Plumbing question

[Scott]

We are having a problem with some sort of airlock - a buzzing noise. I live in a block of flats. I believe the problem lies with the rising main, though neighbours disagree.

The rising main terminates at a storage tank in the loft. I believe think various neighbours have taken feeds from it over the years. At the entry to the storage tank there is an vertical extension to the pipe, about 12 inches long. I *think* that was put there as a silencer previously. Should this extension contain water or air? Is there any action to take, such as bleeding it, if we are now getting water hammer?

I have tried pushing down the ball c*ck in the hope of releasing air. This seems to have helped but not fully resolved the issue. Any advice welcome.

[Fredxx]

The idea of the air column is to provide an air cushion to stop the water hammer. It should be filled with air, and you also hope that trapped air in the cold water supply will keep the air pocket topped up.

Changing the valve to another type can also change the precise characteristics and stop the resonance. It's all very hit and miss.

Even moving the float can change the resonance of the float arm and make a difference.

[Brian Gaff (Sofa]

Some places where the new plastic pipes in the ground have replaced the old metal ones this sort of issue has got worse.Water is funny stuff. I distinctly remember duct taping a plastic bottle to the ballcock in our loft before the tank and valve were replaced for a least ditch fix for strange phutting noises from the mains water plumbing. It way in fact coming from a bit of vertical main in lead that tended to flap about when the sound happened. New tank and valve fixed it till now, some 30 years later, even though the same old bit of lead piping remains. I don' even pretend to understand the reason, but it obviously had something to do with resonance. Brian