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Best vac pump for boiling water

  1. Nov 8, 2011 #1
    Hello all,

    I am seeking advice on the best, relatively cheap vacuum pump to pump water vapor from the 2 kPa range to the 100 kPa range. Essentially any pump that would work well at boiling water at room temperature would work for me. I'm hoping that someone on here may have done that as a demonstration and may have some practical advice for me.

    What I want is to move the water vapor somewhere, not to generate a vacuum, so getters, pre-pump cold traps, etc. aren't really helpful. I need to actually pump the water vapor to a higher pressure location.

    I have tried a few pumps I have on hand. I have a little Gast pump that's great and reliable, but it doesn't have a low enough ultimate pressure. I tried hooking up two Gast pumps in series, but apparently too much air leaks through the piston seals and they still don't have a low enough ultimate pressure.

    I also tried a good old fashioned rotary vane roughing pump. This has (or had) a low enough ultimate pressure. However, I have found that condensing water inside the pump is not good for it. It no longer runs, although I could repair it if it would be useful.

    I was thinking that the biggest problem was that water was recondensing inside the pump. However, I don't know of any pump that could operate at a high enough temperature to keep the water vapor from recondensing. Most pumps will kick out the temperature switches on their motors long before getting that hot. Perhaps some belt-run Welch pumps?

    I've considered a liquid ring vacuum pump, using a liquid with a lower vapor pressure than water. This seems to be just the right thing. Unfortunately, these seem to be only available in large, expensive commercial versions. I have tried building my own, and frankly while I have rebuilt vacuum pumps before, building one from scratch may be beyond me. Since building one or spending $8000+ on a commercial one seem to be my only options, I'm reaching a point of frustration on this project. I'm self-financing this. Can anyone help?

    If this is not the correct sub-forum for this question please move it.
  2. jcsd
  3. Nov 11, 2011 #2
    Could a mod, mentor, or admin please move this post to a sub-forum where it is more likely to receive a reply? Thank you
    Last edited: Nov 11, 2011
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