Inlets and valves
6850
6850
Released: April 2004 6850 Series Gas Chromatograph Service Procedures 86
Forward pressure valve leaks
Occasionally an increase in pressure, rather than
a decrease may be observed. This is usually due
to slight leakage into the module across the
forward pressure control proportional valve.
Although slight leaks of this nature do not create
chromatographic problems, they may obscure
other small leaks that do cause problems by
allowing air into the system.
To check for internal valve leakage:
1. Remove the supply pressure at the carrier
inlet fitting, and quickly cap the fitting with
a Solid 1/8-inch Vespel plug and a Swagelok
nut.
2. Check the actual pressure on the display and
monitor it for 10 minutes. Pressure loss
should not be greater than 0.5 psi.
Locating leaks
If the EPC module appears to have a leak, you
can remove it to locate the leaky component. The
leak test kit (part no. G1530-60960) contains a
longer ribbon cable to allow you to lay the EPC
module on the benchtop for testing.
Caution
Be sure to wear an ESD strap grounded to
the 6850 GC chassis while performing this
procedure.
1. Turn off the main power switch.
2. Disconnect the carrier supply tubing on the
inlet fitting.
3. Remove the top plastic pneumatics cover and
the detector cover.
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