Making progress, changed up the valve design. The piston will be able to move a 1/2" or so before opening. This transition will allow for propane/compressed air to be turned on/off from the pistons movement.
For fueling I'm thinking of using a pneumatic cylinder to meter the propane, then it'll be displaced like a syringe. The compressed air will just be regulated on/off setup. Propane of roughly 1/25th the proportion, has to be more precisely metered because after all I'll be using the same style regulator for the compressed air, and propane source. Also since the propane meter will be displaced I figure that will be all the more volume that doesn't diluted by compressed air, from a metering sense.
I hope that a check valve + dead space + flow restriction should be enough to solve this
anyway I am going to use tubing that is rated fairly low (for example to 100-150 psi) so i think this will work as a safety burst disk
The source pressure should never come close to equalizing with the chamber's pressure. If that happens won't gas have every tendency to circulate with the source?
The valves I have are 24vdc 8w, is it customary to use a variety of different types of batteries in a system? For instance I got some 18 volt whatever amp rechargeable batteries, for electric drill, could they be used with say AA batteries?
^If I can scrounge the bats, I've got some roller micro switches. Something like this,
, attached to the chamber pistons movement to create the on/off phase for the switch->solenoid valve..