Abstract: A gas-blast switch having a hollow support insulator, and and at least one switching chamber housing supported thereon and within which there is arranged a set of fixed contacts, surrounded by a blast chamber, and a set of movable contacts. A blast nozzle coacts with the movable contacts and is connected with a pump device having a pump cylinder surrounding a pump chamber and movable with the movable contacts. The pump cylinder is displaceably arranged upon a stationary piston. A check valve opens towards the pump chamber. During the cut-on stroke pressurized gas is sucked by the valve into the pump chamber. The latter is connected by the check valve with a supply compartment communicating via inlets with the blast chamber and the internal space of the support insulator. A further valve is responsive to the pressure increase in the blast chamber, which valve, when responsive, interrupts the connection between the internal space of the support insulator and the inlets.