Like the hydraulic pump, the hydraulic motor relies on the change of the working volume of the seal to realize the energy conversion, and also has a flow distribution mechanism. Under the action of the input high-pressure liquid, the liquid inlet chamber of the hydraulic motor changes from small to large, and the well produces torque to the rotating parts to overcome the load resistance torque and achieve rotation; At the same time, the liquid return chamber of the motor changes from large to small, and returns liquid to the suction port of the oil tank or pump, reducing the pressure. High pressure liquid constantly enters from the liquid inlet of the hydraulic motor and flows out from the liquid return port, so that the rotor of the hydraulic motor continuously rotates to do work.

Theoretically, except for the hydraulic pump with valve type flow distribution, other forms of hydraulic pump and hydraulic motor are reversible and can be used mutually. In fact, due to different performance and requirements, pumps and motors of the same type are still different in structure.

(1) The hydraulic motor shall be capable of forward and reverse rotation, so its internal structure must be symmetrical. The hydraulic pump usually rotates in one direction, and there is no such restriction in structure.

(2) The speed range of hydraulic motor is large, especially when the speed is low, it should be able to ensure normal operation, so rolling bearing or hydrostatic sliding bearing should be used; If dynamic sliding bearing is adopted, it is not easy to form lubricating oil film. However, the speed of hydraulic pump is high and the change is generally small, so there is no such requirement.

(3) The hydraulic motor should have good starting characteristics and low speed stability. Therefore, the starting torque and efficiency of the motor should be improved as much as possible, and the pulsation of torque shortening should be reduced.

(4) The hydraulic motor is driven to rotate by the liquid with pressure input, so the initial sealing must be ensured without self suction. The hydraulic pump must generally have self-priming capacity.