Abstract: A slide valve, especially for use in a compressed air supply installation, includes a body defining an inlet passageway and an outlet passageway and a vane having an orifice therethrough and movable laterally relative to the passageways between a valve-open position in which the orifice is in register with the passageways thereby permitting fluid to flow through the valve, and a valve-closed position in which the orifice is wholly out of register with the passageways thereby isolating the inlet passageway from the outlet passageway. The vane defines, at least in part, an exhaust passageway that, in the valve-closed position, connects the outlet passageway to atmosphere via a further exhaust passageway formed in the body whereby, in the valve-closed position, the downstream side of the installation will automatically become depressurized.