Using the Agilent 7890A. Column installed with no leaks detected. Both the front and back detector are set to 300°C, gas Flow Rates - Hydrogen: 45mL/min, Air 450mL/min and He 1.0mL/min. The split flow is 80mL/min. Following initial start up the front detector attains and maintains the requisite flow rates and ignites with no issue. The back detector attains and maintains all but the air setting. It only reaches 446mL/min. Oddly when I turn the flow off at the front detector the measured flow rate on the back detector subsequently attains and maintains 450mL/min. If I restore flow to the front detector I once again lose flow at the back detector.
Any thoughts on the cause for the failure to attain the required Air flow when both detectors are on?