Agilent Technologies 6890 Series, Руководство по обслуживанию, Страница: 182 / 867

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Jun 2001
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Agilent 6890 Gas Chromatograph Service Manual
Volatiles Interface 250
Leak testing the EPC module only
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 EPC module 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 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 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 cover on the GC.
4. Disconnect the ribbon cable for the module from the main EPC board.
You may have to remove the adjacent ribbon cable also.
5. Use a Torx T-20 screwdriver to remove the screw from the top of the
module and slide the module out of the back of the GC.
6. Connect one end of the leak test ribbon cable (G1530-61370) to the ribbon
cable connector on the EPC module and connect the other end to the