The factors to be considered when selecting hydraulic motors are working pressure, speed range, operating torque, total efficiency, volume efficiency, slip characteristics, life and other mechanical properties as well as the installation conditions and appearance of mechanical equipment.
There are many kinds of hydraulic motors, the characteristics are not the same, should be for specific use to choose the appropriate hydraulic motor, Table 20-9-54 lists the characteristics of typical hydraulic motors. Low speed motors can be used in low speed applications. A high speed motor with a reducer can also be used. Both have their advantages in structural arrangement, cost, efficiency, etc., which must be carefully demonstrated.
After defining the type of hydraulic motor used, according to the required speed and torque from the product series can be selected to meet the needs of a number of specifications, and then use the characteristics of various specifications of the curve (or calculated) corresponding pressure drop, flow and total efficiency. This is followed by a comprehensive technical evaluation to determine a specification. If the original cost is most important, the minimum flow should be selected, so that pumps, valves, pipelines, etc., are minimal; If the operating cost is the most important, the highest total efficiency should be selected; If the working life is most important, the minimum pressure drop should be selected; Perhaps a compromise was chosen.
For motors that require low speed operation, check the minimum stable speed. In case of lack of data, the decision should be made after the actual test under the desired working conditions of the relevant system. To operate smoothly at very low speeds, the motor must have a constant leakage, a constant load, a certain oil return back pressure (0.3 to 0.5MPa) and at least 35mm2/s oil viscosity.
Bearing life is related to speed and load. If the load is halved, the bearing life is twice as long as the original. When the motor is required to start with load, the blocking torque shall be checked. When the hydraulic motor is used for braking, the braking torque shall not be greater than the maximum working torque of the motor.
In order to prevent the brake motor working as a pump from cavitation or loss of braking ability, it should ensure that the "oil suction port" of the motor has enough oil filling pressure. It can be realized by filling oil pump in closed loop or back pressure valve in open loop. When the hydraulic motor drives the load with large inertia, in order to prevent the motor of inertia movement from lacking oil in the process of stopping, a bypass check valve should be set in parallel with the motor to supplement oil. Hydraulic release mechanical brakes on the motor shaft should be used when long periods of time are required to prevent load movement.
