[TubaMorg]

Without storage tanks, your 120psi volume is very small. With such a system even very small leaks will run you out of air fairly quickly. That being said, there is no reason why you shouldn't have a tight pneumatic system. Check everything that sees pressure. Not just the joints. The gages can leak, the relief valve can leak, the regulator can leak, the fittings can leak, the solenoids can leak. Systematically and throughly check one component at a time with soap bubbles, because you surely have a leak. While in the Navy, we had an apparent leak in one of our systems and it took me 7 months to track it down. Just because you haven't found it, doesn't mean it doesn't exist.