On Sun, 22 Feb 2004 19:24:47 -0000, "Set Square"
wrote:

I am considering overhauling and zoning my central heating later this year,
and would like separate control of each rad. I'm looking for motorised
valves which are as small as possible and which will fit on 15mm pipes. The
only ones I can find are 22mm. [Yes, I know I can use reducers - but the
whole thing is still too big].

Does anyone know whether smaller ones are available and, if so, where from?

TIA.

A good solution for this is to use Sauter drives in place of the TRVs.

The cheapest is the AXT111 F200 which is a thermal drive. These fit
onto the base of a TRV in place of the normal head

http://www.sauter-controls.com/pds/pds/pdf/pd55012e.pdf

The valve is held closed with a spring to turn it off. When heat is
required, power (230v, although there is a lower voltage one) is
applied. This warms an expansion element and opens the valve.
Operation is silent and in operation they use under 3W.

RS have these at about £35, but a better deal should be possible from
Controls Center.

You could also fit one of these drives onto a 15mm base which Sauter
also makes.

I've used some of Sauter's motorised drives (AXM 117S)

http://www.sauter-controls.com/pds/pds/pdf/pd55011e.pdf

These run with a 24v supply and can be set to any position with a
0-10vDC control voltage. They are also silent in operation, but
cost more than the thermal ones. I'm designing a special purpose
system which provides the necessary control voltages.

It should be possible to control a thermal drive with either a simple
thermostat or a pulse proportional controller like a CM67 or
equivalent.



..andy

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