Compressed gas-blast circuit breaker

A compressed gas-blast circuit breaker having first and second coaxially arranged contact pieces which engage one another in a switched-on position, said first contact piece being movable in an axial direction and being surrounded by a blast nozzle which in the switched-on position, is penetrated by the second contact piece, said blast nozzle being arranged on a pump cylinder which moves along with the first contact piece, said blast nozzle being fluidly connected to a blast chamber of constant volume which contains arc extinguishing gas surrounded by said pump cylinder, said circuit breaker having a pumping space which is surrounded by the pump cylinder and fluidly connected to the blast chamber via a nonreturn valve, said pumping space having a volume which is variable by a pump piston, said pump piston being arranged in the pump cylinder such that upon movement of the first contact piece through a stroke segment of a switch-off stroke beginning at the switched-on position and ending at least approximately at a contact-separating position where contact between the first and second contact pieces terminates it causes arc extinguishing gas to be pumped through the nonreturn valve into the blast chamber for the purpose of building up blast pressure, said circuit breaker further comprising at least one toggle lever, said at least one toggle lever having a first member and a second member, said first member being pivotally connected to the pump piston, said second member being pivotally connected to a stationary support, said first and second members being pivotally connected to one another at a toggle joint in such a way that during a switch-off stroke the pump piston initially remains substantially stationary for the purpose of reducing the volume of the pumping space and there after moves in the same direction as the pump cylinder, wherein said at least one toggle lever is guided by at least one guide member which is coupled to the first contact piece such that in said course of the switch-off stroke the at least one toggle lever is initially straightened from an inwardly bent position to a straightened position, then bent from the straightened position to an outwardly bent position, then straightened back to said straightened position and bent inwardly again.