A system for hydraulic systems includes a working cylinder (58) which operates as a consumer of hydraulic energy or as a generator of hydraulic energy. A hydraulic accumulator (1) can be charged by the working cylinder for storing energy and can be discharged for delivering energy to the working cylinder (58). One hydraulic accumulator is provided in the form of an adjustable hydropneumatic piston accumulator (1), in which with a plurality of pressure chambers (19, 21, 23, 25) adjoining effective surfaces (11, 13, 15, 17) of different sizes are on the fluid side of the accumulator piston (5). An adjusting arrangement (51) connects a selected pressure chamber (19, 21, 23, 25) or a plurality of selected pressure chambers (19, 21, 23, 25) of the piston accumulator (1) to the working cylinder (58) as a function of the pressure level that prevails respectively on the gas side of the piston accumulator (1) and on the working cylinder (58).