Water Hammer after pipe repair?

[SirGalahad]

I had some pipes repaired (cold and hot feed into bathroom) - there was a leak - all sorted but now every time the taps are closed there is a shuddering noise - this wasn't present before the repairs.

Now looking into this it's called water hammer, could this have been caused after the repair?

Looking online it seems that this happens because there is a lack of air in the pipes?

Do I need to drain the pipes in a certain order to fix?

 

[baldykev]

Could try turning the stop tap down a bit . they may had turned it off for repair and just turned it back on fully worth a try.

 

[Harry Bloomfield]

As above, plus the repaired pipes might not have been as well fixed as they originally were. Another possibility is that there was some air trapped in a dead-leg of pipework - such a dead-leg, full of air can act as a buffer, with the air being compressed, to help stop the thump of a tap suddenly being shut off.

 

[SirGalahad]

I've turned the pressure down a bit and it has helped but it still exists, well the new pipes are plastic and the old ones they replaced were copper. Replaced about two 1m lengths.

As above, plus the repaired pipes might not have been as well fixed as they originally were. Another possibility is that there was some air trapped in a dead-leg of pipework - such a dead-leg, full of air can act as a buffer, with the air being compressed, to help stop the thump of a tap suddenly being shut off.

How do you put air back into the system?

 

[Harry Bloomfield]

How do you put air back into the system?

A pipe designed to help reduce water hammer would have T pointing upwards and be sealed closed at its top end. Draining water out and refilling, would naturally leave air trapped in the vertical pipe, and compressed a little by the pressure of the water - so still a variable depth of air trapped above the water, acting like a spring. That 'spring' will just give the water somewhere to go/something to compress, when the tap is suddenly turned off.

Aside from draining to ensure air is trapped in the vertical pipe of the T, any bubbles of air in the flow of water, will help to top up the level of air in the T.

Water authorities use a similar system on long pipes, carry lots of very heavy water, where there might be a need for the water flow to be suddenly stopped.

 

[SirGalahad]

Highest to lowest

Bathroom : bath taps, sink, toilet
Kitchen: sink taps, dishwasher outlet/connector
Outside tap at ground level
Cellar : washing machine tap
Boiler: in cellar

So how do I put air into the system to avoid water hammer?

 

[terryplumb]

We're new taps fitted in bathroom as well as pipes repaired ?
Fitting arrestors would reduce water hammer ,forget trying to trap air in pipework.

 

[Harry Bloomfield]

So how do I put air into the system to avoid water hammer?

You cannot, unless the layout includes such a vertical pipe intended for the purpose.

 

[denso13]

A pipe designed to help reduce water hammer would have T pointing upwards and be sealed closed at its top end. Draining water out and refilling, would naturally leave air trapped in the vertical pipe, and compressed a little by the pressure of the water - so still a variable depth of air trapped above the water, acting like a spring.

That doesn't really works. Air is quickly absorbed into the water.