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Plumbing question

Community Veteran
Posts: 38,251
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Registered: 15-06-2007

Plumbing question

Just returned from visiting my daughter's new house and there is an odd thing
The cold tap in the utility - fed from the water softener via the header tank
When the tap is turned on slowly the flow is OK and as it is turned further on the flow increases - all normal up to now - increasing the flow a little more and the flow stops immediately with water hammer felt through the tap as though a check valve has suddenly closed
Non of the other taps in the property exhibit this
Looking at the exposed piping I can't see anything like a valve
17 REPLIES
nanotm
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Re: Plumbing question

sounds like air in the pipes, we used to get it when I was growing up and my dad ended up getting a bigger header tank and moving it slightly so there was always more pressure pushing the air out than letting it flow up, most of the time iirc it happened during low bar pressure days when the heating was on downstairs though, careful not to let it hammer so much or it might fracture a pipe though if there are any loose runs on the way back up to the tank .
just because your paranoid doesn't mean they aren't out to get you
Infinity
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Re: Plumbing question

Withdrawn
Community Veteran
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Registered: 04-08-2009

Re: Plumbing question

I had the same problem with an outside tap. Changing the tap washer fixed it. I've no idea why.
nanotm
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Re: Plumbing question

stops the air getting into the system, often in low pressure areas a faulty valve or washer will be the root of the problem but not always, a lot of new properties don't have header tanks though and are directly connected directly to the mains supply at all cold water points, which is causing some havoc as new estates are becoming occupied and the mains isn't pressurised enough to properly supply them all, ours is fitted out in such a way and they popped a mains pipe trying to get the required 3psi supply required for normal operations when an extra 2 thousand houses were tapped off it .....
just because your paranoid doesn't mean they aren't out to get you
Community Veteran
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Registered: 27-10-2012

Re: Plumbing question

Tap cartridge?
Is it a mixer tap?
Community Veteran
Posts: 38,251
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Registered: 15-06-2007

Re: Plumbing question

This tap is fed from a header tank in the roof
Having said that I can't see how a duff tap washer would cause the effect of permanently stopping the flow - it is as though the the tap closes all by itself
However, from memory, it isn't a normal tap where you can change the washer easily
It isn't a mixer tap
I will ask my daughter to send me a picture of the tap
nanotm
Pro
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Re: Plumbing question

if its one of those really old ones where you have to take the top off to change the washer and in so doing it squirts you in the face I bet it also doesn't have a localised isolator valve so you have to drain the system or swamp the house .....
just because your paranoid doesn't mean they aren't out to get you
Community Veteran
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Registered: 18-01-2013

Re: Plumbing question

My thoughts would be either a dodgy washer or valve seat which when the increased flow through the tap happens, it flexes and seals. Could also be a vacuum forming in the header tank - worth double checking. It could also be a foreign object in the downpipe from the header tank - increased flow leads to the object blocking the outlet.
x47c
Grafter
Posts: 878
Registered: 14-08-2009

Re: Plumbing question

I'd go with change washer
Possible you have got some sort of resonance building up
Could be the washer/jumper unit inside the tap starts to vibrate at a particular flow rate and bounces up and down setting off a pressure wave back from the tap though the system.
If you open the tap wide immediately you may go though the critical point fast enough without triggering it.
Water hammer in really big pipes can be catastrophic
The pressure waves flowing back and fro from the sudden obstruction rapidly mount up in size and can literally split pipes.
There is some (probably semi invented) story about an elephant in India treading on a supply pipe and closing it instantaneously the knock on effects of which blew up some pumping station as the pressure waves multiplied.
itsme
Grafter
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Registered: 07-04-2007

Re: Plumbing question

How do it recover? Will flow return backing the tap or do you have to turn off then on again?
Community Veteran
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Registered: 15-06-2007

Re: Plumbing question

I had turn it off and on again and the flow went back to normal until I opened it up to the high flow
I suspect that the header tank isn't a problem otherwise the bath tap would probably have done the same
Interesting - the washing machine is off the same pipe (via a Tee) and that doesn't have the same problem although the flow may be a bit lower
Moderator
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Re: Plumbing question

In my plumbing days I used to take out the jumper complete with washer, place the jumper stem on a hard surface and hit near the end of the stem with a hammer thus flattening it a little.
The jumper complete with washer was then inserted back into the tap head, helping it in with the hammer as it was now a tight fit.
This was to prevent the jumper and washer being forced back onto the seat and shutting off the flow, sometimes causing water hammer and other times causing the symptoms Jim is experiencing.
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Community Veteran
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Registered: 15-06-2007

Re: Plumbing question

Explain please - what is a jumper in this context
Community Veteran
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Registered: 10-04-2007

Re: Plumbing question

Is there an isolator valve to the tap? If so (I know it's not actually fixing the problem) could you close that a little so that even when the tap is turned on full the problem doesn't happen?
jelv (a.k.a Spoon Whittler)
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