Chromatography Forum

I have limited space for gas tanks and three GC's to get running. Is there issues in piggy backing multiple GC's off the same gas lines (other than running out of gas fast). They are all 6890's. Just wondering if anyone can give some info on their setup. Pictures of setups would be great too.

It depends on how many GC's you plan to supply and the distance between. If you have more than two or three GC's or long distances, use 1/4" tubing from the bottle to at least the first "T" and on long lengths of tubing to avoid excessive pressure drop in the lines.

In some labs, an entire lab building is supplied off a central gas system, withtwo banks of cylinders and an automatic switch that changes to the other bank of cylinders when the first runs low. These save a lot of space in the labs and reduces the number of cylinders on site. I've also seena s sytem incorrectly assembled (soldered joints rather than compression fittings, the wrong grade of tubing, etc.) and cylinders standing beside drops in the unusable house sytem.

It's fairly common to do what you want. As Don points out, make sure the "header" is sufficient diameter to prevent pressure drop. I'd consider adding a single stage regulator at each GC "drop".

We want to do the same thing here, but it will be 2 different brand of GC

We have a Thermo DSQII / FID and we'll add an Agilent 7820/FID.
The 2 GC will be beside each other

Is this a good idea to add toggle valve on each line after the "T".

Should be no problem having different vendor's equipment sharing the gas supply, and yeah a toggle or shut off valve is very useful for troubleshooting (or isolating an unused instrument).

Should be no problem having different vendor's equipment sharing the gas supply, and yeah a toggle or shut off valve is very useful for troubleshooting (or isolating an unused instrument).

what is better

toggle valve http://www.swagelok.com/search/find_pro ... OGS2&item=
or
ON/Off plug valve
http://www.swagelok.com/search/find_pro ... 2P4T&item=

A possible, but unlikely problem with GCs from different makers on the same line is that they might need different gas pressures in the line - simply solved by an extra regulator for the one that needs the lower pressure.

Peter

I'd use the ball (plug) valve. Probably less pressure drop across it. I've also seen too many of the toggle valves with the toggle handle snapped in two.

I'd use the ball (plug) valve. Probably less pressure drop across it. I've also seen too many of the toggle valves with the toggle handle snapped in two.

thanks

Unasked for advice:

If you're using brass ferrules in your (brass) fittings, use copper tubing. The ferrules should be harder than the tubing for a swage-fitting to work correctly. For stainless tubing, you need stainless ferrules.

This video from Swagelok can be useful: How to install a fitting.

Also, make sure you get tubing that has been internally cleaned, and is rated for the appropriate pressure. And, yes, copper is fine for high purity gases as long as you never expose it to air after it's been put in service. Purge air from the CGA nipple at the cylinder--don't push it down the line.