A valve for use in the control of pressurized air from a pressure tank, the pressure tank including a wall in which an outlet port is formed, the wall having an inner surface and an outer surface. The valve comprises a valve body of generally cylindrical configuration having an inner end which in use is located inside the pressure tank and an outer end which in use is located outside of the tank. A flow passage extends through the valve body, the flow passage having an inlet at or adjacent the inner end of the body and an outlet at or adjacent the outer end of the body. A valve seat surrounds the flow passage and a valve closure member is moveable towards and away from the valve seat to close and open the valve respectively. An operating means is provided for moving the valve closure member in order to operate the valve. The valve is characterized in that the valve body has at least one laterally extending mounting formation at or adjacent the inner end thereof, the mounting formation being shaped and dimensioned to enable the inner end and the mounting formation to be introduced into the pressured tank through the outlet port, and when in position, the mounting formation engages with the inner surface of the wall of the tank adjacent the outlet port. The valve includes a mounting collar movable towards the mounting formation so as to engage the outer surface of the wall adjacent the opening and thereby clamp the tank wall between the mounting formation and the mounting collar.