Internal Gear Pump

An internal gear pump is a rotary positive displacement pump that moves liquid by using two gears in a “gear‑within‑a‑gear” arrangement. One gear — the rotor — has inward‑facing teeth, and it drives a slightly smaller idler gear with outward teeth. The idler is offset inside the rotor, and a crescent‑shaped seal between them forms enclosed chambers. As the gears rotate, liquid is drawn into expanding spaces between the teeth, carried around the pump casing, and then discharged as the spaces contract.

1. What is an internal gear pump?
It is a type of gear pump where one gear (the rotor) encloses and drives a smaller idler gear. A crescent seal in the pump head helps seal the fluid cavities formed by these gears, enabling fluid movement and consistent displacement with each revolution.

2. How does an internal gear pump work?
Liquid enters between the teeth of the rotor (outer gear) and idler (inner gear) at the suction side. As the gears rotate and the teeth separate, low pressure draws fluid in. The fluid travels around the pump in the locked cavities between gear teeth and casing. A crescent acts as a seal to prevent backflow. On the discharge side, the meshing of the gear teeth forces the fluid out of the outlet.

3. What are internal gear pumps used for?
They are used in many industrial applications because they can handle a broad range of fluid viscosities, from thin solvents to thick oils and adhesives — for example in chemical processing, food‑and‑beverage, asphalt, and similar industries.