Jules wrote:
On Mon, 22 Jun 2009 23:31:06 +0100, Dave Liquorice wrote:

On Mon, 22 Jun 2009 21:39:48 +0100, Tim S wrote:

However the lack of positive feedback is a pain, especially for
diagnosing problems
snip - complex things with temp sensors or flow switches

Something must move when the valve opens and closes. Get one and see
if you can position the arm of a microswitch in a suitable place or
attach a linkage to operate a microswitch.

That was my thought, too - there must either be a sliding or rotating part
which acts as the actual valve, and this must have *something* going to
the outside of the valve body so that it can be driven by the solenoid
actuator mechanism.

Hopefully there's a spot where either a mechanical switch or some sort of
optical switch can be attached in order to sense the position of the valve
itself (regardless of whatever the drive mechanism is doing).

Of course the sense switch could also fail - but I suspect this doesn't
matter as it can still be detected as a fault condition and a real human
being can be alterted.

cheers

Jules

Why should anything moving outside the valve body? Normal solenoid
valves don't; they use magnetic coupling to operate the valve.

Bob