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Case 2 is a tank in use, with the air pressure at pressure P (gauge) and a water volume of V. Referring to the diagram on the right, a pressure tank is generally pressurized when empty with a "charging pressure" P c, which is usually about 2 psi below the turn-on pressure P lo (Case 1). The total volume of the tank is V t.
Ultra-high vacuum (often spelled ultrahigh in American English, UHV) is the vacuum regime characterised by pressures lower than about 1 × 10 −6 pascals (1.0 × 10 −8 mbar; 7.5 × 10 −9 Torr). UHV conditions are created by pumping the gas out of a UHV chamber.
An oil diffusion pump is used to achieve higher vacuum (lower pressure) than is possible by use of positive displacement pumps alone. Although its use has been mainly associated within the high-vacuum range, down to 1 × 10 −9 mbar (1 × 10 −7 Pa), diffusion pumps today can produce pressures approaching 1 × 10 −10 mbar (1 × 10 −8 Pa) when properly used with modern fluids and accessories.
The ASME definition of a pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. [2]The Australian and New Zealand standard "AS/NZS 1200:2000 Pressure equipment" defines a pressure vessel as a vessel subject to internal or external pressure, including connected components and accessories up to the connection to external ...
Ultra-high vacuum systems are usually baked, preferably under vacuum, to temporarily raise the vapour pressure of all outgassing materials and boil them off. Once the bulk of the outgassing materials are boiled off and evacuated, the system may be cooled to lower vapour pressures and minimize residual outgassing during actual operation.
Normal copper is unsuitable for high vacuum as it is difficult to outgas completely. Copper is insensitive to hydrogen and impermeable to hydrogen and helium, has low sensitivity to water vapor, but is attacked by mercury. Its strength falls sharply above 200 °C (392 °F). Its vapor pressure becomes significant at above 500 °C (932 °F). [2]