Abstract: The invention relates to a multifunctional valve unit (10) for use on a gas cylinder to which it is attached for the controlled filling of the cylinder and for the controlled discharge of gas therefrom. The unit has a unitary or monolithic valve body (32) providing a filling port (12) and a cylinder connector (14) in gas flow communication with the filling port (12), for releasable attachment of the unit to a gas cylinder. The unit further comprises a manually operable manual shut-off valve (16), a gas pressure regulator (18), a minimum retention valve (20), a pressure gauge (22), a flow control device (24), and a pressure relief safety valve (26), all of which are mounted on the valve body. The flow control device is, as a whole, replaceably removable from the remainder of the multifunctional valve unit while the cylinder connector is connected to a gas cylinder containing gas and the manual shut-off valve is closed.