A gas pressure control valve having a valve body with a gas inlet and a gas outlet is described. An inner cap is provided bounding in part a chamber within the valve body in communication with the gas inlet. The valve body contains a spring loaded piston comprising a piston head and a piston rod. The piston rod includes a conduit providing communication between the chamber bounded in part by the inner cap and a chamber adjacent the piston head and the gas outlet. The piston is operable to move between a closed configuration in which the piston rod prevents communication between the gas inlet and the chamber bounded in part by the inner cap and an open configuration in which the piston rod permits communication between the gas inlet and the chamber bounded in part by the inner cap. The piston head is in a sealing engagement with the valve body via a first seal and the piston rod is in a sealing engagement with the inner cap via a second seal contained within the chamber bounded in part by the inner cap, the second seal being held in a fixed position within the chamber.