Vacuum apparatus is widely used in research and industrial establishments for providing and monitoring the working environments required for the operation of many kinds of scientific instruments and process plant. The vacuum conditions needed range from the relatively coarse vacuum requirements in applications covering diverse fields such as food packaging, dentistry (investment casting), vacuum forming, vacuum metallur- gical processes, vacuum impregnation, molecular distillation, vacuum drying and freeze drying etc. to the other extreme involving the highest possible vacuum as in particle...