If hydraulic pumps are classified according to their working principles, they can be roughly divided into the following four types.

2025-05-19

1、 Screw pump

One driving screw and two driving screws mesh with each other, and the meshing line of the three screws divides the spiral groove into several sealing bodies. When the screw rotates, the sealing volume moves axially to achieve the purpose of oil suction and discharge. The function of the pump cannot be changed. The radial load without flow pulsation is smaller, larger, and heavier than that of twin-screw type.

2、 Gear pump

It has a small volume, simple structure, and does not require strict cleanliness of the oil. It is cheap, but the pump shaft is unbalanced in force, severely worn, and has a large amount of leakage. When the gear of the external meshing gear pump rotates, the volume gradually increases due to tooth separation in chamber A, forming a vacuum to suck oil from the oil tank. As the gear rotates, the oil in the tooth groove is carried to chamber B. In chamber B, the volume gradually decreases due to tooth meshing, and the hydraulic oil is discharged. The function of the pump is completed by the change in the closed volume formed by the teeth and pump casing.

3、 Vane pump

Divided into double acting vane pumps and single acting vane pumps. This pump has the advantages of uniform flow rate, stable operation, low noise, high working pressure and volumetric efficiency, and more complex structure compared to gear pumps. When the rotor rotates, the blade tips are tightly attached to the inner surface of the stator under the action of centrifugal force and pressure oil. In this way, the working volume formed by the two blades and the inner surfaces of the rotor and stator first absorbs oil from small to large, and then discharges oil from large to small. When the blade rotates once, it completes two oil suction and two oil discharge operations. The function of the pump is achieved by the volume change between the blades inserted into the rotor slot.

4、 Plunger pump

High volumetric efficiency, low leakage, can work under high pressure, and is commonly used in high-power hydraulic systems. However, the structure is complex, requiring high material and processing accuracy, high price, and high oil cleanliness. Generally, plunger pumps are used when gear pumps and vane pumps cannot meet the requirements. Hydraulic pumps also have other forms, such as screw pumps, but their applications are not as common as the three forms mentioned above. A plunger pump consists of a cylinder body and a plunger. The plunger moves back and forth in the cylinder, absorbing oil when the working volume increases and discharging oil when the working volume decreases. The radial load is balanced by the large bearings around the cylinder block to limit the tilting of the cylinder block. The drive shaft only transmits torque and has a small shaft diameter. Due to the tilting torque of the cylinder, high manufacturing accuracy is required, otherwise it is easy to damage the valve plate.