Abstract: In pumps for conveying gases and providing a differential pressure between the pump inlet and outlet, a pumping space within the pump is hermetically sealed from the pump drive unit. No oil or grease-lubricated parts are located within the pumping space. Accordingly, the pump can be characterized as completely dry running. The hermetical seal is provided by a hollow or tubular member (5) capable of torsion movement and located between a shaft (1) and a container (6). A drive unit (7) connected to the shaft provides it with an oscillating rotary motion transmitted through the shaft to the container (6). Segmented pistons (8a, 8b) are located on the container and oscillate in the pumping space between stationary parts (10a, 10b) and afford the pumping effect.