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Author: Subject: What kind of vacuum pump is suitable for a 24/40 setup?
batsman
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[*] posted on 14-7-2013 at 13:24
What kind of vacuum pump is suitable for a 24/40 setup?


Hey, guys. I wanted to ask what kind of vacuum pump that would be suitable for a 24/40 distillation setup? What would meet my vacuum needs at a minimum, and a maximum, in your opinion? I was thinking about getting a aspirator, but then i thought that maybe it would be best if i got a used vacuum pump that has a higher capacity from the start.

And then i have another question concerning lab equipment while im here posting. I have´t bought a heater or a stirrer, and i am a little bit short on the money front for the moment. I thought that i maybe could find a used oldschool stirrer. The ones that are attached to the stand, not magnetic.

What are your thought on this matter?
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[*] posted on 14-7-2013 at 13:59


Save money until you can get a decent magnetic stirrer and hotplate combo in the time being just use a cheapo Walmart or good will hotplate. Also harbor freight has some decent vacuum pumps for the money you would just need a trap which can be homemade.



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[*] posted on 14-7-2013 at 14:33


Quote: Originally posted by batsman  
...what kind of vacuum pump that would be suitable for a 24/40 distillation setup? What would meet my vacuum needs at a minimum, and a maximum, in your opinion? I was thinking about getting a aspirator, but then i thought that maybe it would be best if i got a used vacuum pump that has a higher capacity from the start.


Capacity, ie, flow rate of air, is not important for vacuum distillation. If you have no leaks the system will come to the full vacuum capability very quickly, no matter the size of your lab scale equipment.

I don't think its important even for vacuum filtration. If I'm doing vacuum filtration I always use my aspirator, as it is handy and perfectly adequate. I only use my vacuum pump if I need to get down to pressures lower than 75mmHg absolute, which is roughly the capability of my aspirator.

Also, an aspirator is pretty much immune to the contaminants sucked through it, whereas a vacuum pump must usually be protected with a cold trap - a real pain in the ass.

Capacity is important to refrigeration technicians as "time is money" and they have a large capacity system to evacuate.

[Edited on 14-7-2013 by Magpie]




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[*] posted on 14-7-2013 at 18:26


Personally, I'm sort of interested in this question, because while running a water aspirator would in most situations be fine, the amount of water wasted using it bothers me. I have seen distillation setups being run with a bucket and a small aquarium pump, where the pump would make the water in the bucket flow through the condenser. I find this sort of recycling ideal



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[*] posted on 14-7-2013 at 19:05


An aspirator can certainly be driven with with a closed system using a reservoir for the water. I don't think an aquarium pump will be adequate, however. I think you will need a centrifugal pump with a higher capacity and pressure. Also, if you run it for an extended period of time the water will heat up. So you will have to cool that water somehow, eg, add ice, replace with cold water, etc. Also, if you are sucking nasty vapors (nitric acid, etc) your piping and pump will have to be able to deal with them.

I run my aspirator right off the tap. So others that use closed systems can give you the best advice.

[Edited on 15-7-2013 by Magpie]




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[*] posted on 14-7-2013 at 19:22


Where did you purchase you're aspirator magpie? Also if you were going to use a aspirator for vacuum distillation what is a estimated liters per minute needed to get a good vacuum for distillation?



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[*] posted on 14-7-2013 at 19:53


Carolina Biological.

I don't know how many LPM is required to reach its best vacuum - I've never measured it. For an aspirator the vacuum attainable is limited by the water temperature - colder the better. As I recall about the best I get is around 65mmHg absolute pressure.

That's plenty for filtering. Vacuum distillation is case specific.




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batsman
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[*] posted on 15-7-2013 at 08:53


Hey guys. Thanx for all replies. :)

I am thinking about the amount of water that i will have to use also. That´s why i´m thinking about getting a vacuum pump.
I have found one that say; application: lab. And "VPO 140". I don´t know what that means. Anybody?

I will get a regular hotplate, and heat through oil bath.
About the stirrer? Maybe its a stupid idea to get the old school stirrer? It´s pretty affordable, as a temporary solution.

Thanx guys. http://www.sciencemadness.org/talk/images/smilies/cool.gif
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[*] posted on 16-7-2013 at 14:17


You can build a recirculating water vacuum pump, this way you don't waste water while doing your distillations. There are several examples of how to build one around, they are all pretty simple and follow the same concept. Just connect a water pump to a bucket filled with water and make the water flow in cycles from the bucket, through the pump, and finally being squirted by your aspirator back to the bucket.

