Forward Pressure Valve Leaks; Locating Leaks On The Flow Manifold - Agilent Technologies 6890 Series Service Manual

270 Pneumatics Control Module
Leak testing the PCM
of 0.5 psi or less in 5 minutes time (approximately 0.1 psi/minute) is
considered to be leak free.
5. If there is a leak, remove the PCM from the GC and isolate the leak as
described in Locating leaks on the flow manifold.
6. If there is an increase in pressure, see Forward pressure valve leaks.

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. The valves can leak
at about
0.2 mL/min and be within specification.
To check for internal valve leakage (when leak testing the PCM only):
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
5 minutes. Pressure loss should not be greater than 0.5 psi.

Locating leaks on the flow manifold

If the PCM appears to have a leak, 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 PCM on the benchtop for testing.
Caution Be sure to wear an ESD strap grounded to the 6890 GC chassis while
performing this procedure.
1. Turn off the main power switch.
2. Remove the top plastic pneumatics cover and the detector cover.
3. Remove the top rear panel on the GC.
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Inlets
Agilent 6890 Gas Chromatograph Service Manual
Jun 2001