Abstract: A reversible gear-type pump providing constant fluid delivery direction on alternating drive direction in which an eccentric ring receiving the outer rotor is pivotal through 180.degree. between two end positions by frictional engagement with the outer rotor wherein the eccentric ring is made contractible as a whole to establish the coupling engagement with the outer rotor and expandable to disengage the coupling engagement. The eccentric ring can be made in one piece from resilient material or can be formed from a plurality of arcuate segments which are pressed together by an annular spring engaging around them.