Pressure equalising valve

[Andrew]

The plumbing in my bathroom seems a little unusual - the hot is supplied via a 22mm pipe from CW tank with about 1.5m head; the cold is mains pressure via a 15mm pipe.

I would like to keep the cold directly mains fed - but not surprisingly, the mixer showers don't work very well.

I've thought about fitting a pressure-equalising valve (one for the whole bathroom, rather than one per shower), such as

anybody have any experience with these? Specifically, do they need any "flow" to work?

- if the hot tap or cold tap alone is turned on, will I still get the expected flow & pressure?

- if the cold pressure drops to zero (stopcock turned off), will I still get any hot flow?

- I'm planning to put a double-check valve on the CW input to the valve as well - is this necessary, or could it cause problems?

thanks for any comments, Andrew

[IMM]

See the makers specs for minimum pressure and flow. They sometimes don't operate too well when the pressure difference is too large.

Yes.

Yes.

Why?

[Christian McArdle]

purpose is to put both supplies on the lowest common denominator. If one supply is poor, it makes the other equally so. You first need to get two good supplies.

The correct solution is to put a single impellor pump on the hot side, to boost the hot water system to mains like pressure and flow. Then you can worry about pressure equalising, although this will only really be advantageous on a shower mixer, which a good model will have built in (along with thermostatic operation).

An alternative to the pump is to fit a "venturi" type shower, which uses energy from the cold mains to boost the hot water through the mixer. This won't help other outlets, like the bath taps, that might also have poor flow.

It is required for hosed shower mixers unless you put one of those intensely annoying clips on the shower hose that prevents you using the shower to clean the bath/cubicle with.

Christian.

[Scott M]

Does anyone know where you can get single impeller pumps? I've not found any on-line and wouldn't mind getting one for our HW system in general.

[Christian McArdle]

I believe someone recently recommended the Grundfos UPA 15-90 "Home Booster".

The other manufacturer normally recommended is the Stuart Turner. They do quite a number of single impellor pumps, from their entry level Showermate

1.2 (around 130 quid) to a Monsoon 3.0 (around 290). Obviously, there are twin impellor versions of these, so check carefully.

Christian.

[IMM]

The Grundfoss is quite cheap. When having booster on hot and cold on the mains, it is best to check the pressure of both. Ideally they should be near each other. If they are then a pressure equalizing valve will trim off.

[Scott M]

Cheers for those. I'll go and see what I can find, but can anyone recommend somewhere that sells 'em?

[IMM]

Plumb Center for the Grudndfos.

[Pete C]

How about using a dual impellor with both sides in parallel?

cheers, Pete.

[IMM]

You can't pump main water.

[Christian McArdle]

I think he meant to use both impellers on the hot side. However, this is unnecessary. Single impeller pumps are widely available and cost less than the equivalent twin impellers.

Christian.

[Scott M]

Having Google'd by brand name I turned up half a dozen places selling 'em. Never realised they were that common as, although I kept hearing about them, I'd never found any before just looking for "single impeller", etc. And the sheds never stock such things.

[Scott M]

Ta very much. I've got one of those local, too.