256
Agilent 7820 GC Service
1 Disconnect the detector from the valve system.
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.
Turn off the gas supply at the source.
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.
If no leak is indicated, actuate all valves and repeat steps 2 to 4.
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 ( 234) should it become
necessary to expose the valve system.
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.
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