Water hammer from outside the house

[88v8]

A few years ago the water board put in a nice new switching station 300yds down our country lane. We're the first house upstream.
This summer they turned up the pressure, we now have a healthy 3.5 bar, but it varies a lot, occasionally more like 2 bar and just now I sat and watched the pressure gauge with nothing running in the house and saw it rise to 4.3 bar.

No complaints from me about the pressure, but sometimes, again with nothing running in the house, we get a hell of a rattling in the pipes.
I presume this is when a valve suddenly shuts in the switching station.

So I want to put an air buffer on the rising main.. I see them globe-shaped, and I see them with a piston.
Any difference?
Which ones do you favour?

 

[KlamathPlumbing]

For a surge coming in from the street like that, go for a sealed potable-water shock arrestor/expansion vessel with a diaphragm rather than the small piston type — the piston units are really meant for a single washing machine or tap, not the whole rising main. The plain globe air chambers work at first but gradually waterlog as the air dissolves, whereas a vessel with a Schrader valve keeps its charge and can be topped up to just below your standing pressure. Fit it as close as practical after the internal stopcock on a tee, sized generously for a 3.5-4 bar main, and clip any loose pipe runs at the same time as that makes the rattling much worse.

 

[Mottie]

Dunno if it’s connected but I had a similar problem a short while ago.

Thread 'Help/advice needed - noisy mains even with all taps turned off.'

23 Aug 2026

I’ve moved this from general chat as it’s gone past that point now. Looking for some advice. Open up the quoted posts to see videos. They may only be up for a few days as they are from a free site.

Troubleshooting - and it’s not even 7.00am!
For the last couple of mornings, when I’ve given the toilet its first flush of the day, I’ve heard a vibrating noise going through the house for a minute or two. I put it down to a dodgy fill valve making a noise just as the cistern is coming to full. This morning it just kept going and going, really loud. Even turning other taps on and flushing...

• Mottie
• Replies: 53
• Forum: Plumbing and Central Heating

• 

Basically it turned out to be a faulty street box. Noise went through the house but was worse in the street by the stopcock.

 

[88v8]

For a surge coming in from the street like that, go for a sealed potable-water shock arrestor/expansion vessel with a diaphragm

So I put in this Caleffi shock arrestor.
Diaphragm, as you say.
It's a dinky little thing, only 0.16ltr, but it's what I had room for... and I'm amazed to say that it has killed the rattling stone dead.
The leaflet says that the pressure should be checked annually - car tyre pressure gauge - and other than that it should be no bother.

Even more amazing it has killed the rattling in the kitchen and in the attic; reason that's amazing is that the pipe I installed it on is a side branch to the kitchen, a side branch that comes off outside the cottage before the internal stopcock, and the attic is on the main pipe around 20ft away. I was intending to put a Caleffi static pressure control valve up there but it looks as if I won't have to bother, which I'm glad of as the access is difficult and in my mid-70s I'm not as good as I was in wedging myself into tight corners.

Nice when something works out.