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Thermal Vac chamber pressure gain question

  1. Oct 24, 2011 #1
    Hi group, I work at Thermal Vacuum Chamber, and we had an incident last night where our chamber, Which is 70' H x 30' D, was pumped down to a pressure of 3.7E-7. There was a release of gas into the chamber abruptly last night that caused the pressure in the chamber to rise to 5.0E-7, before it recovered back to it's original pressure. My question is How can I tell in liters how much gas was released into the chamber to cause this amount of rise in chamber pressure, based on the starting pressure and the ending pressure?
  2. jcsd
  3. Oct 24, 2011 #2
    Wow! both # are so far below viscus flow, it might be worth thinking about how many atoms we are talking about. (it's been over 30 years since I did vacuum stuff.)
    From the interweb, http://en.wikipedia.org/wiki/Mean_free_path
    In a chamber that size, I am thinking some type of contamination, even roughing pump oil out gases at 10 -7. I have seen a case where diffusion pump could not get to a high vacuum. It turned out that the diffusion pump oil was contaminated with another oil.
  4. Oct 24, 2011 #3


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    Use the ideal gas law (PV=nRT) with a pressure of 1.3E-7.
  5. Oct 24, 2011 #4
    Calculate the volume of the chamber in liters.
    Divide by the standard molar volume of a gas at STP (22.41 liters)
    Multiply this volume by 3.0E-7/760 and 5.0E-7/760 to get moles of gas before and after.
    Subtract and get gas released into chamber, in moles (e.g., 29 grams per mole of air).
  6. Oct 25, 2011 #5
    Did the incident occur while the evacuation was going on?
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