Calibration Valves And Vent Valve - Agilent Technologies 5975C TAD VL MSD Troubleshooting And Maintenance Manual

6
Vacuum System

Calibration Valves and Vent Valve

Calibration valves
A calibration valve
hold the tuning compound. When a calibration valve is opened, tuning
compound in the vial diffuses into the ion source. EI MSDs have one
calibration valve; CI MSDs have a second calibration valve for the CI tuning
compound. The valves are controlled by the MSD ChemStation.
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.
The diffusion pump and the standard turbo pump MSD have a calibration
valve with less restriction than that in the performance turbo MSD; this allows
the correct diffusion of calibrant for each vacuum system.
Perfluorotributylamine (PFTBA) is the most commonly used tuning
compound for EI operation. PFTBA is required for automatic tuning of the
MSD. Other compounds can be used for manual tuning.
CI calibration valve
The CI tuning compound is perfluoro-5,8-dimethyl-3,6,9-trioxidodecane
(PFDTD).
module. It is controlled by the ChemStation software. It opens automatically
during CI autotune or manual tuning, allowing PFDTD to diffuse through the
GC/MSD interface and into the ion source.
Vent valve
The vent valve knob
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.
192
(Figure 41) is an electromechanical valve with a vial to
The CI calibration valve is part of the reagent gas flow control
(Figure 42) screws into a threaded port in the front of the
5975 Series MSD Troubleshooting and Maintenance Manual