The hydraulic pump is the power element of the hydraulic system. Its function is to provide pressure oil to the hydraulic system. From the perspective of energy conversion, it converts the mechanical energy output by the prime mover (such as the engine) into the pressure energy of the liquid that is easy to transport. The hydraulic motor belongs to the actuator, which can convert the pressure energy of the input liquid into the mechanical energy of the output shaft rotation, which is used to drag the load to do work. According to the structural form, hydraulic pumps and hydraulic motors can be specifically divided into gear type, vane type, plunger type and other types.
1. Hydraulic pump pressure
The working pressure of the hydraulic pump refers to the pressure of the oil output (or input) of the pump (or motor) during actual work, which is determined by the external load.
The rated pressure refers to the maximum pressure that can be continuously operated under normal working conditions according to the test standards. Its size is limited by life. If it exceeds the rated pressure, the service life of the pump (or motor) will be shorter than the designed life. When the working pressure is greater than the rated pressure, it is called overload.
2. Speed
The working speed refers to the actual rotation speed of the pump (or motor) when it is working.
The rated speed refers to the maximum speed that can be operated normally for a long time under the rated pressure. If the pump works at a speed exceeding the rated speed, it will cause insufficient oil suction, vibration and loud noise, and the parts will suffer cavitation damage and reduce their life.
The minimum stable speed refers to the minimum speed allowed for the normal operation of the motor. At this speed, the motor does not creep.
3. Displacement, flow
The displacement refers to the volume of liquid discharged (or input) obtained by the change in the geometric size of the sealed cavity for each revolution of the pump (or motor). The commonly used unit is ml/r (ml/rev). The displacement can be changed by adjustment to become a variable pump (or variable motor), and the displacement cannot be changed to become a fixed pump (or fixed motor).
The actual flow refers to the flow at the outlet (or inlet) of the pump (or motor) when it is working. Due to the internal leakage of the pump itself, its actual flow is less than the theoretical flow. Since the motor itself also has internal leakage, to achieve the specified speed, in order to compensate for the leakage, its input actual flow must be greater than the theoretical flow.
4. Efficiency
Volumetric efficiency, for hydraulic pumps, refers to the ratio of its actual flow to theoretical flow. For hydraulic motors, it refers to the ratio of its theoretical flow to actual flow.
Mechanical efficiency, for hydraulic pumps, refers to the ratio of its theoretical torque to its actual input torque. For hydraulic motors, the actual output torque is the torque after the theoretical torque overcomes the friction, so its mechanical efficiency is the ratio of the actual output torque to the theoretical torque.
