Mains water pressure too high?

[bruce phipps]

A problem with my plumbing... advice appreciated. I was sitting watching the TV last night. Central heating off. All water taps off. Washing machine off. Everything off. The plumbing in the kitchen sink gave a short, loud rattle. This was repeated roughly every 15 mins. Also, the washing machine vibrated a couple of times!

This carried on into the night until I turned off the stop c*ck under the sink. Also closed the CH boiler down. Still got a few gurgles in the plumbing, though.

To me it sounds like the mains pressure is high and trying to force its way in! Any tips on diagnosis/fixing this are appreciated.

Thanks Bruce

[Set Square]

It sounds to me more like fluctuating mains pressure - coupled with some "springyness" in your system - rather than high pressure per se.

Is there a nearby large user of water, who may have been turning his flow on and off frequently?

If it happens again, try to reduce any compressibility in your pipework by turning off the supply to things like flexible washing machine hoses.

[Gael J. Conrad II]

Got air trapped in your pipes, Harry? It's better out than in, as they say.

[Harry Bloomfield]

bruce phipps wrote on Thursday (12/02/2004) :

Are you sure it wasn't just the water in your area having been turned off and the noise from air trapped in the pipes as a result of them carrying out repairs?

[bruce phipps]

The water pressure earlier in the week was very weak. I couldn't get a bowl full of hot water for my morning wash. I figured that work was being carried out nearby. Cloudy water when I got back that evening seemed to confirm this. Water pressure was OK for 2 days, then the last 2 nights I get the very_loud pipe bangs.

My planned course of action:

• Turn the stop-c*ck only half on to get a reduced water pressure.

• Investigate the washing machine connections.

• Investigate the WC -- this is the only thing I can think of that will "shut off" after the event.

• Stick some towels round the pipes under the kitchen sink.

• Hope it goes away!

Bruce

[bruce phipps]

Harry, see my reply above. Say the work was done on Monday, water was OK for 2 days, would trapped air still come through?

Say I have trapped air in my pipes. Any way to get it out -- just flush the WC a few times, run the cold taps etc.?

Thanks Bruce

[Set Square]

If your water has been turned off externally, you may well have some trapped air in some of the pipes - which will cause vibrations when further pressure fluctuations occur. For example, air can be sucked in through an upstairs open cistern ball valve when you open a downstairs tap.

To get rid of the air, you need to run each cold tap in turn until it runs without spluttering, and then do the same at every cistern, header tank ball valve and washing machine connection.

[Sparks]

This will just reduce the flow of water when you are trying to use it, it will do nothing to the pressure!

Sparks...

[bruce phipps]

Well I did this anyway and (probably coincidentally) the pipe knocking has stopped. I'll open the stop c*ck full again tonight and try out the washing machine...

Bruce

[The Very Rev. Peter Parsnip]

The Lord alerted my mind to the presence of this EVIL article by Harry Bloomfield, and I thusly replied:

Not a common occurence.

[Velvet]

A reduced flow means the increasing pressure once you've turned a tap off will increase slower than if you have full flow. The end pressure will be the same, it just takes marginally longer to get there.

FWIW, my washing machine shuts off water very abruptly, causing a loud clonk/bang. I didn't think this was too good. And the time the cistern filling valve decided to explode and spray water everywhere (even managing to dump large quantities out despite the lid being tightly on) convinced me turning the stop-c*ck partially shut was a good thing.

Net result, less severe shutting off of water. Still full pressure, but like I said, pressure doesn't increase so instantaneously as it did before.

Velvet

[IMM]

The pressure went down and then up and the water cloudy. Is it more pressure than usual? Dirt could have been pushed into your system too and this is on the washing machine valve seats, allowing water to seep through. You could install a filter strainer and pressure reducer after the stop c*ck. then no problems. I think you should do this anyhow. When a washing machine line bursts, you know it.