50L Dual Collection Roto

New guy here and been searching and reading and searching and reading. Great community here! Question (of course). I have a 50L roto with dual collection flasks. I know there’s a way to collect in both flasks but I’m not sure how to either a) collect in both flasks at the same time or b) collect in one flask then swap to the other flaks while not losing vacuum. Losing vac is my biggest roto inefficiency. Advice and or heckling is welcome.

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Show a pic. Most dual collection flasks have seperate valves from most of the companies ive seen. Who made the roto?

Thanks @Concentrated_humbold. Just loaded a pic. Chinese made model is RE-550B.

Just keep one side closed and then switch

When I swap sides I close the active side first, then open the opposite side, but the plunger stays in while the screw separates from the plunger.

Tighten it into the black cap, there usually threaded backwards and then make sure that silver set screw is tight

I ran a buchi-220 pro
It looks similar in flow.
Use one side for majority of solvent recovery when you start going. Use the other side when drop into lower vacuum where you will be pulling more water/impurities of solvent out.

Here is a tip when your running the system and about to release the solvent from the flask. Close the main port on to top of the flask. Release vacuum from the main system a good bit. Keep your other parameter going the same. Open the Bleeder slowly from the flask to fully open. Dump solvent. Close both when done. Open top port slowly. Than vacuum down to your last setting but make sure it doesn’t bubble over. Take it slow. Doing this will prevent solvent sprout hitting the condenser and actually saves time on recovery. And you have more control of your system without air coming in viciously.

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If you don’t mind me asking what are you using for the condenser fluid? And what are the tubings go towards on the flask that are going straight up? I never seen that before that’s why I’m asking :slight_smile:

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We are using ethanol as the condenser fluid. The tubes that go straight up are for vacuum that split for each of the upper condensers.

You’re vacumming the system through those those lines?

Can you provide additional photos by any chance? I would like to see what’s going on. If those are recirculating lines they may have this for reflux.

I can see how to do it on your rig, but in the time it would take me to write the SOP, I could fly out there and show you. lol.

Quickly and without using technical nomenclature:
Open the valve to let air in the receiving flask. It will shut the auto valve at the base and ethanol will collect there. Once the vac is gone from the boiling flask, open the drain valve and let the ethanol drip out the bottom valve into your collection jug. Shut the drain valve. Shut the air valve. Open the vacuum valve. when vacuum comes back into the flask the ethanol will gurgle through the stopper valve. Once it has all fallen into the flask, close the vacuum valve.

those lines are for equalizing receiver flask vacuum depth to the rest of the system so you can drain the recovered solution, without losing vacuum and stopping operation.

a quick order of operations.
step 1: close valve coming from condenser,
Step 2: close vacuum equalization valve, the one with the tube(if you dont do this you will continue to lose vacuum and probably ingress solvent into your pump)
-with both of those valves closed, the receiver flask is isolated from the system.
Step 3: vent atmosphere into the receiver flask, equalize it with ambient pressure.
Step 4: open bottom valve and drain your recovered solvent
Step 5: close bottom valve once empty
Step 6: close vent valve
Step 7: Open vacuum equalization line, system vacuum depth will rise slightly, but if your vent and drain valves are close, the loss of depth is negligible. as this happens you should see “solvent vapor smoke” form and the flask will go foggy momentarily
Step 8: open valve from condenser and flow recovered solvent into the receiving flask.

Hope this helps


Thanks for the response. Just to clarify. the drained flask will be brought back to an equal state of pressure that’s inside the system before the top valve is opened?

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The key here to making the whole process intuitive (and the thing that our lab didn’t realize for a while) is that there is a one-way valve or check valve between the condensors and collection flasks (look at picture)

This valve will automatically close when you cut off the collection flask from the vacuum supply, then start to open up the collection flask to the atmosphere. This happens because there is stronger vacuum in the condensors portion of the system, pulling the valve shut.

If you understand this principle you should be able to make sense of it


I’m gonna test it out and report back, but the logic makes sense.

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@RockSteady, success! Just trimmed 5 minutes off my vacuum recovery time!


woot! glad i could be of assistance!

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@RockSteady do you know if this level of activity at the seals is normal while under vacuum? I know it’s kind of hard to see.