliances in turn and seeing if the problem goes away. For example, if you have a combi boiler, isolate the cold water feed to it and see if the problem goes away - if not, then you've ruled that out. If you have a isolation valves on any appliances or fittings, turn them off individually and see if you can isolate a particular appliance or run of pipework as the culprit. As I said above though, it can turn into a big operation -- lifting floorboards to check pipework, possibly fitting additional valves to allow you to isolate sections of pipework to rule them out.

2. If DWD's suggestion of turning down the flow on the stopcock a bit doesn't have any effect (it should do, but you may have to turn it down so far that you only get a dribble from the taps), then fitting a pressure reducing valve just after the stopcock may help. That will reduce the static pressure of the whole system.

Option 1 is solving the problem by tracing the cause and then fixing it (unfixed pipework, loose or poorly fitted valve, pipework, etc. in a fitting or appliance) . Option 2 is managing/masking the problem by reducing the flow rate and/or static pressure. Option 2 is obviously the easier thing to try first.

I know from personal experience what a pain it can be to track down and fix as the noise travels along the pipework which makes it virtually impossible to pin down by ear. I was delighted when I traced the problem in our house down to the boiler, as that "clunk" every time the loo refilled was really getting on my nerves!

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PostPosted: Mon Jul 31, 2017 8:22 pm 
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looks like it's sorted now ,i gave in and fitted a PRV, according to the pressure valve it was over 6 bar last night i guess that's when the pressure will be highest.
it's now set to about 3 bar and no more water hammer and you don't get soaked turning on the cold tap :)



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