GB411911A - Improvements in or relating to evacuating arrangements for evacuating apparatus, for example, mercury arc rectifiers - Google Patents

Abstract

411,911. High vacuum apparatus. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and GALLIZIA, E., c/o General Electric Co., Witton, Birming- ham. Dec. 16, 1932, No. 35696. [Classes 8 (i) and 71.] Apparatus for evacuating a mercury-arc rectifier &c. comprises a high vacuum pump and a backing pump, and a mercury &c. liquid seal which, in the event of failure of the high vacuum pump, separates the backing pump from the evacuated apparatus. Fig. 1 shows a diffusion pump 1 which evacuates a rectifier through a pipe 2 and a main valve ; the outlet of the pump 1 is connected to a rotary backing pump by pipes 6, 7 and a barometric valve 5. A seal in the pipe 2 is provided by mercury in a gutter formed in an enlargement 18, and a cap 20. The mercury reservoir 23 connected with the gutter is subject through the pipe 24 to the pressure in the pipe 7 in which is a leak valve 8. Opening of this valve gives atmospheric pressure in the reservoir 23 and causes the mercury to rise and close the seal. Closure of the main switch 11 starts the pump 4 and the heater of the diffusion pump, and the valve 8 is closed after a time by a time delay mechanism 13 operated by the heater winding 3. If the heater current fails the leak valve is opened and the seal closed. In a modification, closure of the main switch first starts the heater only, the current supply to operate the pump motor and that to close the leak valve being started simultaneously by the time delay means. Fig. 4 shows apparatus in which a reservoir 28 between the diffusion pump 1 and backing pump 4 carries a pressure-actuated contact 29 to close the circuit of the pump motor and leak valve 32 ; a barometric valve 30 is provided between the reservoir and the backing pump, and a like valve 35 is provided in the pipe leading to the mercury reservoir ; a leak valve 37 in this pipe is controlled by a pressureresponse contact 39 in the return pipe of the pump 1. Surplus mercury condensing in the seal or the pipe 2 is caused to return to the diffusion pump by overflow &c. The mercury reservoir 23 and barometric tube 22 may be replaced by a plunger in a reservoir or by a movable reservoir or one having flexible sides to vary the level in the seal, or the cap 20 may be movable by a solenoid. The seal may be controlled by a Pirani gauge or gauges actuated by the high vacuum and the pressure, e.g. in the mercury boiler.