HP 5973, Hardware Manual

Page: 79 / 297

3 Troubleshooting the MSD
Pressure symptoms
79
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 - 2.0 ml/minute), the foreline pressure will be approximately 20 to
100 mTorr. The vacuum manifold 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.
The foreline pressures listed can only be measured on diffusion pump-equipped
systems. Turbomolecular pumps are controlled according to their speed and do
not have foreline pressure gauges. The vacuum manifold 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 is above 100 mTorr, 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 (usually the sideplate is not pushed in or vent valve is open)
• Foreline pump oil level is low or oil is contaminated
• Foreline hose is constricted
• Foreline gauge is not working correctly
• Foreline pump is not working correctly
Vacuum manifold pressure is too high
If the pressure you observe is above 1.4
×
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
)
• Diffusion pump fluid level is low or fluid is contaminated
• Turbomolecular pump is not working correctly