1. General Definition
Pump: A machine or device used for raising, compressing, or transferring fluids. (Dictionary definition).

2. Internal Gear Pumps Use gears to raise, compress, or transfer fluids
Basic principle: fluid rushes into the cavities and is forced out with the revolutions of the gears

3. How Internal Gear Pumps Work
Liquid enters between rotor and idler.
Liquid travels between gear teeth and gaps created by the motion of the gears.
Pump head flooded when rotor and idler teeth begin to mesh together again forcing liquid out.

4. Advantages 2 moving parts 1 stuffing box
Ideal for high viscosity fluids
Positive suction and non-pulsating discharge

5. Disadvantages
Requires low speeds
Pressure limitations

6. References