GB1015887A - Molecular vacuum pump - Google Patents

Abstract

1,015,887. Molecular vacuum pumps. W. K. ROBERTS. May 27, 1964 [May 27, 1963], No. 21018/63. Heading F1C. In a molecular vacuum pump of the type in which a rotor disc co-operates with spiral stator grooves at each side of the disc, the gases or vapours being pumped from the centre of the rotor to the periphery on one side of the rotor and then from the periphery to the centre on the other side, two or more such discs are arranged to pump in series. The stator grooves may decrease in cross-sectional area from inlet to outlet. To prevent contamination of the vacuum by oil vapour given off from the bearings, the rotor discs may be carried by a stub shaft journalled in bearings at the end adjacent the exhaust side of the pump. To reduce the forces on the bearings, the rotor discs may be made progressively smaller in diameter in accordance with their distance from the bearings. The shaft may instead have a bearing at each end, in which case the bearing at the end adjacent the vacuum may be of a type not producing contamination of the vacuum, such as a magnetic bearing. Where both bearings are of ordinary type, however, the vacuum inlet may be located midway between the bearings, the rotor discs being arranged in two sets of series-connected discs, the sets pumping from the common central inlet towards respective exhaust connections at opposite ends of the shaft. In a modification, one set only may have an exhaust connection, the other set (which may comprise a single rotor disc) acting merely to prevent ingress of oil vapour from the adjacent bearing into the vacuum inlet.