Chromatography Forum

Hi, the gc 7980a fid system I am using seems to take longer time to attain the inlet pressure and then the system down.All rthe white the system beeps with error message low inlet pressure.Once the system is restarted again the pressure is attained at once .but this seems to happens everyday while switching on the system.can anyone help me out with this?

Does the inlet cool to room temperature each night when shutdown?

If so it could be that on the second start the inlet has had time to heat up and is sealing a leak that happens when cold. The expansion of the metal or seals is sealing the leak when it is hot.

With the system on, turn off the inlet heater and allow the inlet to cool to room temperature and see if the pressure holds. If not, then check for leaks and fix those and the problem should go away.

but this seems to happens everyday while switching on the system.can anyone help me out with this?

There is no reason to shut down a GC overnight if you use it everyday. You want to maintain a (low) flow of carrier gas 24/7 so your column is not collecting air/water/dust.

Several causes for the GC not being able to maintain a stable pressure:

- A blockage
- A leak
- A pressure that is outside the range that system can provide
- Method settings that are completely off: the system calculates the pressure needed to provide a flow that the user wants based on the dimensions of the column provided by the user.

Hello

If you have gauge regulated gas supply (cylinders) for carrier gas it shouldn't happen.
Are you using gas generator for carrier gas? (Hydrogen)
If you turn it on with GC (inlet is on) generator needs time to produce gas - if you have generator it could be reason for inlet shutdown.

Regards

Tomasz Kubowicz