Sciencemadness Discussion Board

Rotavap operational concern....

organicchemist25 - 5-4-2016 at 16:56

Just got a gently used buchi Rotovap. It came with new seals. Seems like the bottom part where vapor duct (glass threaded stem goes into motor) should have something to hold the threaded vapor duct stem in? It has a black threaded latch plastic piece. But after assembly the stem kind of comes out and then no longer is turned by the motor. Model is Buchi R-3000

I contacted seller, which is from a university, about it and he said just apply vacuum and then it stays together and continues to turn. This is true. I have an all PTFE component vacuum pump, but the manual states it can do reduced pressure and normal atmosphere solvent removal. But, if the stem comes out and stops turning from less surface joint contact them I can't do normal pressure removals.

Can anyone help with what's going on? I scratched my head for a while before I posted. I feel a bottom part to the motor drive is missing to hold the stem seated in place and will turn without vacuum. Seller told me otherwise.

Thanks!

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chemrox - 5-4-2016 at 17:24

Looks like an extra security device. The part in the middle picture may be meant to attach through the threads and flip down over the flask joint this case a 24/40. Visit the Buchi site and get some diagrams of the various models. You might also have to search online for Buchi parts diagrams. When you figure it out send me a holler and lets commiserate. I think I have one like that. I have lots of Buchi parts and a few Buchler parts as well. Also check with Dr. Bob; he's resourceful! How much did you pay for that dude? I'm selling them and want to know what I can get away with. I will discount anything I sell to members but sometimes I blow it on the costs. As in the case of NaBH4 powder. For members in the UK where everything technical is backwards I have some units wired for 220. The comment was TIC. 220 is more cost effective. Just don't touch the hot side when you're grounded.

[Edited on 6-4-2016 by chemrox]

ScienceHideout - 5-4-2016 at 17:35

I don't know much about fixing rotovaps but I will tell you that the black screwy-thingie with the metal hook is the best thing in the world.

Screw it all the way onto the rotovap before you put your flask on. Then unscrew it until it touches the joint of the flask. Flip the metal hook down, and screw the plastic up again so that the metal hook 'grabs' the flared part of the joint. Now your flask won't fall off into the water!

When you're done rotovapping, you can unscrew the plastic part, and it will sort of 'push' your flask off so that you don't have to pull and twist. Fun!

Good purchase!:)

Dr.Bob - 5-4-2016 at 18:27

The black clip is great, but I would leave it off until you figure out the stem (steam duct) issues. It will hold on the flask and help remove it, but it does not hold the glass stem in place. There is usually a triangular metal retaining clip inside the metal rotating joint that holds the stem in place, but it often gets stuck, corroded, or even is lost. But often, it takes a substantial amount of force to get the stem to seat into the joint right and lock in. I often put the stem in place, push it tight, and then wack it into place with a piece of 2x4. Nope, I'm not kidding. Vacuum will sometimes work, but not if the system is old or bent a little. But if you can't see it, or if there is a space that looks like the retainer is missing, then it might be. It is possible that your model is different, but not sure what model it is.

Look in the bottom left photo, inside the metal joint, there is a round shadow, that might be the clip, can't tell for sure. But once that steam duct/stem is in there, it is hard to get out as well. I have had to remove the condenser before, and wack the other side to knock it loose. The plastic clip can often help pull the stem out, if done right, but make sure it is on the right way, as only one direction is right. That is why I would leave it off until all is good.

Bob

DJF90 - 6-4-2016 at 01:28

Quote: Originally posted by Dr.Bob  
There is usually a triangular metal retaining clip inside the metal rotating joint that holds the stem in place, but it often gets stuck, corroded, or even is lost. But often, it takes a substantial amount of force to get the stem to seat into the joint right and lock in. I often put the stem in place, push it tight, and then wack it into place with a piece of 2x4. Nope, I'm not kidding...

...But once that steam duct/stem is in there, it is hard to get out as well. I have had to remove the condenser before, and wack the other side to knock it loose. The plastic clip can often help pull the stem out, if done right, but make sure it is on the right way, as only one direction is right. That is why I would leave it off until all is good.

Bob


Everything Bob says mirrors my own experience, although I use a rubber mallet rather than a piece of 2x4. It's clear after zooming in on the third image that the retaining clip is present. It really can take some force to get the vapour duct seated, particularly if the clip is corroded (and it's just as bad removing the duct, too!).

[Edited on 6-4-2016 by DJF90]

organicchemist25 - 6-4-2016 at 19:33

yes, the clip is inside the motors metal seat which accepts the ground glass joint. it can be pushed through the clamp ring or removed with a little bit of force too.

Should that clip hold it tightly inside the joint? to seal it? because mine does not. it does seem to prevent it from falling out into the bath water.

im just trying to figure out how to keep the stem seated in the flange/metal joint to stay sealed for solvent removal if I choose not to run a vacuum because at this point that is not happening.

applied vacuum pulls the stem to stay seated into the motor, but no vacuum it loses contact and only the motor spins.

hope I am making sense.

thanks for all the input!

organicchemist25 - 6-4-2016 at 19:38

Quote: Originally posted by chemrox  
Looks like an extra security device. The part in the middle picture may be meant to attach through the threads and flip down over the flask joint this case a 24/40. Visit the Buchi site and get some diagrams of the various models. You might also have to search online for Buchi parts diagrams. When you figure it out send me a holler and lets commiserate. I think I have one like that. I have lots of Buchi parts and a few Buchler parts as well. Also check with Dr. Bob; he's resourceful! How much did you pay for that dude? I'm selling them and want to know what I can get away with. I will discount anything I sell to members but sometimes I blow it on the costs. As in the case of NaBH4 powder. For members in the UK where everything technical is backwards I have some units wired for 220. The comment was TIC. 220 is more cost effective. Just don't touch the hot side when you're grounded.

[Edited on 6-4-2016 by chemrox]


Chemrox, I paid 1700.00 with shipping and everything to make a complete set up. also sent two brand new seals and an all PTFE component lab vacuum which can bring it down to 6 torr/mmHg.

i thought it was a pinch high, but both look practically brand new and run very quietly . Others i had been looking at looked rough from spills and corrosion. So, I just went with the gently used gear. Hope that helps!

[Edited on 7-4-2016 by organicchemist25]

organicchemist25 - 6-4-2016 at 19:45

Quote: Originally posted by Dr.Bob  
The black clip is great, but I would leave it off until you figure out the stem (steam duct) issues. It will hold on the flask and help remove it, but it does not hold the glass stem in place. There is usually a triangular metal retaining clip inside the metal rotating joint that holds the stem in place, but it often gets stuck, corroded, or even is lost. But often, it takes a substantial amount of force to get the stem to seat into the joint right and lock in. I often put the stem in place, push it tight, and then wack it into place with a piece of 2x4. Nope, I'm not kidding. Vacuum will sometimes work, but not if the system is old or bent a little. But if you can't see it, or if there is a space that looks like the retainer is missing, then it might be. It is possible that your model is different, but not sure what model it is.

Look in the bottom left photo, inside the metal joint, there is a round shadow, that might be the clip, can't tell for sure. But once that steam duct/stem is in there, it is hard to get out as well. I have had to remove the condenser before, and wack the other side to knock it loose. The plastic clip can often help pull the stem out, if done right, but make sure it is on the right way, as only one direction is right. That is why I would leave it off until all is good.

Bob




Thanks Dr. Bob!!
Your advice is always helpful, as well as appreciated.