[Edited on 16-7-2013 by simba]
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batsman
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[*] posted on 19-7-2013 at 05:35


I like that idea. I will definently use that one. :)

Thanx to all you guys. :)
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[*] posted on 19-7-2013 at 09:42


Don't forget to add some sort of cooling to your setup btw...the water pump will heat up and transfer that heat to the water which will eventually weaken your vacuum. It is good to add ice to your bucket to keep the water as cool as possible.
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[*] posted on 24-7-2013 at 03:24


I ordered a aspirator yesterday, and i found a good water pump in the storage room. I knew that i had one, but i just couldn´t find it. :)
I have also bought a used Fisher sci hotplate, and i was thinking that if i find a cheap overhead stirrer would get it, and some boiling granuals. What´s your thoughs on that matter?

Now i just need a stand with clamps, and retorts and stuff, and probably some more glassware, like a vigreux column for example.

Thanx to all you guys for your help. :)
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[*] posted on 26-7-2013 at 20:12


Hello,

I bought a 2.5 cfm vacuum pump from harbor freight, the kind used for refrigeration and air conditioning. I have had it for about three years using it routinely with nitrous and chlorine solutions.

I change the oil about once every two months.

I connected it to an old 8 gallon air compressor tank replacing the air pump on the tank with the vacuum pump - so instead of pumping air to the tank, the vacuum pump draws a vacuum on the tank.

The vacuum pump draws a vacuum on the 8 gallon air compressor tank. The tank acts as a vacuum reservoir. The tank draws vacuum on a 20 foot section of air hose. The air hose is connected to a brass ball valve. The ball valve is connected to a 3 foot section of vacuum hose. The hose can be attached to a filter flask or distillation rig.

I recently installed a vacuum operated switch that is adjustable 0 to 29 inches of mercury. I keep it set at 5 inches which is plenty for vacuum filtering, but I usually reduce down to 2 inches for distillation. The switch cuts power to the motor on the vacuum pump when the pre-set vacuum is achieved. It has a 1 inch "dead band". With the switch set to 5 inches, the pump cuts off when the vacuum in the tank hits 5 inches Hg, and restarts at 4 inches Hg.

It's very nice as I can leave it running while filtering slowly and I don't have to worry about the vacuum getting too high and causing a filter paper failure.

kadriver

<hr width="800" />
Here is a photo of the vacuum switch

P1240001a.jpg - 198kB

<hr width="800" />
I may have posted this before, but here is a photo (turned sideways to get it to fit the photo size limit) of the vacuum pump.

This thing is a work horse. I forgot to change the oil for several months a while back and it seized up. The oil looked terrible. It looked more like grease (emulsified) when I drained it out.

I took the cover off and put a pair of vice grips the end of the shaft to get it to spin (with the power off of course).

Then I added new oil and it ran perfectly. I immediately changed the oil again, and change it regularly now.

Its inexpensive and durable, if you keep it maintained.

And I don't have any traps or driers on it. I feed a cup of sodium carbonate dissolved in hot water through it to neutralize any acid that may form in the metal tank, then flush and drain it.

It has served me well over the last three years.

I paid $80 plus tax, but I think they are closer to $100 now.

kadriver

image_18961.jpg - 213kB

<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: merged sequential posts]

[Edited on 7/27/13 by bfesser]
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bfesser
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[*] posted on 26-7-2013 at 21:12


<strong>kadriver</strong>, I just merged your <em>three</em> sequential posts (<em>made within half an hour</em>;) into one. In the future, use <img src="./images/xpblue/edit.gif" />. Next time I may be less <em>helpful</em>...

P.S. Learn to <a href="http://windows.microsoft.com/en-us/windows7/resize-a-picture-using-paint" target="_blank">resize</a> <img src="../scipics/_ext.png" /> images. It's not difficult.




