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781. A tail-dewar for liquid helium
Classified abstracts 777-791 23 777. Gasket assembly. IGreat Britain) The gasket is produced by depositing sealing material using a screen printing process and forming an aperture in part of the supporting member face. Thus no sealing material eg acrylonitrile rubbers and silicone rubbers, is wasted. (Author) Dowty Seals Ltd, Brit Patent 1,051,747, Patent Abstr, 7 (3) part A, 19th Jan 1967, 1. 24. VALVES 24 : 64 778. The use of ceramics in valves. (Czechoslovakia) A review of the Proceedings of the Symposium held on 29th-30th March, 1965, edited by P Popper, is given. Papers are compared with other publications on this problem and 11 of them are highly evaluated. This book is recommended to every vacuum technology engineer. W Espe, Elektrotech Cas, 17 (10), 1966, 804-805 (ht Czech). 24 779. A simple glass electromagnetic valve suitable for low pressure systems. (Great Britain) The construction of an electromagnetically operated glass valve for handling gases at pressures l0 -~ to 760 tort is de~ribed. Glass and silicon rubber are the only materials which come into contact with the gases. A R Burgess et al, J Sci htstrum, 43, 1966. 943. 24 780. Vacuum system valve. (Germany) This valve is intended for systems with chambers which are hermetically sealed with respect to each other, one chamber of which is connected to a low pressure chamber, such as a vacuum pump, while the other is connected to a chamber in which pressure is higher, eg in electron microscopes. A third chamber serves as a lock chamber and is arranged in such a manner with respect to the first two that the first two chambers have a wall which is common with the third chamber-as is conventional for mixer valves. Apertures in this wall connect the chamber and may be hermetically sealed by means of a cap spring received by the third chamber. (Author) Siemens AG Berlin and Munchen, German Patent 1,230,634, Patent Abstr, 7 (3) part D, 19th Jan 1967, 5.
heat conduction between the two sheets is minimal and if a vacuum is maintained with the chamber wall excellent insulation is provided against temperature extremes. Grove Valve and Regulator Co, Brit Patent 1.051,961, Patent Ahstr, 7 (3) part D. 19th Jan 1967, 5. 26, AUTOMATIC MENT
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26 785. Water vapour and heat transfer during vacuum freeze drying, with reference to optimal process conditions. (Germany) The parameters influencing the rate constants of freeze drying processes are reviewed and some experimental investigations described. J Strasser et al, Kaeltetechnik, 18, 1966, 286-293 (in Germany) 26 786. A simple liquid nitrogen level control. (Great Britain) A thermal expansion on-off control is described, which keeps the liquid nitrogen level in a glass Dewar constant to within a few millimcters. K P Klein, J Sci Instrum, 43, 1966, 957. 26 787. Simple, inexpensive transistorized, continuously monitoring liquid helium and liquid nitrogen indicator. (USA) A schematic of the oscillator and sensing probe used is given, and the operation of the level indicator described. H J Seguin and R W Leonard, Rev Sci htstrutn. 37, 1966, 1743-1744. 26 788. Reliable, inexpensive, transistorized liquid nitrogen level controller. (USA) A self-contained liquid nitrogen level controller, having positive switching action without jitter, was designed and constructed utilising a transistorized Schmitt trigger as the switching clement. The circuit of the device is described and illustrated. H Seguin et al, Rev Sci Instrum, 37, 1966, 1747-1748. 26 789. Inexpensive liquid-nitrogen level control fur cold traps. (USA) A relay actuates a liquid-nitrogen valve depending on the resistance of carbon resistors at liquid-nitrogen temperature. P T Perdue, Nucl Instrum Methods, 44, 1966. 169-170. 27. LEAK DETECTORS AND LEAK DETECTION
25. BAFFLF-,~;, TRAPS and REFRIGERATION EQUIPMENT 25 781. A tail-dewar for liquid helium. (Great Britain) Description and constructional details are presented of a sealed-off glass tail-dewar for liquid-helium with conduction cooled metallic radiation screen in the dewar tail. The difference thus obtained between inner and outer diameter of the dewar tail is only 10 ram. D J Kroon, J S c i Instrum, 43, 1966. 831. 25
