How Hydraulic Gear Pumps Work

There are several components that make up a hydraulic system and enable it to be a dependable way to provide power and force. Hoses, reservoirs, cylinders and the fluid itself each provide a specific function that is critical to system operation. Another essential piece of equipment is the pump. There are various designs in existence and the one chosen can depend on the application and the amount of pressure involved. One of the more common types is a hydraulic gear pump. This is a mechanical way of delivering fluid to the rest of the system.  

How Hydraulic Gear Pumps Work

Classifying Based on Design

There are two main classifications of gear pumps – external and internal. The names are a bit deceiving since in both cases the gears are contained within one unit or housing. The terminology actually refers to how the gears are set up:

  • External – The two spur gears are identical in that they both have teeth that face outward. One is driven and one is an idler.
  • Internal – In this layout, there is one spur gear with teeth that face outward and one that has teeth that face inward. Basically the one gear is surrounded by or “internal” to the other.

Functions of a Gear Pump

No matter what the design is the gear pump is intended to serve two basic purposes. First, fluid needs to be drawn into the pump from the reservoir. The rotating gears effectively create a seal and develop suction at the inlet side of the pump. This is the mechanism that draws the hydraulic fluid from the reservoir and into the pump housing.  

The second action is to transfer the fluid from the inlet side to the outlet side. This is what the rotation of the gears accomplishes. In an external gear setup, the fluid fills the space between the teeth and the housing wall and is transferred from one side to the other as the gear rotates. When the fluid reaches the output area it comes to the area where the two gears mesh together. At this point, the volume changes, and the fluid is then forced out of the outlet port under pressure. Fluid cannot move in reverse because of the tight tolerances at the mesh area and the rotational action of the gears.

Selecting or replacing a hydraulic pump can present you with a multitude of options. Understanding the benefits and limitations of each design will help lead you to the correct choice for your application.

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