Hydrogen flow is higher than the set number 7890

Question

Hi everyone, 
 I operate a gc 7890, after changing the hydrogen cylinder, the gc doesn't succeed in achieving the set flow. In the method the hydrogen flow is set to 30 but the reading is 50. 
 Also we uninstalled the cylinder expecting the flow to come down to zero but it didn't. It stayed at 50

CMZainea · Answer

Hello Samehalsharawy , 
 
 Can you please elaborate on the statement we uninstalled the cylinder expecting the flow to come down to zero but it didn't. It stayed at 50? 
 
 If no physical tank is connected to the GC, the GC gas connections are capped and the detector base is capped, and flow still reads 50, this is exclusively an EPC issue, as there is no gas coming from any gas source. 
 Otherwise, the most common reasons for flow mismatch between actual and setpoint are: 
 - Physical gas supply (tank or generator) is different than the gases configured. In your case, please make sure the tank you are connecting the right gases to the back connections: IN other words, make sure the H2 tank is connected to the H2 fitting at the FID, the Air tank is connected to the Air fitting at the FID, and that the correct makeup gas type (He or N2) is connected to the MUG connection at the FID. Make sure also that the MakeUp Gas is correctly configured on the GC (on the GC keypad, go to Config -> Back/Front Detector -> Makeup Gas). 
 - defective flow sensor on the EPC is defective. 
 - Sometimes low H2/Makeup Gas could be indicative of a plugged jet, but this is not your case, as the H2 is high, not low.