Agilent Technologies G7035A Operation Manual page 21

Table 4
Mechanism
Mass spectrometer turned off
Mass spectrometer automated
shutoff valves closed
Mass spectrometer manual shutoff
valves closed
GC off
Power failure
5977 Series MSD Operation Manual
Hydrogen accumulation mechanisms
Results
A mass spectrometer can be shut down deliberately. It can
also be shut down accidentally by an internal or external
failure. There is a safety feature that will shut down the flow
of carrier gas in the event of an MSD foreline pump shut
down. However, if this feature fails, hydrogen may slowly
accumulate in the mass spectrometer.
Some mass spectrometers are equipped with automated
diffusion pump shutoff valves. In these instruments,
deliberate operator action or various failures can cause the
shutoff valves to close. Shutoff valve closure does not shut
off the flow of carrier gas. As a result, hydrogen may slowly
accumulate in the mass spectrometer.
Some mass spectrometers are equipped with manual
diffusion pump 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.
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 Series GC
equipped with Electronic Pressure Control (EPC) is shut off,
the EPC stops the flow of carrier gas. If a GC's 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.
If the power fails, both the GC and mass spectrometer shut
down. The carrier gas, however, is not necessarily shut
down. As described previously, in some GCs, a power failure
may cause the carrier gas flow to be set to maximum. As a
result, hydrogen may accumulate in the mass spectrometer.
1
Introduction
21