Differential hydraulic jack for operating electric breakers.

摘要

Jack in which the annular chamber 14 of the cylinder 4 is always subjected to the high pressure of an accumulator 18. The piston 6 of the jack is free of any sealing lining in regard to the inner surface 38 of the cylinder and this piston mechanically actuates a valve 42 which sealingly closes off a seat 44 surrounding the feed/purge orifice 28 of the cylinder, at the bottom end of travel of the piston 6. The invention allows the cylinder 4 to be made in the form of a casting whose inner cylindrical surface 38 requires no accurate machining such as grinding or honing. <IMAGE>