Patent GB-411362-A (GB)
Title: Improvements in and relating to the production of low pressure gaseous atmospheres in the envelopes of electric discharge devices and like vessels
IPC: H01J9/395
Filed: 1933-10-27
Abstract: 411,362. Discharge apparatus. BRITISH THOMSON-HOUSTON Co., Ltd., Crown House, Aldwych, London.-(Assignees of Foulke, T. E.; 30, Evelyn Place, Nutley, New Jersey, U.S.A.) Oct. 27, 1933, No. 29884. Convention date, Oct. 28, 1932. [Class 39 (i).] In a method of filling with an attenuated gaseous atmosphere the envelopes of electric discharge devices and like vessels, the substantially evacuated envelopes are connected through a valve to the source of gas, and atmospheric leakage through the valve to the gas source is prevented by maintaining a zone about the valve port at a pressure less than that of the atmosphere. The apparatus comprises a geneva gear supporting a spider which carries at its outer edge a series of hollow arcuate segments 4 Fig. 2, each provided with openings 30 at regular angular intervals to receive a portion 33, Fig. 5, of the discharge tube, which fits within indiarubber socket 31. The geneva mechanism is coupled by pins 23, Fig. 4, to a bar 22 secured to the top plate 21 of a rotary valve which rotates axially upon the fixed bottom plate 20 provided with a series of ports 26 Fig. 3 spaced at the same angular intervals as the positions of rest of the driving mechanism, one port being omitted, however, at the sealing-off position. Ports 27 in the plate 21 correspond with the ports 26, and a series of oil glands 28 between the plates provide seals against leakage. The ports 27 of the plate 21 are connected by tubes 35 to the indiarubber sockets 31 which receive the open ends of the discharge tubes. The lower port 26 which is connected by the rotary valve to the tube 35 terminating at position A, Fig. 2, is connected to a source of dry air by the tube 36, while the next port 26 in a counter-clockwise direction is connected by tube 37 to a vacuum pump. The next port is connected to a leak-detector, and the subsequent ports are connected in turn to the air supply and evacuating-devices, the final evacuating-devices being sufficient to maintain an extremely high vacuum. The last port 26 is connected through the tube 44 to the source of the gaseous atmosphere. The means for preventing impairment of the purity of the gaseous supply system comprises a channel 45, Fig. 3, cut in the upper surface of the valve plate 20 and opening into the port 26 which is connected to the last exhausting-pump, the channel also extending about the port 26 which is connected to the gaseous source and the port 27 in the rotary plate which is at the sealing-off position. In this manner, due to the high vacuum in the channel, any leakage between the valve plates will be away from the protected ports 26, 27. The channel 45 may be extended along the surface of the valve plate, so that more of the ports are protected from atmospheric leakage. An arcuate oven, heated to a temperature of about 500‹C. by flames from perforated pipes, extends a substantial distance around the path of the discharge vessels. The leak-detector which is connected to the tube 38, Fig. 2, consists of a mercury manometer with two electric contacts which are closed by the mercury whenever the vacuum falls below a certain value, thereby closing the circuit of an electric alarm bell. When a leaky envelope is detected its socket 31 is clamped to disconnect it from the system, and a stop cock 59 is opened temporarily to connect the tube 38 to the pump tube 40 to re-evacuate the manometer. The vacuum in the vessel is checked in the last stage of the exhaust, and the purity of the gaseous filling subsequently admitted is tested by the apparatus shown in Fig. 5. This comprises a conducting-rod 66 which is mounted on a fibre post 65 and supports a flexible conductor 67 arranged to hang in contact with the inleads 68 of the envelope 34 at the exhausting position, while a wire 69 hanging from the rod 66 is adjacent to, but spaced from, the constriction 33 of the envelope 34 at the gas filling position. A lead 70 connects rod 66 to a high frequency current source 71 which is earthed, as is the bed plate 1. During evacuation of the envelope a visual indication of the effect of the pump is provided by the discharge in the envelope, this discharge ceasing when the desired vacuum is reached. The gas is then introduced into the evacuated envelope until a pressure of the order of 10 to 100 m.m. of mercury is attained, the purity of the gas being indicated by the visual inspection of the colour of the discharge induced in the tubulation 33 of the envelope.