Hmmm... we've had no problem with reliability. In fact we bumped the pressure up to 85 psi the other day just to see what would happen and darn near shot a hole in the ceiling of the shop. Darn, but you can make that big blue ball fly when you want to!
We had 4 1.5"x15" cylinders doing the launching, all pressurized through ONE valve. We put two clippard tanks in line with them, just for a bit of extra punch... although I'm not sure how much that helped. The launch arm would fall back into the "cocked" position, which was just slightly over centre, so that when we pressurized the cylinders they would lock the launch arm in posiiton. They would be extended about 1/3 of the way.
Then a second set of cylinders (1.5"x2" if I recall) would pop up and force the arm up and over centre, and... WHEEEeeeeee.... off goes the big ball.
It took a while to reload, which was one of the weaknesses of the system, but it was fun... and still is.
http://www.trobotics.ca/#MAXX 3
Jason
EDIT: Mind you... we're careful to not "dry fire" the thing. That happened once and it was kind of scary.
EDIT2: Oh, yes.. we also only connected fittings to one end of the cylinder... the other end was open to air so it could dump air more easily as we launched.