782. Capacity and economic performance of a large 5°K helium refrigerator. (USA) A description is given of a high-capacity 4.5°K mixed-phase, closedcycle helium refrigerator, successfully installed and operated. The thermodynamic cycle and equipment arrangement allow a wide versatility in operation as an efficient mixed-phase refrigerator, a dense-gas system and as a liquifier. The economies of operation are also analyzed and described. A R Winter and W A Snow, Advances in Cryogenics Engineerin.e. I1, Ed K D Timmerhaus. Plenum Press 1966, 116-125. 25 783. Constant low-temperature vessel for use between room temperature and - 1 5 0 °. (China) A constant low-temperature vessel was designed for use in metal research. Liquid nitrogen is employed to maintain a constant temperature down to - 150° with an accuracy of +0.I °. Temperature of the vessel is regulated by a Pt/Pt-Rh thcrmocouple control system. The vessel is safe, simple, efficient and operable as low as - 269 ° if liquid helium is used. Ts'ui-Chang Hsu, K'o Hsueh i Ch'i. 3, 1966, 457-459 (in Chinese). 25 784. Cryogenic chamber. (Great Britain) A series of walls form a duct for the fluid. Sheets are secured together face to face in a fixed pattern over the surfaces. A duct is connected to each panel for delivering the cryogenic fluid. Clips loosely support the edges allowing for expansion and contraction. As contact is minimal, 250
27 790. Increasing leak detection sensitivity by means of liquid indicators. (USSR) Using a mass-spectrometer leak detector it is possible to obtain higher sensitivity by means of a liquid indicator instead of the conventional helium gas for the following reasons: current mass-spectrometers have higher sensitivity to masses of 30-50 than for He; the quantity of a fluid passing through a leak is higher than the quantity of any gas since the fluid surface tension completely fills capillaries; and at high vacuum only molecular flow pumping exists so the partial pressure of the indicating material depends on the square root of the mass number, eg the pressure of ether is 3 times higher than that for passage of the same quantity H'e. The only disadvantage of this method is the greater time of exhausting the leak (as high as 1.4 hollrs for a long capillary of leakage 10 13 torr litre:'sec), but the sensitivity may be 3 orders higher. Also the liquids are easily stored by means of cold traps which condense the liquid as the air is evacuated. All parameters were calculated for ether, alcohol, chloroform, N-hexane, acetone, cyclohexane, tetrachloromethane and benzene and the results are tabulated. The highest gain is obtained with a cyclohexanc, but because of its long time of filling and exhausting, the following liquids are of more interest: diethylether (mass 31), chlorol~'~rm (mass 83) and acetone (mass 57). V E S k u ~ t et al, Prihory Tekh Eksper, l l (6), Nor- l)ec 1966, 143 -147 (in Russian). 27 791. Method of checking the vacuum-tightness of the fuel elements of a VVR-M water-cooled water-moderated reactor. (USSR) A method of testing reactor fuel elements for vacuum-tightness is described. The fuel clement to be tested is placed in a vacuum chamber and all radioactive water passing into the latter with the fuel element is removed, final traces of damp being eliminated by means of compressed air. The space surrounding, the fuel element is reduced to a low pressure; in the event of the fucl element not being vacuumtight, radioactive gases leak from inside and may bc recorded by
heat conduction between the two sheets is minimal and if a vacuum is maintained with the chamber wall excellent insulation is provided against temperature extremes. Grove Valve and Regulator Co, Brit Patent 1.051,961, Patent Ahstr, 7 (3) part D. 19th Jan 1967, 5. 26, AUTOMATIC MENT
PROTECI'IVE
AND
CONTROL
EQUIP-
26 785. Water vapour and heat transfer during vacuum freeze drying, with reference to optimal process conditions. (Germany) The parameters influencing the rate constants of freeze drying processes are reviewed and some experimental investigations described. J Strasser et al, Kaeltetechnik, 18, 1966, 286-293 (in Germany) 26 786. A simple liquid nitrogen level control. (Great Britain) A thermal expansion on-off control is described, which keeps the liquid nitrogen level in a glass Dewar constant to within a few millimcters. K P Klein, J Sci Instrum, 43, 1966, 957. 26 787. Simple, inexpensive transistorized, continuously monitoring liquid helium and liquid nitrogen indicator. (USA) A schematic of the oscillator and sensing probe used is given, and the operation of the level indicator described. H J Seguin and R W Leonard, Rev Sci htstrutn. 37, 1966, 1743-1744. 26 788. Reliable, inexpensive, transistorized liquid nitrogen level controller. (USA) A self-contained liquid nitrogen level controller, having positive switching action without jitter, was designed and constructed utilising a transistorized Schmitt trigger as the switching clement. The circuit of the device is described and illustrated. H Seguin et al, Rev Sci Instrum, 37, 1966, 1747-1748. 26 789. Inexpensive liquid-nitrogen level control fur cold traps. (USA) A relay actuates a liquid-nitrogen valve depending on the resistance of carbon resistors at liquid-nitrogen temperature. P T Perdue, Nucl Instrum Methods, 44, 1966. 169-170. 27. LEAK DETECTORS AND LEAK DETECTION
