Gear Pumps and Straight Spur Internal by Cardiff Metropolian University

Pulsation Damper choice for Gear pumps of the Straight, Spur, and Internal Gear, types. Simple external Gear Pumps are usually for high rpm producing high frequency Spur - or "progressive" gears are used for higher viscosity and lower RPM, producing less pulsation. "Internal Gears" are usually run even slower and produce small volumetric pulses.

A gear pump uses the meshing of gears to pump fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications. Gear pumps are also widely used in chemical installations to pump fluid with a certain viscosity. There are two main variations; external gear pumps which use two external spur gears and internal gear pumps which use an external and an internal spur gear. Gear pumps are positive displacement (or fixed displacement), meaning they pump a constant amount of fluid for each revolution.

As the gears rotate they separate on the intake side of the pump, creating a void and suction which is filled by fluid. The fluid is carried by the gears to the discharge side of the pump, where the meshing of the gears displaces the fluid. The mechanical clearances are small, on the order of a thousandth of an inch (micrometers). The tight clearances, along with the speed of rotation, effectively prevent the fluid from leaking backwards.

Rigid design of the gears and housing allow for very high pressures and the ability to pump highly viscous fluids. Many variations exist, including; helical and herringbone gear sets (instead of spur gears), lobe shaped rotors similar to Roots Blowers (commonly used as superchargers), and mechanical designs that allow the stacking of pumps.