Maximum Vacuum ```Name: Don C. Status: other Age: 40s Location: N/A Country: N/A Date: 1999-2001 ``` Question: What is the maxium obtainable vaccuum (in inches of mercury) at an altitude of 3200 feet? Replies: In principle, of course, the best possible vacuum anywhere is nothing at all in the container, and under ideal circumstances this is achievable. In common practice, the achievable vacuum at 3200 feet would not be much different from that at ground level because atmospheric pressure at 3200 feet is not that different from that at ground level. The best vacuum for a system is achieved when the pump rate equals the leak rate. At low pressures, the biggest leak contributor is usually not an actual leak, but the result of gas escaping from materials inside the vacuum chamber. For commonly available pumps, well-chosen materials, and good practice, a pressure of 10^-9 Torr is achievable. Tim Mooney Hi, Don!! Don, forgive me if I say things that you already know. First of all, what is vacuum? Answer: vacuum is absence of air (in the common sense) or - better - vacuum is the absence of matter !!! You will not find matter in the space where the astronauts work repairing the Hubble, so to speak. Or even there, you will find some molecules lost in the space. Better, you move between stars, and even there, you still will find some lost atoms or molecules. Anyway, it is estimated that it is possible to find a molecule in a cubic meter of space !! Now, lets go back to Earth. Here we are at the top of a mountain ( 3200 ft ca. 1 km) and you wish to produce a vacuum and measure it in inches of Mercury. Well, it all depends on how good your machine is, to remove the air from a given space. The best vacuum obtained till today could remove almost all the air, but ca. 100.000 molecules in a cubic centimeter still remain...what is pretty good, if you consider that at the sea level, you will find ca. 30 billion billion of air molecules in a cubic centimeter. To speak a litte more about vacuum machines, you can find several types of them like lab vacuum pumps ( they use an oil-sealed rotor ), water-sealed rotary pumps, ejectors where high pressure water-vapour removes air molecules, till to cryogenic pumps, that removes the air by condensing the gas molecules on a very cold surface. And - believe it - ion pumps, which make use of an electron flow that ionize the air through collisions between them, draw the ions (air) and collect them in a collector, causing almost perfect vacuum. Alcir Grohmann Beschaffung SAM I am not sure what your constraints are. Given the appropriate mechanical vacuum "roughing pump" and "diffusion pump --- mercury or oil" and a leak free, de-gassed system it would be easily possible to achieve 10^-6 to 10^-8 mm of Hg. There are many chemistry and / or physics labs that operate at these altitudes. Vince Calder Click here to return to the General Topics Archives

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