I have success installed 50 Ohm 10W resistor is series with US Solid ball valve 9-24 AC/DC. I tried solution by Thinkpeace, but 100 Ohm in parallel didn’t work for me at all, probably Thinkpeace has different type of ball valve than I have. I suggest use series other than parallel, it is better for power consumption and will not make resistor hot, because when ball valve is opened, current though the circuit is very low.
