thanks i do have a cold trap. il hook it up and use it. i just dont have access to dry ice all the time. i wonder if i can do something to cut the pull of the pump?
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If you put a cold trap in line then you will catch some of the ethanol vapor blow-by and keep most it out of your pump oil. It still won’t remove the fire hazard entirely, and on top of that it’ll make your pump pull even harder and won;t fix your bumping problem.
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Is it that fire hazardous?
Care to explain more on that? I’ve never had issues
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Ethanol vapor collects in the vac pump oil, lowers it’s viscosity, pump heats up and the ethanol can ignite. A dry ice cold trap will definitely remove most of the risk. As a daily practice for someone who’s inexperienced I definitely wouldn’t recommend it though. A friend at his previous job saw a coworker running a rotary vane on a 20L roto. As he approached the pump to shut it off it blew up and covered him in flaming pump oil. He healed up but I got to throw plenty of Freddy Krueger jokes his way for a while.
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Wtf thats wild
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do you need a cold trap with a diaphragm pump? if so is a single sufficient
A cold trap will help to collect vapor that’s gotten past the condenser coil, and it’ll help improve and stabilize the pump’s performance. So it’s certainly not a bad idea.
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This is why buying cheap equipment that isn’t spec’d Together properly becomes a dangerous combo.
I’ve never had this issues with rotovap work but I will help with my two cents as much as I can.
—first, try running your equipment at atmosphere. You will have to set your bath at 70-80C.
—your chiller set to 0C. If you go down to -10 or lower the equipment will Overwork and be “cycled on” more than it needs to be.
The condenser should really be able to condense the etoh at the proper rate Or the equipment should be returned or thrown in the trash.
—once you know how to work your equipment without vacuum, setup your vacuum.
Start by turning on your chiller, then vacuum. Check for leaks and turn on the heated bath and roto. Does this have a 100-200rpm range? Experiment with that when you have Done your atmosphere run. Also, if you get high evaporation of your water bath you can fill the bath with ping pong balls. This problem is exacerbated if and when you don’t have AC. 90F plus evaporating water sucks. Been there, done that.
Hopefully you have adjustable vacuum, if so, you want to target 40C temperature on your heating bath with solid flow of ethanol.
Another trick is to take your Chiller output line (cold line going to condenser) and cut the line and Install stainless steel coils submerged in dry ice/acetone or dry/ice ISO — then your flex line up to the condenser. This will not throw off your chillers temperature regulator.
If you’re pulling solvent past the condenser and into the vacuum you have too much vacuum and the cold trap will help but it’s definitely not normal and a sign this isn’t a properly working tool.
Good news is, this isn’t a huge problem and looks like youlll get this working correctly soon.
You can order cheap vacuum pumps on amazon that are used for automotive HVAC jobs that will work with your roto. Vent the exhaust gas outside, you don’t want to breathe that in your lab.
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Holy $shit
I thought that said 20L roto
Ya wow, that’s wayyyyyyyyyy tooo much vacuum pump and wrong pump.
Who sold you that setup??!!!
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Bruh, you could probably use a hand vacuum pump lol 
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Get that grip strength up to level 5000
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if youre spending $1500 on one step of your process, please spend that amount on a year of chemistry classes at local uni.
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Cool bro il think about that next time
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That pump will work fine. Sure it will be more hassle and a pain in the ass to deal with versus a properly spect pump but it’s still usable and if you’re cheap like me you tend to find a way to make things work. You need ewe to bleed atmosphere into your vacuum line whether it’s with a t and a ball valve or something inline so you’re able to adjust the vacuum depth you’re pulling way too much vacuum on that system and it’s bumping your feedstock
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Depending on how hard you’re running that thing, I would recommend getting an aspirator like this one:
https://www.fishersci.com/shop/products/vacuum-pump-water-aspirator/nc0577126
You can find cheap used ones on ebay, I picked up a nice Japanese one a few years ago for like $120. You could also use the continuous feed and keep your boiling flask with a tiny amount of liquid in it at any given time, just barely crack the stopcock and ease it closed until it’s flowing at a quick drip (no solid stream). It’s impossible to bump over if there isn’t physically enough liquid to make it through the joint. I’m somewhat of a 2L roto virtuoso, I learned very early that you can never trust a full flask on those things, even with an aspirator with lukewarm water in it. Using continuous feed and low volumes will allow you to maximize your surface area, I can recover well over the rated liters/hour as long as my chiller can keep up.
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i never even considered that someone would use it any other way than continuous feed. Wouldn’t loading the flask fully also tear out your motor more rapidly?
Wait so would I be correct in assuming since the diaphragm that runs in this unit is PTFE doesn’t that mean I wouldn’t need a cold trap at all for rotovaping ?
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also next time read the whole thread at least before asking the same person the same question i already asked him 
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Deterministically, running a full flask vs a nearly empty flask is going to be worse for the motor, but I’ve never met someone that’s burned out a motor on a 2L. Those things are typically overbuilt, even the cheap BVV chinese ones.
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