Vacuum System 6
Troubleshooting and Maintenance Manual 141
Calibration Valve and Vent Valve
Calibration valve
A calibration valve (Figure 23 and Figure 24) is an electromechanical valve
with a vial to hold the tuning compound. When a calibration valve is opened,
tuning compound in the vial diffuses into the ion source. The valves are
controlled by the MassHunter Workstation software.
EI Calibration Valve
The EI calibration valve is held onto the top of the analyzer chamber by two
screws. A small O-ring provides a face seal.
Perfluorotributylamine (PFTBA) is the most commonly used tuning
compound for EI operation. PFTBA is required for automatic tuning of the MS.
CI Calibration Valve
The CI tuning compound is perfluoro-5,8-dimethyl-3,6,9-trioxidodecane
(PFDTD). The CI calibration valve is part of the reagent gas flow control
module. It is controlled by the MassHunter Workstation software. It opens
automatically during CI autotune or manual tuning, allowing PFDTD to diffuse
through the GC/MS interface and into the ion source.
Vent valve
The vent valve knob (Figure 25) screws into a threaded port in the front of the
calibration valve. An O-ring is compressed between the knob and the valve to
form a seal. The threaded end of the knob has an air passage inside it, allowing
air to flow into the manifold when the knob is partially unscrewed. If you turn
the knob too far, the O-ring can come out of its slot.
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