15
Site Preparation
The gas plumbing
Figure 2. General plumbing diagram
• Two-stage regulators are strongly recommended to eliminate pressure
surges. High-quality, stainless-steel diaphragm-type regulators are especially
recommended.
• On/off valves mounted on the outlet fitting of the two-stage regulator are not
essential but are very useful. Be sure the valves have stainless-steel, packless
diaphragms.
• FID, FPD, and NPD detectors require a dedicated air supply. Operation may
be affected by pressure pulses in air lines shared with other devices.
• Flow- and pressure-controlling devices require at least 10 psi (138 kPa)
pressure differential across them to operate properly. Source pressures and
capacities must be high enough to ensure this.
• Auxiliary pressure regulators should be located close to the GC inlet fittings.
This insures that the supply pressure is measured at the instrument rather
than at the source; pressure at the source may be different if the gas supply
lines are long or narrow.
Two-stage regulation
Main supply
on/off valve
Main gas
supply
On/off valve
Moisture
trap
Hydrocarbon
trap
Oxygen
trap
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