156 5977B Series MSD Troubleshooting and Maintenance Manual
6 Vacuum System
Common Vacuum System Problems
Air leak symptoms
The most common problems associated with any vacuum system are air leaks.
Symptoms of air leaks include:
• Loud gurgling noise from the foreline pump (very large leak)
• Inability of the turbo pump to reach 95% speed
• High foreline pressure in diffusion pump MSDs
• Higher than normal high vacuum gauge controller readings
The 5977B Series MSD will not pump down successfully unless you press on
the side plate (analyzer door) when you turn on the MSD power. Continue to
press until the sound from the foreline pump becomes quieter.
Pumpdown failure shutdown
The system will shut down both the high vacuum and the foreline pump if the
system fails to pump down correctly. Two conditions that trigger shutdown
are:
• Diffusion pump MSDs, shutdown occurs if the foreline pressure is above
300 mTorr after 7 minutes.
• Turbo pump MSDs speed below 80% after 7 minutes.
This is usually because of a large air leak: either the side plate has not sealed
correctly or the vent valve is still open. This feature helps prevent the foreline
pump from sucking air through the system, which can damage the analyzer
and pump.
To restart the MSD, find and correct the air leak, then switch the power off
and on. Press on the side plate when turning on the MSD power to ensure a
good seal.
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