The valve we run is a check valve run in reverse. We move the whole valve and engage it into the shell to release the valve. Clear as mud? I can try to get some pictures that will be rightside up this time to help out if not.
We had to do a little machining (i.e. sanding and filing) to make a threaded end that would fit inside our valve.
Brass with pneumatic actuation
Brass
We actually run a plastic valve that has a burst rating of 200 psi and is rated for gas to 100 psi. I don't remember where we got it from though.
Our tank is a hot water expansion tank like
this. Yes it is for water and not for gas, but we are running at less than 20% of the rated pressure and it is a steel tank that has a safety vent built in.
We have had no issues and pressure tested one to 130 lbs prior to using it by filling it and draining, repeating then using some force to deform and filling and draining again. No leaks, no failures, and no worries with 10-30 psi being contained.
The benefit of how we built ours is that we use a cylinder to push the actuator to release gas. If we pressurize over 30 psi the regulator on the cylinder won't allow the cannon to fire or engage. It just hisses a little and reminds you that you are trying to do more than was designed for.