H09- Internal gear pump

    A gear pump consist of two meshing gear. One of the gear is connected to a driving shaft known as Driver gear which drives 2nd gear called Driven OR Idler gear. These gear are enclosed inside the housing. These pumps are particularly used to transfer viscous fluid.

Constructional feature: In this type of the pump the meshing of the teeth takes place internally and hence the name internal gear pump.it consist of external gear which meshes with gear which contains internal gear as shown in figure.

    The pumping chamber is formed between the gear teeth. A crescent seal is machined into the space between the inlet and outlet OR meshing and unmeshing region of the gear where the clearance between the internal gear( annular gear) and external gear is maximum. Thus the crescent seal separates both inlet and outlet and it will not allow the fluid to return the inlet.

Working: Low pressure oil from the inlet port is converted into high pressure oil at outlet as follows.

      As gear rotates unmeshing takes place nearer at inlet port, in presence of tight seal as cavity volume increases the pressure in the chamber decreases. Since the pressure inside the chamber is comparatively lower than that of outer atmospheric pressure the suction of fluid takes place.

      The oil is trapped within the internal and external gear teeth on either side of the crescent seal and is carried to the outlet cavity of the pump.

    The meshing of the gear teeth reduces the volume nearly at the outlet. This reduce in volume causes the fluid to rush out the oil trough the out let port. 

Note:

    How the pressure is created? a pump creates flow and pressure by resistance to flow I.e pressure results whenever the flow of the fluid is restricted. The fluid is drawn into pump chamber through the inlet port due to the partial vacuum, due to reduced in the space causes resistance to flow in the upstream side causes pressure to build up. 

Advantages :

- Only two moving parts.

- Non pulsating discharge.

- Excellent for high viscosity liquids.

- Constant discharge regardless output resistance.

- Operates in both direction.

Dis-advantages :

- Presence of contamination in working fluid causes wear in pumping element.

- Not effective for fluid is having low viscosity.

- It costs more.

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