25. BAFFLF-,~;, TRAPS and REFRIGERATION EQUIPMENT 25 781. A tail-dewar for liquid helium. (Great Britain) Description and constructional details are presented of a sealed-off glass tail-dewar for liquid-helium with conduction cooled metallic radiation screen in the dewar tail. The difference thus obtained between inner and outer diameter of the dewar tail is only 10 ram. D J Kroon, J S c i Instrum, 43, 1966. 831. 25
782. Capacity and economic performance of a large 5°K helium refrigerator. (USA) A description is given of a high-capacity 4.5°K mixed-phase, closedcycle helium refrigerator, successfully installed and operated. The thermodynamic cycle and equipment arrangement allow a wide versatility in operation as an efficient mixed-phase refrigerator, a dense-gas system and as a liquifier. The economies of operation are also analyzed and described. A R Winter and W A Snow, Advances in Cryogenics Engineerin.e. I1, Ed K D Timmerhaus. Plenum Press 1966, 116-125. 25 783. Constant low-temperature vessel for use between room temperature and - 1 5 0 °. (China) A constant low-temperature vessel was designed for use in metal research. Liquid nitrogen is employed to maintain a constant temperature down to - 150° with an accuracy of +0.I °. Temperature of the vessel is regulated by a Pt/Pt-Rh thcrmocouple control system. The vessel is safe, simple, efficient and operable as low as - 269 ° if liquid helium is used. Ts'ui-Chang Hsu, K'o Hsueh i Ch'i. 3, 1966, 457-459 (in Chinese). 25 784. Cryogenic chamber. (Great Britain) A series of walls form a duct for the fluid. Sheets are secured together face to face in a fixed pattern over the surfaces. A duct is connected to each panel for delivering the cryogenic fluid. Clips loosely support the edges allowing for expansion and contraction. As contact is minimal, 250
27 790. Increasing leak detection sensitivity by means of liquid indicators. (USSR) Using a mass-spectrometer leak detector it is possible to obtain higher sensitivity by means of a liquid indicator instead of the conventional helium gas for the following reasons: current mass-spectrometers have higher sensitivity to masses of 30-50 than for He; the quantity of a fluid passing through a leak is higher than the quantity of any gas since the fluid surface tension completely fills capillaries; and at high vacuum only molecular flow pumping exists so the partial pressure of the indicating material depends on the square root of the mass number, eg the pressure of ether is 3 times higher than that for passage of the same quantity H'e. The only disadvantage of this method is the greater time of exhausting the leak (as high as 1.4 hollrs for a long capillary of leakage 10 13 torr litre:'sec), but the sensitivity may be 3 orders higher. Also the liquids are easily stored by means of cold traps which condense the liquid as the air is evacuated. All parameters were calculated for ether, alcohol, chloroform, N-hexane, acetone, cyclohexane, tetrachloromethane and benzene and the results are tabulated. The highest gain is obtained with a cyclohexanc, but because of its long time of filling and exhausting, the following liquids are of more interest: diethylether (mass 31), chlorol~'~rm (mass 83) and acetone (mass 57). V E S k u ~ t et al, Prihory Tekh Eksper, l l (6), Nor- l)ec 1966, 143 -147 (in Russian). 27 791. Method of checking the vacuum-tightness of the fuel elements of a VVR-M water-cooled water-moderated reactor. (USSR) A method of testing reactor fuel elements for vacuum-tightness is described. The fuel clement to be tested is placed in a vacuum chamber and all radioactive water passing into the latter with the fuel element is removed, final traces of damp being eliminated by means of compressed air. The space surrounding, the fuel element is reduced to a low pressure; in the event of the fucl element not being vacuumtight, radioactive gases leak from inside and may bc recorded by