A gas bottle assembly includes a container for containing a pressurized gas, and an operating head, the operating head including a valve member which in the absence of any demand for the gas, is positioned close to a valve seat such as to permit only a minimal flow of gas from the container past the valve seat, and an actuator moveable to move the valve member away from the valve seat thereby to permit a greater flow of gas past the valve seat, to an outlet for use, and wherein the actuator includes a plunger with which the valve member is integral or to which the valve member is affixed, and the actuator includes a piston part which is movable in a piston chamber in one direction in response an actuator spring acting at a first side of the piston part, to move the valve member away from the seat, and in an opposite direction in response to a combination of gas pressure and a valve return spring which is located in the piston chamber at a second opposite side of the piston part to the actuator spring.
