24 5977B Series MSD Troubleshooting and Maintenance Manual
1 Introduction
Mass spectrometer automated shutoff
valves closed
Some mass spectrometers are equipped with
automated diffusion pump shutoff valves. Some
mass spectrometers are equipped with automated
shutoff valves. In these instruments, deliberate
operator action or various failures can cause the
shutoff valves to close. Closing the shutoff valves
does not shut off the flow of carrier gas. As a result,
hydrogen may slowly accumulate in the mass
spectrometer.
Mass spectrometer manual shutoff valves
closed
Some mass spectrometers are equipped with
manual diffusion pump shutoff valves.Some mass
spectrometers are equipped with manual shutoff
valves. In these instruments, the operator can close
the shutoff valves. Closing the shutoff valves does
not shut off the flow of carrier gas. As a result,
hydrogen may slowly accumulate in the mass
spectrometer.
GC off A GC can be shut down deliberately. It can also be
shut down accidentally by an internal or external
failure. Different GCs react in different ways. If a
7890 GC equipped with Electronic Pressure Control
(EPC) is shut off, the EPC stops the flow of carrier
gas. If the carrier flow is not under EPC control, the
flow increases to its maximum. This flow may be
more than some mass spectrometers can pump
away, resulting in the accumulation of hydrogen in
the mass spectrometer. If the mass spectrometer is
shut off at the same time, the accumulation can be
fairly rapid.
Tab le 4 Hydrogen accumulation mechanisms (continued)
Mechanism Results
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