An aerospace manufacturer has a vehicle with a 50-ft, 4-stage double-acting telescoping cylinder mounted to the front. The largest movable section has a buggy with wheels that support the cylinder tube when it is extending or retracting. The vehicle has six outriggers that engage steel recesses in the floor when the cylinder is actuated, giving it a fixed point so that when the cylinder extends, it will develop the necessary force to push and form the part being fabricated.

The manufacturer had a nuisance problem with the cylinder drifting out when the directional valve was in the neutral position and the vehicle was moved to a different location or position.

The engineer in charge of the project added a double pilot-operated check assembly to hold the cylinder in place. He figured a mechanical device could cause a major problem if the operator forgot to disengage it and thought the hydraulic solution would avoid this potential safety problem.

After the piloted-operated check valves were installed, and the system cycled several times — removing most, if not all of the air — they moved the assembly into position to form a part. Much to their surprise, the smallest moving stage ballooned and blew the rod gland out. The picture shows the deformation near the end of the rod.

Any idea what caused the problem?