According to the working principle, the hydraulic pump can be divided into four types, as follows.
1. Gear pump
It is small in volume, simple in structure, not strict in oil cleanliness requirements, and cheaper in price; however, the pump shaft suffers from unbalanced force, serious wear, and large leakage. external engagement gear pump when the gear rotates, in cavity a, the volume increases gradually due to the tooth disengagement, forming a vacuum to draw oil from the oil tank, with the rotation of the gear, the oil filled in the tooth slot is taken to cavity B, in cavity B, the volume decreases gradually due to the tooth engagement, discharging the hydraulic oil using the change of the closed volume formed by the tooth and the pump housing to complete the function of the pump.
它体积小，结构简单，对油液清洁度要求不严格，价格便宜，但泵轴受力不平衡，磨损严重，泄漏量大。 外啮合齿轮泵 齿轮转动时，在a腔中，由于齿分离，容积逐渐增大，形成真空从油箱中吸油，随着齿轮转动，齿槽中的油被带到B腔，在B腔中，容积因齿啮合而逐渐减小，排出液压油 利用齿和泵壳形成的闭合容积的变化来完成泵的功能。
2. Vane pump
It is divided into double acting vane pump and single acting vane pump. The pump has the advantages of uniform flow, stable operation, low noise, higher working pressure and volumetric efficiency than gear pump, and more complex structure than gear pump. when the rotor rotates, the tip of the blade clings 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 surface of the rotor and the stator first absorbs oil from small to large, and then discharges oil from large to small. When the blades rotate for a circle, two oil suction and two oil discharge are completed. The function of the pump is completed by using the volume change between the blades inserted into the rotor slot.
3. Plunger pump
With high volume efficiency and small leakage, it can work under high pressure, mostly used in high-power hydraulic system; however, with complex structure, high requirements for material and processing accuracy, high price and high requirements for oil cleanliness. Generally, the plunger pump is used when the gear pump and vane pump cannot meet the requirements. There are some other forms of hydraulic pump, such as screw pump, but the application is not as common as the above three. The plunger pump is composed of a cylinder body and a plunger. The plunger moves back and forth in the cylinder body, sucks oil when the working volume increases, and drains oil when the working volume decreases. The radial load is balanced by the big bearing around the cylinder block to limit the inclination of the cylinder block. The transmission shaft only transmits torque and the shaft diameter is small. Because of the inclination moment of the cylinder, the manufacturing accuracy is required to be high, otherwise the valve plate is easy to be damaged. A kind of
4. Screw pump