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[*] posted on 27-7-2013 at 05:41


Quote: Originally posted by kadriver  
I recently installed a vacuum operated switch that is adjustable 0 to 29 inches of mercury. I keep it set at 5 inches which is plenty for vacuum filtering, but I usually reduce down to 2 inches for distillation. The switch cuts power to the motor on the vacuum pump when the pre-set vacuum is achieved. It has a 1 inch "dead band". With the switch set to 5 inches, the pump cuts off when the vacuum in the tank hits 5 inches Hg, and restarts at 4 inches Hg.
A switch of this form is one way of building a manostat, a device to maintain constant pressure (in this case negative). It's not the most effective way, because the dead band is fairly large. It would, however, make a good backing vacuum source for a more accurate device. Accuracy of this sort only really matters if you're doing vacuum distillations.

For your edification and/or amusement, here are a couple of advertisements for them from the ACS.
1947: http://pubs.acs.org/doi/abs/10.1021/ac60010a725?journalCode=...
1955: http://pubs.acs.org/doi/abs/10.1021/ac60099a704?journalCode=...
The second one, in glass, works the same way a Cartesian diver does.
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[*] posted on 27-7-2013 at 08:57


Yeah, I am using a HVAC vacuum pump I bought at HARBORFREIGHT.COM, I added a manifold out of brass pipe and used rector seal true blue sealant on the threads, and I also added a gauge and adj. vacuum vent so I can maintain a certain level of vacuum (both the gauge and vent were bought from grainger.com). The setup works well, just remember to get some good vacuum pump oil to refill the pump with and to keep an idea on the condition of the oil in the pump. You could build a simpler unit yourself using a motor, some wood to build an eccentric cam and a few cheap modified bicycle pumps connected together for your vacuum.



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[*] posted on 27-7-2013 at 09:35


Do you guys know what the maximum vacuum for, say, a 1L Pyrex filter flask is?
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[*] posted on 29-7-2013 at 17:45
Maximum Vacuum for Glassware


Hello, I have almost completed a distillation setup with graham condenser, 1000ml receiving flask, vigreux column, etc. Most of it is Pyrex, except for a connector.

I purchased a small Hargraves C117H 12 BTC vacuum pump with an AEDPM diaphragm, 24v motor, and max vacuum of 25 in Hg. I have the pump connected to a gauge that reads up to 30 in Hg and it is connected to a pulse width modulation motor speed controller to control its power, i.e. vacuum.

My question is what is the maximum vacuum standard glassware can withstand? I've searched quite a bit for this information, but since none of my standard glassware is vacuum rated, it is not available. What are the highest vacuums you all have reached with your glassware safely?

[Edited on 30-7-2013 by malford]
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[*] posted on 29-7-2013 at 17:57


I don't think pulse width modulation (PWM) will be a feasible means to control the vacuum, you might just destroy your pump&mdash;but I could be wrong. It seems like a controlled leak or a specialized regulator are preferred. Personally, I've never experienced a vacuum implosion, so you'd best wait for other members advice on that.



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[*] posted on 29-7-2013 at 18:07


bfesser,

I heavily considered the controlled leak concept, but was afraid of a small speck clogging the valve and imploding all of my glass! I have contacted the manufacturer regarding the use of PWM for power control of the pump and am awaiting their response. The pump uses an electric motor and PWM is designed for electric motors.

My discussion is of the glassware not of which vacuum to buy. The brands, types of glass, thickness, size and many other variables all play a part in the maximum vacuum or pressure that the glassware can withstand.
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[*] posted on 29-7-2013 at 18:22


Well, you could put a filter on the leak. Like I said, I haven't experienced a glassware implosion, and I've used most of my glassware under the full vacuum that my rotary vane pump can pull (ca. 28.2 inHg vacuum).



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[*] posted on 29-7-2013 at 22:44


Quote: Originally posted by malford  
Do you guys know what the maximum vacuum for, say, a 1L Pyrex filter flask is?


Regardless of the hardness of the vacuum you pull the pressure on the outside of the vessel in not going to exceed atmospheric.ie about 15psi.




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[*] posted on 30-7-2013 at 11:13


Uhm, if I may ask, forgive my ignorance:
What is meant by "24/40 setup"?
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[*] posted on 30-7-2013 at 11:28


24/40 is one of several standard tapers for ground glass joints for chemistry, see
http://en.wikipedia.org/wiki/Ground_glass_joint

[Edited on 2013-7-30 by ElectroWin]
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[*] posted on 30-7-2013 at 18:58


Attachment: ground_ware.pdf (41kB)
This file has been downloaded 419 times




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