Abstract: A valve for connection to a pressurized gas cylinder includes a housing including a gas cylinder aperture which is connectable to a gas cylinder, and a housing conduit which extends through the housing from the gas cylinder aperture to one or more inlet/outlet apertures so that the valve is capable of providing fluid communication between the gas cylinder through the housing conduit and the one or more inlet/outlet apertures. A flow control ball within the housing conduit is movable between open and closed positions. Ball seals have sealing surfaces corresponding to a shape of the flow control ball for substantially sealing the flow control ball in the housing conduit.