Colin Wilson wrote:

Screwfix do a shower mixer that looks like an unfeasibly high flow
rate compared to most other bar mixers, their ref: 31693 - apparently
does 8L/min at 0.1bar - does this sound "right" to those who've fitted
them ?

THe 8L/min I can believe, but at 0.1 bar sounds a bit unlikely. At 1 bar
it may be right.

While i'm at it, how the hell do you figure out what your pressure is?

If you really want to know, something like:

http://www.screwfix.com/prods/82412/...ure-Test-Gauge

Not that it tells you much of interest usually.

We're on a combi-boiler (WB28SIii), have good cold water pressure, and
at the moment, c/o the kitchen sink, it chucks out 9 litres of hot
water per minute - although I believe from a previous thread you can't
equate throughput with pressure.

Not really. There is also a difference in the flow rate the main will
supply (probably well in excess of 9 lpm), and that which the boiler can
heat to a reasonable level.


I've tried to play safe when ordering taps for the bath / sink by
going for 0.2bar jobbies, but I don't know how low I should be setting
my sights at for a shower mixer valve (i.e. would a 0.5bar be ok ?)

Chances are you have mains pressure of at least 1 bar.

Any advice would be much appreciated :-}

While i'm at it, because of the difference in pressures, would you fit
a pressure equalising valve / pressure reducing valve on the cold ?

With a combi the pressure should be equal (roughly) anyway.

Last but not least, and this might sound really dumb :-} but as a
shower fed by a combi won't get any hot water for several seconds, how
does the temperature setting work - does it let the hot flow until it
gets to temp, then let cold through ?

Some wax capsule types allow hot to flow until the output mix reaches a
limit temperature, and then they progressively constrict the flow of the
hot. The valve normally being such that you can't select just hot - you
must also have some cold. Hence throttling the hot supply cools the mix.
Depending on the flow rate you are demanding from the combi, you can get
a self defeating mechanism that comes into play here and slows the
reaction time of the mixer. Say you boiler can heat 10 lpm to 45
degrees, but you have the boiler limit stat set to 60 degrees, you may
find the combi responds to the reduction in flow imposed by the mixer by
simply allowing it to get hotter, just negating the change made by the
mixer. A mixer that responds to a rise in temp by increasing the cold
flow rate works better in these cases.


--
Cheers,

John.

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