Vacuum Tests of Rubber, Lead, and Teflon Gaskets and Vinyl Acetate Joints

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Abstract
Rubber, Teflon, and vinyl acetate sealed systems are compared, by an approximately quantitative method, with a lead gasket sealed system which is shown to give off negligible gas at room temperature. Rubber is shown to evolve relatively large amounts of gas with an apparent vapor pressure above a micron at room temperature and about 0.1 micron at liquid air temperature. Continuous pumping for several days produces no improvement, nor does the use of metal‐to‐metal joints. Vinyl acetate joints are shown to improve with pumping over a period of several days, reaching a condition exhibiting an ``apparent vapor pressure'' of 5×10−7 mm of mercury, or less, at room temperature. Heating to 45°C raises the apparent vapor pressure to the 10−5 mm range, and heating to 100° raises the apparent vapor pressure to the micron range. If this behavior is caused by the vapor pressure of the vinyl acetate itself, continued baking in vacuum will, of course, produce no improvement.

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