Agilent Technologies 6890 Series, Service Manual, Page: 670 / 867

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Jun 2001
Valves
Agilent 6890 Gas Chromatograph Service Manual
1150 Troubleshooting
Most of the problems associated with sampling valves are related to peak
broadening in transfer lines and inlets, sample adsorption by the valve or
transfer lines, leaks, and perturbations in the baseline.
Chromatographic symptoms
Troubleshooting valves and their related plumbing is primarily a matter of
systematic checking and verification of unimpaired mechanical operation of
any moving part. This requires an understanding of how the valve functions
internally and how the plumbing is configured. A plumbing diagram is
essential for effective troubleshooting.
The following “symptom-cause” list gives the most commonly encountered
problems found with valves and their solution.
Table 1150-1 Troubleshooting valve related chromatographic problems
Symptom Possible cause Solution
Lost peaks (degradation) Valve or transfer lines too hot Reduce temperature 50°C, reevaluate
Transfer line activity Use nickel or Hastelloy tubing
Lost or tailing peaks Valve or transfer line too cold Increase temperatures 50°C, reevaluate
Baseline perturbation Slow valve rotation Increase actuator pressure
Rotor distorted Replace rotor
Sample/column pressure too
different Add back-pressure regulator to sample
drain
Peak tailing broad peaks Column overload Use smaller sample loop
Increase split flow
Flow too slow Increase column flow
Increase split flow
System voids Check connections
Reduce volume of connecting tubing