water hammer noise solved, what causes it?

[chrisw99]

Over the weekend I had a terrible case of banging pipes, whenever the hot water tap was turned off in the bathroom, the whole house clunked, particularly the kitchen.

Eventually narrowed it down under the kitchen sink, and when I held on to some pipes under there I could feel the vibration when the upstairs hot tap was turned off. holding the pipe limited the banging a lot but it was still there.

After a couple of hours of head scratching, I realised it was all due to the red wheel valve for isolating the outside garden tap. I'd turned this off last week to prevent the outside pipe freezing, but hadn't fully tightened the wheel. As soon as I'd tightened the wheel, the banging completely stopped. Experimenting, this wheel can be fully open, fully closed, half open, etc, all OK, but just having it in that 99% off but not fully tightened causes the massive banging.

Was well chuffed to figure it out, but I'm really curious as to how having the outdoor isolator wheel not quite fully closed causes such a racket through the house?? Is there an underlying problem I need to be investigating?

 

[Nige F]

It shouldn't be a wheel handle valve - wants a lever ball valve and a double check valve for outside tap And a cover over tap outside for frost. Those red gate valves are terrible old things for low pressure water- the gate was probably chattering.

 

[chrisw99]

Cheers. The valve was on when we moved in. I'm guessing it's not full bore either, so was considering switching to a full bore at some point to increase the flow from the garden hose.

 

[Madrab]

A gate valve is in essence an old style full bore valve, when the gate is lifted the valve bore is practically full pipe size. Gate valves are notoriously dodgy, especially when used on mains pressure pipework.

As @Nige F mentions, the gate part of the valve would have been loose, creating a sympathetic vibration in the pipework when the tap was closed and hence the pipes banging. Ideally is should be replaced for a new valve.

 

[Hugh Jaleak]

Probably snapped off half way open/closed, with the gate rattling about as Nige suggests. Amazing it hasn't frozen solid this last week, needs sorting so it can be isolated in these cold months, and correct backflow protection to comply with regs.

Often find with these things, the pipework acts as an amplifier, allowing the sound to resonate through the building. Water Hammer is actually when a washer vibrates like a reed in a wind instrument, creating a very loud hum or wail through the pipework.