I'm in the process of fitting a new sink + mono mixer tap (ie. single
hole mixer). (see
http://www.diy.com/diy/jsp/bq/nav/na...141744 746842)

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 wrote:
David Hearn wrote:

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


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

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

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

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.

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!)

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.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

In an earlier contribution to this discussion,
David Hansen wrote:

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

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.

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!)

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.

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.
--
Cheers,
Roger
______
Please reply to newsgroup.
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spam.

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?

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.