GEAR PUMP AND METHOD FOR RUNNING-IN OF SAID GEAR PUMP

PROBLEM TO BE SOLVED: To improve the life and efficiency of a gear pump and lower the manufactureing accuracy by forming an addendum gap capable of being changed in response to the pressure characteristics when the gear pump is operated, between the addendums of the gears and a pump casing of the gear pump. SOLUTION: Springly-elastic addendum circle walls 26 for gears 14, 16 are provided in a pump casing 12. The addendum circle walls 26 are set to be radially moved, and are positioned outside the addendum circle surface defined by addendums 28 to be extended outside the gears 14, 16 in circular arc ranges about 90 degrees from the suction side of a gear pump 10. The delivery side ends 30 of the addendum circle walls 26 can be freely radially moved, and the suction sides are integrally made with the pump casing 12 not to be axially moved. Liquid conveyed by the gear pump 10 enters a pressure chamber 32 to press the addendum circle walls 26 inwardly in the radial direction. Thus, when the pressure difference between the delivery side and the suction side is increased, the addendum gaps become narrower.