A valve for a pressurized fluid cylinder. The valve comprises a shut off valve biased against a seat to seal the cylinder. An actuation element is movable linearly to open the valve against the biasing force. A linkage element couples the actuation element to the shut off valve and comprises a first piston towards its top and a second piston towards its bottom. The valve also comprises a gas refill inlet between the pistons such that refill gas pressure biases the linkage element away from the valve. The actuation element is a depressed position pushes against the linkage element to hold the linkage element down and the valve open so that the cylinder can be refilled. When the actuation element is in a non-depressed position, the linkage element is free to move with the refill gas pressure so that it is spaced from the valve.