In article , John writes
Ok, I thought I was on a roll with this one, situation is this:

Gravity system, CW tanks in loft with 28mm feed to large HW tank in basement
(approx 7-8 metres of head between bottom of CW tank and top of HW tank).

I have installed a new thermostatic shower
http://www.victoriaplumb.com/tec10.jpg (also in the basement which has a
large (8" wide) shower rose on it. The head of which is approx 1 metre above
the top of the HW tank.
Pipework sounds fine but your pressure (calc 0.7bar) is only just above the
(high) minimum required by the mixer. Sounds like the valve or head is
restrictive. Suggest you measure the flow with & without the head. If it's
fine w/o the head then that sounds like the problem area. Just see how
long it takes to fill a 2gal (10l) bucket & calculate from there.

I have taken 2 x 22mm feeds from both the HW tank (22mm tee off main
outlet), and a tee off the 28mm CW feed to the tank. These run approx 3m
under the floor up to the shower valve from which they rise approx 1m (in
15mm) to the shower rose (only 1 or 2 elbows max).
Having connected it all up, the flow from the shower is absolute crap. The
manufacturer states that the shower works with pressures from 0.5bar to 2
bar, what I get is basically a dribble out of all the holes.
When I take the shower head off, I get a ok flow from the pipe, I haven`t
measured it yet to see litres per minute or anything.

I don`t understand why I get such a poor flow rate when I have a decent head
between tanks, my thoughts are as follows:

1.) The feeds to the shower are in 22mm but in the last 1/2 metre reduce to
15mm in order to connect to the shower valve which has 15mm compression
inputs.
2.) If you look at the inlet to the shower rose when its unscrewed from the
supporting pipe, you can see a white 'valve' which I can only assume is
restricting the flow further.
3.) I have tee'd off the 22mm outlet from the HW tank rather than use a
Surrey or Essex flange.
4.) The rose is larger than normal and the manufacturer isn`t telling the
whole truth by saying it 'works' within those pressure parameters
5.) When I turn the tap on to the bath which is in the room above the
shower, the flow rate is excellent (using the main 22mm feed from the HW
tank).

What`s going wrong, dare I say it - do I need a pump? I though pumps were
only designed for setups where the head available is next to nothing.

John

--
fred