Air flow drop during flame ignition

[ChemDoc]

Greetings all, I am using an Agilent 7820A with a packed column and it has recently begun giving us issues with respect to the flame. I have tried most of the usual checks to no avail:

Manually verified individual flow rates - 400/40 air/hydrogen
System temps are above the limits for ignition
Flame jet is clean and not clogged
Output pressure from the tank regulators is within specified range (tanks shared by another system and it isn't having issues)
Glow plug is functioning
Reduced lit offset with no effect

One thing I have noticed is that when attempting ignition the air/hydrogen flows drop to near 0 momentarily. The hydrogen is back up to nominal (40mL/min) within a second while the air literally takes 10-15 seconds to build back to 400 mL/min. After the ignition fails and the gas flows are automatically shut off by the instrument, if you manually turn the air back on it reaches nominal much more quickly.

Any thoughts before we have the EPC checked out?

[Peter Apps]

The slow air flow during ignition is supposed to be there - it gives a fuel rich flame that is easier to ignite.

If you are having a problem with the flame not igniting according to the flame out sensor you first need to check whether the flame really is buring or not by holding a cool shiny surface above the FID chinmey. Condensation means a flame burning.

What is the carrier gas and how fast is it flowing - do you have the right flame tip for packed columns ?

Peter

[ChemDoc]

Thanks for the quick response.

The carrier gas is nitrogen at 35mL/min; no makeup gas flow is used.

The FID jet is 0.46mm X 63.6mm which should be good for this packed column. As an aside I have actually used this same method in the past with a 0.29mm jet, meant for capillary columns, with no issues.

I have been performing the condensation check for a flame throughout the condition variations with no evidence of any.

[Peter Apps]

I see no reason to think that the EPC is the problem, if the flows are correct then it must be working right.

There are all sorts of tricks to get FIDs to light, including blowing gently across the chimney, waving your hand or clapping just above it, or sacrificing chickens.

Before you do any of those, check that the ignitor coil has not been bent out of position.

Peter

[kubowicz.tomasz]

Hello

Check "lit offset" for FID - perhaps is to high.
Go to "config" detector and check lit offset value. If it is 2.0 change it to 1.0

Regards

Tomasz Kubowicz