Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Vacuum filtration sucking fluid
DocX
Hazard to Others
***




Posts: 179
Registered: 22-10-2015
Member Is Offline

Mood: No Mood

[*] posted on 16-10-2022 at 04:22
Vacuum filtration sucking fluid


So I'm using ny new vacuum pump to vacuum filter some newly synthesised lovely salts.
Problem is, when I run it, the fluid gets sucked into the vacuum hose and into the pump. I hate that.

I use a Buchner connected to a conical flask. Nothing fancy. I don't get why the fluid travels upwards to the hose connector instead of down into the flask. Anyone had this happen? Is there an easily preventable cause?
View user's profile View All Posts By User
Gammatron
Hazard to Others
***




Posts: 125
Registered: 30-8-2022
Location: Abandoned Uranium Mines
Member Is Offline


[*] posted on 16-10-2022 at 05:08


Flask too small? You could have a 2nd flask as a water trap. Also I have found that because of vacuum lowing the boiling temp of water it will sometimes condense in the tubing. This was a big problem when I was using an oil filled rotary vane pump but now I use an oilless piston pump and it handles it a lot better.

trap.jpg - 26kB

[Edited on 10-16-2022 by Gammatron]




View user's profile Visit user's homepage View All Posts By User
Tsjerk
International Hazard
*****




Posts: 3022
Registered: 20-4-2005
Location: Netherlands
Member Is Offline

Mood: Mood

[*] posted on 16-10-2022 at 07:02


Can you post a picture of your setup? This should be an easy fix when we get a view.
View user's profile View All Posts By User
unionised
International Hazard
*****




Posts: 5107
Registered: 1-11-2003
Location: UK
Member Is Offline

Mood: No Mood

[*] posted on 16-10-2022 at 07:43


Vacuum pumps are designed to suck fluids.
A fluid is something which will flow.
They are not designed to suck liquids or foams.

That trap will work even better to protect your pump if you add a bit of tubing inside the flask. (apologies for the awful drawing of a tube.)

On the other had, doing that makes the trap less good as a "suck back" preventer.

trap.jpg - 34kB
View user's profile View All Posts By User
DocX
Hazard to Others
***




Posts: 179
Registered: 22-10-2015
Member Is Offline

Mood: No Mood

[*] posted on 16-10-2022 at 09:05


Quote: Originally posted by Tsjerk  
Can you post a picture of your setup? This should be an easy fix when we get a view.


Sure, I'll post one as soon as I get the chance. But it's not a very complicated setup. A Buchner like the one below connected to a 1- liter conical. And the Buchner funnel connected to a small vacuum pump.

I know a trap would solve the problem, but if possible I would prefer not to complicate the setup.
Although I guess the problem is foam. Liquid being sucked through the porous plate that foams and gets sucked up into the vacuum tube.

Screenshot 2022-10-16 at 19.03.39.png - 283kB

[Edited on 20222222/10/16 by DocX]

[Edited on 20222222/10/16 by DocX]
View user's profile View All Posts By User
Gammatron
Hazard to Others
***




Posts: 125
Registered: 30-8-2022
Location: Abandoned Uranium Mines
Member Is Offline


[*] posted on 16-10-2022 at 09:27


Quote: Originally posted by unionised  


That trap will work even better to protect your pump if you add a bit of tubing inside the flask. (apologies for the awful drawing of a tube.)



Yeah I noticed that, water could easily get sucked up. I found the pic on google and it worked to illustrate what I was saying, I just use a pipette through a stopper, not sure how you could attach a tube to the inside of the vacuum port.




View user's profile Visit user's homepage View All Posts By User
DocX
Hazard to Others
***




Posts: 179
Registered: 22-10-2015
Member Is Offline

Mood: No Mood

[*] posted on 16-10-2022 at 21:14


But maybe I could attach the hose to the exit tube from the Buchner funnel? And make it so the inflow to the vacuum bottle is further from the vacuum outlet? That way foam shouldn't travel so easily into the vacuum hose.
View user's profile View All Posts By User
Tsjerk
International Hazard
*****




Posts: 3022
Registered: 20-4-2005
Location: Netherlands
Member Is Offline

Mood: Mood

[*] posted on 17-10-2022 at 02:08


Although foam should fall to the bottom without an extra tube, if it doesn't a tube would probably be a fix indeed.
View user's profile View All Posts By User
DocX
Hazard to Others
***




Posts: 179
Registered: 22-10-2015
Member Is Offline

Mood: No Mood

[*] posted on 17-10-2022 at 07:26


Well, SOMETHING makes fluid enter the vacuum hose. I'll try the extra tube thang (next time I'm doing a filtration) and get back. With pictures.

[Edited on 20222222/10/17 by DocX]
View user's profile View All Posts By User
Texium
Administrator
********




Posts: 4530
Registered: 11-1-2014
Location: Salt Lake City
Member Is Offline

Mood: PhD candidate!

[*] posted on 17-10-2022 at 09:34


Sounds like you’re using a lot more vacuum than you need for the job. If your only vacuum source is a powerful vacuum pump, I’d recommend installing a bleed valve so you can adjust the level of vacuum being pulled. Full vacuum for distillations of high boiling stuff and residual solvent removal, lower vacuum for filtration. Regardless, putting a trap in line to protect your pump (preferably chilled) is ALWAYS a good idea, no matter what you’re using it for.



Come check out the Official Sciencemadness Wiki
They're not really active right now, but here's my YouTube channel and my blog.
View user's profile Visit user's homepage View All Posts By User
DocX
Hazard to Others
***




Posts: 179
Registered: 22-10-2015
Member Is Offline

Mood: No Mood

[*] posted on 18-10-2022 at 20:18


Quote: Originally posted by Texium  
Sounds like you’re using a lot more vacuum than you need for the job.


Yes, I figured that also. I haven't had time to buy or add a valve though, so just adding a longer outlet from the Büchner funnel is way easier.
View user's profile View All Posts By User
Sulaiman
International Hazard
*****




Posts: 3580
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Offline


[*] posted on 19-10-2022 at 02:21


A long tube will reduce airflow when there is air to flow
(eg air drying a filter cake)
But when filtering there is negligible airflow,
so full vacuum will be applied.
(boiling/frothing/foaming likely)




CAUTION : Hobby Chemist, not Professional or even Amateur
View user's profile View All Posts By User
DocX
Hazard to Others
***




Posts: 179
Registered: 22-10-2015
Member Is Offline

Mood: No Mood

[*] posted on 23-10-2022 at 13:10


Sorry, no picture, but the extra bit of tubing attached to the outlet of the Buchner did the trick. The real problem is of course that I'm using unnecessary strong vacuum, like Texium figured, sucking froth and fluid right into the vacuum pump inlet. But the quick fix did the trick. I will post a picture, just haven't gotten around to it yet.
View user's profile View All Posts By User

  Go To Top