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New Vacuum Pump Idea Answered

I have a new idea about a new type of positive displacement vacuum pump.  Its of the piston variety, but instead of a one way valve which doesn't work when the pressure gets low enough, another piston is used to act as a valve switching between the vessel to be evacuated (when the main piston is pulling a vaccum) and the atmosphere (when the piston pushes the air evacuated out).

This solves the one way valve problem.  Could this pull a much lower vacuum?  I need a fairly strong vacuum, but I don't want to have to build/buy a turbomolecular pump.

Also, i have a metal lathe, that's why i'm going with the piston variety.

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One thing that limits vacuum is the vapour pressure of the lubricant. For hi-vac you need a multi-stage set-up. Oil-filled hi-vac pumps often use vanes rather than pistons. I've seen multi-head diaphragm pumps get down to 0.1 mm (I think), but pistons ain't good. I thought you had a hi-vac pump already? Back that up with another on the exhaust?

L

yeah, about that pump from way back when.  It wasn't pulling a decent vacuum, so i took it apart to see what's wrong.  Turns out that all of the rubber pieces were completeley dissolved, a decent amount of the springs were broken, and quite honestly the only thing that was keeping the whole thing together was dirt and gunk inside of it.

The end result was oil all over the place and a total mess to clean up.  It was a pain.

I still have the very nice motor, though! haha

so piston pumps arn't good for what i want, i'll check out vane pumps

You'll have seen how that old pump is built then - any chance of a repair? I don't know of any hi-vac piston pumps.

L

the man that  made those vacuum tubes himself also built his own pumps.  He used a piston pump as a primary and a turbomolecular pump as a secondary:
http://translate.google.com/translate?u=http://paillard.claude.free.fr/&langpair=fr%257Cen&hl=en&ie=UTF-8
his pump (and it actually seems like he tried to use electric valves instead of one-way valves, but said it was too difficult for some reason) go down to 1.5 torr, where he then uses the turbomolecular pump in addition to it.

nixie tubes need 30 torr of neon, so if i do without a turbomolecular pump, if I just flush out the tube several times with neon, it should be adequete.

if I do use a turbo molecular pump, isn't it just essentially a bunch of fans, some spinning and some not, and that's it?
It seems like such a thing should be fairly cheap to make.

On a side note, I'm probably going to use helium because it's much easier to get a hold of.

30 Torr - just flush it a few times, I thought you had need for much less than 1. The description of the turbomolecular sounds about right, but at very high speed, and there's the difficulty in making one...

L

here's my source for the 30 torr thing:
http://tubedevices.com/alek/pwl/lc1d/homemade_nixie_tubes.pdf

That's pretty good, but a lot of work. He reminds us that neon ain't cheap...

L

i accidentily hit flag when i meant reply, we'll see how that works :P


that's why i'm going to use helium, i found a brand for baloons which is 99% pure so im just going to try that and see if it works.

Yellow nixies should look awesome

I got down to 10 mm Hg using a converted electric auto tire pump.  It is slow though and you would likely have to evacuate a tank and then use the tank for your tube building.  How much vacuum do you need?

pretty much yeah, but is there some other problem of this type of vacuum pump besides the one way valve (which would be fixed with this solution)?

I'm trying to make nixie tubes again :D

.  The only other "problem" I see is sealing the piston rings. With good valves and good rings, you should be able to pull a decent vacuum.
.
.  I'd use a refrigeration service pump.