Posted by Peter Ceresole on March 11, 2006 at 02:01:40 from 80.177.22.49 user PeterC.
In Reply to: Re: Beckfoot posted by Peter H on March 10, 2006 at 23:51:27:
most British houses have a water storage tank ......I imagine the reason for the tanks is that water is supplied from the main at pressure. If a hot water system or radiator circuit was supplied direct from the main, it would be subject to that pressure and would be prone to leak. Instead they are fed from the tank, by gravity.
I believe that there were two principal reasons. Remember that British water supply systems broadly date back to the beginning of the 20th century when disease was rife in cities and technology was much less reliable than it is now.
(1) A ballcock feeds water from a pipe into the tank by squirting it in- it's in free fall from the ballcock to the water surface in the tank. This means that there is no continuous water path from the house system to the water mains, so no path for germs to travel from the house to the mains. If there is a mains pressure tap in an English house, as there often is, it'll be in the kitchen where conditions are relatively clean. The lavatories are the most likely source of really nasty pathogens like typhoid and they are always fed from the tank- and they have their own water break because of their own ballcock mechanisms.
The free falling ballcock feed is damn noisy and in the sixties people started to fit 'quietening pipes' which went from the ballcock supply and dipped well below the normal surface level of the water in the tank. Nobody was thinking of the disease risk, because it was now so rare, and they were only thinking of the noise. This was quite rightly felt to be a very bad idea by the water supply companies, and all new ballcocks now have an 'anti-quietener pipe' fitting that casts a blade-like structure to the the output pipe nozzle and makes it impossible to simply fix any kind of pipe to it.
(2) It allows the supply company to treat the supply as 'interruptible' so they can do repairs on the mains while not depriving users of all their water supply. This is good for a few hours... And very good for the suppliers' costs.
Modern British water supplies have caught up with the continental European pattern of being at mains pressure. As in all such systems there is a pressure reduction valve at the house input, to keep the domestic pressure under control. I believe that this also incorporates a non-return valve, that prevents infected water travelling easily back into the supply if the mains pressure temporarily fails. I believe also ('believe' because I've not properly read the regulations on this) that lavatory cisterns connected to mains pressure systems have to incorporate a ballcock and a 'water break'. They may not use a simple tap. But this isn't gospel. Well, none of this is, but I think it's broadly accurate.
Bring on the Tarboard plumbers to refute me!