gravityzero
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Registered: 14-6-2013
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vacuum question
Got a vacuum chamber coming in soon. Can't wait to put it to the test. This will allow for purging or degassing, such as epoxies. I'd imagine I
could use it as a desiccating chamber as well.
My question is totally separate, but I wanted to throw this out there and get any neat ideas on using this chamber as well.
My question deals with using a distillation setup with a vacuum. First, what pressure is safe for good pyrex?
I'm running on my vac around 40 kPa / 300 mmHg. Can I go much higher without safety concerns?
I also am curious if the veterans out there have ever discovered how to hold a vacuum, once created, so the vacuum pump can be shut off?
I have not really tried this, but don't think the vacuum would hold very long. Am I wrong?
Thanks in advance. I know I'm a bottom feeder, but I do appreciate any assistance.
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macckone
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The safety is entirely dependent on the glassware.
Some glass really isn't safe for vacuum usage, while other
glass can go down to basically absolute vacuum.
If your glassware has good seal you can put a pair of good
valves in-line and maintain vacuum for as long as necessary.
Of course that assumes out-gassing is occurring inside of your
vacuum apparatus.
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gravityzero
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Yeah. Thanks for the info.
I was curious if that could be done. Seems like I saw a youtube video with that going on before.
I forgot all about the out-gassing. I have a self made trap that works great for protecting the pump and I've seen bubbles go through from time to
time, which is the gas.
I don't really have a way to deal with that unless there is an item I'm not aware of.
I do have quality glassware, mostly Pyrex and Chemglass.
I will probably just try different levels, until I find what I like.
I've also been using too long a column and not sealing properly.
Thanks again for the suggestions.
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zed
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For ordinary undamaged pyrex, high vacuum is usually not a problem. It can become a problem with larger vessels.. With our standard atmospheric
pressure of ~15Lbs/Sq In, the tons of pressure build up on the outside of large containers. At a certain point, glass just isn't the best material.
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