High pressure vs. low pressure ball valves.

[p_telford]

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.

[Roger Mills]

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.

[Andy Hall]

Low pressure types are intended for toilets etc. that are filled from the roof tank.

For the mains feed to the roof tank, a high pressure valve should be used unless the mains pressure is really low.

Since you are changing, it would be a good opportunity to fit an equilibrium float valve such as a Torbeck.

These are quite inexpensive and as well as operating a lot more quietly than the traditional Portsmouth type, have a clean shut off.

[Chris Bacon]

It's mains pressure, so use the high-pressure cone. The low pressure ones are for gravity-fed stuff (e.g. the bathroom WC).

[Guy King]

The message from Andy Hall contains these words:

The potential drawback is that where previously you may not have had any resonance as the valve shuts, with a Torbeck type valve you sometimes get a mighty slam as it closes. It's down to loose pipework, and isn't really the fault of the valve, but it's often a bastard to track down where it's loose.

[Ed Sirett]

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).

[p_telford]

Hi, Thanks to everyone who replied. It's really very much appreciated.

Time to don my waders I guess :^) Cheers, Peter.

[<me9]

I had a problem with Torbecs both in the bog and the tank. If the basin taps were turned on and off again quickly after using the bog, the two valves rattled until the cold tap was eased open again. This always happened early in the morning while the water pressure was highest, and unfortunately whilst I was still in bed.

It was cured by changing the washer in one of the valves.

A clunk from the pipes feeding my downstairs bog when the valve shut off was cured in a simlar fashion, presumably with a stiffer washer than the original.