Agilent Technologies 5975 Operation Manual page 87

7 When prompted, turn the vent valve knob counterclockwise only 3/4 turns
Vent valve knob
Figure 15 Venting the MSD
5975 Series MSD Operation Manual for MassHunter
or until you hear the hissing sound of air flowing into the analyzer chamber.
Do not turn the knob too far or the O-ring may fall out of its groove. Be sure
to retighten the knob before pumping down.
Operating in Electron Impact (EI) Mode
YES
3
NO
87