Agilent Technologies 6890 Series, Service Manual, Page: 674 / 867

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Jun 2001
Valves
Agilent 6890 Gas Chromatograph Service Manual
Troubleshooting 1150
Pressure check
Pressure check
Leak checking the plumbing involved in a valve system must be done carefully
and methodically. The pressure check method below will indicate, but
sometimes not isolate, a leak in the flow path. Since this method does not
necessarily isolate the leak, other leak check methods may be needed to locate
the leak specifically.
Note Each valve in a system has two flow paths, ON and OFF. A leak sometimes
occurs in only one of these two positions. Check both.
1. Disconnect the detector from the valve system.
2. Cap the valve system at its outlet and pressurize to 689 kPa (100 psi).
Allow 2 to 5 minutes for pressure to equilibrate. If your instrument has
flow control, it should read zero flow.
3. Turn off the gas supply at the source.
4. Generally, the pressure will drop quickly for approximately 30 to 60
seconds, then stabilize. After this initial pressure drop, the gauge should
not indicate more than a 7 to 14 kPa (1 to 2 psi) drop during a 10 minute
period.
5a. If no leak is indicated, actuate all valves and repeat steps 2 to 4.
5b. If a leak does show up, try to pinpoint the source using a soap bubble
meter. Do not assume that the leak exists only at the valve. Often plumbing
connections such as unions or bulkhead fittings are at fault. See Valve
Box should it become necessary to expose the valve system.
6. If the leak cannot be found easily, divide the system in half and repeat
the pressure check. Continue dividing in halves, and pressure check until
the leak is isolated.