Abstract: As a new type of positive pump, the differential velocity 4-vane pump is presented. It’s mainly composed of noncircular gear driving system, hull and two coaxial impeller fixed inside the hull. It forms compartments of varying volume depending on the movement of closing and stretching between the two neibouring vane which is driven by two pairs of noncircular gears to make liquid in and out. The operation principle of this pump and the designing method of noncircular gear’s pitch and delivery ports are investigated.The solution to the trapped liquid and the vane meddling is described.

Key words: Differential velocity vane, Non-circular gear, Positive pump