Know Your Pumps: Internal Gear Pumps

Sometimes there’s nothing quite like a reminder about the basics of various product categories. So we thought we’d take the time to review some of the major pump categories. Starting with the ever reliable Internal Gear Pump.

How Does Internal Gear Pumps Work?

The crescent internal gear pump has an outer or rotor gear that is generally used to drive the inner or idler gear. The idler gear, which is smaller than the rotor gear, rotates on a stationary pin and operates inside the rotor gear.

The gears create voids as they come out of mesh and liquid flows into the pump. As the gears come back into mesh, volumes are reduced and liquid is forced out the discharge port. Liquid can enter the expanding cavities through the rotor teeth or recessed areas on the head, alongside the teeth. The crescent is integral with the pump head and prevents liquids from flowing to the suction port from the discharge port.

The rotor gear is driven by a shaft supported by anti friction bearings. The idler gear contains a journal bearing rotating on a stationary pin in the pumped liquid. Depending on shaft sealing arrangements, the rotor shaft support bearings may run in pumped liquid. Abrasive liquid can wear out a support bearing.

The speed of internal gear pumps is considered relatively slow compared to centrifugal types. Speeds of up to 1,150rpm are considered common, although some small designs operate up to 3,450 rpm. Because of their ability to operate at low speeds, internal gear pumps are well suited for high-viscosity applications and where suction conditions call for a pump with minimal inlet pressure requirements.

For each revolution of an internal gear pump, the gears have a fairly long time to come out of mesh allowing the spaces between gear teeth to completely fill and not cavitate. Internal gear pumps have successfully pumped liquids with viscosities above 1,320,000 cSt / 6,000,000 SSU and very low viscosity liquids, such as liquid propane and ammonia.

Internal gear pumps are made to close tolerances and are damaged when pumping large solids. These pumps can handle small suspended particulate in abrasive applications, but gradually wear and lose performance. This can be limited for a time by adjusting the pump end clearance (the closeness of the rotor gear to the head of the pump).

What Do We Use It For?

Internal gear pumps have successfully pumped liquids with viscosities above 1,320,000 cSt / 6,000,000 SSU including peanut butter, asphalt, chocolate and adhesives and very low viscosity liquids, such as liquid propane and ammonia.

Score Card

E = Excellent, G = Good, A = Average, P = Poor