De-pressurize FID air line

[Vox]

How do I depressurize the FID air line on a 5890? Its a used GC and I haven't run my machine yet, but I was checking gas pressures, and discovered I need a new regulator for my carrier gas. So I turned of all the regulators and they slowly dropped pressure (possibly through leaks?) except for air. The air line is still holding it's pressure. I've turned the air knob on the FID panel to increased air flow and that lowers the pressure on my little gauge inside the left panel, but the regulator remains pressurized.

Thanks to anyone who can help this poor GC newb. Thanks.

[chromatographer1]

The regulator controls the flow/pressure which goes past it. It does not control the pressure BEFORE it. Turn the gas supply OFF before the regulator (back track the line until you find the valve) and the gauge will go to zero.

best wishes,

Rod

[Consumer Products Guy]

Just loosen the nut partially, wiggle the line, air will come out with less than full force. Wear safety glasses. There will a small poof of air, will be audible. Even taking the fitting off in one step, usually some air will bleed out before you get it completely separated..

[Bruce Hamilton]

A significant number of older regulators will leak through, producing a small amount of gas past the seat, and consequently you will have pressure unless you close off the upstream ( high pressure source ).

It's best to turn off the upstream, unless it exposes in-line traps to ambient air. I've always installed toggle valves immediately upstream of the instrument ( between purifiers and instrument ) so I can turn gases off without compromising the purifiers ( which stay pressurised ) or the instruemnt settings, as the shutoff/pressure controls on the front of the 5890 are best only touched for non-routine adjustements.

Many regulators also do not vent when the pressure is backed off, so you have to wait until the residual gas has passed through the GC.

I would note that I've found several of the rubber diaphragms in the 5890 gas control regulators have hardened on older 5890s ( 15 year + ), so it's a good idea to replace them as well if you plan on using the instrument for a while.

Bruce Hamilton