The Lemon Fool

My gas boiler was serviced today. I mentioned the high number of water leaks we had experienced since the installation of a water meter. Our gas engineer said that Thames Water should have been informing all customers that the water meters they install have a non-return valve which puts more pressure on internal plumbing. He gave the example of quickly turning off a cold water tap in the house that might previously have caused water to back up a little, but now the non-return makes this impossible and hence water seeks an escape elsewhere e.g. finding a potential weakness and leaking.

The remedy he suggests is a small expansion vessel on the incoming main water pipe. The is totally new information for me. Has anyone else heard about this? Should I have the expansion vessel fitted?

I can't answer the question exactly. But if indeed you are getting noise when you stop a flow of water quickly (for example the fill solenoid valve on a washing machine closes) the answer could well be an expansion vessel. It would act like a kind of shock absorber in the water piping.

bruncher wrote:He gave the example of quickly turning off a cold water tap in the house that might previously have caused water to back up a little, but now the non-return makes this impossible and hence water seeks an escape elsewhere e.g. finding a potential weakness and leaking.

I would be surprised if the expansion requirements of the cold water system are sufficient to require an expansion vessel to be fitted.

I've got a double non return valve on my incoming cold water and I've not had any leaks.
Although I do my own plumbing, so am heavily incentivised to ensure the plumbing work I do doesn't leak .

I believe non-return valves are needed by law, so presumably all new houses have them.

I have an under sink water heater. This required a non-return valve and a vessel to cater for expansion with a pressure relief valve, vented outside. It is connected direct to the incoming main. I suspect that a Quooker has a similar requirement.

TJH

jaizan wrote:

bruncher wrote:He gave the example of quickly turning off a cold water tap in the house that might previously have caused water to back up a little, but now the non-return makes this impossible and hence water seeks an escape elsewhere e.g. finding a potential weakness and leaking.

I would be surprised if the expansion requirements of the cold water system are sufficient to require an expansion vessel to be fitted.

What we are dealing with is two very similar things called different names and used for different purposes.
Modern central heating systems have an expansion vessel as water expands when it gets hot. It use to be an expansion tank, but is now a vessel with a pressurized balloon inside it.
Modern plumbing does not use a local cold water tank. As water flows it's mass gains kinetic energy. Stop the flow and that energy causes a pressure spike. It's called a water hammer because it's very like a hammer. A large force spike.
As Bulldog says, you can get a water hammer arrester, which is, wait for it.
A vessel with a pressurized balloon inside it.

BTW, you might like to look up ram pumps, which use check valves and the water hammer effect to pump water.
https://www.youtube.com/watch?v=ZHwjhLVDWfc

Urbandreamer wrote:

jaizan wrote:I would be surprised if the expansion requirements of the cold water system are sufficient to require an expansion vessel to be fitted.

What we are dealing with is two very similar things called different names and used for different purposes.
Modern central heating systems have an expansion vessel as water expands when it gets hot. It use to be an expansion tank, but is now a vessel with a pressurized balloon inside it.
Modern plumbing does not use a local cold water tank. As water flows it's mass gains kinetic energy. Stop the flow and that energy causes a pressure spike. It's called a water hammer because it's very like a hammer. A large force spike.
As Bulldog says, you can get a water hammer arrester, which is, wait for it.
A vessel with a pressurized balloon inside it.

BTW, you might like to look up ram pumps, which use check valves and the water hammer effect to pump water.
https://www.youtube.com/watch?v=ZHwjhLVDWfc

Exactly.



(Though the word you were looking for when describing a moving column of water is momentum).

Urbandreamer wrote:Modern plumbing does not use a local cold water tank.
As Bulldog says, you can get a water hammer arrester, which is, wait for it.
A vessel with a pressurized balloon inside it.

No cold water tank... and a very stupid idea that is too.

The pressure vessel must be blue. Blue vessels are non-corrodible.
Red vessels are for corrosion-inhibited systems, ie central heating.
If you put a red vessel on your mains water, one day it will rust through and explode and take your legs off.

V8 (other body parts are available)

I had a WRAS approved Shock Arrestor fitted (in a blue box) selected by the plumber, so hopefully that's the right item.