Classified abstracts 1083-1098

21 1083. The "Snecma" turbomolecular pump. (France) A new type of vacuum pump is described which maintains pressure between 10 -3 and 10 -11 torr and provides for the pumping of inert gases and for the compression of heavy molecules such as oil vapours. The pump is designated "turbomolecular" because it is a multistage axial compressor. H Gamier, Entropie, 8, 1966, 65-70 (in French).

21 1084. Cryopumps. (East Germany) The field of cryopumps is reviewed covering types of pumps, auxiliary equipment, choice of coolants and adsorbents, suction velocities, operating variables and typical constructions. L Bewilogua, Wiss Z Tech Univ Dresden, 15, 1966, 11-19 (in German).

21 1085. High vacuum cascade pump system. (Poland) Design and construction of a cascade pump system with final vacuum of 5 × 10 -s torr and a pumping rate of 300 litres/sec, are described. A diagram and details of the main elements (oil baffle, vacuum cold trap, high vacuum straight run valves and a multi-direction block valve) are included. Z Kozlowski and M Sadowski, Inst Nucl Res (Poland), Rep 1NR 740, 1966.

21 1086. Vacuum pump systems. (USA) The operating principle and characteristic of diffusion pumps and of ion pumps are given. The general characteristics of the two types are compared and examples given of selection criteria. E Winzenberger et al, Instrum Control Systems, 39, 1966, 99-104.

21 1087. Vane pumps. (USA) The principle of operation, construction and the factors affecting the application and selection of vane pumps are discussed. R O Griffiths, Machine Design, 38, 1966, 13-15.

21 1088. Piston pumps. (USA) The general types of piston pumps and criteria for pump selection are discussed. R O Griltiths, Machine Design, 38, 1966, 16-18.

21 1089. A simple laboratory gas-circulation pump. (Great Britain) A simple gas circulation pump is described. Circulation is caused by the oscillation of a Hg column and the flow controlled by electrically operated glass ball and socket valves. The pump will work over a range of pressures from 760 tort down to 0.1 tort and against considerable back pressure. Typically the range of circulation rates is from zero to 500 ml/min. The pump is robust, reliable and will operate continuously for long periods without attention. M R Hills, J Sei Instrum, 44, 1967, 213-214.

21 : 41 1090. Properties of titanium-molybdenum alloy wire as a source of titanium for sublimation pumps. (Great Britain) The evaporation rate characteristics of 85 per cent titanium--15 per cent molybdenum alloy wire, used as a source of titanium in sub- limation pumps, has been investigated when operated at constant current. Some 40 per cent of the titanium present in the alloy can be evaporated and at constant voltage 24 per cent can be evaporated at a constant predictable rate and this is the preferred method of operation. The growth of macrocrystals occurs when the wire composition reaches 74 per cent titanium 26 per cent molybdenum and the total and spectral emissivities then change; these emissivi- ties have been measured and the total emissivity change explains the observed evaporation characteristics. The principal gas present in the wire is hydrogen for which the diffusion rate has been determined. R W Lawson and J W Woodward, Vacuum, 17 (4), April, 1967 205-209.

21 1091. A working vane for turbomolecular vacuum pumps. (USSR) A modified version of a turbomolecular vacuum-pump working vane (of the type fixed into the rotating disc, or made in one piece with the latter, and twisted smoothly along its whole length) is described. In the proposed vane, the angles between the coaxial sections and the plane of the disc are smoothly and continuously reduced as one passes from the tip to the root, the degree of reduction depending on the angular velocity in each section. The effect of this variation

362

is to produce a degree of compression which remains constant along the whole vane. L A Belyaev, USSR Patent No 182,842, Appl 17th Sept 1964, publd 28th July 1966.

21 1092. Cooling trap for an oil-vapour pump. (USSR) A cooling trap for an oil-vapour vacuum pump is proposed. The trap consists of an outer frame containing coaxial truncated cones arranged with their smaller ends towards the pump. A special feature of this arrangement is that, in order to increase the transmission factor, the cones are made with generators inclined at different angles, the slope of the generators gradually decreasing on passing from the centre to the periphery, and the areas of the end sections between the cones increasing in the pumping direction. B A Osanov, USSR Patent No 182,843, Appl 19th Feb 1965, publd 28th July 1966.

21 1093. Vacuum pump. (Germany) In a getter ion-pump having an anode-cathode region in which a glow discharge is produced, the discharge is prevented from spreading beyond this region by fitting a metal mesh screen, or other gas permeable device, between the region of discharge and the region of gas access. The screen is maintained at a suitable electrical potential. The arrangement may also facilitate the starting of the pump. Varian Associates, German Patent 1,234,353, Patent Abstr, 7 (12), part C, 29th March 1967, 8.

21 1094. lou pump. (Great Britain) This has a single electrode assembly and provides a high efficiency pump of 25 I/sec capacity. The chamber houses an anode in the form of a grid attached by insulation to the support, sputter shielding around this insulation, a pair of spaced cathode grids supported by the insulation and one on each side of the anode grid. The cathode grids have openings less than that of the anode grid. A glow discharge is established so that the cathode material is sputtered and deposited on housing for entrapment. (Author) General Electric Co, Brit Patent 1,058,093, Patent Abstr, 7 (9), part C, 3rd March 1967, 6.

21 1095. Roots blower. (Great Britain) In this design, the usual two rotors co-operate with respective auxiliary rotors, all rotors revolving at the same speed, and the auxiliary rotors being shaped and arranged so that compression of the blower throughflow occurs in regions opened to the blower outlet only after such compression, whereby outlet pressure pulsations may be reduced. (Author) Polysius GmbH, Brit Patent 1,058,224, Patent Abstr, 7 (9), part B, 3rd March 1967, 3.

21 1096. Getter vacuum pump. (Great Britain) The electrode of getter material is raised to sublimation temperature by electron bombardment from an electron emitter. Control of the pump is by measurement of the electron emission from the bombarded electrode, the number of electrons emitted being dependent on electrode temperature and time. The associated electron current may be used to produce a signal for control of pump operation. Varian Associates, Brit Patent 1,060,537, Patent Abstr, 7 (12), part C, 23rd March 1967, 5.

22. GAUGES 22

1097. Method for measuring pressure dependence of thermal con- ductivity of gases. (USA) A simple and sensitive method has been devised for measuring the pressure dependence of the thermal conductivity of gases. The method uses the high thermoelectric power of a semiconductor for the accurate measurement of a temperature difference. P J Freud and G M Rothberg, Rev Sci Instrum, 38, 1967, 238-242.

22 1098. Vacuum gauge calibration. (USA) The problems of vacuum gauge calibration are briefly surveyed. Above 10 -~ torr the McLeod gauge can be used for calibration with accuracies from 4-1 per cent. In the range 2× 10 -4 to 4× 10 -7 torr the Veeco Cs 775 calibration apparatus will calibrate gauges to an