Abstract: The invention relates to a safety device for protection against the rise of pressure in a pneumo-hydraulic control circuit which includes, upstream, a pressure generator and downstream, a pneumo-hydraulic accumulator. The device is characterized in that it includes, between the generator (3) and the accumulator (1) a non-return valve (6), a first safety valve (4) capable of a discharge at least equal to that of the generator upstream from the non-return valve, a second safety valve (5) downstream from the non-return valve and means for the second safety valve to be subjected to only a small discharge. The invention applies in particular to the pneumo-hydraulic control of very high tension cut-out switches.

Abstract: A gas-blast circuit-breaker comprises arcing contacts provided with nozzles of the same diameter, operating means ensuring an original movement of a mobile one of the arcing contacts in the opposite direction to that of the mobile main contact at the opening of the device.