Patent GB-977185-A (GB)
Title: High vacuum pumping method and apparatus
IPC: F04F9/00
Filed: 1963-03-19
Abstract: 977,185. High vacuum apparatus. VARIAN ASSOCIATES. March 19, 1963 [March 26, 1962], No. 10850/63. Heading FIN. A high vacuum apparatus comprises a hollow manifold 12 having within it a cryogenic vacuum pump 32 which is provided with valve means including a valve plate 46 which forms a portion of an auxiliary chamber 49 when the valve means is in the closed position. The manifold 12 is covered by a removable vacuum bell jar 15 to one side of which is mounted the cryogenic vacuum pump 32 and to the other side of which is mounted a valve assembly 18 having attached thereto an electrical sputter-ion pump 31, and the manifold 12 has a pair of valves 16 to each of which is connected a sorption vacuum pump 17. The valve assembly 18 includes a screw drive assembly 22 provided with a bellows seal 23 and is attached to a valve plate 24 which is guided by rods 26. The cryogenic vacuum pump 32 comprises a flange 34 covering an opening 33 in the manifold 12, the flange 34 having a recessed shoulder 37 to the underside of which is attached a bellows plate 41 by bolts 43. A vacuum-tight bellows 44 is attached, e.g. by brazing, to the plate 41 and to a nut 45, the latter being secured to the cover plate 46 which is guided by rods 51. Mounted on the flange 34 by concentric tubes 54, 55 is a hollow metallic doughnut 52, the inner tubes 54 providing inlets for filling the doughnut 52 with liquid coolant, e.g. liquid nitrogen. A tube 59 provided on the flange 34 is adapted for connection to pumping mechanism (not shown). A screw shaft 67 extends through the bellows 44 and engages with a nut shaft 63 to which is secured a hand wheel 68, the turning of which produces vertical movement of the shaft 67 and the valve plate 46. In operation a main vacuum chamber, including the manifold 12, is first evacuated to about 50 m.m. Hg. by an oil-free vacuum pump, e.g. a water jet exhauster (not shown), with the valves 16 and the valve plates 46 and 24 in closed position. The exhauster is then shut off and the valves 16 are sequentially opened to reduce the pressure to about 10<SP>-2</SP> m.m. Hg. Next the valves 16 are closed and the valve plates 46 and 24 are opened to reduce the pressure to below 10<SP>-8</SP> m.m. Hg. If the gases condensed on the doughnut 52 have a high vapour pressure at liquid nitrogen temperature the valve plate 46 is again closed at that pressure to prevent re-evolution of these gases; the auxiliary chamber 49 can then be connected to pumping mechanism through the tube 59 for removal of gases formed by removing the liquid nitrogen from the doughnut 52 which is thus cleaned of condensate. In a second embodiment, Fig. 5 (not shown), the hand wheel 68 is disposed below the manifold 12 enabling the doughnut 52 to be removed for cleaning while the valve plate 46 remains closed. In a third embodiment, Fig. 6 (not shown), the doughnut 52 is replaced by concentric bellows the space between which is filled with liquid nitrogen. In a fourth embodiment, Fig. 7 (not shown), the outside of the doughnut 52 is provided with a plurality of compartments which are filled with a highly gas-absorbent material, e.g. activated charcoal or molecular sieve. In a fifth embodiment, Fig. 8 (not shown), a cryogenic pump is mounted within a manifold which is adapted to replace a bell jar of an existing vacuum system, the bell jar being then mounted on top of the manifold. The sorption vacuum pumps 17 may be used to reduce the pressure directly from atmosphere. Specification 939,395 is referred to.