Rotary hydraulic jack device

Claim 1

A hydraulic jack device comprising a rotary cylinder, a piston in said cylinder parting the same into two compartments, conduit means including rotary joint means for connecting each of said compartments to a source of liquid under pressure, said conduit means including, between said rotary joint means and each compartment, a liquid flow-path provided with a pressure responsive nonreturn valve, pressure operated piston means for forcibly opening a respective non-return valve in one flow path responsive to pressure in the other flow path, first duct means connecting said piston means with each flow path upstream of said non-return valves, associated with each flow-path, means defining a stepped cylindrical cavity comprising a first portion of small diameter and a second portion of large diameter forming an extension of said first portion, second duct means connecting the end of said first portion remote from said second portion with the associated flow-path downstream of the corresponding said non-return valve, a differential piston in said cavity having two sections secured to one another and respectively cooperating with both cavity portions, a spring in said second portion urging said piston toward said first portion, third duct means connecting the annular space comprised between the junction of said portions and the two sections of the differential piston with the associated path upstream of the corresponding non-return valve.