Water hammer.

[TerryH]

Ladies and Gents,
I have been called to see a customer who has recently developed water hammer on her rising main. The hammer is close to the kitchen sink. The washing machine is connected to the rising main from a tee and hammer occurs when the machine valves operate. I know that is nothing unusual although she says it is a new occurence. It also happens when she closes the cold mixer on the kitchen sink, if she closes it slowly there is no problem.
The pipes are secure, not vibrating nor touching other pipes.
I tried reducing the incoming water pressure by closing down the stopcock but to no avail.
Any ideas.... better still, any solutions?
Thanks for your time.
Terry.

 

[Mike Jackson]

Closing down the stopcock will not reduce the water pressure it will only reduce the flow so you have proved nothing by doing so. If you wish to reduce the pressure you need to fit a pressure reducing valve.

If there is a double check valve on the incoming main I would suspect this. If there is one, unless it is a shared main through a block of flats, there is no need for one. We had an estate a few years ago and all of the houses had them fitted and over a period they all caused water hammer so we took them all out.

A lot of new builds also have them fitted prior to the cold WM tap. As long as the hoses are WRC approved most domestic washing machine connections don't require one.

Mike

 

[tonyn]

you could try as a last resort putting in another tee before the washing machine tee and a small piece of pipe of it elbowed up again with a small pipe in it and solder a end cap on .This will act as a air brake hopefully stopping the hammer. I had the exact problem this seemed to be the only remedy available to me as all pipework was concealed behind new fitted kitchen, It worked a treat ,,,,,,,.dead legs in pipework is not officially allowed so check up first.

 

[Mike Jackson]

If you go that route you can get a mini expansion vessel designed to stop water hammer.

Mike

 

[tonyn]

excellent idea mike

 

[Mike Jackson]

It's come back to me what it's called, a shock arrestor. Have a look at item 11355 in the BES catalogue or on bes.co.uk .

Mike

 

[tonyn]

very reasonably priced too , never used or seen one before looks like a great product

 

[TerryH]

Now, that's what I call quick.
Thanks very much!

The house is detached and the problem recent, no check valve either.
I have heard of the arrestors and the separate pipe as a buffer.
I wanted to make sure there was nothing I had overlooked.
I think I will contact the customer and offer her the option to put an arrestor in. They are just short of £13 plus delivery (guess who put an order in last night!!!!), so I imagine she would be happy with that.

Thanks again.
Terry.

 

[tonyn]

good luck terry let us know how you get on

 

[emergencyman]

I know that this is a very old thread, but did it work? I had a job today with bad water hammer and fitted a PRV in the incoming main just after the stoptap and it worked a treat. The reason I ask is that this is not always possible if the stoptap is buried behind the kitchen units. The reference to the dead leg in the Tee to stop hammer made me smile. I asked my boss ( 30 years ago) why the connection to the toilet cistern had a tee with a short piece of pipe with a stopend. I was told that the original plumber must have run out of elbows and I believed that this was the case for at least 10 years!