Both hydraulic pumps and hydraulic motors are energy conversion components in a hydraulic transmission system.

What is the difference between the two?

How to differentiate?

Where are they applied?

Next, TorcStark will introduce the difference between hydraulic motors and hydraulic pumps in detail.

Similarities between hydraulic motors and hydraulic pumps

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

Structurally, the two are similar.

Hydraulic Pump

The hydraulic motor and the hydraulic pump have the same basic structural elements-a closed but cyclically variable volume and corresponding oil distribution mechanism. The working principle of hydraulic motors and hydraulic pumps is to use the change of the seal working volume to suck and discharge oil.

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.

The difference between hydraulic motors and hydraulic pumps

  1. A hydraulic pump is a conversion device that converts the mechanical energy of a motor into hydraulic energy. It outputs flow and pressure, and it is hoped that its volumetric efficiency is high; a hydraulic motor is a conversion device that converts the pressure energy of liquid into mechanical energy, and outputs torque and speed. It’s hoped to have high mechanical efficiency. Therefore, the hydraulic pump is the energy device, and the hydraulic motor is the 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. And some hydraulic pumps (such as gear pumps, vane pumps, etc.) have clear regulations for steering, and they can only rotate in one direction, and can’t change the direction at will.
  3. In addition to the oil inlet and outlet ports, hydraulic motors have separate oil leakage ports; hydraulic pumps generally only have oil inlet and outlet ports (except for axial piston pumps), and the leaking oil is connected to the oil inlet port.
  4. The volumetric efficiency of hydraulic motors is lower than that of hydraulic pumps.
  5. Generally, the working speed of hydraulic pumps is relatively high, while the output speed of hydraulic motors is relatively low.
  6. In addition, the oil suction port of the gear pump is large and the oil discharge port is small, while the oil suction and discharge ports of the gear hydraulic motor are the same size.
  7. The gear motor has more teeth than the gear pump.
  8. The vane of the vane pump must be installed obliquely, while the vane of the vane motor is installed radially. The vane of the vane motor is pressed against the surface of the stator by the swallow spring at the root, while the vane of the vane pump is pressed against the surface of the stator by the pressure oil at the root and centrifugal force.

In terms of working principle, both hydraulic motors and hydraulic pumps rely on changes in the volume of the sealed working chamber. However, due to the different purposes of use, there are many differences in structure, and generally they cannot be used directly and inversely.

Hydraulic pump classification

According to the structure: plunger pump, gear pump, vane pump three categories.

According to whether the displacement is adjustable, it can be divided into: quantitative pump and variable pump.

According to the direction of oil discharge: one-way pump, two-way pump.

According to the pressure level: low pressure, medium pressure, medium high pressure, ultra high pressure pump.

Gear pump: small in size, simple in structure, less demanding on oil cleanliness, and cheaper in price; but the pump shaft is subject to unbalanced force, severe wear, and large leakage.

Gear pumps are widely used in mining equipment, metallurgical equipment, construction machinery, construction machinery, agricultural and forestry machinery and other industries.

Vane pump: It is divided into double-acting vane pump and single-acting vane pump. This kind of pump has uniform flow, stable operation, low noise, higher working pressure and volumetric efficiency than gear pumps, and more complicated structure than gear pumps. High-pressure vane pumps are used in the hydraulic systems of lifting and transporting vehicles and construction machinery.

Plunger pump: high volumetric efficiency, low leakage, can work under high pressure, mostly used in high-power hydraulic systems. However, this kind of pump has a complex structure, high requirements for materials and processing accuracy, high prices, and high requirements for oil cleanliness. Plunger pumps are commonly used in automobile diesel engines to deliver high-pressure fuel.


Hydraulic motor classification

According to the structure, it is divided into several main types: gear type, vane type and plunger type.

According to the speed and torque range, it is divided into: high-speed motor and low-speed motor.

Gear-type hydraulic motors are simple in structure and low in price. They are often used in occasions where high speed, low torque and smooth motion are not required, such as driving grinders, fans, etc.

The vane-type hydraulic motor has small moment of inertia, sensitive action, low volumetric efficiency, and soft mechanical characteristics. It is suitable for occasions above medium speed, low torque, and frequent starting/reversing.

The axial piston motor has high volumetric efficiency, large adjustment range, good low-speed stability, and poor impact resistance. It is often used in high-pressure systems with higher requirements.

Hydraulic motors and hydraulic pumps seem to be the same, but in fact there are many differences, in terms of classification, principles and applications.

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