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

Hydraulic pumps and motors are indispensable hydraulic components on every excavator, and their structures and working principles are very similar. Sometimes small whites outside some industries confuse the two. Some people say that hydraulic pumps and motors are like a couple of sweethearts, one against the other; Some people say that hydraulic pumps and motors are like generators and motors, in one position or another. Is that a correct description? What's the difference between them?

Similarities between a Hydraulic Motor and a hydraulic pump:

(1) In principle, the hydraulic motor and the hydraulic pump are reversible. If the motor drive is used, the hydraulic energy (pressure and flow) is output, which is the hydraulic pump; When pressure oil is input and mechanical energy (torque and speed) is output, it becomes a hydraulic motor.

(2) Structurally, they are similar.

(3) In terms of working principle, they both absorb and drain oil by using the change of working volume of seal. For hydraulic pumps, oil is sucked 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 pumps:

(1) Hydraulic pump is an energy device and hydraulic motor is an actuating element. Hydraulic pump is a device which converts mechanical energy of motor into hydraulic energy. It outputs flow rate and pressure and expects high volumetric efficiency. Hydraulic motor is a device which converts pressure energy of liquid into mechanical energy, outputs torque and speed, hoping for high mechanical efficiency.

(2) The rotation of the output shaft of the hydraulic motor must be positive and reverse, so its structure is symmetrical; While some hydraulic pumps (such as gear pump, Vane Pump, etc.) have specific steering regulations, they can only turn in one direction and can not change the direction of rotation at will.

(3) In addition to inlet and outlet ports, the hydraulic motor also has separate leakage ports; Hydraulic pumps generally only have inlet and outlet ports (except axial piston pumps), in which leakage fluid is connected with inlet port.

(4) Volumetric efficiency of hydraulic motor is lower than that of hydraulic pump.

(5) Generally, the working speed of the hydraulic pump is higher, while the output speed of the hydraulic motor is lower. In addition, the suction port of gear pump is large and the discharge port is small, while the suction and discharge port of gear hydraulic motor are the same size.