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Gear Pumps

What is a gear pump?

Gear pumps are the most common type of positive displacement pump. They are considered fixed displacement pumps, meaning that an unchanging volume of liquid moves through at a constant rate provided the pump speed is constant.

Gear pumps generally work within the following ranges:

  • Flow rate ranges between 1 and 1,500 gpm
  • Total head (pressure) ranges between 10 and 2,500 psi
  • Horse power ranges between 0.5 and 2,000 hp
  • Viscosity ranges from clear liquids to 2 million SSU

How do they work?

Gear pumps work by using a rotating set of gears, which are spur or helical for standard types, and herringbone gears for specialty applications. The moving gears create suction at the inlet port of the pump that draws the fluid into the gears. The rotating gears then move the liquid between the teeth of the gears and the walls of the casing and direct the fluid flow to the discharge port, where the pressure continues to build as the volume of the casing gets smaller near the outlet of the pump.

There are two main types of gear pumps, which both consist of a drive gear (the gear that pushes) and an idler (the gear that is pushed). External gear pumps, which are usually found in lower flow applications, use two side-by-side spur, helical, or herringbone gears that mesh together; while internal gear pumps consist of a smaller idler gear that fits inside of the larger drive gear. The internal configuration contains a crescent-shaped internal barrier that helps direct flow through the pump. Both types often contain built-in pressure relief valves to protect the pump and the system in the event that a valve in the discharge piping is inadvertently closed.

Gear pumps are designed to have very tight clearances and are ideal for thicker, high viscosity fluids such as automotive oils, plastics, paint, adhesives, or soaps.

Here is some additional information on gear pump operation and maintenance.

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