That engineer is correct. You want a solenoid that is open at rest, (normal) and closes under power. You also want to be sure the solenoid is rated for continuous use.
I got this response from a engineer that sells one on Ebay. Thoughts?
Hello. It sounds like you would need a normally open valve that you would normally keep powered (closed) and it would open upon power failure. However, a normally open solenoid valve would have coil life issues being powered basically indefinitely. The only type of valve that could handle this is a motorized ball valve. They don't have coils that get hot. Instead, they use limit switches to stop current flow to the motor when open and closed positions are reached. You would be looking at about $60 for a 1/2" normally open motorized ball valve with a brass body. They use an internal capacitor to drive the valve back to the open position after external power is removed.
