Hydraulic circuit breaker

A hydraulic circuit breaker comprising a housing with an inlet orifice connectable to the outlet of a hydraulic pump, a first outlet orifice connectable to the pressure chamber of a hydraulic pressure accumulator, and a second outlet orifice connectable to an open-centre hydraulic circuit, a stepped bore in said housing, a piston of the differential type having faces of smaller and larger cross sections slidable in a fluid-tight manner in said bore and defining therewith an inlet chamber communicating with the inlet orifice and a control chamber, the pressures in said inlet chamber and control chamber acting respectively on those faces of the differential piston having the smaller and larger cross sections, a constriction orifice whose cross-section is variable according to the position of the differential piston being provided between the inlet chamber and the second outlet orifice, said inlet chamber communicating with said control chamber through a first passage comprising a first restriction and being also connected to the first outlet orifice by a connection comprising a non-return valve, said circuit breaker further comprising a resilient vessel having a variable-volume compartment connected to said control chamber, said resilient vessel comprising a second bore defined in said housing, a second piston slidable in a fluid-tight manner in said second bore so as to divide said second bore into a first compartment defining said variable-volume compartment and into a second compartment, the second piston being urged towards the end of said first compartment by resilient means located in said second compartment, an axial passage connecting said first and second compartments being provided in said second piston and opening towards said first compartment to define a valve seat cooperating with a valve forming element resiliently urged onto said seat, a valve lifter element fixed relative to the housing being provided in said axial passage of the second piston, said valve lifter element being adapted to lift said valve forming element off said seat to permit fluid flow in a leakage passage when the second piston has moved a given distance which corresponds to a first predetermined value for the pressure in said first compartment, said leakage passage comprising the space defined between said valve lifter element and said axial passage, said second compartment being connected to said second outlet orifice, said leakage passage forming a second restriction, whereby said first compartment is connected to said leakage passage when the pressure in said compartment reaches a first predetermined value and said connection is interrupted when the pressure in said compartment falls below a second predetermined value.