Tap making knocking noise

Galvo

I have a mixer tap with a swan neck. Whenever I turn it on it makes a very loud knocking noise & the water comes out in spurts. It has fairly high mains pressure but any other mains taps in the house are fine. I don't think it's airlocked - the problem seems to be in the tap unit itself. I suspect a faulty washer but before I shut the house down, does anybody have an idea?

CJhaughey

Galvo wrote:

I have a mixer tap with a swan neck. Whenever I turn it on it makes a very loud knocking noise & the water comes out in spurts. It has fairly high mains pressure but any other mains taps in the house are fine. I don't think it's airlocked - the problem seems to be in the tap unit itself. I suspect a faulty washer but before I shut the house down, does anybody have an idea?

This is called water hammer and is quite damaging to plumbing.
http://en.wikipedia.org/wiki/Water_hammer.
I would fix it as soon as you can.

rogue-entity

The hammer is caused by the high pressure water being forced to suddenly stop, or change direction, and can apparently be solved by installing an arrester device between the tap and the pipe run.

I have a similar problem with a toilet cistern, periodically their is this vibration in the pipework that is audible through out the house, I dont know how to solve it as it is random, and I cannot make it happen. I dont know if it is water hammer, or just the fact that the toilet is off the rising mains, that when the pressure reaches a certain point it forces the valve open, which tries to close itself again, causing the hammer.

Galvo

Thanks for that advice folks. It's not water hammer though (I've heard this in other people's houses). Water hammer happens when the flow is stopped (ie you turn off the tap). In my case, the noise is when I turn ON the tap, ie when the water should be flowing freely. That's what leads me to believe it must be something in the tap (ie a washer). I guess I'll try to find a plumber....