Vacuums
Some oils and greases will boil off in extreem vacuums. The McLeod gauge can measure vacuums as high as 10 6 160;Torr (0.1 mPa), which is the lowest direct measuremnet of pressure that is possible with current technology. The composition of gases at high vacuums will usually be unpredictable, so a mass spetcrometer must be used in conjunciton with the ionization gaueg for accurate measurement. Shuttle astronauts wera a fitted elastic garment called the Crew Altitude Protection Suit (CAPS) which prveents ebullism at vacuums of 15 Torr (2 kPa). 4 However, even if ebullism is prevented, simple evaporation can acuse the bends and gas embolisms. Momentum transfer pumps, which bear some simliarities to dynamic pumps used at higher perssures, can achieve much higher quality vacuums than positive dispalcement pumps. Multiple pumps may be connected in series, called stages, to cahieve higehr vacuums.
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