DocX
Hazard to Others
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 179
Registered: 22-10-2015
Member Is Offline
Mood: No Mood
|
|
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?
|
|
Gammatron
Hazard to Others
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 125
Registered: 30-8-2022
Location: Abandoned Uranium Mines
Member Is Offline
|
|
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](http://www.sciencemadness.org/talk/files.php?pid=677651&aid=95159)
[Edited on 10-16-2022 by Gammatron]
|
|
Tsjerk
International Hazard
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 3026
Registered: 20-4-2005
Location: Netherlands
Member Is Offline
Mood: Mood
|
|
Can you post a picture of your setup? This should be an easy fix when we get a view.
|
|
unionised
International Hazard
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 5109
Registered: 1-11-2003
Location: UK
Member Is Offline
Mood: No Mood
|
|
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.
|
|
DocX
Hazard to Others
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 179
Registered: 22-10-2015
Member Is Offline
Mood: No Mood
|
|
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](http://www.sciencemadness.org/talk/files.php?pid=677656&aid=95167)
[Edited on 20222222/10/16 by DocX]
[Edited on 20222222/10/16 by DocX]
|
|
Gammatron
Hazard to Others
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 125
Registered: 30-8-2022
Location: Abandoned Uranium Mines
Member Is Offline
|
|
Quote: Originally posted by unionised ![](images/xpblue/lastpost.gif) |
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.
|
|
DocX
Hazard to Others
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 179
Registered: 22-10-2015
Member Is Offline
Mood: No Mood
|
|
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.
|
|
Tsjerk
International Hazard
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 3026
Registered: 20-4-2005
Location: Netherlands
Member Is Offline
Mood: Mood
|
|
Although foam should fall to the bottom without an extra tube, if it doesn't a tube would probably be a fix indeed.
|
|
DocX
Hazard to Others
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 179
Registered: 22-10-2015
Member Is Offline
Mood: No Mood
|
|
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]
|
|
Texium
Administrator
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 4552
Registered: 11-1-2014
Location: Salt Lake City
Member Is Offline
Mood: PhD candidate!
|
|
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.
|
|
DocX
Hazard to Others
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 179
Registered: 22-10-2015
Member Is Offline
Mood: No Mood
|
|
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.
|
|
Sulaiman
International Hazard
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 3647
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Offline
|
|
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
|
|
DocX
Hazard to Others
![*](images/xpblue/star.gif) ![*](images/xpblue/star.gif)
Posts: 179
Registered: 22-10-2015
Member Is Offline
Mood: No Mood
|
|
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.
|
|