Using the Pressure Flow Calculator

Answer

This Information Applies To: GC Pressure Flow Calculator

Issue

Instructions for the correct use of the Pressure Flow Calculator.

Background

The Pressure Flow Calculator uses the column dimensions, oven temperature, and detector outlet pressure to calculate either the pressure required for a target flow, or the flow provided at a target pressure. Use this calculator to see the impact of different column dimensions, or different carrier gases, or to see the change in pressure/flow relationship when the detector is changed, for example from an FID to an MSD.

Items Required

Agilent GC Calculators application needs to be installed.

Steps to Follow

To calculate a pressure or flow:

1. Open the GC Calculators application and click the Pressure Flow Calculator.
   

   
   
   Figure 1. Opening the Pressure Flow Calculator
   

2. Enter the following known parameters (Figure 2):
   • Column dimensions (Length, Inner Diameter, and Film Thickness)
   • Column Temperature
   • Inlet Pressure (gauge)

               
     
     Figure 2. The Pressure Flow Calculator window.

3. Select the Carrier Gas (note the recommended Optimum velocity range for your selected gas).
4. Enter the desired input conditions. Enter a value for one of the following in order to see, at your input conditions, the values of the other two parameters:
   • Inlet Pressure
   • Outlet Flow
   • Average Velocity
     
5. To estimate split vent flow or ratio at input conditions, enter either the Split Vent flow or Split Ratio. (Figure 3.)
6. To estimate splitless mode purge time at input conditions, enter the Inlet Temperature and Liner Volume. (Figure 3.)

           
   
   Figure 3. Example showing calculated Split Vent flow and suggested splitless mode purge time based on input conditions.

7. It is sometimes useful to calculate a "corrected column length" based on the Inlet Pressure setting and a measured flow rate (for example, when the column ends have been cut and the exact length in not known). To do this:
   1. Enter the known value of Inlet Pressure (and other known parameters).
   2. Adjust the value for column Length until the Outlet Flow agrees with the measured value.

Learn how to effectively operate your Agilent GC: GC-MULTI-2190e - GC Calculators: An Introduction eLearning course available from Agilent education