There's a bit of a thread going on VZi regarding folk who've bought the cheaper/bargain fuel cutoff valves, which are likely made in a dark Chinese shed. The issue is that these things appear to get hot - damn hot, in fact - once they've been energised for a while. If you've been tempted by a valve from the Wun Hung Lo Cutoff Valve Company, you might want to check yours ...
I asked Tinley Tech Ltd, the supplier of these valves, if they were suitable for continuous operation without overheating - their reply: “Yes they certainly are suitable for continuous operation with fuel running through them - they will warm up if no fuel is flowing but there would be no point in powering the solenoid if you don't want fuel to go through.”
I have the version of the valve without the manual override. http://www.valtek.it/Prodotti/Elettrovalvola-per-idrocarburi-multiuso/Tipo-06-Gpl-Benzina-Metano-Gasolio.aspx?lang=en-US Valtek is part of the American Flowserve Corporation with headquarters in Irving, Texas. The valve is probably manufactured in Italy, the solenoid is from Holland.
I have received some additional information from Tinley Tech Ltd: “We have had a guy send one back but he wouldn't tell us what he was doing, just got a bit grumpy for some reason. I can see no reason why these valves cannot be used for your application - fuel will be flowing all the time you are running and would only ever be on for a few seconds with the ignition on if powered from the pump relay. All solenoids will get warm to some degree when energised (can't deny the laws of physics) but these valves have been used for many many years on pretty much every lpg conversion in the world on carb vehicles - the valve is energised any time the vehicle is running on petrol. Of course the valve will get warm if left open on a bench with no fuel flow - think of an electric fuel pump running with no fuel or running a water cooled engine with no water flowing though it!!”
