MS not holding vacuum

[brinker]

Hello, we have a Sciex 4000QTrap that is not holding vacuum. The pumps get up to speed but then time out with an error message like "Vacuum Gauge or Vacuum System Failure". Covering the hole in the orifice plate helps, but doesn't completely solve the problem; the system just takes longer to timeout. The ion gauge filament turns on and off when it is supposed to. We are wondering whether the temperature sensor in the turbo pump could be the problem. Does anyone have any experience with this, or any suggestions? We're about to try swapping out the rough pump.

[James_Ball]

My 3200 did that when the vacuum gauge tube was going bad. You may need to change it, which is pretty easy.

Also, it could be a leak in the O-ring behind the ceramic interface plate on the front of the analyzer. I have to press in on mine when I start the vacuum go get it to seal.

[brinker]

Thanks for the suggestions. We finally brought in a service engineer, and he determined that the problem was due to a faulty pressure switch.
Now we're having a similar problem, but not quite the same. This time, the turbos shut down for no apparent reason. When restarted, they come up to speed and all the indicators are that the system is ready to run, but after an hour (or maybe less) the turbos shut down again. Eventually, after several tries, things keep running.

When you say "vacuum gauge tube", do you mean the thing next to the analyzer turbo, with the little coil that glows when it's on?

[James_Ball]

Thanks for the suggestions. We finally brought in a service engineer, and he determined that the problem was due to a faulty pressure switch.
Now we're having a similar problem, but not quite the same. This time, the turbos shut down for no apparent reason. When restarted, they come up to speed and all the indicators are that the system is ready to run, but after an hour (or maybe less) the turbos shut down again. Eventually, after several tries, things keep running.

When you say "vacuum gauge tube", do you mean the thing next to the analyzer turbo, with the little coil that glows when it's on?

Yes, that it the ion gauge tube that measures the high vacuum in the analyzer. When mine went out I thought I was have problems with the turbo pump because it would keep shutting down, but it was just because it didn't read the true pressure in the analyzer. Watch the pressure in the analyzer as the system pumps down, it should get down to the 3*10^-5 torr range within less than a half hour, probably much faster than that. If it is not dropping to levels near that quickly, it could be the gauge tube.

[brinker]

It seems to be dropping to that level well within a half hour...