Originally posted by Grampy Bobby
What does this "minus 14 torr or so, a million times better a vacuum than we can make in standard industrial uses." suck?
Yeah, the way industrial vacuum goes, there is a level of vacuum that goes from zero to about about 30 inches of mercury, that's where in a column of mercury where it is in a u shaped tube say three feet high on both necks, and you put mercury in it and pump down one side of the tube while the other side is open to atmosphere, the more you pump out the one side the more the mercury moves from where it was level between the two tubes to higher up on the side that is being pumped.
That movement though, ends when the level changes by about 30 inches because atmospheric pressure pushing down on the open end pushed the mercury up the side with the vacuum but only up to a point. Doesn't matter how much better the vacuum gets (how much less air is left on that side) the mercury will refuse to move any more than that 30 inches or so because Earth's atmosphere can't push any harder than that.
On Venus, however, the pressure there is almost a thousand times that of Earth, just like biblical hell, 1500 pounds per square inch and a thousand degrees...
So there, if you had the same set up, the tube would have to be thirty THOUSAND inches high because that is how hard Venus' atmosphere would push down on a column of mercury when the other side is sucked out.
Conversely, if that same setup was on the moon, no matter how good your vacuum is on the side you are pumping out, the mercury won't move at all since the vacuum on the other side is already WAY better than anything we can achieve on Earth.
Get that part?
Now, that is the level of vacuum used to hold down stuff like wafers to a chuck or the high end vinyl record players that have a vacuum to suck down the vinyl record flat.
That's the first level of vacuum and is easy to get with cheap pumps.
The next level is where you start to think about atmosphere pressure in terms of Torr (the name of an early atmosphere scientist).
One atmosphere is 760 torr and that 30 inches of mercury thing would be getting down to MAYBE 1 torr.
But that is only the beginning of vacuum levels.
Now more complex mechanical pumps can go down a thousand times lower, to around 1/1000 th of a torr, called in the trade, one millitorr.
Now that represents the second level.
The third level which uses a variety of different kinds of high vacuum pumps, google that for more info, it would take me several pages just to list the different technologies that do that job.
But from 1 milltorr you go down to micro torr level, where 1 E -6 (one millionth of a torr) is starting to be useful for industrial purposes.
My machine gets down one to two orders of magnitude lower yet, one of them into the -8 range, one hundred millionth of a torr.
Another machine is in the - 7 range, on tenth of a millionth of torr, ten times worse vacuum but still way good enough for most industries.
Now there is a third level much lower than that using a bunch of techniques I won't bore you with but the big guys at CERN and so forth, go WAY lower than I do here at work, more like one TRILLIONTH of a torr, down in the -13 or so level.
That is about as good as we can get here on Earth. If they open the doors to space on a chamber in the ISS, they can get instant -15 or better vacuum. I don't know if they are actually doing experiments like that but it is funny, just open a door and you get vacuum levels way way better than any we can do with on Earth, same as on the moon.
My machine running on the moon wouldn't even need a vacuum pump, instead it would need to be sealed up so the levels we use when it operates won't just get totally sucked out but the incredible vacuum on the moon
The best vacuums for R&D labs and some production outfits go down to the -12 level for a process called "Molecular Beam Epitaxy" where they build up layers basically atom by atom and that takes a very good level of vacuum.
My machine is WAY to dirty for that kind of job, when it runs, it is in the millitorr range and my high vac pump has to be throttled back to allow those higher pressures to exist in the main chamber, otherwise that level would just gum up the pump and the pump would try to keep the vacuum level in the -5 or -6 range (-5 is worse than -6) where we run argon gas into the system a thousand times thicker than that, -3 level.
So that's the skinny on high vacuum, hope it doesn't give you a headache