Vacuum in a Can

Discussion in 'Electronic Projects' started by alfa88, Mar 20, 2017.

  1. alfa88

    alfa88

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    In anticipation of my receiving an order of a couple H.P. Friedrichs' books I've been contemplating how to achieve a vacuum for some of the projects. There are those CO2 cartridges so I wondered if anyone has come up with a vacuum cartridge. In lieu of that is there a low cost alternative to achieve a light bulb/ thermionic valve worthy vacuum?
     
    alfa88, Mar 20, 2017
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  2. alfa88

    BobK

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    A vacuum pump comes to mind.

    Bob
     
    BobK, Mar 21, 2017
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  3. alfa88

    Audioguru

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    If you connect a vacuum cartridge to something that has normal gas or liquid pressure then the pressure in each would become the average.
     
    Audioguru, Mar 21, 2017
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  4. alfa88

    shrtrnd

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    BobK's advice is the right choice for creating a vacuum in a closed container.
    You said you want this low-cost. Find somebody in your area with a vacuum pump and make a deal with them.
     
    shrtrnd, Mar 21, 2017
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  5. alfa88

    KMoffett

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    KMoffett, Mar 21, 2017
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  6. alfa88

    BobK

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    Did anyone ever think about the term "vacuum cleaner?" Isn't a vacuum perfectly clean already?

    Bob
     
    BobK, Mar 21, 2017
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  7. alfa88

    alfa88

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    I pretty much suspected I'd be hitting the same vacuum issues as the old light bulb guys of yesteryear. Even a 2 stage vacuum pump is purported as insufficient. I was just hoping someone was aware of a solution. 'Vacuum in a can' was just a pipe dream.
     
    alfa88, Mar 21, 2017
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  8. alfa88

    KMoffett

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    You gave no indication on the level of vacuum or flow rate need for your "projects". Maybe roughing and diffusion pumps are what your looking for?

    The devil's in the details! :(

    Ken
     
    KMoffett, Mar 22, 2017
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  9. alfa88

    alfa88

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    I found a site that suggests 10-4 Torr to 10-6 Torr. Also suggesting a 3 stage diffusion type pump. Too rich for my blood. A typical vacuum cleaner is 25 Torr at best. The air con. vacuum pumps I've looked at are using different specs but I'm assuming they're inadequate and a 2 stage diffusion pump is still too pricey. I guess I should shelve this idea.
     
    alfa88, Mar 22, 2017
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  10. alfa88

    alfa88

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    Canned vacuum no. Helium possibly.
     
    alfa88, Mar 24, 2017
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  11. alfa88

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The problem with vacuum in a can is that all I've ever been able to get is the diluted vacuum. I want a concentrated vacuum so that (say) 100mL of concentrated vacuum can evacuate a couple of cubic metres.

    Hmmm... if that was positive pressure, that would make it 20,000 bar (approx). That's 2 * 10^5 bar.

    Now because I want negative pressure, that would only be 2 * 10-5 bar, right? (hahahaha)
     
    (*steve*), Mar 24, 2017
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  12. alfa88

    alfa88

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    The more I delve into this the more I am impressed how the old timers were able to push the limits back then. ~20 years after the Edison bulb the extreme vacuum was replaced by using an inert gas ,argon or nitrogen. But that's light bulbs.
    As the name implies a vacuum tube is an evacuated glass tube. In the distant future I'll try using helium at atmospheric pressure and see if I can make a home made light bulb and then triode.
    I never took physics so I'm really out of my league.
     
    alfa88, Mar 24, 2017
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  13. alfa88

    duke37

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    I don't think you can make a valve, the electrons will bump into the helium atoms.
     
    duke37, Mar 24, 2017
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  14. alfa88

    BobK

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    And ionize them if there is enough energy.

    Bob
     
    BobK, Mar 24, 2017
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  15. alfa88

    alfa88

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    Well that's no fun.
     
    alfa88, Mar 25, 2017
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  16. alfa88

    duke37

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    That could be a lot of fun:)
     
    duke37, Mar 25, 2017
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  17. alfa88

    Audioguru

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    I think my tummy has a vacuum when I am hungry.:)
     
    Audioguru, Mar 25, 2017
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  18. alfa88

    BobK

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    Aw, suck it up, AG.

    (which is probably what you do when hungry, anyway)

    Bob
     
    BobK, Mar 25, 2017
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  19. alfa88

    alfa88

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    Not to belabor this subject but I had a brain-fart. A CRT might make a good source of high vacuum if proper plumbing was attached to the neck and a method was devised to rupture said neck in the right place. Walla... Canned vacuum!
    Sounds dangerous as Heck.
    I feel stupid even suggesting a gas filled vessel would work as a triode. Regulator or light bulb maybe.
     
    alfa88, Mar 31, 2017
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  20. alfa88

    ChosunOne

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    A vessel filled at anywhere near atmospheric pressure (760 torr) would not work as a light bulb. The high-grade (for that day) vacuum originally used was eventually replaced with a low-grade vacuum and rarefied inert gas, I think mostly argon with some nitrogen. Even gas-discharge tubes use a rarefied gas (low-grade vacuum) to work. Any gas starting at atmospheric pressure would (1) take too high a voltage to ionize and (2) build up pressure when heated and burst the vessel. There's a reason incandescent and gas-discharge vessel glass is so thin: Much less problem with coefficient of expansion variation between inner and outer walls of the glass. Even Pyrex glass has its limits.

    That wasn't a bad idea about the CRT, as long as you recognize how dangerous it would be to try actually to do it.

    A few years ago I had occasion to do a few hours research on how the first light bulbs were made. I was surprised to discover just how difficult making a light bulb can be--the high-grade vacuum needed was just one major hurdle that Edison and his contemporaries had to get over. The famous carbon-filament light bulb picture we all see in history books was not the first practical incandescent bulb: It burned for (IIRC) 13.5 hours. It was the proof-of-concept that it could be done.

    I don't know what you're going for, alfa88, but if you're looking to make your own incandescent light source from scratch, I would look into the Nernst lamp. It was starting to replace carbon-filament bulbs in the lighting market until tungsten-filament bulbs came along, and it doesn't require a vacuum or even a gas-tight vessel.

    However, you might need to invest in a refractory oven and a very short length of thin platinum wire.
     
    ChosunOne, Apr 1, 2017
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