Loud banging sound after turning off faucet

[James johnson]

Dear All,

After turning off faucet or after the toilet completes filling the cistern, there is a loud metal clunking sound coming from pipework.

I have drained all the water from the pipes twice to get rid of water hammer. This helped stop the sound for a few weeks but the sound always came back.

What is a permanent solution to this problem?

I would appreciate any help and advice.

Kind regards
James

 

[TomFOhio]

Its a possibility that you have a loose pipe someplace that needs fastened. If you can see the pipes have someone turn the
faucet on and off to get the noise to happen and you watch the piping to see if anything is loose.

 

[jeffmattero76]

Tee off the existing pipe with a vertical new pipe, larger than the existing pipe if possible, with a cap on it. This creates an "air cushion", since the new pipe will have trapped air in it. That should stop the water hammer.

 

[Diehard]

Dear All,

After turning off faucet or after the toilet completes filling the cistern, there is a loud metal clunking sound coming from pipework.

I have drained all the water from the pipes twice to get rid of water hammer. This helped stop the sound for a few weeks but the sound always came back.

What is a permanent solution to this problem?

I would appreciate any help and advice.

Kind regards
James

Does it do it only when you turn off faucet fairly fast?
Does it happen when you turn it off a bit slower?
Does it do it when you turn it off from a low to medium flow rate or just at higher flow rates?
Since water hammer is based on the velocity of the water flow and how rapidly it is stopped, I am just trying to make sure that's what it is.
It may not be severe enough to require a water hammer arrester and just finding the lose pipe causing the noise may be sufficient.
Water hammer gets critical when it causes pressure surges of 100's of PSI. Very easy to get extremely high surge pressures if velocities are high when the flow is stopped very quickly. Such as a solenoid valve in a washing machine. But in that case the hoses typically absorb it.

 

[Diehard]

Tee off the existing pipe with a vertical new pipe, larger than the existing pipe if possible, with a cap on it. This creates an "air cushion", since the new pipe will have trapped air in it. That should stop the water hammer.

That would only be temporary since it only takes a few weeks before the air is absorbed into the water, leaving the air chamber waterlogged and completely ineffective.
Water hammer arresters can be purchased, which have a compressible cushion of air or gas, and equipped with a separation from the water.

 

[jeffmattero76]

That would only be temporary since it only takes a few weeks before the air is absorbed into the water, leaving the air chamber waterlogged and completely ineffective.
Water hammer arresters can be purchased, which have a compressible cushion of air or gas, and equipped with a separation from the water.

Diehard - do you have some article I could read to verify that? I had a water hammer problem in my house when the washing machine shut off the water. I installed what I described at least 20 years ago, and have not had a problem since.

What would cause air to be absorbed into the water?

 

[Diehard]

Diehard - do you have some article I could read to verify that? I had a water hammer problem in my house when the washing machine shut off the water. I installed what I described at least 20 years ago, and have not had a problem since.

What would cause air to be absorbed into the water?

"laboratory tests confirm that the air is depleted by simple air permeation and by interaction between static pressure and flow pressure."

The above was taken from a manufacturers Engineer Report entitled,
WATER HAMMER CONTROL
An Explanation and Solution to Water Hammer
Here's a link to it. (It's a PDF which is about 4 MB's.)
Water Hammer Control - Sioux Chief

Granted they are selling the product and may exaggerate a little. But it's pretty much a known fact.
I believe one of the reasons they switched to bladder equipped expansion tanks on heating systems, etc., years ago, was for the same reason.

EDIT: If I ever had to do it, I would be inclined to install the pipe trapping the air, with a stop and waste valve. That would allow it to be drained periodically.

 

[jeffmattero76]

"laboratory tests confirm that the air is depleted by simple air permeation and by interaction between static pressure and flow pressure."

The above was taken from a manufacturers Engineer Report entitled,
WATER HAMMER CONTROL
An Explanation and Solution to Water Hammer
Here's a link to it. (It's a PDF which is about 4 MB's.)
Water Hammer Control - Sioux Chief

Granted they are selling the product and may exaggerate a little. But it's pretty much a known fact.
I believe one of the reasons they switched to bladder equipped expansion tanks on heating systems, etc., years ago, was for the same reason.

EDIT: If I ever had to do it, I would be inclined to install the pipe trapping the air, with a stop and waste valve. That would allow it to be drained periodically.

Thanks for that! I learned something new. I love your idea about the stop and waste valve!

 

[Geofd]

check your faucet for loose washers on the stems or check your stop and waste washers floating wahers will also cause banging