Agilent Technologies 6890 Series Service Manual page 670

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
Symptom
Lost peaks (degradation)
Lost or tailing peaks
Baseline perturbation
Peak tailing broad peaks
Jun 2001
Troubleshooting valve related chromatographic problems
Possible cause
Valve or transfer lines too hot
Transfer line activity
Valve or transfer line too cold
Slow valve rotation
Rotor distorted
Sample/column pressure too
different
Column overload
Flow too slow
System voids
Valves
Agilent 6890 Gas Chromatograph Service Manual
Solution
Reduce temperature 50°C, reevaluate
Use nickel or Hastelloy tubing
Increase temperatures 50°C, reevaluate
Increase actuator pressure
Replace rotor
Add back-pressure regulator to sample
drain
Use smaller sample loop
Increase split flow
Increase column flow
Increase split flow
Check connections
Reduce volume of connecting tubing
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