What is the difference between internal gear pump and external gear pump

The difference between internal gear pump and external gear pump is: different composition, different principle and different leakage.
1、 Different composition
1. Internal gear pump: the internal gear pump is composed of a pair of internal gears which mesh with each other, crescent shaped parts and pump shell in the middle.
2. External gear pump: external gear pump is composed of external driving gear, driven gear, pump body, pump cover and safety valve.
2、 Different principles
1. Internal gear pump: the internal gear pump adopts the principle of internal gear engagement. The internal and external gear pitch circle is close to one side, and the other side is separated by the "crescent plate" on the pump cover. The driving internal gear on the main shaft drives the external gear to rotate in the same direction. At the inlet, the gears separate from each other to form a negative pressure and suck in the liquid. At the outlet, the gears are continuously embedded and meshed to squeeze the liquid out.
2. External gear pump: the external gear pump adopts the principle of sealing volume change, and the shell, front and rear end covers and gear teeth are composed of many sealing working chambers. When the gear rotates as shown in the figure, an oil suction cavity is formed on the right side as the gear disengages, and an oil pressure cavity is formed on the left side as the gear engages. The contact line of the tooth surface at the meshing point divides the gear into high and low pressure cavities, which plays the role of oil distribution.

3、 Different leakage
1. Internal gear pump: the internal gear pump has low discharge pressure and small leakage.
2. External gear pump: the external gear pump has high discharge pressure and large leakage.