Supply Tubing For Carrier And Detector Gases - Agilent Technologies 6890 Series Service Manual

520 Gases
The gas plumbing
• 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.

Supply tubing for carrier and detector gases

Caution Do not use methylene chloride or other halogenated solvent to clean tubing
that will be used with an electron capture detector. They will cause elevated
baselines and detector noise until they are completely flushed out of the
system.
Gases should be supplied to the instrument only through preconditioned
copper tubing (part no. 5180-4196). Do not use ordinary copper tubing—it
contains oils and contaminants.
Caution Do not use plastic tubing to supply detector and inlet gases to the GC. It is
permeable to oxygen and other contaminants that can damage columns and
detectors, and can melt if near hot exhaust or components.
The tubing diameter depends upon the distance between the supply gas and
the GC and the total flow rate for the particular gas. One-eighth-inch tubing
is adequate when the supply line is less than 15 feet (4.6 m) long.
Use larger diameter tubing (1/4-inch) for distances greater then 15 feet (4.6
m) or when multiple instruments are connected to the same source. You
should also use larger diameter tubing if high demand is anticipated (for
example, air for an FID).
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Agilent 6890 Gas Chromatograph Service Manual
Jun 2001