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Differences between Hydraulic Motor and Hydraulic Pump
Views: 14457 Update Date: Jan 03 , 2019

In principle, hydraulic motors and pumps are reciprocal, that is to say, they can be interchanged. However, due to their different purposes of use, there are some structural differences. The structure characteristics of the high-speed hydraulic motor are basically similar to those of the same type of pump. However, it should be noted that valve distributor hydraulic pump can not flow backwards, so it can not be used as a hydraulic motor, and there is no valve distributor high-speed motor.

1. From the definition of two kinds of hydraulic components, they are different. Hydraulic pumps are components that absorb mechanical kinetic energy to produce hydraulic energy. Hydraulic motors are just the opposite.

2. Hydraulic pump is connected with the prime mover, and the pump shaft has no additional radial load; while hydraulic motor is connected with the load, such as sprockets, pulleys, gears and so on, its main shaft will bear a higher radial load.

3. The low pressure chamber of the hydraulic pump is usually vacuum. In order to improve the oil absorption performance and anti-cavitation ability, the suction nozzle is usually larger than the high pressure nozzle; but the hydraulic motor has no such requirement.

4. Hydraulic motors need positive and negative rotation, so the internal structure should be symmetrical; and hydraulic pumps generally rotate in one direction, so there is no such requirement. For example, the blades of the vane motor can only be arranged radially, not inclined like the vane pump, otherwise, the blades will be broken when reversing; the distribution plate of the axial plunger motor requires symmetrical design, but the axial plunger pump is not; the gear motor must have a separate leakage tube, and can not directly lead the leakage into the low-pressure chamber like the gear pump.

5. The speed range of hydraulic motor is very wide, so it should be satisfied when choosing bearing form and lubrication mode. For example, low-speed hydrodynamic bearings, because it is difficult to form oil film, it is appropriate to choose rolling bearings or hydrostatic bearings; while hydraulic pumps, although high speed but small change, do not have this harsh requirement.

6. The minimum stable speed of hydraulic motor is low. Some hydraulic motors require variable speed and brake.

7. Hydraulic Motors should have large start-up torque to overcome static friction during start-up and sufficient start-up torque when the minimum pressure fluctuation occurs. For example, in order to reduce the internal friction of the hydraulic motor, the number of teeth of the gear motor is more; the compression coefficient of the axial clearance compensation device is smaller than that of the pump.

8. Hydraulic pumps must be structurally self-priming. The reason why point-contact axial plunger motors (with no springs at the bottom of the plunger) can not be used as pumps is that they have no self-priming ability.

9. The blade of vane pump is thrown out by centrifugal force to form working chamber; if it is used as motor, it will not work because the blade does not form external force of working chamber when starting.

10. In order to reduce friction, some plunger motors remove slippers and become point-contact hydraulic motors, while plunger pumps can not do without slippers.

11. The internal leakage of the same type of hydraulic motor is larger than that of the hydraulic pump. This is because the leakage direction of the hydraulic motor is the same as that of the motion direction, resulting in the motion speed involved. Hydraulic pumps are not.

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