"Matthew Smith" wrote in message
...

The landscapers who installed the valves advised that these AC units
were suitable for 24V DC (no reduction) and were in regular use on water
trucks, running off the 24V truch supply. They claim that they had
never had a failure before - but then every vendor says that...

What do they know about electrics? FWIW, you could check that the amps are
OK, see what they draw on AC and don't exceed that on DC.

As for getting warm, they can. The original system has cycles lasting
up to 30 minutes and yes, the solenoids get pretty warm, but not too hot
to touch. The ones that have just failed have a programmed runtime of
only 10 minutes each.

Another way, run them up on a DC supply until they operate then add 10% to
that.

N