Help new pipes causing water hammering noise

[TraceyMP]

Hi Im a new member with a problem - Our upstairs water supply comes under the floor boards in a bedroom into a toilet then through a wall into the bathroom . we have replaced the section of 2metre piping in the bathroom. but every time we flush the toilet the pipes are making a hammering noise which seems to come from the 'old' piping under the floor boards in the bedroom. the old pipe is 22m but the new pipe is 15m - do I need to replace all piping. I hope not? Any advice

 

[JCplumb]

First thing to try is to clip the pipe, not just the new section but all of the run. My thinking is that the old 22mm was much sturdier stuff than the new 15mm and this new section will have weaked the span of pipe.
I doubt you can have too many clips, but you can have too few - so don't be shy with them
The regs say 1.2m intervals for 15mm copper, I'd over cook that a little if I was trying to resolve a water hammer issue.

 

[helpsy]

Shock arrestor? Surely having restricted the flow going from 22 to 15 it has now speeded up the velocity (Bernoulli principle ) whereas prior you had the larger bore pipe.

 

[Subby]

It is quite possible that your fill valve was fitted without the flow restrictor. Replace the WC fill valve with a fluidmaster or similar, this should stop any water hammer. Failing that you could fit a shock arrestor near the WC end of the pipe run.