Hydraulic system comprising a main pump and a precompression pump

Hydraulic system (1) comprising a main pump (12) and an admission-pressure pump (5), wherein the outlet (8) of the admission-pressure pump (5) is connected by a connection line (9) to the inlet (11) of the main pump (12), wherein the outlet (16) of the main pump (12) is connectable by a working line (17) to at least one consumer (A, B), wherein the volumetric flow at the inlet (11) of the main pump (12) is variable, wherein a compensating apparatus (25) for the hydraulic medium is selectively arranged between the connection line (9) or a connection line branch (9a) and a tank (2) or a suction line (3) which extends between said tank (2) and the admission-presence pump(s), said compensating apparatus (25) being formed by a bypass (26, 27) which bypasses the admission-pressure pump (5), a non-return valve being located in said bypass so as to enable a flow in the one flow direction and blocking a flow in the opposite flow direction, characterized in that the admission-pressure pump (5) has an adjusting apparatus (6) for adjusting its delivery quantity, and wherein there are provided two of said bypasses (26, 27), each having valves (28, 29) which open and block flows in said bypasses in mutually opposite flow directions.