Make-up gas flow rate on HP 5890

[tiggeria]

I am pluming an old HP 5890 ( not 5890A, not 5890 series II) with FID.

Use helium as carriers gas, while nitrogen as make-up gas.

I am checking the flow rate of gas supplies without running the GC/detector. The problem is the nitrogen makeup gas does not have any flowrate when I plugged in the bubble flowmeter into the FID outlet.

I think it is abnormal. I did not find anything in the GC manual to say one way or another, but I suspect that the control valve for the carrier gas is broken.

Anybody has experience on similar problems?

[Peter Apps]

Just to be sure - you have plugged the bottom of the detector where the column would connect ?

The 5890 is a real vintage instrument - if I recall from thirty years ago there is a pressure regulator and gauge behind a flap on the left hand side that you use to adjust the makeup flow and a needle valve on the front to turn it on and off. If this is what you have - do you see pressure on the gauge ?

Peter

[tiggeria]

Thank you for your reply.

There is no pressure regulator inside the left panel. I am hooking up the gas line directly to the detector gas manifold (whatever it is called, the gas connector with needle valves).

I found the problem though. The instructions are on page 11-4 to 11-5 of the manual: Setting capillary make-up flow rate. The revealing thing is that this valve for AUX Gas is not a typical valve, like the other two on the same panel. Instead a screw at the center of the valve needs to be turned. I suspect that many people might have missed this "NICE" design since the valve handle on this machine was kind of broken. I can image that people were trying to get more flow by cranking the valve like crazy I now know for sure a person before me was not using the makeup gas because this restrictor was turned all way to the right = no flow.

[MSCHemist]

I think it depends on the 5890 whether it is a 5890A series II or series IIa. My series IIa has no guages though I am thinking of buying Restek's guage pack. There is just a knob on the front pannel. There is also a black inline regulator on each of the three gas lines I believe.

I think the makeup flow to the FID is governed by pressure and a restictor frit similar to the auxilary EPC on my 6890. I haven't had to mess with mine so I'm not sure but there is a page in the manual about it.

Restek sells a nifty guage pack that mounts to the side of the 5890 for air and hydrogen but it doesn't inlcude makup.
https://www.chromspec.com/pdf/e/rk125.pdf
part 22071

[Johnny Rod]

Are you using a packed or capillary column?

[tiggeria]

I am using a capillary column.

Thank your all for your replies. As I pointed out in my 2nd post, I solved the problem.

As I mentioned there, there is a screw in the middle of the valve handle. This screw (/restrictor) restricted all the makeup gas flow. After finding the instructions in the 5890 GC manual, I was able to adjust the screw and get the flow rate I wanted.

[Yama001]

Congrats on the long lost skill of reading manuals - its amazing what you can find in there.

I just finished showing some of our techs how to work that old flow controller - they were ready to run when I took out the bubble meter.