Abstract: A gas cylinder of the present invention comprises a housing having a tube, a front head and an rear end cap defining a chamber. A pair of ports are provided to allow for the input and exhaust of gas in the chamber. A piston is received in the chamber for axial movement within the chamber and separates the chamber into two cavities. A rod is operatively connected to the piston and extends forwardly from the piston, through a bore in the front head to exit the chamber through the front head. The rod is loosely or floatingly connected to the piston, to be movable relative the piston by a plate at an end of the rod which is trapped in a bore in a forward end of the piston. A piston seal is received in a groove in the piston to form a seal between the piston and the cylinder tube. The piston is flexible and changes shape due to pressure changes within the chamber. A rod seal is also provided between the rod and the front head bore.