Sciencemadness Discussion Board

CONSTRUCTION OF WATER ASPIRATOR PUMP

poppy straw - 9-1-2010 at 11:23

Materials required:

Harbor Freight, Item 2955-7VGA 3/4 HP, 1" Cast iron shallow well pump, $129.99, Pacific Hydrostar, 20-60 psi

OR

Item 47906-1VGA, 1HP, 1" Shallow well pump with stainless steel housing, $99.99, 72 psi

Stainless steel is best option in my humble opinion,

Water tank considerations, use 55 Gallon plastic trash container with lid, plastic is chosen due to corrosive pump gases, Et. cetera, plastic lid chosen due to ease of inlet and outlet hole construction, and ease of ice addition, control of dirt, leaves....

Water Aspirator Pump, plastic or metal

Wards Natural Science Co. $17.80
Cole-Parmer (plastic) $15.25
Avogadro's Lab Supply (ebay).......$24.99

Construction of apparatus

use one inch intake and output piping, use stainless or plastic, use valves on both intake and especially output, place output valve after tee where aspirator is located, thus water pressure can be regulated through aspirator, do not place pump on plastic lid.....

Place holes in plastic lid, three are required, one for intake, one for aspirator, and finally one for bypass on the pressure side. Use large linear hose to control output of aspirator or gross splashing will occur, construct aspirator pump device in open area, i.e., outside.... and protect from freezing.

I will post answers to questions concerning this construction...

bbartlog - 9-1-2010 at 18:52

While this works, isn't it quite inefficient compared to buying a vacuum pump?

Also, why a 55 gallon water tank rather than just a five gallon one?


watson.fawkes - 10-1-2010 at 08:04

Quote: Originally posted by bbartlog  
While this works, isn't it quite inefficient compared to buying a vacuum pump?
This plan is for a high-volume pump, of the kind used on a scale they call "pilot plant", the kind you use with a 5L reaction flask. While the ultimate pressure is no better than any other aspirator pump, it will pump higher volumes of gas.

gsd - 10-1-2010 at 08:18

Quote: Originally posted by bbartlog  
why a 55 gallon water tank rather than just a five gallon one?


Because the higher the volume of recirculated water, lower the rise in its temperature and hence lower the drop in vacuum.

gsd

aonomus - 10-1-2010 at 08:37

Quote: Originally posted by gsd  
Quote: Originally posted by bbartlog  
why a 55 gallon water tank rather than just a five gallon one?


Because the higher the volume of recirculated water, lower the rise in its temperature and hence lower the drop in vacuum.

gsd


Also probably the less chance of bubbles from the aspirator getting sucked into the pump, they will have a chance to float back to the surface due to a lower flow velocity in the bulk of the fluid with a larger container radius.

hissingnoise - 10-1-2010 at 08:44

Drug chemists have been using this kind of set-up for years - they work well as long as outlet bubbles are kept out of the pump-inlet.
And the bigger the reservoir the better!
A small amount of ordinary antifreeze will protect against frost and the corrosion inhibitors will afford some protection for the pump. . .

poppy straw - 10-1-2010 at 08:49

EXCELLENT QUESTIONS

The water aspirator pump as configured with LARGE volume of water resolves two problems, the first is function of use versus increase in water temperature, maximum vacuum is achieved with minimum water temperature, if for example using a rotary flash evaporator will increase water temperature of the pumping system, addition of ice will help... acid neutralization by hydroxide addition to pump water... antifreeze addition.... complete control of contaminated pumping water...,

Additionally, toxic and corrosive gasses are pulled through the system and are dissolved or released to ambient environment, this is why the pumping aspirator system is used at all university laboratories.... for general lab. functions like filtration.... distillation, etc.

Expensive oil driven vacuum pumps require cold traps to freeze out harmful vapors from the vacuum stream...corrosion is very harmful to mechanical vacuum pumps.. cold traps requirements are expensive, dry ice/acetone, alcohol, liquid nitrogen, and dewar vessels, etc.

Then, for practical purposes, the following ranges of pressures are distinguished:

water pump vacuum (ca. 10-700 mm)
oil pump vacuum (0.001-1 mm)
mercury pump vacuum(<10 to neg. third mm)

see, Organicum, B.J. Hazzard pages 25-32 for excellent discussion. isbn 0-201-05504-X or there a bouts

anotheronebitesthedust - 10-1-2010 at 15:41

Any pictures?

gsd - 10-1-2010 at 16:57

Quote: Originally posted by aonomus  

Also probably the less chance of bubbles from the aspirator getting sucked into the pump, they will have a chance to float back to the surface due to a lower flow velocity in the bulk of the fluid with a larger container radius.


