A reversible gerotor pump system is provided. The gerotor pump system includes a cylindrical housing with a 180° slot, an eccentric ring with a locking pin fixed thereto and movably engaged in the slot; an outer rotor and inner rotor with meshed teeth, and shaft for driving inner rotor and system. The eccentric ring has a convex profile on the outer diameter. A positive contact system, which can be a spring-and-plunger system or frictional disc brake system is provided to increase frictional force between the eccentric ring and the outer rotor. The locking pin moves in the slot with clearance at both rotation directions to provide a self-damping effect. The suction port has prolongations at both upstream and the downstream sides to increase filling time such that the pump can have a fill speed of above 5000 rpm, and the volumetric efficiency is at least 90% at 5000 rpm.