Wednesday, October 23, 2013

Vacuum problems during sample intro


  • Granville phillips micro ion gauge controller shows 2e-5 air lock pressure
    • degass gauge, jiggle connector cable, no help
  • Leave pump running ~ 1.5 hour during sample transfer, analysis, then open gate valve
    • prep still 8.8e-6, would expect better
    • prep chamber 1.8e-7 (low 10's before opening), consistent with intro gauge
    • close gate, pressure drops low 9's prep, increase to 1.7e-5
  • Connect VQM cable to prep mass spec, turn on, mostly 18 amu in UHV
    • open to air lock, lots of 32, 28, leak...
  • pump air lock with prep ion pump, turbo valved off
    • now mini IG 4.6e-7, prep 3.8e-8
    • close valve to air lock, 14 and 28 drop, 18, 2, 44 relative rise, 1.9e-9
  • reopen gate
    • prep back to 3.8e-8
    • 28, 14, 40, 32 rise, water related peaks fall
  • now open turbo pumping valve
    • pressure to 2.4e-7 prep, 9.8e-6
    • 28, 32, 14 rise, also 40, air leak
  • close turbo valve, pressure drops, 5e7 in air lock, 4.6e-8 prep, 14, 28, 32, 40 drop
  • even with turbo valve closed, air lock pressure rises rapidly from mid 7's to 5's

Air leak in pumping, probably in manifold

  • biggest leak was swagelock connected to mini flange at manifold pumping valve, tighten to reduce manifold to 1.1e-6 from 2e-5. 
  • gasket (already suspicious) at 2.75" tee caught between flanges, ie offcenter, replaced.
  • marginal improvement, still possible leak in manifold somewhere

No comments:

Post a Comment