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Subject: Re: Helium Pump down time
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Date: 07/22/02 at 3:47 PM
Posted by: Phil Danielson
In Reply to: Helium Pump down time posted by Anton De Beer on 07/18/02 at 9:31 PM:
You've already gotten some really good possible explanations to your He pumping problem, but I'd like to add another. You might well be building upso much He in the foreline that it is back-migrating through the turbos into the chamber much like what happens in a "counter-flow" He leak detector. The backing pump might not be removing the He from the foreline as efficiently and quickly as expected. You could easily check this out by bleeding a little dry gas into the foreline (N2 or Ar) following your He dosing of the chamber. It might sweep the He through the backing pump quicker and allow a quicker pumpdown.
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