On Mon, 27 Mar 2006 16:58:28 +0100, Roger Mills wrote:

In an earlier contribution to this discussion,
wrote:

Hi,
The ball valve in our cold water header tank seems to be causing some
knocking and
generally seems to be due for a change (intermittent overflow for
example). In my local
B&Q there are two varieties of valve: high and low pressure. My
Collin's DIY manual gives
no guidance on this subject so I'm wondering if there is some decisive
factor in which to use.
The house is a normal two storey semi with a good mains pressure.
Thanks in advance for any advice,
Peter.

High pressure are for mains input - as your header tank will be. Low
pressure are for toilets etc. fed by gravity from header tanks rather than
being directly connected to the mains.

Many modern torbeck-type valves are suitable for either - and are supplied
with 2 or more flow restrictors. You fit the appropriate restrictor
depending on the supply pressure.

Likewise the bog standard diaphragm type float valve only differs in the
size of the nozzle (white for high pressure with about a 3mm hole and red
for low pressure with about an 8mm hole).

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html