1. According to the rated speed (i.e. the input speed of hydraulic coupling or drive unit) and required transmission power of motor, refer to the power characteristic curve (P-n) and technical parameter schedule in the catalogue to select the model and specification of hydraulic coupling and drive unit.
2. When selecting a drive unit for YOCz acceleration type coupling, first divide the rated speed (nT) of working machine by the hydraulic efficiency (ηy=0.97) of hydraulic coupling to calculate the speed (nB) of pump impeller in the coupling, then divide the shaft power (PT) of working machine by the hydraulic efficiency of hydraulic coupling to calculate the power (PB) of pump impeller in the coupling. Select the required specification in the power characteristic diagram according to the values of PB and nB. 
3. The coefficient design must take into account the efficiency loss of hydraulic coupling or drive unit and shaft coupling. When making type selection matching for variable speed coupling, the design margin of the rated power of motor relative to the shaft power of working machine is 1.04~1.06; when making type selection matching for drive unit of coupling, the design margin of the rated power of motor relative to the shaft power of working machine is 1.06~1.08. 
4. The rated slip ratio of hydraulic coupling is 1.5~3%, the range of transmission power listed in the technical parameter table is that corresponding to the rated slip ratio in high efficiency area, the selection of coupling with the transmission power beyond the lower limit in the technical parameter table will be favorable to improving the transmission efficiency, but will reduce the cost performance. 
5. When the hydraulic coupling and drive unit are used for centrifugal machinery with M∝n2, the range of speed regulation is 1~1/5; when they are used for constant torque machinery with M=C, the range of speed regulation is 1~1/3. 
6. The characteristics of speed regulation when the hydraulic coupling is matched with different loads (see the attached characteristic curve diagram). 
7. When making type selection, the rotational direction of equipment must be indicated, i.e. when viewing from the end of motor, the input shaft of coupling and drive unit rotates clockwise or counterclockwise.