Internal and External Gear Pumps

Internal gear pumps have a larger rotor (outer gear) and an idler (inner gear) that is smaller. The two gears mesh together and create voids where the liquid flows. The liquid is sucked into the void and as the gears mesh, they reduce the volume in the void and then force the liquid out the discharge at a higher pressure. External gear pumps are similar to internal gear pumps with the difference being identically sized gears. As the gears mesh, they pull liquid, reduce the volume and discharge it. External gear pumps are not suited for high suction applications.
    
Lobe Pumps

The lobe pump, or rotary lobe pump, has a similar design to an external gear pump with the exception that the gears have larger, curved ends. The lobes rotate but do not contact one another. As they rotate, a void larger than the gear pump is formed that pulls the liquid into the suction side. The volume is reduced and the liquid is expelled at high pressure into the discharge line.

Vane Pumps

A vane pump or sliding vane pump has a central rotor with radial slots. It is positioned slightly off-center. The vanes fit snugly inside the rotor slots. As the pump rotates, the vanes slide in and out of the slots. The pumping action is created by the expanding and contracting liquid void volumes contained by the rotor, vanes and housing. Vane pumps produce high pressure discharges and are ideal for thin liquids.

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