External / Internal Gear Pump

External  Gear Pump

An external gear pump uses two gears rotating against each other to provide fluid movement.

One gear is driven by a motor connected to a shaft. this is called the drive gear because it is driven by a motor. and it turn meshes with and drives the movement of the second gear. As the gears rotated away from each other and come out of mesh they create an expanding volume on the inlet side of the pump. this creates a vacuum at the inlet port allowing fluid into the pump, then fluid flows into the cavities and is trapped by the gear teeth, as the gears rotates a flow created around the outside of each one.

fluid trapped in the slots between teeth, is carried around and discharged into the cavity with the outlet port , meshing of the teeth in the center of the pump seals the outlet port from the inlet port. No fluid passes between the gears.

Advantages of the external gear pumps are:
1.     Their high speed and pressure
2.     Relatively quiet operation
3.     And their design accommodates a wide variety of materials

Disadvantage of external gear pumps is bushings in the liquid area can become worn and they have fixed in end clearances.

Internal Gear Pump

Internal gear pumps are exceptionally.

This type of pump has one inner gear which is inside a second outer gear. The inner gear has a shaft driven by a motor, and has teeth that protrude outward. The outer gear has teeth that protrude inward toward the center of the pump.
As the inner gear rotates it meshes with and moves the outer gear liquid is trapped in the gear spaces and carried from the inlet to the discharge.
A stationary crescent-shaped divider separates the intake and discharge portions of the fluid,

Advantages of internal gear pumps are
1 Smooth and almost pulseless flow
2 Slightly more horsepower for its size

Disadvantages are
1.    Higher cost
2.     Limited size range
3.     Low to moderate pressure ratings
4.     And few sources of manufacture

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