Vacuum pump

[Alchemist]

Hello all,

Does anyone have or seen plans on making a vacuum pump or converting a ice box compressor, pool pump, trailer pump, etc. for vacuum distillation?
Even idea's for a hand pump are welcome, but electric would be the best.

Thanks!!!

[Rhadon]

There are some designs on <a href="http://www.rhodium.ws" target="_blank">Rhodium's site</a>. Look in the chemistry section under "Equipment & Lab Technique".

[shooter3]

A vacuum aspirator works very well and if made out of plastic you will not have corrosion problems. Drag nitric acid through a mechanical pump and it won't last very long.

[PYRO500]

I made one of those aspirator recirculating stations and if I ever get the time I'll photograph it. But for now I am VERY busy, I still have a half completed pdf on chemical weapons their synthesis and the synthesis of their precursors :) .

[McGuyver]

Check out ebay. There's tons of vacuum pumps on there. Nice electric ones too, for good prices.

[PYRO500]

Just make sure your pump can handle the acid vapors/etc that you are going to feed it. Remember now that water will boil away at lower tempetures so if you use wash bottles along witha pump you have to have a cold trap if your pump goes up to any decent level.

[Alchemist]

Thanks all! Good info!

[grimreaper]

I use a long piece of ¼” pneumatic tubing connected to one of the vacuum ports on the inlet manifold of my pick up truck to vacuum bag things,
Pulls about 20”Hg at idle , this could be used to “pot” transformers etc
If used for “other things” be aware that the fumes will be burned in the engine , you may corrode your engine or maybe melt pistons or may produce some very toxic gases etc

[hydra]

The way that pump-damage is avoided in the lab (besides using very expensive resistant pumps of course :D ) is to pull -through- absorption solution bottles.

In other words, coming out of your reactor, you run the vac line to a tube in a 2-hole stopper in an absorption bottle; and the tube goes down near the bottom. Fill the bottle with appropriate fluid. The 2nd tube ends is in the 'airspace' above the absorption fluid; and this tube is connected either to the pump; or to a 2nd absorption bottle down the line.

I have seen setups with 4-5 bottles in a row...each with a solution to absorb a specific item; i.e. ammonia in bottle 1, H2S in bottle 2, CO2 in bottle 3, etc.. The vac-pump is way down at the end of the line.

edit: sometimes this setup is used not so much to protect the pump; but as an analytical technique in and of itself. I.e., the solutions can be tested to measure quantities of various off-gases which were generated. Sometimes indicators are included with the solutions; to tell when a reaction or distillation has reached a certain point, etc..

Generally, the first bottle is going to absorb the most water-soluble components anyway; so you go ahead and choose solutions to foster that; e.g. doing ammonia in the first bottle.

Just be aware of what your off-gas products are, and in what combinations they're likely to be absorbed in a -single- bottle (i.e. mixed together); and what the possible effects of that are (i.e. possible formation of some compounds you might not expect, or want).

Pumps: simple diaphragm-pumps can be surprisingly tolerant of chems. Some will go to junk almost immediately; but many of them will tolerate corrosive fumes for a surprising number of hours. And if you're getting them as surplus dirt-cheap, then it's a reasonable decision to just throw one away every 10 hours. Besides, you can get all kinds of valuable elements out of a pump. :D I.e., copper, zinc, etc. etc..

If you're off-grid like I am, then you might want to keep an eye out for the electric vac-pumps used on certain models of GM vehicles; espcially the older diesel trucks/burbans/blazers with the 6.2/6.5. Some used an electric vac pump for the brakes that will pull a pretty good vacuum...like 26-29". There were several sedans which used the same kind of pump too...I used to have a list of all years/models, but can't find it this moment. Google on it tho, and you'll find a list on some diesel-pickup forums.

Also, just about any compressor will work as a pump. Even the little $10 tire-inflater 12-volt compressors. They wear out pretty quickly; so if you're looking for something to run continuously for days, these may not be the best choice. For best vacuum, at least for a short term, squirt a little synth oil into the intake while its running; then hook your line up.

Any old lawnmower engine will produce quite a good vacuum if you put a check-valve in the intake-line. And we're talking some serious volume with one of these too.

Well....any OLD engine might not pull down as far as we'd like, I suppose... :D

But if the rings/valves are in decent shape, they can make excellent large-volume vac-pumps. Note: run -synthetic- oil in the crankcase. You don't even need to fill it....just enough for the 'splasher' on the crank to do its thing; but you do want synth oil. It makes a much better seal on the cyl-walls; i.e. gives better vacuum.

ps; chainsaw or other 2-stroke engines won't work well for this job...use a 4-stroke like a little Briggs or Honda 2hp. Almost any washing-machine motor or similar will drive it just fine. Gear down the rpm with hardware-store pulleys...or even sprockets and chain from bicycles or motorcycles.

If you can't find a suitable check-vavle; you can assemble your own pretty easily using a sphere, a suitable light-force spring, and pipe-fittings.

