Viking’s simple “gear-within-a-gear” principle has only two moving parts. The positive displacement of the liquid is accomplished by the complete filling of the spaces between the teeth of the rotor and idler gears.

With every revolution of the pump shaft, a definite amount of the liquid enters the pump through the suction port. This liquid fills the spaces between the teeth of the rotor and the idler.

The crescent on the pump head splits the flow of the liquid as it is moved smoothly toward the discharge port. The idler gear, which carries the liquid between its teeth and the inside surface of the crescent, rotated on the pin supported by the pump head.

The rotor gear, which carries the liquid between its teeth, travels between the casing and the outside surface of the crescent and is connected to the pump shaft. The four schematic drawings give a graphic illustration of flow characteristics through the pump.

Below is a demonstration of how the positive displacement pump works:

1. The coloured portion at left indicates the liquid as it enters the suction port area of the casing and the area between the rotor teeth and corresponding concave area between the idler teeth. The two black arrows indicate the pump rotation and progress of the liquid.	2. Notice the progress of the liquid through the pump and between the teeth of the "gear-within-a-gear" principle. Also note how the crescent shape on the head divides the liquid and acts as a seal between the suction and discharge ports.	3. This illustration shows the pump in a nearly flooded condition just previous to the liquid being forced into the discharge port area. Notice how the gear design of the idler and rotor form locked pockets for the liquid so as to guarantee absolute volume control.	4. This view shows the pump in a completely flooded condition and in the process of discharging the liquid through the discharge port. The rotor and the idler teeth mesh, forming a seal equidistant between the discharge and suction ports, forcing liquid out the discharge port.

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