
3 of 6
Jun 2001
Valves
Agilent 6890 Gas Chromatograph Service Manual
Troubleshooting
1150
Chromatographic symptoms
Extraneous peaks
Air peaks are sometimes seen in a chromatogram when leakage occurs
because the valve rotor does not seal properly. These leaks may not be
detectable using the soap-bubble method.
If a leak is suspected but cannot be located with soap bubbles, a pressure
check will determine definitely if a leak exists. Extraneous peaks can occur
due to contamination or improper conditioning of the valve. If leaks are not
apparent, clean or condition the valve.
Other causes, totally unrelated to the valve, may produce similar symptoms.
Impure carrier gas (i.e., containing water) can cause extraneous peaks.
Peak broadening and tailing
Voids in the flow system (valve and connecting tubing) cause tailing and peak
broadening. Use inlets and liners with small internal diameters and connect
the valve to the inlet or column with short lengths of connecting tubing of
narrow inner diameter.
If early-eluting peaks are too broad, stationary phase or thermal focusing
effects should be used with packed-column ports or increased split flows
when capillary split inlets are used. Inlets should be equipped with narrow
inner diameter liners, and narrow-bore connecting tubing should be used
between the valve and inlet.
Baseline shifts
Baseline perturbations are caused by changes in column flow as the valve is
rotated and as the sample loop equilibrates to system pressure. Slow valve
rotation momentarily stops carrier gas flow and, when the valve stops
rotating, a sudden increase in flow occurs which slowly returns to the set
point. Check actuator pressure (usually 40 to 75 psi), valve rotor tension, and
valve temperature to ensure that the valve rotates as quickly as possible. A
restrictor or backpressure regulator can be added to the sample vent line to
maintain the sample loop at system pressure. This will reduce the time it
takes for the flow to stabilize after the valve is switched.
Содержание 6890 Series
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Страница 27: ...24 of 24 Jun 2001 Contents Contents Agilent 6890 Gas Chromatograph Service Manual ...
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Страница 195: ...260 Solvent Vapor Exit Accessory Leak testing 10 of 10 Jun 2001 Inlets Agilent 6890 Gas Chromatograph Service Manual ...
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Страница 389: ...360 Auxiliary EPC Replacement procedures 16 of 16 Jun 2001 Detectors Agilent 6890 Gas Chromatograph Service Manual ...
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Страница 479: ...520 Gases Supplying valve actuator air 14 of 14 Jun 2001 Site Preparation Agilent 6890 Gas Chromatograph Service Manual ...
Страница 485: ...530 Power Grounding 6 of 6 Jun 2001 Site Preparation Agilent 6890 Gas Chromatograph Service Manual ...
Страница 491: ...540 Instrument Specifications Detectors 6 of 6 Jun 2001 Site Preparation Agilent 6890 Gas Chromatograph Service Manual ...
Страница 492: ...600 Performance Verification How to check the performance of the 6890 instrument 610 Checkout Chromatograms ...
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Страница 555: ...840 Shutdowns 10 of 10 Jun 2001 Error Codes and Internal Diagnostics Agilent 6890 Gas Chromatograph Service Manual ...
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Страница 637: ...1110 Valves Liquid sample valves 6 of 6 Jun 2001 Valves Agilent 6890 Gas Chromatograph Service Manual ...
Страница 647: ...1120 Valve Box Removing the valve box assembly 10 of 10 Jun 2001 Valves Agilent 6890 Gas Chromatograph Service Manual ...
Страница 675: ...1150 Troubleshooting Pressure check 6 of 6 Jun 2001 Valves Agilent 6890 Gas Chromatograph Service Manual ...
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Страница 717: ...1225 Main Board 6890N Fuses 6 of 6 Jun 2001 Electrical Agilent 6890 Gas Chromatograph Service Manual ...
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