The principle of the lobe pump is equal to the principle of the externel gear pump. The lobes however, are considerably larger than the teeth from a gearpump. Because of this difference in size, each rotor consist of 2 or more lobes. One of these rotors is directly driven, while the other rotates with it.

As the rotors rotate, liquid is trapped between two lobes of each rotor and the walls of the pump chamber and carried from the inlet side, to the outlet side. As liquid leaves the suction chamber, the pressure in the suction chamber is lowered, and additional liquid is sucked into the chamber.

The lobes are constructed in this way creating a continuous seal at the points where they meet at the center of the pump. Some lobes are fitted with small vanes at the outer edge to improve the seal of the pump. Although these vanes are mechanically held in their slots, they are, to some extent, free to move outward. Centrifugal force keeps the vanes snug against the chamber and the other rotating members. There are 3 basic types of lobes. wing lobes, single lobes, and tri-lobes. In our example we use the single lobe.

See the pictures:

(1) The bottom lobe has begun sucking the liquid into the empty space. The upper has the liquid in it's empty space stuck between the casing and the lobe. So it can be transported to the outlet side.

(2) The bottom lobe is ready to suck the liquid in it's empty space. The upper lobe is on the point of pushing the liquid into the outlet.

(3) The bottom lobe has liquid inside it's empty space and is transporting it to the outlet side. The upper lobe is pushing the liquid into the outlet side while liquid is being sucked at the inlet side because of the empty space that is being created.

(4) Here the same principle as with picture (2) is happening, only the rotors are doing the opposite thing.

The rotors suck and push the liquid while rotating simultaniously.

(1)	(2)	(3)	(4)