IPT E&C VACUUM PUMP CALCULATION to ; e-mail : buypump@naver.com Introduction to VacuumThe earth's atmosphere exerts a pressure upon us, known as the atmospheric pressure, which can be measured in a number of ways. At sea level the standard pressure is 14.7 psia or 29.92" Hg or 760 mm of Hg (Torr). Because the barometric pressure varies, the above sea level pressures are used as a refe..