Flow and Pressure Control Part 4. Flow and pressure problems
The measured flow is not equal to the displayed flow
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• Large volumes have been added to the system (this may occur if you are
using a sampling valve). Decrease the sample volume. Use EPC inlets which
correct for variations in temperature and pressure.
The measured flow is not equal to the displayed flow
You checked the flow at an inlet with a bubble flow meter, corrected the
measurement to NTP conditions, and discovered that it does not match the
calculated flow displayed on the GC.
• The column length, internal diameter, or gas type is configured incorrectly.
Enter the correct information. Press [Config] [Column 1] or [Config]
[Column 2] to enter the column specifications. Press [Config] [Front Inlet]
or [Config] [Back Inlet] to enter the gas type. If a considerable amount has
been cut off a capillary column, its actual length may no longer match its
original. Configure the column with a new length.
• A new pressure setpoint was not entered after constant flow mode was
selected. Enter a new pressure setpoint each time constant flow is turned
on or off.
• A short (<15 m) 0.58 to 0.75 mm id WCOT column is being used with a split/
splitless capillary inlet. The total flow controller is set for a high flow rate,
which creates some pressure in the inlet and causes column flow even with
a setpoint pressure of zero. (In these situations, an actual pressure may be
shown on the display, even with a zero setpoint.) With short, 530 to 750 mm
columns, keep the total flow rate as low as possible (for example,
20 to 30 mL/min). Install a longer column with higher resistance (for
example, 15 to 30 m).
• The split vent line may be partly plugged, creating an actual inlet pressure
higher than the setpoint pressure. Replace the split vent line.
• A Mass Selective Detector is in use and vacuum compensation is not
selected.
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