Gas spring with overtravel pressure relief

An industrial gas spring comprising:

• a casing including an axially extending side wall, an open end, a transversely extending end wall axially spaced from the open end, a gas pressure chamber defined in part by the side and end walls, and a passage through the end wall and communicating with the pressure chamber and the exterior of the gas spring;
• a piston rod received at least in part in the casing for reciprocation between extended and retracted positions and having an inner end communicating with the pressure chamber and an outer end extending generally axially outwardly of the open end of the casing when the piston rod is in the extended position;
• and
• a pressure relief assembly carried by the end wall and including
• a body received in the passage through the end wall of the casing, and including a blind bore communicating with the pressure chamber,
• a membrane configured with a first face communicating with the pressure chamber and a second face communicating with the exterior of the casing, and being carried by the body and at least in part in the blind bore in the body,
• a plunger received in the blind bore of the body and having
• a first end adjacent the membrane and configured to breach the membrane, and
• a second end axially spaced from the first end, disposed in the pressure chamber, and configured to be engaged by the piston rod to move the plunger to breach the membrane when the piston rod overtravels its design intended maximum retracted position, and
• a protective tubular portion projecting into the pressure chamber axially beyond the second end of the plunger to prevent the piston rod from accidentally moving the plunger to breach the membrane when there is no compressed gas in the pressure chamber.