36 Troubleshooting and Maintenance Manual
2 General Troubleshooting
Pressure Symptoms
This section describes unusual pressure readings and their possible causes. At
typical column flow rates (0.5 to 2.0 mL/minute), the foreline pressure will be
approximately 16 to 18 mTorr. The Quad pressure with collision cell gas on or
off will be approximately 1 × 10
-4
to 2 × 10
-4
Torr. These pressures can vary
widely from instrument to instrument so it is very important that you are
familiar with the pressures that are typical for your instrument at given
carrier and collision gas flows.
Foreline pressure is too high
If the pressure you observe for a given column flow has increased over time,
check the following:
• Column (carrier gas) flow is too high
• Collision cell gas flow is too high
• Air leak (usually the side plate is not pushed in or vent valve is open)
• Foreline pump oil level is low or oil is contaminated
• Foreline hose is constricted
• Foreline pump is not working correctly
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