There exist today many versions of gear pumps, each with its own set of drawbacks and strengths. The three main pumps that I am interested in are internal, external and cycloidal gear pumps. Internal are constructed with an internal ring spur gear with a smaller spur pinion inside of it that mesh together and force the fluid to travel in a circular motion and be squeezed out at the end of the circle. They rotate at different rates because of their different number of teeth and have different central axes in order to mesh. In combination with a spacer that prevents fluid backflow, these two gears, which rotate in the same direction, pull fluid from one side to the other, and then expel the fluid as the gears attempt to compress it while approaching their contact region.

When dealing with incompressible fluids, this effect can be leveraged to produce a consistent and powerful head pressure but can lack in the area of flowrate when compared to traditional impeller pumps. External gear pumps function similarly but instead feature two external spur gears within a cavity meshing and rotating. The synchronized motion of the gears generates a net directional flow in one direction around the outside of the cavity and an opposing net flow in the middle. However, the fluid flow through the center Is largely inhibited again by the meshing of the gears, allowing the pump to function with a much larger net flow around the outside and barely any backflow through the meshing teeth.