Water hammer / knock in wc?

[Neilcon]

Hi all, The local school has 4 wc's all in a row, all coming off the same cold water 15 mm feed pipe one after the other. The 3rd wc in the row has terrible water hammer once flushed that can be heard around the school. All wc's come off the clipped cold feed then through a service valve a further 18 inches of copper (unclipped) to a flexi connector and then onto the bottom fill cistern float valve. This has apparently been happening ever since they had new cabins plumbed into the playground. So is the problem 1) a dodgy float valve?(need a high pressure one)? 2) Do we have to get a pressure reducing valve installed above the main stopcock? 3) Can we just turn the stopcock down to the minimum to restrict flow (although I have been told this will not reduce the pressure)? 4) something else 5)all of the above. Thanks in advance to any advice given. regards Neil

 

[Neilcon]

Sorry its not water hammer knocking its a constant errrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr noise that lasts the duration of the fill.

 

[Ermintrude]

Get a prv fitted on run into loos set it to 1.5 cars

 

[tamz]

Swap the ballcock. Problem solved for under a tenner plus your labour.

 

[PlumbBobBob]

diaphragm in fill valve needs replacing or replace with fluidmaster, you will get no more problems

beat me to it lol

 

[Ermintrude]

Replace diaphragm, I would measure pressure tho.

 

[tamz]

Why bother measuring pressure. Any ballcock will work fine at 10 bar +. The problem is the diaphragm washer is vibrating on its seat, It sounds like it is farting.
You could swap the washer but the valve might be made slightly out of tolerance so better to replace it. Fluidmasters are quieter (don't squeal) on higher pressures.

 

[Ermintrude]

Last longer when lower pressure as valves don't distort , most only rated for 3 bar ??

 

[tamz]

Fluidmasters are rated up to 20 bar so it doesn't make any difference. I've yet to find anywhere with a 20 bar supply.


Torbecks are 12 bar so will cover 99% of jobs with no problem

 

[Ermintrude]

Point well made!

 

[iiplumbing]

Agree with Tamz and Steveb

Russ