A gear pump is a positive displacement pump that uses the meshing of gears to pump fluid. Most gear pumps are available in either aluminum or cast iron flanges, and are in one of four groups below. The higher the pump group, the large the displacement and body size. There is some overlap in sizing between groups, so if your application does not meet the speed requirements or isn't as robust as you'd prefer, you may go up one group size to find a better-suited pump. Rotation of all gear pumps is based on the rotation of the pump shaft when the pump shaft is facing directly toward you.