Structural differences between external gear pumps and internal gear pumps

Structural differences between external gear pumps and internal gear pumps



1、 Structure of External Gear Pump


The external gear pump is mainly composed of a pair of bearing supported gears and a housing (with front and rear covers). The drive shaft extends out of the front cover and is sealed by a shaft seal. The bearing force is absorbed by special bearing pads (thin-walled bearings) with sufficient elasticity, resulting in surface contact rather than line contact.


External gear pump

They can also ensure good wear resistance, especially at low speeds. A 12 tooth gear pump can minimize flow pulsation and noise. By using a compression force proportional to the oil discharge pressure, internal sealing can be achieved to ensure optimal efficiency.


At the end of the gap between the gear teeth that transport pressure oil, sealing is achieved by bearings. By introducing the working pressure into the rear of the bearing, the sealing area between the gear teeth and the bearing can be controlled. Special sealing is the boundary of this area. The radial clearance of the gear tooth tip is sealed by internal force, which presses the tooth tip tightly against the housing.



2、 Internal gear pump structure


Oil suction and pressure process: The small gear shaft 3 supported by pressure drives the inner ring gear 2. In the oil absorption zone at an angle of approximately 90 °, the rotational motion process increases the volume of the oil absorption chamber. This creates a negative pressure that causes the oil to flow into the suction chamber. The crescent shaped oil distribution plate component 9 separates the suction chamber and the pressure chamber. In the oil pressure chamber, the teeth of the small gear shaft 3 re-enter the teeth of the ring gear 2. The liquid is squeezed out through the pressure oil channel P.


Internal gear pump

Axial compensation: The axial compensation force FA acts in the oil pressure zone and acts on the axial plate 5 through the pressure zone 10. The end face gap between the rotating component and the fixed component in the axial direction becomes relatively small, thereby ensuring optimal axial sealing of the oil pressure chamber.


Radial compensation: The radial compensation force FR acts on the oil distribution plate 9.1 and the oil distribution plate frame 9.2.


Due to work pressure, the oil distribution plate 9.1 and the oil distribution plate holder 9.2 are pressed against the tooth tips of the small gear shaft 3 and the inner ring gear 2. The area ratio between the oil distribution plate and the oil distribution plate frame, as well as the position of the sealing roller 9.3, are designed to achieve a gap seal with as little leakage as possible between the inner gear ring 2, the oil distribution plate assembly 9, and the small gear shaft 3.


The spring element below the sealing roller 9.3 can provide sufficient squeezing force even under extremely low pressure.


Hydraulic dynamic pressure and hydraulic static pressure bearings: The force acting on the small gear shaft 3 is received by the radial sliding bearing 4 lubricated by hydraulic dynamic pressure, and the force acting on the inner ring gear 2 is received by the hydraulic static pressure bearing 11.


Mesh: It is the involute tooth mesh. Due to its large meshing length, it has very small flow and pressure pulsations; This extremely small pulsation characteristic has made outstanding contributions to low-noise operation.