Micromass/Waters ZMD vacuum problem

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Jul 26, 2010, 6:05:46 PM7/26/10
Dear all,
After a (pretty horrible) crash of the Edwards EXT250HI turbomolecular
pump in our Micromass/Waters ZMD, we had to replace this pump with a
refurbished one. After putting it in, we ran happily samples on this
LCMS system for about a week, but one morning...instead of showing a
green 'vacuum' light, it shows now a steady 'amber'. However, the
(EXT70 and EXT250HI) pumps are all up to 100% speed and do not seem to
be too hot. Also the Masslynx software shows a low vacuum (in the
green). Strangely enough, the light turns about 2 times per day
suddenly to green, but within an hour back to amber. What would be the
first steps to diagnose where the problem lies?! Thanks a lot for the
Joris Beld


Jul 27, 2010, 10:47:14 AM7/27/10
I am not familiar with the Micromass/Waters, but it sounds like a small
air leak to me. What does m/z 28 and 32 look like? Also, how long was the
system open to the atmosphere? I have found that if a system is shut down
for an extended time, it can take days to get it equilibrated to working
pressure (vacuum). Look at m/z 18. Do you have any accurate pressure
gauge on the system? That's what I go by. A really small leak may not
heat up the pump(s), but it can kill your vacuum and response. Did you
install new seals when you changed the pump? You may have to reseat
it/them. Good luck!


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