Automating emptying of the cold trap...

I can’t be the first person to think about this, why isn’t there a self-emptying cold trap?

Maybe I just haven’t found it, but I’ve done some searching and haven’t seen anything. Tempted to build one with a PLC I have lying around and a couple of solenoids.

I get that almost every possibility I can think of will mean a reduction in vacuum while the system is cycling, but I don’t need insane high vacuum to run several 50L rotovaps. I would like to reduce ethanol loss as much as possible. During colder months a big stainless tank I have in line fills up with ethanol that I can isolate from the system and drain, but during the summer months between the ambient temp and the vacuum it collects very little.


Setuo two cold traps. Not in series but parallel to one another. Setup a switch for the inlet/outlet for each and now you will always have a coltrap and can switch when one fills up.


Problem isn’t so much the draining that bothers me - and I’ve got an AI unit with 2 glass traps, its expecting subordinates to do the draining. Unless programmed to, robots don’t tend to slack off.

@greenbuggy are you trying to drain the dry ice reservoir or the ethanol in the receiving flask?

Draining the ethanol in the receiving flask. The AI unit is a refrigerated cold trap and does not use dry ice

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agreed. wetware is proven unreliable. if the robot gets it wrong, it’s usually still a wetware problem.

@Plant2pipe thought this might be useful to somebody. I nominate you @greenbuggy !

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The only roto I’ve seen that does this is a Heidolph and the price tag is 150k+ if I remember right. Let me know what you figure out though. A hack for an Ai vap that accomplishes this would be a godsend to a lot of us in the industry!

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I think we switched objects here.
Afaik there is no “cold trap” (trap between the pump and ~) that will empty itself. Your best bet is to get extra cold wells and switch them out. Let the cold used one warm up and get cleaned while the second one does it’s job.

The Heidolph 20L has a “Distimatic Automatic Module” This sticks to the side of a 20L and will do; Automatic Refill, Automatic Condensate Discharge, and Automatic Drainage of Residue for 24/7 unattended operation. Price tag for a complete setup is $77,500.00(20L)+$34,590.00 = $112,090. Throughput is ~300 Liters in a 24 hour period.


What’s your throughput with the 50 Liters?

I was talking about the vac lines coming out of my rotos not emptying the rotos themselves. When I said AI I was referring to this mechanical cold trap:

Depends very much on the vacuum level we’re able to maintain on them and ambient temperature (no AC in our building so ambient temps above 80 definitely put some stress on our chillers) and its been in the 90’s almost every day this week

With that said I think the best performance we’ve got out of the rotos has been right around 20-25 L/Hr recovered ethanol, though I don’t have a super precise way to judge that (yet)

Very clearly explain what exactly it is you are trying to empty automatically.

The receiving flasks under the main condenser, the cold trap, or the lines between the pump-trap-condenser somewhere?!

Take a picture.

At the VERY least it is tempting to design a concept. I like your thinking. I have code that rests on all sorts of embedded gizmos generally called computers lolz and hundreds of those are PLCs (programmable logic controller). The others are recognizable or not to tech types but the point is they all open and close valves, move motors, etc. The logic is the same for all types as far as valving. The automatic triggering of the valves could be accomplish myriad ways involving sensors of all sorts so a different post. For this post it is mnaual triggering.

In the task at hand of valving for your concept. The valves need to be two way vacuum selectors. I have a plastic one for vacuum control projects like this. There would be one just before and after the vapor trap inline with the vacuum. With power off the valves should rest open to normal flow through the vapor trap. The normally closed ports of the valves would be connected by vacuum line as a bypass to the trap. When energized under vacuum those valve would open the line around the trap and close the lines between the trap thus isolating the trap without any bumping of the vacuum.

Then after a slight delay, a vent port valve opens on the vacuum line but in the isolated portion of the line, and bottom a wet valve opens for collection. Four valves. Almost the same sequence in reverse to reestablish system operation, except for a delay needed between the isolation valves to minimize bumping the pressure. The ladder logic would be pretty straight forward. For the period of time it took to drain the trap all vapor would bypass and if this is unacceptable then more complexity is unavoidable.

I might have this logic wrong but a first stab at ladder logic would be written as described above. There is a conceptual way to incorporate a single valve into both port and drain as well but that would take a bit to think through. Most valve banks have a normally open and normally closed port. I have seen entire “logic” circuits built up in rudimentary fashion by cross connecting ports and valves in the right order although the logic output was machine movement. Thanks for the idea and opportunity to try to think through valves and such again. :nerd_face:


Or just slap one of @Lilibel peristaltic pumps + the liquid level sensor mentioned before, on the unit that needs to be drained?

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The glass flasks that capture solvent in an AI mechanical cold trap.

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How viscous is the liquid in your trap when cold?

A piece I hope!

Yeah, I’d be VERY upset if that were all five of them combined!

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Not bad, it looks and smells like its exclusively ethanol, moving about the viscosity I expect for ethanol around -30-40 *C