The structure of the vane pump

This outward radial movement of the vanes and turning of the rotor causes the chamber between the vanes to increase as the vanes pass further away from the inlet port. This incrase in volume results in a lowering of pressure until the atmospheric pressure is sufficient enough to force oil from the reservoir into the inlet chamber. Oil from the inlet is swept away by the vanes toward the outlet port chrough a decreasing (volume) series of chambers until it is forced through the outlet port.