Mono mixer tap and mains and gravity water

[David Hearn]

I'm in the process of fitting a new sink + mono mixer tap (ie. single hole mixer). (see

We have mains cold water and gravity hot water (not gravity heated - just gravity pressure). It was advertised as being suitable for all water systems (not mains pressure hot).

Upon reading the instructions it states:

"Water supplies shall be at reasonably balanced pressures from a common source (eg. hot and cold supplies from the same storage or both from a supply pipe). Where the fitting is supplied from unbalanced supplies (eg. hot and cold supplies from separate sources) a "Listed" single check value or some other no less effective backflow prevention device shall be fitted immediately upstream of both hot and cold water inlets."

As we have unbalanced supplies, it sounds like we need them - but what is the purpose? To stop mains pressure water ending up in our hot water pipes, or to stop contamination going back up the cold water pipe from the hot water?

If it's the former, then I'll fit one on the hot pipe, if it's the latter, I'll probably not worry too much (based on advice on here in the past about their benefits).

Oh, and I've also read that check valves reduce the pressure of the water. We have quite poor hot water pressure, which I'd like to avoid making any worse if possible.

Thanks

D

[Owain]

Officially the latter, but in practice the former as well. If it's a single outlet mixer you will probably find that it won't "mix" very well on the different pressure supplies.

Separate outlet mixer strongly preferred for kitchen sinks and other potable water applications. The concentric outlet type with the cold wired to the outer also helps keep the spout cool to touch.

Owain

[David Hearn]

The diagram of the tap included in the 'instructions' shows 2 separate channels with it being open at the spout before going into the 'flow straightener' (weird name!)

So, do you think that I'll actually need a check valve with this arrangement?

Thanks

D

[David Hansen]

On Tue, 07 Mar 2006 19:24:02 +0000 someone who may be David Hearn wrote this:-

Can you take the piece of black plastic off the spout? If you can then can you see two water channels in the spout? If you can then I don't see that a check valve is needed.

[Roger Mills (aka Set Square)]

I think that, officially, it's probably still required because some fool could - in theory - put a hosepipe on the tap and block off the other end, which could send cold water back up the hot feed - or hot water up the cold feed in the event of a failure of the cold mains.

But it needs a fairly unlikely combination of circumstances to cause a problem, and is a regulation which I would - and *do* - ignore. Also, if you have a check valve in the hot supply, it scuppers any possibility of back-feeding mains into the hot system to clear an air-lock.

[Christian McArdle]

Personally, I would expect a gravity hot supply through a check valve and a narrow bored single lever mono mixer to be unacceptable. I would only fit such a tap on a pumped or mains pressure system. You might get away with it on a gravity only system with no check valves.

The most important check valve is on the cold water side to prevent contamination of the mains supply in the event of mains failure.

Mains cold entering the hot system is unlikely to either occur or have particularly bad side effects. The most likely effect is to overflow the header tank, but probably not.

The check valve on the hot side will also seriously impact performance, so I would personally leave it off. If the performance of the hot supply is not good enough even without the valve, you'll need to look at pumps or mains pressure hot water systems.

Christian.