Thread: pipe knocking

boydi, if its happening when the other unit uses water it could be a number of things, inlet valve on the cistern, washing mashine, a flick mixer, a dodgey washer or the common pipework could be poorly secured. The best way would be to get the strata's plumber (assuming the unit block has a strata plan) to have a look. It may take some work for them to come to the party so make a fuss over it, the squeaky wheel gets the grease!

One of the issues with modern ceramic disc taps and mixers (as well as appliance soleniod type valves) is that they often cuase waterhammer noises in older pipes.

It is possible to get an inline hammer arrestor but these have to go within 2 meters of the offending valve.

You can also buy screw in arrestors to fit onto threaded taps in the luandry for washing machines and under sink for dishwashers. I have used these also in vanity units to stop water hammer in vanity taps - but trying to fit one to shower and bath taps is impossible.

If you can trace the pipes and discover where the knocking seems to start - a nice blob of polyurethane sealant between the pipe and the framework sometimes does the trick.

Harsh and fast cut-off of newer style mixers can make the noise worse, but the most common issue is not from the water hammer itself (ie: noise generated by shock waves moving back and forth along the pipes) but the transfer of these shockwaves into physical movement of the pipe where it is adjacent to timberwork, another pipe or other building infrastructure.

The usual cause is pipework that has been affixed using saddles (up to recently using clouts or nails - screws are mostly used now) to studs that were green (hardwood) and have shrunk away leaving a gap between the pipe and the timber. Often pipe was passed through holes drilled in studs with no fixing except at taps or corners (nowadays a squirt of builders foam stops that issue). The actual tape bases in older kitchens, laundry and were affixed with saddles and can work loose through use over time. In any case the shock waves make the pipe shake and it bangs on the timber.

If you can find the source of the banging and it can be accessed by removing some wallboard or some other cladding then re-fixing using screws and adding silicone or some other flexible insulation material that is best and will stop the noise. Access is problematic in many cases, but if you can find the source of the banging often a hole drilled through plasterboard and a spray with expanding builders foam will stop the noise.

The noise arrestors sold to fit on various machines and fittings work to an extent (they are shock absorbers with springs and usually have a spring and washer system with an airspace that dissipates the energy of the rapid water shut-off), but these are expensive and noise often remains.