An internal rotary gear pump is a positive displacement pump which employs a rotor and idler gear assembly to generate its flow. The assembly is offset, using a crescent adjacent to the inner gear, all within an outer gear.. As the rotor gear drives the idler gear, the space caused by the crescent offsetting the gears and the meshing of the gear teeth displace the fluid, expelling it to the discharge port.
An internal rotary gear pump is typically specified for viscous fluids such as oils, bitumen, fats, syrups, chocolate and resins as the more viscous the product is, the more efficient the displacement aspect of the working principle becomes. An internal rotary gear pump can handle fluids with a viscosity of 100,000cSt!
An internal rotary gear pump employs a positive displacement principle. The pump features a casing in which a dual gear (an outer rotor gear and an internal idler gear) and crescent assembly is housed. As the rotor gear begins to turn, the idler gear rotates with the teeth beginning to mesh accordingly. It is the space between these gears and the meshing action which both draws in the fluid and displaces it. The crescent shape both offsets the idler gear and provides a seal between the suction and discharge ports.