Thanks guys you are the best.
Im not using a dry ice or vaccum jackets around my columns so I would think it would be hard to get it to -40 but would hate to see what happens when the viton gaskets fail =O
What does it mean when the PTFE "cold flow"?
Lately I have been liking the very slow drip method because it freezes the columns nicely and seems to make things lighter, not to mention it's the only way to run three of the 5# terpp tubes at once on a tank holding 22# of solvent (takes an hour to run out of solvent in the tank). Never seen the outside of the tubes get below 0 degrees with a Newport 20-30% propane mix, so I would think reaching -40 would be tough, although I would like to try to the vaccum jackets here they keep the temps down well.