A control device (1) for a hydraulic elevator drive (11) with a first and second control valve (21, 22) for controlling the volume flow of a working fluid wherein the flow is detected (610) and compared (52) with a reference value (51) and a pilot (3) with a first and second pilot valve (31, 32) to control the first and second control valve in which the pilot has an actuator (4) and a coupler (33) that can activate and decouple each pilot valve. A hydraulic drive system (16) for an elevator having the control device and a method for retrofitting such a drive system. The control device is simple in design and operation and provides for cost advantages and an increased reliability. The hydraulic drive system with the control device permits an overall improvement in the starting quality of an elevator by automatic compensation of drive-side and output-side interference variables and load-induced fluctuations in the working fluid pressure.