The internal-gear pump also uses a pair of intermeshing gears, but now a spur gear rotates within an annular internal gear, meshing on one side of it. Both gears are divided on the other side by a crescentshaped separator. The drive shaft turns the spur gear that meshes with the annular internal gear driving it— meaning that both gears will rotate in the same direction. As the gear teeth come out of mesh, oil from the inlet is trapped between their teeth and the separator and unloaded to the outlet. As with the external-gear pump, when the gear teeth mesh, a seal is formed, preventing back-up.
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