Change carrier gas

[carol]

Hi everyone,
My carrier gas is nearly empty, I’ve never change the cylinder and as we are on Easter holidays there is nobody in the lab who knows how to change it. My question is. Can I leave the GC with no carrier gas? Will be that a problem? Do I have to do something else? Apparently the gas is consumed even if you are not using it, what should I do?

Thanks a lot in advance,
Carol

[MikeD]

Carol,

The safest option while you wait for a cylinder change is to turn off the oven/injector/detector heaters, or at least set them below 100 C.

[Peter Apps]

Hi Carol

Options:

1. At the back of the GC, connect the carrier gas input to nitrogen instead of the hydrogen or helium that you are using for carrier gas. This assumes that you have nitrogen (for makeup gas usually) and that the cylinder has plenty in it, and that you are able to do this.

2. If you are not using a mass spec; cool all the heated zones (oven, inlet, detector) on the GC to room temp, reduce the split (total) flow and septum purge flow to 0 in the hope that the bit of gas you have left will last until after Easter. As long as all the heated zones are cool the column will survive even if the gas runs out.

3. If you have a mass spec, first vent it and then do 1 or 2.

4. Phone one of your colleagues and get them to come in for 10 min to change the cylinder, or talk you through the process.

Happy Easter !! Peter

[carol]

Thanks and have a nice Easter,

Carol

[pi3832]

My carrier gas is nearly empty, I’ve never change the cylinder and as we are on Easter holidays there is nobody in the lab who knows how to change it.

To change the carrier all you need is a full cylinder and a 1-1/8" wrench.

Steps:

1 - Make note of the outlet pressure of the regulator.

2 - Back the regulator dial out all the way (turning counter-clock-wise).

3 - Shut off the valve on the cylinder (clockwise when looking from the top).

4 - Loosen the nut connecting the regulator nipple to the cylinder valve. For helium, nitrogen or argon, the nut is a right-hand thread. (Turn the nut counter-clockwise when looking at it from the regulator side.) For hydrogen, the nut is left-hand threaded, so turn it the other way. (Note: left-hand threaded nuts have a notch cut into the corners.)

5 - Screw the metal cylinder cap on the empty cylinder. (If you don't have the cap anymore, use the one from the full cylinder.)

6 - Move the full cylinder into place, and restrain it from falling with a chain or strap.

7 - Connect the regulator to the cylinder valve, and tighten the nut.

8 - Briefly open the cylinder valve.

9 - Briefly loosen the nut holding the nipple, venting the pressure in the nipple, and then re-tighten the nut.

10 - Repeat steps 8 and 9 at least two more times. This purges the air out of the nipple and the inlet of the regulator.

11 - Open the cylinder valve all the way, and check for leaks. (You can use Snoop or somesuch.)

12 - Dial in the regulator's outlet pressure to the level you noted way back in step one.

Seems like a lot of steps, but it shouldn't take you more than five minutes.

In general, you shouldn't let a cylinder of high purity gas get below 200 psig.

If losing carrier is a re-occuring problem, you can add a back-up cylinder to the system. Just T into the supply line, and set the outlet pressure on the regulator of the back-up well below the outlet pressure on the main regulator. Gas will only flow from the back-up when the main cylinder runs out of pressure and the pressure in the line falls below the set pressure on the back-up. The flows on your GC will be all screwy but you won't have to worry about damage to the column.

[CE Instruments]

Hmm have you managed to change the cylinder ? How low is low ? If the cylinder is just getting low and not yet hit the 0 reading you may still have enough Helium in the bottle for the weekend. Has everyone left for Easter or is the GC/MS user coming in on Monday ?
To save gas and ensure no damage is done in the event of the cylinder running out.
Reduce the injectot temp to 100C, oven temp to 50C.
Make sure the MS filament is off
Reduce the carrier flow to 0.1 ml/minute or lowest settable value. Check the split flow is also low 10ml or less preferably. You will then be using no more than 10ml/minute of Helium and the remaining gas in the cylinder will last a long time.

[MikeD]

To Pi3832 I respectfully suggest that a written procedure is good but, for the OP who has never changed a cylinder, not good enough without a practical demonstration.