154 5977B Series MSD Troubleshooting and Maintenance Manual
6 Vacuum System
Overview
The vacuum system creates the high vacuum (low pressure) required for the
MSD to operate. Without the vacuum, the molecular mean free path would be
very short and ions would collide with air molecules before they could reach
the detector. Operation at high pressures also would damage analyzer
components.
The 5977B Series MSDs use two vacuum pumps to obtain the vacuum levels
needed. One of two foreline pumps (standard or dry) creates a low vacuum,
then a high vacuum pump engages to create the vacuum needed for
operation.The 5977B Series MSD uses one of two kinds of high vacuum pumps:
a diffusion pump or a turbomolecular (turbo) pump. The pump type
determines the maximum column flow supported by the MSD. The 5977B HES
Series MSD model G7079B uses a turbomolecular (turbo) pump for high
vacuum. It has a maximum column flow rate of 4.0 mL/min.
Most vacuum system operation is automated. Operator interaction is through
the data system or control panel. Monitor the vacuum system through the data
system or GC control panel.
Tab le 10 Recommended maximum flow rates by model
Model number
Description
Maximum recommended
column flow
G7080B Diffusion pump, EI 1.5 mL/min
G7077B Turbo pump, EI 4.0 mL/min
G7078B Turbo pump, EI 4.0 mL/min
G7081B Turbo pump, EI 4.0 mL/min
G7079B Turbo pump, EI HES 4.0 mL/min
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