GB928440A - Sealing and centering device for rotary shaft - Google Patents

Abstract

928,440. Screw-type vacuum pumps; stuffing-box substitutes. COMMISSARIAT A L'ENERGIE ATOMIQUE. Feb. 7, 1962 [Feb. 9, 1961; June 6, 1961], No. 4710/62. Classes 110 (1) and 122 (5). A rotary shaft 3, Fig. 1, passing through a wall assembly 4, C between enclosures A, B containing gases 1, 2 under different pressures is centred and sealed by a fluid bearing 6, 8 and a rotary pump-type seal 9, 11 comprising at least one groove 9a and disposed in series with the bearing, means being provided for sucking gas to maintain round the shaft between the seal and the bearing a pressure close to the lower of the gas pressures. The fluid bearing comprises a rotor 5 mounted on or integral with the shaft and separated by a clearance 7 from a portion 8 of a sleeve 4 which sealingly passes through a metallic diaphragm forming a partition C. The grooves 9a are helical and are formed as two sets of opposite hand on a portion 9 of the shaft which is spaced by a clearance 12 from a portion 11 of the sleeve 4 and is separated from the rotor 5 by a groove 10. Alternatively, the grooves may be formed in the portion 11 and the groove 10 replaced by an annular chamber in the sleeve. The depth of the grooves decreases from the centre towards the ends of the portion 9. In operation, the gas 2 is sucked through the clearance 7 by a vacuum pump V into the groove 10 and out through orifices 13 connected by flexible pipes 14 to orifices 15 and the grooves 9a force back the gases 1, 2 respectively into the enclosure A and the groove 10. Alternatively, the gas 2 may be sucked through an axial passage inside the shaft communicating with the groove 10 or the clearance 7. In Fig. 2, the shaft 27 of a motor-driven rotary molecular vacuum pump is provided on each side of the rotor with a helically-grooved type seal 29 and a fluid bearing 30 which are disposed between the shaft and the pump stator 18 with a suction conduit 33 between them. The seal grooves may be formed in the stator or the shaft. The rotor 20 operates in a chamber 19 which is formed, on both sides of an annular chamber 21, with multiple thread-like helical grooves 23 having decreasing depths from the chamber 21 towards exhaust chambers 24 which communicate through passages 25 to a conduit 26 coupled to a fore-vacuum pump. The chamber 21 is connected by a conduit 22 to a vessel to be evacuated. The grooves 23 may alternatively be formed in the rotor or in both the rotor and stator. The conduits 33 may be coupled to the vacuum pump connected to the conduit 26 or to a different pump. The conduits 25 may be eliminated in which case discharge is through the seals 29 towards the conduits 33, the seals functioning as molecular pumps. The grooves 31 of each seal 29 may be formed either in the shaft 27 or in the internal wall of the chamber 19, or they may be cut in the fiat end wall of the rotor 20 in which case the chamber 24 is formed by an annular groove formed in the pump body between the grooves 23 and 31. Specifications 820,348 and 885,793 are referred to.