The Difference Between Hydraulic Pump and Hydraulic Motor

Hydraulic pump vs hydraulic motor

Hydraulic pumps and hydraulic motors are essential hydraulic components on every excavator, and their structure and working principle are very similar. Some people often confuse these two things.

Hydraulic pump

A hydraulic pump converts mechanical energy (such as the rotation of a motor) into pressure energy, and sends the pressure oil to places where work is required throughout the system.

The hydraulic motor converts pressure energy into mechanical energy, and the pressure oil drives the blades in the hydraulic motor to rotate, thereby driving the machinery connected to the hydraulic motor shaft to do work.

First, let’s look at the types of hydraulic pumps and hydraulic motors.

Classification of hydraulic pump

Divided by structure:

  • plunger pump
  • gear pump
  • vane pump

Divided by whether the displacement can be adjusted:

  • fixed displacement pump
  • variable displacement pump

Divided by oil discharge direction:

  • one-way pump
  • two-way pump

Divided by pressure level:

  • low pressure pump
  • medium pressure pump
  • medium high pressure pump
  • ultra high pressure pump

Gear pump:

relatively small in size, simple in structure, low in oil cleanliness requirements, and cheaper in price; however, the pump shaft is subject to unbalanced forces, severe wear, and large leaks. Gear pumps are widely used in mining equipment, metallurgical equipment, construction machinery, engineering machinery, agricultural and forestry machinery and other industries.

Vane pump:

  • double acting vane pump
  • single acting vane pump

The pump has uniform flow, stable operation, low noise, higher operating pressure and has volumetric efficiency, a more complex structure than a gear pump. High-pressure vane pumps are used in the hydraulic systems of lifting transport vehicles and engineering machinery.

Plunger pump:

high volumetric efficiency, small leakage, can work under high pressure, mostly used in high-power hydraulic systems; but complex structure, high requirements for materials and processing accuracy, expensive, and high oil cleanliness requirements. Plunger pumps are commonly used in automotive diesel engines to deliver high-pressure fuel.

Classification of hydraulic motors

Divided by structure:

  • gear type motor
  • vane type motor
  • plunger type motor

Divided by speed and torque range:

  • high speed motor
  • low speed motor

Geared hydraulic motor:

simple structure, cheap price, often used in places with high speed, low torque and low motion stability requirements. Such as driving grinders, fans, etc.

Vane type hydraulic motor:

small moment of inertia, sensitive action, low volumetric efficiency, soft mechanical characteristics, suitable for occasions above medium speed, low torque, and frequent starting and commutation.

Axial plunger motor:

high volume efficiency, large adjustment range, good low-speed stability, poor impact resistance, high-pressure system with high common language requirements.

Hydraulic pumps and hydraulic motors are energy conversion elements in hydraulic transmission systems. What is the difference between the two? How to differentiate?

1. In principle, hydraulic motors and pumps are reversible. If driven by a motor, the output is pressure energy (pressure and flow), so this is a hydraulic pump; if the pressure oil is input, and the mechanical energy (torque and speed) is output, so, it’s a hydraulic motor.

2. Structurally, these two are similar.

hydraulic motor

3. Hydraulic motors and hydraulic pumps have the same basic structural elements-a closed volume that can change periodically and a corresponding oil distribution mechanism. The working principle of the hydraulic motor and the hydraulic pump are both suction and discharge by utilizing changes in the sealed working volume.

For hydraulic pumps, oil is sucked when the working volume is increased, and high pressure oil is discharged when the working volume is reduced.

For hydraulic motors, high-pressure oil enters when the working volume increases, and low-pressure oil discharges when the working volume decreases.

8 differences between hydraulic motors and hydraulic pumps

1. The hydraulic pump is a conversion device that converts the mechanical energy of an electric motor into hydraulic energy. It outputs a flow rate and a pressure. It is expected that the volumetric efficiency is high.

The hydraulic pump

The hydraulic motor is a conversion device that converts the pressure energy of the liquid into mechanical energy, and outputs torque and speed. It is hoped that the mechanical efficiency is high.

Therefore, the hydraulic pump is an energy device, and the hydraulic motor is an actuator.

2. The steering of the output shaft of the 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 for steering, which can only be rotated in one direction and cannot be arbitrarily change direction.

the hydraulic motor

3. In addition to the oil inlet and outlet of hydraulic motors, there are separate oil leakage ports; hydraulic pumps generally have only oil inlet and outlet ports (except axial piston pumps), and the leaked oil inside is connected to the oil inlet.

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

5. Generally, the working speed of the hydraulic pump is relatively high, while the output speed of the hydraulic motor is low.

6. In addition, the gear pump has a large oil suction port and a small oil discharge port; while the gear hydraulic motor has the same suction and oil discharge port size.

7. Gear motor has more teeth than gear pump.

8. The vane of the vane pump must be installed diagonally, while the vane of the vane motor is installed radially.

The blades of the vane motor rely on the swallow spring at the root to press it against the surface of the stator, while the blades of the vane pump rely on the pressure oil and centrifugal force on the surface of the stator to press the blade.

From the working principle, both the hydraulic motor and the hydraulic pump work by changing the volume of the sealed working chamber, but because of the different use purposes of the two, many differences in the structure, so generally they cannot be directly interchanged with each other.

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