vibrating cold water pipe rising main puzzle

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Apologies in advance for this long rambling post - I`ll try to be brief.

Moved into house in February. Cold water tanks in the attic, gravity fed hot water cylinder etc. All cold water taps come off the mains. The whole house is half way up a hill, and is supplied by the reservoir another 100 metres (at least) up the hill (to which water is pumped). The cold water main enters the house through the ground below our bedroom.

Over the summer we started to notice intermittent vibrating noise in the cold water pipes going up into the cold water tanks in the attic. We assumed water hammer, so got all the ball valves replaced. This did not solve problem. Vibration was worse at night. To be honest, it seemed to happen with no relation to the tanks filling up or not filling up, although we could stop it by leaving a tap running. Plumber had told us we had pressure of 7 bar coming into house. So we got a pressure reducing valve installed on the pipe coming into our house (just below bedroom floorboards). This made things better insofar as pipes going up to the tank were no longer vibrating. However, pipe prior to the pressure reducing valve was still making awful noise. Next step - contacted the water board as we noticed the Toby? (I think this is what Scottish people call the external stop cock) was vibrating. The Toby was a 4 years old and plastic looking. They replaced it and reported that it was actually leaking. Following replacement the vibrating noise was dramatically reduced. However there is still a audible vibration on the pipe coming into the house, prior to the internal pressure reducing valve. It is much better than it was now the toby is repaired . However it is particularly noticeable and seems to be worse, at night. Water company told me that the toby outside our house was previously replaced around 4 years ago due to failure.

So to summarise - we have a persistent vibration in our cold water mains pipe that seems to be coming from somewhere upstream from our internal presure reducing valve (ie I don`t think anything in the house is causing it and it even continues with the internal stop cock turned off). We have two tobys that have failed in 4 years. We know we have high pressure coming into our house (7bar). I`m wondering whether the tobys failed because of high pressure and/or pressure wave that it making the pipe vibrates. I have no idea what the source of the pressure wave is.

At the moment I am hoping that the noise can be stopped by reducing high pressure coming into the house, and that I can convince the water company to install an external pressure reducing valve. My neighbours told me when they built their house, they had to get an external pressure reducing valve installed in the street.

My fear is, is that it is not the high pressure per se that is causing the vibration, but some other bit of equipment on the network that is failing causing the pressure wave in the pipe. If this were the case, maybe an external pressure reducing valve won`t stop the pressure wave making it`s way to our property.

I`ve tried numerous googles on this subject but nothing similar comes up - which is a bit worrying. Mostly the posts are to do with water hammer caused by ball valves etc but that doesn`t seem to be a problem. It is more like water hammer on the main network...

Any wise words - even some reassurance that this might be fixable would be good!!
 
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Solution might be a a PRV (with non-return valve) and an expansion vessel as a shock arrestor downstream of these on your property. Or even upstream!
I'm clutching at straws here: it does seem most odd.
 
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okay I was too lazy to google! I had assumed the way the water supply worked was that it was electrically pumped up to the reservoir on top of the hill, then gravity did the work to get it to our properties. Not sure whether a water ram is involved but will ask the water company when I see them
 
Did you resolve the vibrating pipes? I am experiencing a similar problem in Newport Wales. At night I hear vibration in the cold water pipes. At 2.00 this morning was checking all internal appliances and water feeds but nothing was running...however the was vibration in the cold water feed to my house.
I suspect that the vibration occurs during the day too but as there is a higher level of background noise I do not notice it

Any thoughts?
 
go into the loft and look at the ball valve in the cold water tank (and in the Central Heating cistern if there is one).

Is it vibrating?

get someone to run a hot tap. Does it vibrate during or towards the end of refilling? Push the float down. Pull the float up. Does the vibration stop?

Do your WC cisterns fill at mains pressure, or from the loft tank?
 
You'll be glad to hear we worked out the cause as got it fixed. Scottish water came out an acknowledged the continual noise on the pipe. However they at first maintained the cause was internal. This was because they turned off the internal stopcock and the noise stopped. However I pointed out that although the noise has stopped you could still feel the vibration in the pipe prior to the stopcock. You had to be really sensitive to pick this up though. Turning off the stopcock was preventing the pressure wave entering the house and rattling the pipes off wood work (thus causing te noise to dissapear). The scottish water guy was really good and said he would carry out pressure studies over the external network. They also had a audio check of a external major pressure reducing valve that served the properties at the bottom of the hill further along the network(this was a massive PRV apparently). Following this investigation they identified that this PRV was faulty and causing a pressure wave (water hammer) to travel back up the network and into our property. This would also explain the previously broken Toby's. They serviced the big PRV and noise gone. What a relief I can tell you.

What really helped here was turning off the internal stopcock on the mains feed and still feeling a vibration on the pipe prior to this ie upstream. (Turning off the stopcock did seem to interrupt the vibration temporarily but it would soon resume )
 

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