1. Select the model and specification of fluid coupling and transmission device by referring to the power characteristic curve (P-n) and technical parameter table in the product catalog based on the rated motor speed (i.e., input speed of fluid coupling or transmission device) and required transmission power. 2. When selecting YOCz speed-increasing coupling transmission device, first calculate the pump wheel speed \(n_B\) of the coupling by dividing the rated speed \(n_T\) of the working machine by the hydraulic efficiency of the coupling (\(\eta_y=0.97\)). Then calculate the pump wheel power \(P_B\) of the coupling by dividing the shaft power \(P_T\) of the working machine by the hydraulic efficiency of the coupling. Select the required specification from the power characteristic diagram according to the values of \(P_B\) and \(n_B\). 3. Efficiency losses of fluid coupling, transmission device and coupling shall be taken into account in coefficient design. For variable-speed coupling selection, the design margin of rated motor power relative to the shaft power of the working machine is 1.04~1.06; for coupling transmission device selection, the design margin is 1.06~1.08. 4. The rated slip of fluid coupling ranges from 1.5% to 3%. The power transmission range listed in the technical parameter table refers to the power transmission within the high-efficiency zone corresponding to the rated slip. Selecting a coupling with power below the lower limit of the parameter table helps improve transmission efficiency but reduces cost performance. 5. When fluid couplings and transmission devices are applied to centrifugal machinery with \(M\propto n^2\), the speed regulation range is 1 ~ 1/5. When applied to constant-torque machinery with constant torque \(M=C\), the speed regulation range is 1 ~ 1/3. 6. Speed regulation characteristics of fluid couplings matched with different loads. 7. The rotation direction of equipment must be specified during model selection, namely clockwise or counterclockwise rotation of the input shaft of coupling and transmission device viewed from the motor rear end.