The invention relates to a hydraulic system (1) comprising a main pump (12) and a precompression pump (5), whereby the outlet (8) of the precompression pump (5) is connected by a connecting line (9) to the inlet (11) of the main pump (12). The outlet (16) of the main pump (12) can be connected by a working line (17) to a consumer (A, B). The volume flow at the inlet (11) of the main pump (12) is changeable. The aim of the invention is to achieve greater efficiency. The precompression pump (5) comprises an adjusting device (6) for adjusting the flow rate.