The difference between hydraulic motor and hydraulic pump

1. Hydraulic motors and hydraulic pumps

In principle, hydraulic motors and pumps are mutual, that is to say, they are interchangeable. However, because they are used for different purposes, there are some structural differences. The structural characteristics of the high-speed hydraulic motor and the same type of pump are basically similar. However, it should be noted that split-valve hydraulic pumps cannot backflow, so they cannot be used as hydraulic motors, and there is no split-valve high-speed motor.

2. Understand the difference between hydraulic motors and hydraulic pumps

From the definition of the two hydraulic components, they are different. The hydraulic pump is a component that absorbs mechanical kinetic energy to produce hydraulic energy. Hydraulic motor is the opposite. The hydraulic pump is connected to the prime mover, the pump shaft has no additional radial load; when the hydraulic motor is connected to the sprocket, pulley, gears and other loads, its main shaft will be subject to higher radial load. The low-pressure chamber of a hydraulic pump is usually a vacuum. To improve suction performance and erosion resistance, the suction nozzle is usually larger than the high pressure nozzle; this is not required for hydraulic motors.

Hydraulic motors require forward and reverse rotation, so the internal structure has to be symmetrical; whereas hydraulic pumps generally rotate in one direction, so there is no such requirement. For example, the blade of the vane motor can only be arranged radially, can not be tilted like the vane pump, otherwise the blade will break when changing direction; axial piston motors require symmetrical design of the distribution plate, while the axial piston pump is not; gear motor must have a separate leak tube, can not be like the gear pump will leak directly into the low pressure chamber.

Hydraulic motor speed range is wide, in the choice of bearing form and lubrication method should meet. For example, low-speed dynamic pressure bearings, because it is not easy to form an oil film, it is appropriate to use rolling bearings or static bearings; and hydraulic pumps, although high speed but small changes, without this demanding requirements. Hydraulic motor minimum stable speed is low. Some hydraulic motors need variable speed and braking. Hydraulic motors should have a large starting torque to overcome static friction during start-up and have sufficient starting torque when pressure fluctuations are at their lowest. For example, to reduce internal friction in hydraulic motors, gear motors have a high number of teeth; the compression coefficient of the axial clearance compensation device is less than that of the pump.

The hydraulic pump must be self-priming in construction. Point contact axial piston motors (no spring at the bottom of the plunger) cannot be used as pumps because they are not self-priming. Vane pump vanes are thrown out by centrifugal force to form a working chamber; if used as a motor, the vanes do not form an external force in the working chamber when started and therefore do not work. To reduce friction, some plunger motors have had the slipper removed and become point contact hydraulic motors, whereas plunger pumps cannot be used without the slipper.