water hammer - flexible pipe?

[Malc]

So new cistern connected to cold water mains via plastic push fit and old copper pipe. New cistern valve seems to snap off rather than the slow close of ball valves. The creates a hammer more in the old pipe work which was "professionally" done when the house was built. That is supported and clipped with nails. That's a given unless I lift all the floors and fix it properly with plastic clips. And that would just cure the bang not stop the shockwave. The new plastic pipe is clipped.

One option is to add an arrestor (cheapest at toolstation it seems) but I wonder if fitting a piece of flexible hose would also do the trick. Gut feel is that the rubber hose would absorb the shock, at least some it. I wonder if anyone has tried this and has it worked? A rubber hose is only a few quid so about 1/10 the price of an arrestor.

 

[Whitespirit66]

What fill valve have you got?

I sometimes find that Torbeck valves give this problem, but Fluidmasters are better.

 

[Malc]

Cistern is a roper rhodes cascade. Dunno what valve that is.

 

[Charnwood]

Dunno what valve that is.

This one, according to the fitting instructions:
View media item 57072
We suffer from quite bad w/hammer, but the Fluidmaster PRO400 we have had for 5 years makes no hammer-associated noise whatsoever.

 

[Malc]

Yes that is what it looks like. Form the pictures of Torbeck and fluidmaster I would have said it was fluidmaster. I suppose it might be worthwhile taking the valve apart to check there is no muck in, but I would have though that would give leaking or slow filling rather than making the action snappier.

 

[Charnwood]

It's neither a Fluidmaster nor a Torbeck Eco.

Any markings on the valve visible?

 

[Malc]

It looks similar to a fluidmaster but it's not exactly the same as any of pictures on screwfix so it looks like a copy.

I tried a flexible hose and that didn't help, or at least not by that much.

I tried slowing down the fill by closing the service valve partly. Results were 50s fill (fully open), and 70s = hammer. 100s and 80s no hammer.

I did wonder if I was running the valve to fast so I gave Fluidmaster a call (not their valve but very helpful and if need be I could fit fluidmaster as a replacement). Any one looking for the fulidmaster web site need this URL

http://www.fluidmasteruk.com/

not the plain .com which is USA stuff. From what fluidmaster told me my fill times weren't over fast. BUT, when on the FM uk site I looked at their troubleshoot suggestions. One of which was turn off cold water, open all taps. Close all taps and turn on water and then open taps starting nearest stopcock to get rid of air or move the air around. I tried this and the hammer stopped so I must have had some air trapped in the cold pipes acting like a spring. Filling the cistern took the pressure off the "spring" and then when the valve closed this spring bounces around.