Abstract: A pumping unit having a pump chamber with a rotor mounted in a rotatable manner within the chamber. The pumping chamber is formed by a circumferential wall and two end walls. The circumferential wall is formed on an annular collar of a pump part and has on its inner surface a track on which sealing bodies of a rotor roll. To avoid deformation of the pump part by hydraulic forces or by pressing-in forces, ribs are arranged on the outer surface of the circumferential wall which extend away from the pump chamber. A shoulder is arranged on the side of the end wall which is directed away from the pump chamber. The shoulder is connected by a press fit to the pump housing and has thin walls so that pressing forces do not result in any deformation to the end wall of the pump chamber.