Specifications

42 5975 Series MSD Troubleshooting and Maintenance Manual
2 General Troubleshooting
Pressure Symptoms
This section describes unusual pressure readings and their possible causes.
The symptoms in this section are based on typical pressures. At typical
column flow rates (0.1 to 2.0 mL/minute), the foreline pressure will be
approximately 20 to 100 mTorr. The analyzer chamber pressure will be
approximately 1 × 10
-6
to 1.4 × 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 gas flows. Also,
foreline pressures can only be measured on diffusion pump MSDs.
Turbo pumps are controlled according to their speed and do not have foreline
pressure gauges. The analyzer chamber pressures can only be measured if
your system is equipped with the optional gauge controller.
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
• Air leak (usually the sideplate is not pushed in or vent valve is open)
• Foreline pump oil level is low or oil is contaminated (standard foreline
pump)
• Foreline hose is constricted
• Foreline pump is not working correctly
Analyzer chamber pressure is too high (EI operation)
If the pressure you observe is above 1.0 × 10
-4
Torr, or if the pressure you
observe for a given column flow has increased over time, check the following:
• Column (carrier gas) flow is too high
• Air leak
• Foreline pump is not working correctly (see Foreline pressure is too high)
• Turbo pump is not working correctly
• Diffusion pump fluid level is low or fluid is contaminated