The hydraulic motor is the actuating element that converts the hydraulic energy of the hydraulic pump into mechanical energy. Theoretically, the hydraulic motor and hydraulic pump are reversible, and their structures are basically the same. Refer to the method of hydraulic pump for troubleshooting. But in fact, due to different purposes, the structures of the same type of hydraulic motor and hydraulic pump are also different. In order to find out the cause of the fault, we must understand the difference between the two.

The low-pressure chamber of the hydraulic pump is generally vacuum. In order to improve the oil absorption performance and cavitation resistance, the import is generally larger than the export. The pressure in the low-pressure chamber of the hydraulic motor is slightly higher than the atmospheric pressure, so there is no such requirement.

The hydraulic motor must be in positive and reverse rotation, and the internal structure is symmetrical. The hydraulic pump generally rotates in one direction, without symmetrical requirements. For example, the gear hydraulic motor must have an independent oil leakage passage and cannot be introduced into the low-pressure chamber like the hydraulic pump; The vane hydraulic motor is arranged axially in the rotor, and the vane of the vane pump must be placed forward or backward.

The speed range of the hydraulic motor is very wide, which requires stable low speed and large starting torque. The speed of hydraulic pump is generally very high, and the self-priming capacity compared with the structure of hydraulic pump must be guaranteed, while the hydraulic motor has no such requirement. The point contact shaft plunger hydraulic motor has no spring at the bottom of the plunger and cannot be used as a hydraulic pump because it has no self suction capacity.

As a result of the above reasons, in fact, many types of hydraulic pumps and hydraulic motors cannot be used together, and the causes and diagnosis of faults are different.

The special problems of hydraulic motor are starting torque and starting efficiency, which are also related to the fault of hydraulic system.