80
3 Troubleshooting the MSD
Pressure symptoms
Foreline pressure is too low
If the pressures you observe are below 20 mTorr, check for the following:
• Column (carrier gas) flow is too low
• Column plugged or crushed by an overtightened nut
• Empty or insufficient carrier gas supply*
• Bent or pinched carrier gas tubing*
• Foreline gauge is not working correctly
* These could create a fault condition in the GC that would prevent the GC from
operating.
Vacuum manifold pressure is too low
If the pressures you observe are below 1 × 10
-6
Torr, check for the following:
• Column (carrier gas) flow is too low
• Column plugged or crushed by overtightened nut
• Empty or insufficient carrier gas supply*
• Bent or pinched carrier gas tubing*
* These could create a fault condition in the GC that would prevent the GC from
operating.
Gauge controller displays 9.9+9 and then goes blank
This indicates the pressure in the vacuum manifold is above 8 × 10
-3
Torr.
• Solvent peak from an on-column injection
• MSD has not had enough time to pump down
• Excessive foreline pressure
• Bad connection or bad cable between the triode gauge and gauge controller
• Diffusion pump fluid level is low or fluid is contaminated
• Triode gauge tube has failed
• Line voltage too low
• Turbomolecular pump is not working correctly
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