Tap comprising a body delimiting an internal circuit for the filling and drawing off of a fluid, said internal circuit extending between an upstream end configured to be connected with a user member for drawing off or dispensing a pressurised fluid through the internal circuit and a downstream end configured to be connected to the storage volume of a pressurised fluid tank, the tap comprising, arranged in a series in the internal circuit: an isolation valve and a dustscreen valve, the isolation valve being movable with respect to a seat between an upstream position of closure of the circuit and at least one downstream position of opening of the circuit, said isolation valve being urged towards its upstream position by a return member, the dustscreen valve comprising a downstream end and being arranged upstream from the isolation valve and being movable with respect to the body between an upstream position of closure of the upstream end of the circuit and at least one downstream position of opening of the downstream end of the circuit, said dustscreen valve being urged towards its upstream position by a return member, characterised in that the tap further comprises, in the internal circuit, a residual-pressure valve separate from the isolation valve, the residual-pressure valve being arranged in a series with the isolation valve and downstream from the isolation valve, and in that the dustscreen valve is movable from its upstream closed position to: - a first determined downstream so-called "no contact" position opening the upstream end of the circuit, in which the downstream end of the dustscreen valve does not push the isolation valve, or - a second determined downstream so-called "contact" position opening the upstream end of the circuit, in which the downstream end of the dustscreen valve pushes an upstream end of the movable isolation valve to move by contact the isolation valve out of its seat to a first downstream position of opening of the circuit in which the isolation valve does not push the residual-pressure valve, or - a third determined downstream so-called "filling" position opening the upstream end of the circuit, in which the downstream end of the dustscreen valve pushes an upstream end of the movable isolation valve to move by contact the isolation valve out of its seat to a second downstream position of opening of the circuit in which the isolation valve pushes the residual-pressure valve to a position of opening of the downstream end of the circuit. - a first determined downstream so-called "no contact" position opening the upstream end of the circuit, in which the downstream end of the dustscreen valve does not push the isolation valve, or - a second determined downstream so-called "contact" position opening the upstream end of the circuit, in which the downstream end of the dustscreen valve pushes an upstream end of the movable isolation valve to move by contact the isolation valve out of its seat to a first downstream position of opening of the circuit in which the isolation valve does not push the residual-pressure valve, or - a third determined downstream so-called "filling" position opening the upstream end of the circuit, in which the downstream end of the dustscreen valve pushes an upstream end of the movable isolation valve to move by contact the isolation valve out of its seat to a second downstream position of opening of the circuit in which the isolation valve pushes the residual-pressure valve to a position of opening of the downstream end of the circuit.