In a cylindrical housing, the rotor is positioned eccentrically on the shaft so the rotor is positioned near the top of the cylinder. Rotor blades are positioned into numerous rotor slots. When the rotor starts turning, centrifugal force causes the blades to be thrown out and slide against the internal surface of the cylinder. A cell is formed between two blades with a volume that changes constantly during rotation. Air enters from the inlet port into a cell until the rear blade reaches the inlet port, at this point the cell has achieved its maximum air volume.
As the cell then moves away from the port, its volume becomes smaller and smaller. The air is compressed and the pressure rises. This continues until the pressure in the cell exceeds that in the pressure chamber. The air then exits through the outlet port. Some models are fitted with exhaust valves that stop the backflow of this discharged air, if the maximum pressure has been reached. In a vacuum pump the process is similar, but the cell gives decreasing pressure and the chamber is at atmospheric pressure.