you also have a semi-permeable membrane salvaged from a Nitrogen generator so that your vacuum pump only pulls N2 right?
most folks don’t have such technological wonders installed & imo should probably not be sucking on their solvent tanks when there is liquid in them.
other end is in the employee smoking area in the parking lot right?
I had an N2 vent just like that once upon a time.
Even venting an n-butane tank that was at -30C it would set my meter off.
(which is why I would be concerned about pulling vac)
Actually had to poke my head outside to check that there wasn’t an impromptu gathering in the parking lot every single time. I was much happier once that line was plumbed directly into the exhaust ducts.
With controlled release to exp ventilation and using a compatible vac pump it will only be removing the nitrogen from the tank. Having the membrane is definitely the best way to go about it, agreed.
When I vent off, I even entertain myself and put my sensor near the vent and it doesn’t register. I am also far colder than -30. But, it’s not boiling off.
But, think about the science. What’s the boiling point of butane? 0c/30.2f anything above that it will emit pressure. Anything below that, it doesn’t emit pressure. The further below that, it pulls vacuum. It’s science, it doesn’t care what you think. I am removing the nitrogen head pressure that is above my solvent pulling a vacuum on its own. I’m not pulling a vacuum to micron like a short path. I’m pulling a vacuum that is only removing the nitrogen.
And yes, I plan on getting a membrane, once I find a manufacturer that I can supply myself with one.
If water boils at 100C, and that meant water could not turn into a gas below that temperature, how would it rain?
A substance “boils” when it’s vapor pressure is above ambient. Whatever that happens to be.
N-butane contributes “vapor” to that “ambient”, even 30C below its boiling point in my experience.
You’re running colder than that, and your experience is clearly different from mine.
That doesn’t make anybody wrong 
U would vacuum down ur solvent tank with solvent in it?
Yep!
…but only after tearing apart a nitrogen generator to pilfer the membrane.
Is it ok to bleed n2 from the solvent tank while I’m running or should I wait till after the run. my solvent tank is at 15 degrees and my heat exchange is at -3 degrees so I’m not sure it’s freezing the butane enough and I’m venting it out with the n2
At 15f? yes you’d probably be venting off gas. I’m doing this when I’m below -50c
thank you!!!
Ypu can ventbwhile running. But as mentioned youll lose some gas. Thats how i do it if needed
Me telling the new guy.
“you shouldn’t do it this way, but this is what I do”
Haha i did say if needed. Not preferred. With that being said listen to dred he has sound advice
Stupid question but wen using a recovery pump do y’all run the pump while nitrogen is still in system or it has to be purgednout
I believe @bhogart sells cold rated valves, they have a longer handle
not recommended. I’ve done it. actually used the same N2 charge for weeks using two pumps and two solvent tanks. one was cooled one was not. pressure in the second tank needed careful monitoring and I would not advise playing this trick.
I don’t use a recovery pump with nitrogen assist. Strictly passive with dry ice and ethanol baths on everything. At a point, I will have to bleed off some nitrogen to a line I have run outdoors which, again, is why everything is chilled super low so I’m not bleeding any solvent. I have passable recovery speeds and a much quieter time running passive with my setup so my recovery pump doesn’t get used anymore.
If you’re ever upgrading, get a venturi pump and you can vac out the nitrogen and not have to be venting for as long. Just vac the nitrogen out and resume
Sorry if this seems spoon fed, but can you link the pump your talking about thats safe to pull out nitrogen with? I’m unsure which pump on the website thats safe to use. Thank you.
I’m pretty sure he posted the one he uses somewhere on here but I might be mistaken.
Edit: my quick search says I’m wrong
Venturi pump is an air driven vacuum pump. Zero moving parts or any mechanics. It is 100% intrinsically safe.
@Badcookieextracts I didn’t post the model. Let me find a picture and I’ll edit this comment.
Cole Parmer. They have a range of models that pull down to 29.5 or lower if you want. This one is a 1.2 cfm pump that can pull down to 29.5.
These new pumps take advantage of the venturi effect—as a stream of compressed air exits a constricted orifice the resulting pressure drop draws air through a vacuum port. Since they require no oil or electricity, the resulting vacuum (up to 29.5" Hg) is clean and efficient. With no moving parts or electrical hazards, these air-powered pumps are also intrinsically safe. The remarkably compact size of these pumps enables you to design vacuum systems with smaller, less expensive components and reduced maintenance costs. Each model (except 79165-40) includes a replaceable silencer that reduces noise levels up to 30% while offering minimal resistance to air flow.
Select the model of vacuum pump best suited to your specific application. Model 78165-20 includes a vacuum gauge which provides easy visual monitoring—helpful when troubleshooting. We recommend an air filter upstream of the pump to prolong service life. Filter should have a pore size of 50 µm or smaller.
