Distinguish between internal and external gear pumps

Gear pumps are rotary positive displacement pumps. According to their structural characteristics, they are divided into internal gear pumps and external gear pumps. Internal and external gears can be distinguished literally, one is internal gear and the other is external gear. The external gear pump is mainly composed of main parts such as main and driven gears, the drive shaft, the pump body, and the side plate.

The main and driven gears mesh with each other in the pump body together with the two end caps and the pump body form a sealed working volume. The meshing point of the gears separates the left and right cavities, forming the suction and pressure oil cavities. When the gears are in the direction shown in the figure When rotating, the gear teeth in the oil suction chamber on the right side are disengaged, and the volume of the sealed working chamber continues to increase, forming a partial vacuum. Oil pressure chamber on the left. The gear teeth in the left oil pressure chamber are continuously engaged, which reduces the volume of the sealed working chamber, and the oil is squeezed and discharged to the system. This is the oil suction and oil pressure process of the gear pump. During the meshing process of the gear pump, the meshing point is along the meshing line, which separates the oil suction area and the oil pressure area. The external gear pump is suitable for the viscosity of 5~1500cSt. It is often used as a fuel delivery and booster pump in the fuel delivery system; it can be used as a fuel pump for delivery, pressurization, and injection in the fuel system; it can also be used as a lubricating oil pump for large equipment.

The internal gear pump adopts the principle of gear internal meshing. The pitch circles of the internal and external gears are close to one side, and the other side is separated by a “crescent plate” on the pump cover. The driving inner gear on the main shaft drives the outer gears to rotate in the same direction. At the inlet, the gears are separated from each other to form a negative pressure to suck in the liquid, and the gears are continuously embedded and meshed at the outlet to squeeze the liquid out. Due to this unique structure, it is especially suitable for conveying media with high viscosity, the viscosity range is: 1.0cSt-300000cSt

The lift that the external gear pump can achieve is much larger than that of the internal gear pump, mainly because the double-bearing load capacity of the external gear pump is larger. For a gear pump, if the flow rate is not considered, how high the liquid column can depend on the speed of the pump, the flow rate of the outlet line, the gap between the gear pump rotors, and between the rotor and the casing, the viscosity of the conveyed liquid, and the pressure of the outlet safety valve. The setting value is the pressure resistance of the manufacturing material, etc., the clearance of the gear pump is constant, and the relationship with the motor power is not very large. It is proportional to the speed of the motor and pump. Under ideal conditions, the positive displacement pump can reach the infinite head, but the reality does not exist.


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