Hello,
I bought some full bore 15mm isolation valves for my shower, as I thought the "standard" valves with their narrow centres might impede the flow. Was I right to be worried?
Anyhow, I realise the full bore ones need some space for their mechanism and would not be 15mm wide but all the same, they don't seem to have an internal diameter that much bigger, so what's the point?
Thanks.
Yes.
15mm tube has a 15mm outside diameter, so something like 13mm approximate ID (cue for resident pedant to provide size to 2 decimal places) supply .A straight tube has a pressure loss due to friction; any fitting (restriction, expansion, elbow, bend, etc.) will have more resistance. Service ball valves can have a very small bore (6 or 8mm?)and cause a big restriction to flow. It's not very relevant on mains outlets (where there's usually excess pressure) but can cause a noticeable loss of pressure with a shower. They can very seriously knob up a central heating system where there isn't much differential pressure to start with. If you've worked through a few systems, estimating the pressure losses in every metre of pipe and caused by every fitting, an installation by an idiot with a bumper bag of bargain service valves is a bad sign. Service valves in inaccessible voids are a very bad sign.
It's critical on the hot suction side to a pump (where you'd use
22mm) where excess restriction/pressure loss will cause cavitation in the pump impeller, shredding the impeller.
Thank you. What is the best way to isolate a shower then: gate valves or will a full bore 15mm valve do?
I bought some 22mm valves for the bath but I was surprised how small their internal diameter is. I'm wondering whether to fit them or not.
On Thu, 19 Apr 2007 11:49:07 GMT, snipped-for-privacy@nospam.org mused:
Full bore valves every time. Gate valves are only fit for weighing in.
Are you sure you bought full bore valves and not just some valves that someone thought were full bore? All the full bore valves I have ever fitted have the same bore as the pipe size they are designed for, which is why they are called full bore.
Were they from Toolstation? Or maybe not, but TS do some 'full-bore' valves which are nothing like full bore: just a bit wider bore than standard 'ballofix'-type isolation valves. Cue Trading Standards ...
But in answer to your first point I would use genuine full-bore valves on the gravity inlet to a shower but could use a less-than-full-bore valve on the higher-pressure outlets, or on a mains-pressure-fed system (e.g. electric shower, combi, unvented or heat bank).
[...]
How did you guess? Could you recommend someone who sells the "real" ones?
Thank you very much.
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