I have used a 5hp Briggs to pump down a pretty large chamber for experiments in large-area plasma treating of surfaces. I had a 3:1 pulley setup from a normal 1725rpm motor...1/2hp I think it was...and that sucker pulled down that chamber -fast-. :D

As I recall, it ran around 24-26" vac pretty easily; which was plenty good enough for what I was doing (which fed argon to the chamber anyway, so I didn't need high-vac).

With any reciprocating pump; consider using an accumulator to remove pulsations from the vac-line (unless they're beneficial to your process). Just about any rigid-wall tank will do. Even a stout 5-gal plastic bucket will take full vac without collapsing; especially if you put a simple wood "x-brace" halfway down inside, against the walls.

Any air-cylinder or hydraulic cylinder that's in good shape makes an excellent vac-pump. Again, with a check valve added to the suction side. Hyd-cyl seals are designed to hold 2,000+ psi without leaking...they're pretty good seals. And some of them have both a chromed rod and chromed cylinder. That might give them quite a bit of corrosion-resistance; although I've no personal experience to back that up.

Some of the refrigerator compressors made very good vac-pumps. Some designs didn't pull very well; but some of them were excellent. All you can do is try the one you have and see if it'll pull 29" or not. Remember that most refrigeration pumps are designed to have oil circulating with the gas. It's a good idea to pop off the line every now and then and squirt a little synth in there.

edit: forgot to mention....in any pump, it's the volume of dead-space that determines how far it can pull down; even with everything else perfect. In the briggs I used on the large chamber, I pulled the head and filled some of the space with epoxy. This increased comp-ratio, so it was a little harder to drive; but it also improved the inches of vac it would pull.

Ideally, if you were going to use an engine as a pump; you'd replace the spark-plug with a check-valve; to blow off the compression. I didn't get around to doing that because my experiment was a quick-and-dirty one-shot. But the next time I use that pump, I'll probably take the time to do this. It'd be a big improvement...and would also allow me to completely fill every bit of combustion-chamber volume (which isn't necessary, or wanted, for use as a vac pump).

[Charles Owlen Picket]

The above post by "HYDRA" is excellent. Independent of that I have experienced THE SAME results! I have actually used several techniques to the same end.

I have tested a cheap pump procured for next to nothing and utilized an absorption bottle. Pure and HOT NO2 fumes for months and that damn thing still pulls as hard as it did when new. Frankly, the pump I use now is approx 8 months in use.

I deeply believe that this concept works well and there is little need for a Teflon-lined, high end pump for a hobby (acid, corrosive, etc) production agenda.

[nbk2000]

One good thing to do with a water-filled gas trap is to use crushed ice in it.

Cold water dissolves more gas than warm, the ice acts like Raschig rings to ensure thorough gas/water mixing, and keeps the vapor pressure of the water as low as it can get, increasing the efficiency of the vacuum. :)

[senjoronie]

I would look on Ebay (check sellers' feedback), or if possible, check out university surplus auctions. The only downside to surplus auctions is that the equipment is probably near the end of its useful lifetime. If you're not doing high-vacuum work and just need some vacuum for filtration or solvent removal, try to get a diaphragm pump like the KNF Laboport. The Laboport is really neat. It's oilless, reliable, easy to move around, and its solid Teflon parts are resistant to most caustic chemicals.

I have read that refrigerator compressors can be used as vacuum pumps, although I personally would just go for an actual laboratory unit.

[Boomer]

Fridge compressors are surprisingly good at pulling vacuum, given they usually come for free. After my old fridge broke down (leaking freon, no more cooling), I cut out the compressor, and connected it via plastic tube to a flask with acetone solution of (you don't want to know). It flash-boilled in seconds, at room temp.

These are made to run many hours, and unlike what some people say, they *can* run non-stop. While it's true they normally cycle on/off, if newly filled with food, they run some hours without problem. And while they *do* rely on cooling via the liquid flow, they don't overheat in vacuum mode since instead of working against 200+ PSI pressure, they only work against 14PSI max (ambient). Keep them healthy and:

- Never suck acids, or use more than one wash-bottle

- If pulling solvents, like I do, put a trap on the outlet. The solvents condense inside, and squirt out together with the oil. Either evaporate the solvents and return the oil, or dispose both and add some drops of new oil now and then.

- At least some cannot start against vacuum. Use a T-section with a ball valve, and start against ambient, then switch to your working vessel.

[Charles Owlen Picket]

A quick word of caution about aspirators. IF your water pressure fluctuates you may get water back in the line. It doesn't happen often but it can happen. the only thing that you can do to be sure you don't get water backed up IF you think you may have a pressure fluctuation is to get some hose distance from the source on both sides; that will at least give you some chance of not getting water back in your work.

NOTE: this issue doesn't arise often. In fact it's rare as I believe the fluctuation has to be substantial (the toilet flushes and pressure goes way down,etc) HOWEVER it can happen in some situations with annoying results.

I tried an aspirator and decided to stick with an actual pump as in my area (rural) fluctuations did occur. There ARE ways to make a pump acid resistant but unless you are getting one that is designed for acids you really need to keep in mind that they will only be resistant not acid proof.

