Why is my flat suffering water hammer?

Mr_Rumbold

I live on the top floor of a three storey building in the UK. Recently, when the neighbour's of the flat(s?) below mine use water, there is often a repeating crack or loud noise in the airing cupboard of my flat. This noise appears to originate at the point at which the water supply pipe enters emerges through the floor into my flat and just before it connects to the flat's internal stopcock.

Please note that the supply pipe does not rise through the floor of my flat from the flat below. Rather, each flat in the building has an independent water supply from the mains, so the water supply to any one flat is isolated from the others. This I know because on the ground floor, there is a wall-mounted panel which contains three external (to the flats) stopcocks, i.e. one for each flat per floor of the building. So from this point, the water supply to a given flat can be turned on or off 

However, and this is the point of my post: assuming it is not a pressure, or other, issue with the common water supply to the flats in general, how can the use of water by a neighbour in the flat below mine cause a shockwave in the plumbing through the building that results in water hammer in my flat given that the supplies are isolated? 

This is not a new problem given that it has occurred before but it varies in intensity: only in the last few days has it again become annoying. In the past it has been investigated by several plumbers without success, and I would like to (finally) resolve the issue before any damage may occur.

Can anyone advise? 

WIAWSNB

Do you know what the mains pressure is like? Are there any Pressure Reducing Valves fitted anywhere - near the stopcocks or within your flat? 

Where your pipe comes through, is there a gap around the pipe? If so, can you plug it with stiff card or similar to see if that helps?

Has any plumber suggested a Shock-Arrestor? 

Mr_Rumbold

I am not aware of any pressure reducing valves fitted anywhere, the mains pressure is good and there is no gap around the pipe. The only water hammer arrestor present is one on the hot water supply once the pipes branch after the stopcock. But the noise occurs before this point.

Lorian

Have they had a new dishwasher or washing machine about the time it started? If so it could be an agressive aquastop valve on the new appliance shutting off too quickly. Easily enough fixed by fitting a Sioux chief hammer suppressor in front of the aquastop, but that would be something they would need to do.

Mr_Rumbold

It is possible that the neighbour in question has had a new washing machine or similar fitted recently.

However, this is a repeat of an old problem which has recurred in the last few days, so I am uncertain.

Mr_Rumbold

I am informed that a neighbour below me did have a new washing machine installed recently. But they also report that they are also having water hammer noises and that these predate the installation of the new machine.

Lorian

They could back off their stopcock just a small amount, like half a turn and see if that helps.

If not the Sioux chief may cure it, even if it predates the new machine as it adds a little air buffer to which should help to arrest other shocks in the pipe. Apart from backing off their stopcock it's about the cheapest thing they could try. Screwfix/Toolstation stock them.
The one with the screw fittings to fit in-between the appliance supply hose and the supply.

Obviously turn off water (or the supply isolator) when fitting.

Mr_Rumbold

For now, I am referring the issue to the company that manages the flats (which are leasehold). We shall see ...

Mr_Rumbold

But I still don't understand why water hammer, if caused by in a neighbour's flat downstairs and on an independent supply, should affect my own flat's plumbing! It is curious.

Eldi_Dos

Mr_Rumbold said:

But I still don't understand why water hammer, if caused by in a neighbour's flat downstairs and on an independent supply, should affect my own flat's plumbing! It is curious.

I can only hazard a guess that the three supplies go back to one main and are not isolated from each other unless the stopcock is shut.

Lorian

I agree and ultimately the pressure wave being created is bouncing back off something.

The OP could possibly get a suppressor soldered in where their supply enters their property but it's likely easier and cheaper to do it at the source of the rapid valve shutting. 

Making sure pipes are properly secured in clips can help a little but won't fix it in my experience.

Like I said though turning the stopcocks off just a tiny amount can sometimes be enough.