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Vacuum Pump

  1. Jun 29, 2012 #1
    Dear All,

    Appreciate if you can guide me on understanding the ultimate pressure of vacuum pump.

    I have two models for review.

    One has ultimate pressure of 1 x 10^-4Torr the other has 2 x 10^-3Torr.

    From this can it be said that the vacuum capability of the first pump (1 x 10^-4) larger range? is better than the second pump?

    Both has speed 35CFM.

    Model 1 Pump WELCH 1375
    Model 2 Pump PFEIFFER DUO65

    Thanks for your help.
  2. jcsd
  3. Jun 30, 2012 #2


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    These specs indicate coarse vacuum pumps, where the quality of the ultimate vacuum is not that critical.
    My guess is other parameters, such as price, size, power use, noise or durability are also factors in the purchase decision.
    If those don't matter in your case, then yes there is a factor of 20 difference in the vacuum quality produced by the two pumps.
  4. Jul 3, 2012 #3
    Hi, thanks for replying.

    What is the signifance of the curve for the Speed vs the Ultimate Pressure. What does the curve implies?

    ie if i found a machine that is running at 20CFM (15 less) but having 1 x 10^-4torr. is that ok?
  5. Jul 4, 2012 #4


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    The pump will not exhaust the volume to the ultimate pressure immediately,
    A higher CFM rating unit will pump down a volume faster than the lower rated pump, but if you can afford the time, the lower CFM rated pump will serve equally well.
    Do note that if you have any sort of a setup where you need to repeatedly access some element that is operating when in vacuum, it can be a real pain to wait for the pumpdown each time you adjust something.
    What drives the need for a vacuum?
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