Andy wrote:

cupboard on 1st floor. The shower in question is gravity fed from pipes
leading from the
airing cupboard. The problem is the appauling flow rate of both HW and CW,

If the shower is gravity fed (i.e. HW from the cylinder and CW from the
header cistern in the loft) then there is no need for any sort of non
return valve in the setup.

for the poor flow is the non-return valves (check valves) fitted just before
the bath
mixer taps. The picture below shows the scene with the bath front panel
removed.
The two pipes feed the HW/CW bath mixer taps and the two valves are
presumably
the two check valves ?

http://www.knownentity.com/pics/bath/bath_valves.jpg

They don't look like any check valves I have used... not to say they
aren't mind you ;-)

(I think your equi-potential bonding ought to be on the other side of
the valves as well)

I guess the check valves are there due to water regs required when a shower
head
on a flexible lead is used in a bath environment with the potential for
drawing
contaminated water back into the house water tanks/supply.

Since you are not suppose to drink the tanked water it is a bit of a non
issue. The time a double check valve would be required was if there was
a danger of contaminating the rising main.

1. Try to prove that it's the check valves which are responsible for the
poor flow by
measuring the CW flow with valve in place, removing valve and then measuring
the
new flow rate.

Sounds like a good plan...

2. If the flow rate differences are substantial then remove both check
valves and
replace the flexible hose shower with a fixed head unit. I was thinking of
the following
retro-fit unit from Screwfix :-

http://www.screwfix.com/app/sfd/cat/...01187&id=64439

or leave it as it is....

Things I'm not too confident about:-

Removing the check valves and fitting a new connector from the pipe to the
tap.
Presumably the bit of the supply pipes where the check valve compression
olive
has bitten will not be reusable for fitting a new connector and I'll have to
cut away
some pipe and either fit a new compression joint to a fresh bit of pipe ?

As long as your new compression fitting is the same thread as the
existing (highly likely), just reuse the existing olive and back nut.
Add a few turnd of PTFE over the olive if in doubt or try sealing
compound like Fernox LS if you prefer.

You will need a little bit of play in the pipes to get the old valves
out. If they are fixed rigidly, then cut away the valve with a pipe
cutter, and use a soldered slip connection to make the last joint.


--
Cheers,

John.

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