Hydraulic pump

A hydraulic pump comprising at least one alternating-cycle piston sliding in a fixed cylinder and having a suction phase and a delivery phase, a non-return suction valve normally closed and placed between a source of fluid under low pressure and a working chamber defined in said cylinder, and a non-return delivery valve normally closed and placed between said working chamber and an output chamber feeding fluid under high pressure to an application circuit, wherein said output chamber has a wall which is movable as a function of high pressure of fluid in said output chamber, said movable wall controlling locking of the delivery valve in an open position during a substantial part of the suction phase when the high pressure of the fluid in said output chamber is greater than a predetermined pressure and effecting closing of said suction valve, said movable wall comprising a second piston sliding in a bore and having one piston face receiving the high pressure of the fluid in said output chamber and a second piston face loaded by a spring having a predetermined stiffness, wherein said second piston face also receives a pressure prevailing in a circuit communicating a working chamber of a master cylinder with the second piston face.