Normally the bubble menace is tackled by proper partitioning / baffling of the receiver tank so that the suction to the pump and the input from ejector are in two separate sections.

gsd

Panache - 10-1-2010 at 23:59

Just use mains water straight down the drain, no cooling worries, no pump required, might want a cold trap to guard against accidents, then sit back in your baby seal fur jacket, turn on your CFC driven air-conditioning on full to compensate for having no insulation and watch the megalitres piss down the drain. Quite a show.

Magpie - 11-1-2010 at 19:29

Quote: Originally posted by Panache  
Just use mains water straight down the drain, no cooling worries, no pump required, might want a cold trap to guard against accidents, then sit back in your baby seal fur jacket, turn on your CFC driven air-conditioning on full to compensate for having no insulation and watch the megalitres piss down the drain. Quite a show.


Or, if in the northern hemisphere, substitute "wall mounted electric heater on full" for "CFC driven air-conditioning on full." :D

Your mention of the cold trap is a good point, Panache. Just the other day I was attempting to remove some ethanol from a diethyl malonate esterification by vacuum distillation at 50C when, being a bit casual with vacuum management, I had a massive suckback. I normally don't use a safety bottle and this poor practice finally caught up with me. So I consulted Vogel, and here is what I came up with as a safety bottle. It works very well and by using the Hoffman screw clamp on the air bleed I can fine tune the pot vacuum to within a gnat's eyelash:

safety suckback bottle.jpg - 110kB

poppy straw - 12-1-2010 at 17:40

These images might be helpful:




Vacuum Pump 005 (Medium) (Small).jpg - 58kB

Panache - 19-1-2010 at 03:28

Quote: Originally posted by Magpie  
Quote: Originally posted by Panache  
Just use mains water straight down the drain, no cooling worries, no pump required, might want a cold trap to guard against accidents, then sit back in your baby seal fur jacket, turn on your CFC driven air-conditioning on full to compensate for having no insulation and watch the megalitres piss down the drain. Quite a show.


Or, if in the northern hemisphere, substitute "wall mounted electric heater on full" for "CFC driven air-conditioning on full." :D

Your mention of the cold trap is a good point, Panache. Just the other day I was attempting to remove some ethanol from a diethyl malonate esterification by vacuum distillation at 50C when, being a bit casual with vacuum management, I had a massive suckback. I normally don't use a safety bottle and this poor practice finally caught up with me. So I consulted Vogel, and here is what I came up with as a safety bottle. It works very well and by using the Hoffman screw clamp on the air bleed I can fine tune the pot vacuum to within a gnat's eyelash:


How do you bore out your rubber stoppers? No method i have tried seems universally foolproof. Do you fix the stopper in a sleeve or have it just clamped? Hole saw, spade bit, drill bit. I finally figured out a great way to seal a teflon thermocouple wire through a rubber stopper, drive a thick syringe needle through, feed the wire through the needle, remove needle, voila, not at leak to be seen.

I always try not using anything other than glass or polyolefins in the safety trap/cold trap, that way i never have to consider its survival from exp to exp.

I took a photo quickly but the labs so messy i was embarrassed, i'll post a photo tom, but in short my setup is very adhoc but works great.

Is that galvanised iron against the wall, i'm too sloppy (my minds on more important things:D) to have anything other than tiles, my sink always ends up looking like an old tinnie before too long.

[Edited on 19-1-2010 by Panache]

aonomus - 19-1-2010 at 05:56

I have found that sticking the stopper into a freezer for a few days, then quickly taking it and drilling it does an ok job. I have a rubber stopper sized for a 24/40 joint, with a K type thermocouple probe running through it (metal insertion probe). No leaks with hot solvent yet surprisingly...

Magpie - 19-1-2010 at 09:30

Quote: Originally posted by Panache  


How do you bore out your rubber stoppers? No method i have tried seems universally foolproof.

I always try not using anything other than glass or polyolefins in the safety trap/cold trap, that way i never have to consider its survival from exp to exp.

Is that galvanised iron against the wall, i'm too sloppy (my minds on more important things:D) to have anything other than tiles, my sink always ends up looking like an old tinnie before too long.

[Edited on 19-1-2010 by Panache]


>I use a regular cork boring device, with the different size cutters for different size holes. It works only so-so for rubber stoppers. Use of a drill on a frozen stopper sounds interesting - I'll have to try that next time.

>My use of copper is unorthodox but not without reasons: (1) The only stopper I had that size already had a large hole in it. A 1/8" brass pipe nipple fit it perfectly giving a good seal. (2) I wanted to use the rugged brass hose barbs at the connections as this flask must also server for filtrations and therefore must be disconnected/reconnected occaisionally. (3) I needed this right away and it was all I could cobble together the same day.

>That wall is not galvanized iron but is the outside of my aluminum fume hood. It looks like my fabricator used an orbital sander on it. I don't know why he did this. My sink and aspirator are about 3 meters away.



[Edited on 19-1-2010 by Magpie]

[Edited on 19-1-2010 by Magpie]