On Wed, 1 Mar 2006 14:52:08 -0000, "Bob Mannix"
wrote:

I think this sort of
operation would be a lot harder to achieve with a 12V DC motor, which is
probably why you can't find them. As another poster has suggested, the
use
of 2 12V solenoid valves and appropriate controls would be a better bet,
although this arrangement could fail with all shut (which a 3-way valve
can't) giving rise to potential hazards.

I *Think* on the Winnebago one valve is N/O (HW) and the other is N/C
On energising they switch state, so even with power off there is always a
water path
open.

True, but that is only one failure mode. It's still possible for a single
stick shut to result in no water path. It is physically impossible in a 3
way valve.

Don't forget that there is Honeywell S-plan. This consists of two
port valves, with one normally being open at a time.

A microswitch in each is used in the path to fire the boiler such that
unless at least one valve is open, the boiler can't fire.

Whether this exists for 12v valves, I am less certain, however a look
through the web site of Sauter may reveal something suitable.

http://www.sauter-controls.com/pds/pds/indexe.html

Their products are orderable through PlumbCenter or ClimateCenter


--

..andy