Abstract: The construction and principle of the balanced compound gear pump is introduced. According to the mesh rule of the inner and outer gear pump, the position of mesh point and the instantaneous flow characteristic in any moment during the periodic-angle is analysed for each type of the gear pump. The best form of construction for the balanced compound gear pump is derived from analysing the odd-even property of the numbers in the central gear and the idle gears on the flow characteristic.

Key words: Compound gear pump, Instantaneous flow, Mesh point