Does a single check valve in a cold mains pipe result in a pressure
drop?

I have installed a venturi shower (Trevi Boost) exactly according to the
manufacturers instructions. Unusually the water temperature is
excessively hot. After pretty exhaustive investigation I believe the
problem may be due to inadequate cold mains pressure. However the mains
pressure to the house is certainly adequate. As recommended by the
manufacturers installation guide the cold water mains supply to the
shower has an isolating stopcock and a single check valve. The
instructions state that the check valve is ideally 22mm but can be 15mm
on the cold side. I have installed a 22mm on the hot side and a 15mm
inline check valve on the cold side.

The cold mains gives over 12 litres/minute at the kitchen tap, but less
than 6 l/min from the shower head. Could the check valve be causing a
reduction in flow/pressure?
--
Matthew Barnard

In message , David W.E.
Roberts writes

"Matthew Barnard" wrote in message
.. .
Does a single check valve in a cold mains pipe result in a pressure
drop?
Possible - the best way to check this is to close your check valve, detach
the cold pipe from the back of your shower, then point into measuring device
and turn valve on again. This will give you the flow rate available at the
back of the shower. You will then know if it is the valve or the shower
restricting the flow.

It could be that you trade off 50% of the cold flow to boost the hot flow.

If the manufacturers have a help line, give them a ring.

You could also try slowly closing the check valve on the hot side until you
get a reasonable temperature,


Thanks David,

The shower is a concealed fitting - and is now fully fitted into a tiled
wall. Detaching the back will be rather difficult.

Your recollection of the mechanism is entirely correct. You may well be
right that the cold flow is reduced by the venturi valve. Although I
have found via Google a description of another venturi shower which
achieves 8 to10 L/min. I believe this unit should be broadly similar.

I have contacted the manufacturers - and will pursue them - but so far
their technical advice has constituted : have you flushed the
pipework?...

As you suggested partially closing the hot supply results in an
acceptable temperature and a reasonable shower. However the shower is
new and is supposed to provide water from cold to hot - which it
currently does not do. The water pressure with this arrangement is
reasonable - but not much different to a low pressure system. This is
not what I wanted - and I would like to exclude my setup before pursuing
the manufacturers.

Thanks again
--
Matthew Barnard