Name: Don C.
What is the maxium obtainable vaccuum (in inches of
mercury) at an altitude of 3200 feet?
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
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.
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
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.
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
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Update: June 2012