Hydraulic system: How does a hydraulic pump work?

Hydraulic pumps are crucial core components in hydraulic systems. They can be categorized into various types based on their operating principles and structural form. Common hydraulic pump types include gear pumps, vane pumps, and plunger pumps, each with distinct operating principles, applications, and performance characteristics.

1. Classification of hydraulic pumps: can be classified according to flow regulation method and structure type

(1) Classification by flow regulation method

Hydraulic pumps can be divided into variable displacement pumps and fixed displacement pumps.

①Variable displacement pumps:

The output flow of variable displacement pumps can be adjusted according to demand and are suitable for systems where the flow requirements vary with the working conditions.

②Fixed displacement pumps:

The flow of fixed displacement pumps is fixed and cannot be adjusted. They are suitable for applications where the flow requirements are stable.

(2) Classification by pump structure type

The structural type of a hydraulic pump determines its performance characteristics. Common hydraulic pump types include gear pumps, vane pumps, and plunger pumps.

① Gear Pumps:

Gear pumps have a simple structure, are compact, low-cost, and require minimal oil cleanliness, making them suitable for low-pressure systems. Their advantages include low cost and simple manufacturing, making them widely used in applications requiring high flow rates but less precise precision. However, gear pumps are susceptible to unbalanced forces on their shafts, which can easily cause wear and leakage, resulting in less stable performance than other types of pumps.

② Vane Pump:

Vane pumps offer high volumetric efficiency, uniform flow, low noise, and smooth operation, making them suitable for medium-pressure hydraulic systems. While their structure is more complex than gear pumps and their price is higher, they offer superior volumetric efficiency and noise control, making them widely used in systems requiring uniform flow and high efficiency. However, their complex structure leads to higher manufacturing and maintenance costs.

③ Plunger Pump:

The plunger pump is the most superior type of pump, suitable for high-pressure, high-power hydraulic systems. It features extremely high volumetric efficiency and low leakage. It operates stably under high pressure and is widely used in high-power applications such as construction machinery and mining equipment. However, the drawbacks of the plunger pump are its complex structure, high price, and strict requirements for oil cleanliness and machining precision, resulting in high operating and maintenance costs.

2. Working principle of gear pump

A gear pump typically consists of two meshing gears. One gear rotates due to a drive source (such as a motor), causing the other gear to rotate accordingly. During rotation, the volume on one side of the meshing gears gradually increases, creating a partial vacuum that draws oil into the pump. As the gears rotate, oil is drawn into the pressure chamber and discharged through the outlet. Seals between the gears separate the suction and pressure zones throughout the process, preventing oil leakage.

Gear pumps come in two types: external and internal. Internal gear pumps are more compact, quieter, and offer superior sealing.

Gear pumps have the advantages of simple structure, low cost, and small size, making them suitable for medium- and low-pressure hydraulic systems. However, their disadvantages include lower efficiency, susceptibility to noise and vibration, and a limited pressure range.

3. Working principle of vane pump

Vane pumps are divided into single-acting vane pumps and double-acting vane pumps. Vane pumps are usually used in hydraulic systems where smooth flow and low noise are required.

(1) Working principle of double-acting vane pump:

The inner wall of the stator of a double-acting vane pump is approximately elliptical, and the rotor is eccentrically installed in the stator. When the rotor rotates, the vanes slide along with the change of the curve of the inner surface of the stator, and the volume of the sealed working chamber between the two adjacent vanes increases and decreases, forming the process of oil suction and oil pressure. In a complete rotation cycle, the rotor completes two oil suction and two oil pressure processes.

(2) Working principle of single-acting vane pump:

The inner surface of the stator of a single-acting vane pump is cylindrical, and the rotor is eccentrically installed in the stator. Under the action of centrifugal force and pressure oil, the vanes are tightly attached to the inner surface of the stator. When the rotor rotates, the volume of the sealed working chamber formed by the vanes gradually increases, forming oil suction; when the volume decreases, oil pressure is formed. For each rotation, the vanes complete one oil suction and one oil pressure process.

4. Working principle of plunger pump

A plunger pump is a high-efficiency, high-pressure hydraulic pump that is commonly used in hydraulic systems requiring high pressure and high power. The plunger pump uses the reciprocating motion of the plunger to achieve the oil suction and oil pressure process. It has high volumetric efficiency and can work under high pressure. The basic principle of the plunger pump is to use the suction and discharge valves to complete the oil suction and discharge process through the reciprocating motion of the plunger. The structure of the plunger pump can be divided into axial plunger pump and radial plunger pump.

(1) Axial plunger pump:

It has high volumetric efficiency and compact structure and is commonly used in medium and high pressure hydraulic systems. The displacement of the axial plunger pump can be adjusted by adjusting the inclination angle of the swash plate to adapt to load changes.

(2) Radial plunger pump:

It is commonly used in high-power, heavy-load hydraulic systems. Radial plunger pumps have high efficiency and small leakage, but their design and manufacturing requirements are high and the cost is high.