AT the meeting of the Wireless Section of the Institution of Electrical Engineers on February 6, a paper entitled “Continuously Evacuated Valves and their Associated Equipment“was read by Mr. C. R. Burch and Dr. C. Sykes. This paper describes the development of demountable thermionic transmitting valves of various power ratings, the valves being evacuated continuously by means of oil condensation pumps. This work has arisen out of some experiments carried out in 1929 on the distillation of lubricating oil in a molecular still. It was found that one of the fractions was about a thousand times less volatile than mercury, so that if such a liquid could be used as the working fluid in a condensation pump, a vacuum of the order of 10−6 mm. should be attainable without the use of liquid air or other refrigerants; and such a vacuum is quite adequate for valve exhaustion. These expectations have been fully realised in the development of oil-condensation pumps which will work against a fore-vacuum of 0–05 mm. and will produce a vacuum of 10−3-10−6 mm. at a speed of 20 litres per second. Such pumping equipment is described in the paper in some detail, and reference is made to its application to the production of thermionic valves of a power rating ranging from 20 kw. to 500 kw. for high-frequency furnaces and for radio transmitting stations. Several valves of the 30 kw. order have been in use on commercial radio traffic at the Post Office station at Rugby for long periods, and they have given satisfactory service. A 500 kw. valve is in the stage of experimental trial on the long-wave transmitter at Rugby. The relative merits of these valves and those of the sealed-off type were discussed briefly in the paper, and were enlarged upon by several speakers in the discussion which followed the reading of the paper.