Pneumatics Power Problem

Our single-acting pneumatic cylinder has more power when we manually snap it back and release than when we use it normally. What is the problem?

A cylinder like that is only powered one way- hence the name single acting. When pressurized, the cylinder pushes out. When unpowered, a spring returns it to its resting position. This spring force is the same if you were to move it with your hand and when it is powered by air. I would recommend not relying on this force, and instead re-design the mechanism so it can work with the powered stroke of the cylinder.