Do you know how does an internal gear pump work?

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internal gear pump work

A gear pump is a device used to draw oil from a tank and then fill it with a higher pressure. The gear pump structure consists of two gears that mesh together and the casing.

Along with the development of technology today, more and more types of pumps are being introduced on the market. In which industrial gear pumps are favored by their application features in almost every field from low to high. 

Gear pumps are classified: based on the matching characteristics of two gears, which are internal and external, there are two types of gear pumps with internal gearing and external gear pumps. External gear pumps are mainly used in hydraulics, while internal gear pumps are used extensively in explosive engines such as oil and lubricant pumps.

Internal gear pump

Internal gear pump is one of the two typical gear pumps commonly used with the ability to pump priming, the ability to run dry in a short time. The pump has internal teeth that mesh with the gear and has a crescent-shaped piece of metal placed in the gear to create a liquid-filled space to bring out the oil, solution and substances to be pumped out.

The advantages of internal gear pumps are compact structure, small size, light weight, long service life, low pressure pulsation and noise; their disadvantages are complex tooth profile, high machining accuracy requirements, and high cost. Now the powder metallurgy process is used to press molding, the cost is reduced, and the application is developed. Under the condition of constant speed, the pump whose output flow can be changed is called variable pump, and the one that cannot be changed is called fixed pump. The displacement of the gear pump cannot be changed, so it is a quantitative pump.


  • Internal gear pumps have a very low rotational speed, so you have to use a gearbox to convert the rotational speed of the motor. Thus, the price of this pump is always higher than that of an external gear pump. Internal gear pumps use a variety of materials such as stainless steel 304 or 316.
  • Internal gear pumps are very flexible. They are commonly used to transport fluids such as hydraulic oil and fuel oil, they can pump thick liquids such as asphalt, chocolate and glue.

Internal gear pumps are undisturbed, self-priming, and can run dry for short periods of time. They are also reversible, meaning the same pump can be used to feed and drain oil.

Working principle of internal gear pump

  1. The active gear is driven by the crankshaft, when the active gear rotates, the passive gear rotates, and the oil is sucked from the crankcase into the pump and then sent to the fine filter. This type of pump has a very compact structure, so it is difficult to manufacture. Fluid transport according to the principle of “gears”. A crescent-shaped element divides the liquid and acts as a separator between the suction and discharge ports.
  2. The rotor and the drive gear form a bulkhead between the discharge and intake. The liquid is forced out along the way that pushes the oil away. They are kind of precision series pumps which transfer a precise amount of fluid to the other end.

So, this is how an internal Gear Pump works. Whether internal or external, gear pumps have made the industrial work smooth and easy.

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