What is the difference between a hydraulic pump and a hydraulic motor?

Hydraulic pumps and hydraulic motors are essential hydraulic components on every excavator. Their structures and working principles are very similar. Some people outside the industry sometimes confuse the two. Some people say that hydraulic pumps and hydraulic motors are like a pair of lovers, one is the top and the other is the bottom. Some people say that hydraulic pumps and hydraulic motors are like generators and electric motors, one identity and two positions. Is this description correct? What is the difference between the two?

Similarities between hydraulic motors and hydraulic pumps:

(1) In principle, hydraulic motors and hydraulic pumps are reversible. If they are driven by an electric motor, the output is hydraulic energy (pressure and flow), which is a hydraulic pump; if pressurized oil is input, the output is mechanical energy (torque and speed), which becomes a hydraulic motor.

(2) In terms of structure, the two are similar.

(3) In terms of working principle, both use the change of sealed working volume to absorb and discharge oil. For hydraulic pumps, oil is absorbed when the working volume increases, and high-pressure oil is discharged when the working volume decreases. For hydraulic motors, high-pressure oil enters when the working volume increases, and low-pressure oil is discharged when the working volume decreases.

Differences between hydraulic motors and hydraulic pumps:

(1) Hydraulic pumps are energy devices, while hydraulic motors are actuators. Hydraulic pumps are conversion devices that convert the mechanical energy of motors into hydraulic energy, output flow and pressure, and hope for high volumetric efficiency; hydraulic motors are devices that convert the pressure energy of liquids into mechanical energy, output torque and speed, and hope for high mechanical efficiency.

(2) The direction of the output shaft of a hydraulic motor must be able to rotate forward and reverse, so its structure is symmetrical; while some hydraulic pumps (such as gear pumps, vane pumps, etc.) have clear regulations on the direction of rotation and can only rotate in one direction and cannot change the direction of rotation at will.

(3) In addition to the inlet and outlet ports, hydraulic motors also have separate leakage ports; hydraulic pumps generally only have inlet and outlet ports (except axial piston pumps), and the internal leakage oil is connected to the inlet port.

(4) The volumetric efficiency of hydraulic motors is lower than that of hydraulic pumps.

(5) Generally, the operating speed of hydraulic pumps is relatively high, while the output speed of hydraulic motors is relatively low.

In addition, the gear pump has a large suction port and a small discharge port, while the suction and discharge ports of the gear hydraulic motor are the same size.

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