"BigWallop" wrote in message
...

"Murdo MacKenzie" wrote in message
...
Hi,

I'm planning on fitting a mixer shower and the instructions suggest that
when used with a combi system, it may be a good idea to also install a
pressure equalising valve (PEV). Does anyone have any experience of
this?
Is it worth the extra expense to install a PEV?

They are worth it. B&Q Warehouses sell them for about £20.
http://www.plumbworld.co.uk sell them too.

Thanks,

Murdo

The valve does help in the mixing of the hot and cold water at the mixer
unit itself
if the water is being fed from cold storage tank and the mains hot water
through the
boiler. It might also help if there is a big difference between a cold
mains supply
and the lower pressure coming through the boiler supply. But if both are
at the same
pressure then the valve isn't really needed. Check it out first and if
you need a
valve then retro fit into the system, but don't go to the cost of buying
one when you
don't know if it isn't needed.

The hot and cold must come from the same pressure source. If a combi both
from the mains. Where it is needed is when taps are turned on, or a toilet
flushed. It instantly balances the hot and cold supplies, well a little
glitch is felt, when say a toilet is flushed taking pressure from the
shower. Some mixers have them built-in. You don't need a thermostatic
mixer with them.

When fitting a combi, it is best to take the mains from the stop cock
directly to the combi, uisng 22mm pipe, with no tee-offs on this run. At
the stop cock install a tee and take a pipe to all the cold outlets. It may
be worth installing a pressure reducing valve here to reduce the cold
supplies. Just before the combi on the cold feed to it, tee-off and use
this for the cold to the mixer. This reduces the effect of other outlets on
the shower when turned on.