Hydraulic apparatus for producing different delivery quantities at different working pressures in at least one piston arrangement, in particular a synchronous or differential arrangement, of hydraulic cylinders, hydraulic pivot drives or hydraulic motors, having - a piston arrangement, - a first motorized pressure pump for generating a first working pressure P N, and - a second pressure pump which is motorized so as to run in the same direction as the first pressure pump for generating a second working pressure P H which is higher than the first working pressure P N, and - a hydraulic switchover device for switching over a high pressure/low pressure state with combined working pressures P N + P H in a high pressure state with a working pressure P H in the case of a pressure increase in the piston arrangement, - the switchover device being configured as a circulation valve which comprises a first and at least one second valve device (8, 9) which are arranged jointly in a common valve block with in each case one valve element VB and VA which is mounted in an associated valve seat, - the two valve elements VA, VB being coupled in terms of movement via a connecting element for synchronous movement and being prestressed together by way of a spring in a basic position, in which the first valve seat is closed and the second valve seat is open, - and the first pressure pump being pressure-connected via the second open valve seat and the second pressure pump being pressure-connected directly to the piston arrangement, and, - in the case of a pressure increase in the piston arrangement as a consequence of an increase in the pressure on the output side of the second valve seat, the said second valve seat being closed counter to the force of the spring and the first valve seat being opened, - a partially opened position which is active between a closed position and an opened position being provided in the case of at least one valve seat (11, 12) of the valve device, in which partially opened position a defined partially opened volumetric flow flows through the valve seat (11, 12) which is smaller than the volumetric flow which is generated by the second pressure pump at the pressure P H, characterized in that the partially opened position is formed by way of a defined annular gap in the respective valve seat (11, 12), the annular gap surrounding a cylindrical shell-shaped section of the respective valve element VA, VB. - a piston arrangement, - a first motorized pressure pump for generating a first working pressure P N, and - a second pressure pump which is motorized so as to run in the same direction as the first pressure pump for generating a second working pressure P H which is higher than the first working pressure P N, and - a hydraulic switchover device for switching over a high pressure/low pressure state with combined working pressures P N + P H in a high pressure state with a working pressure P H in the case of a pressure increase in the piston arrangement, - the switchover device being configured as a circulation valve which comprises a first and at least one second valve device (8, 9) which are arranged jointly in a common valve block with in each case one valve element VB and VA which is mounted in an associated valve seat, - the two valve elements VA, VB being coupled in terms of movement via a connecting element for synchronous movement and being prestressed together by way of a spring in a basic position, in which the first valve seat is closed and the second valve seat is open, - and the first pressure pump being pressure-connected via the second open valve seat and the second pressure pump being pressure-connected directly to the piston arrangement, and, - in the case of a pressure increase in the piston arrangement as a consequence of an increase in the pressure on the output side of the second valve seat, the said second valve seat being closed counter to the force of the spring and the first valve seat being opened, - a partially opened position which is active between a closed position and an opened position being provided in the case of at least one valve seat (11, 12) of the valve device, in which partially opened position a defined partially opened volumetric flow flows through the valve seat (11, 12) which is smaller than the volumetric flow which is generated by the second pressure pump at the pressure P H,