There are some techniques (to deal w/ acids) that involve replacement of diaphragm, tubing and coating w/ acid resistant materials that may work well for a time but they need to be followed by a thorough wash-out. It's a lot of work. There are few easy or cheap answers to acid. I tried the techniques listed by both Hydra & NBK and they are effective. A compressor (the bigger and easier to access the better) can be easier to make resistant as the contact surfaces are easy to access and the diaphragm can be dealt with in a variety of ways.

[tmp]

Wouldn't be easier to build or buy a hydroaspirator ? I paid $9, IIRC, for the
glass model I have and it pulls sufficient vacuum for distilling nitric acid. I
cringe at the idea of even attempting to do that with my mechanical pump.
There was a thread on the Forum from member Frogfot about a home made
aspirator. I was very impressed. This is the link:

http://www.roguesci.org/theforum/showthread.php?t=3357&highlight=aspirator

The beautiful thing about hydroaspirators is that they wash corrosive acid
fumes down the drain and in the case of a glass model, no damage to the
aspirator.

[Charles Owlen Picket]

Personally I think an aspirator is a better bet as well. It's just that I didn't get a decent one or the pressure issue was more significant with my place than most. The one I tried was for a water bed and simply not up to the task.

[Boomer]

Can't you put an empty wash bottle between pump and your setup to catch any waster getting sucked back when the pressure fluctuates? This is common practice me thinks.

Another idea is a biggish reservoir, to equal out fluctuations like a capacitor smoothes a rectified voltage.

You could even pump it down, then turn the pump off (if using a closed circuit). A pressure actuated switch would make an automated system, with the pump cycling, so it does not run longer than necessary. If the switch is adjustable, you get a regulated vacuum for fractional distillations, without having to adjusting underpressure via the flow (which is much less reproducable)!

[Cobalt.45]

Can't you put an empty wash bottle between pump and your setup to catch any waster getting sucked back when the pressure fluctuates? This is common practice me thinks.I don't know how commonplace the practice is, but that's what is done when an automobile's vacuum is used to evacuate its AC system when making repairs.;)

Baffling the container will prevent splashing from being drawn into the pump, vapor separation is a consideration, also.

[HIM]

Ice box compressor pumps are great, I keep a surplus of 2 or 3 on hand at all times. As mentioned above, many times they can be obtained for free!

If one looks at the wiring before they are pulled, hook up is easy. One thing I have found is sometimes there is a round plastic housing usually touching the pump body. This is a thermo-switch, which will shut off the pump if it gets to warm. I usually remove these. (I have a small fan blowing on the pump to cool it).

Also, there is usually 3 pins in a triangle shape. The top one is for your neutral line for power. The bottom two usually have a inductor/thermo-switch in a housing connecting the 2 pins. Some pumps work without this inductor, others need it. I have found though that these plastic inductor housings are usually interchangeable. If the pump doesn't start right away, disconnect the power and remove the plastic housing/coil and cool it off abit. Reconnect and aply power. If it still fails to start, tilt the suction side tube downwards and drain out some oil (if one put in too much). If it still doesn't work, remove the power cord, trash the compressor and hook up another pump.

Though these pumps will on average pull only about 20 - 22 in/Hg, they can reach that in a reasonable time.

[kurtz]

It is best to use the attached electrical parts as well, if you don't know what you're doing. One of those "3 pins" goes to the start winding, and you don't want to run power through there for more than a second or two. Taking off the relay that is supposed to drop out the start winding will fuck up the compressor, unless you quickly take off power from the start winding by hand. The run winding is the one with the lower resistance value between hot and neutral. The older compressors pull more vacuum, I've heard. If there are run or start capacitors then you might as well use them too.

Nice metal hand pumps (http://www.pacsciusa.com/physics.html#handpump) are available in the US. These pull OK vacuum (better than fridge compressors) and are a much better choice than those cheap little plastic pumps from Harbor Freight or online. More convenient than aspirators as well though you need something in between for neutralizing corrosives, and vacuum is perhaps very slightly less than aspirators.

I have one of those twin recirculating aspirator thingies (Brinkmann, loud) and couldn't believe that those fuckers would dare to sell these new for $900 or so without a 50¢ ball valve to prevent water suckback when turned off. I can't even find a $10-15 plastic or metal aspirator WITHOUT a ball valve!

[tmp]

The $11($9 years ago) borosilicate glass hydroaspirator I have pulls a lot of
vacuum with cold water, especially in winter. I always setup a trap between
the aspirator and the rest of gear to prevent water flowback.

[JouMasep]

One good thing to do with a water-filled gas trap is to use crushed ice in it.

Cold water dissolves more gas than warm, the ice acts like Raschig rings to ensure thorough gas/water mixing, and keeps the vapor pressure of the water as low as it can get, increasing the efficiency of the vacuum. :)

NKB’s explanation - as to why ice in a gas trap would contribute to lower pressures shows some confusion on the subject.

In fact one does not really use a “gas trap” (very low temp. cold trap) in line with water aspirators –there is no point to that

But using a dedicated (with anti-splash tube) “water trap” in such a case is a very safe idea! (Boomer referred to this common practice)

A gas trap is used in higher vacuum systems where contamination (vacuum reduction) of the pump (oil) is feared. Or where corrosive vapours would cause harm to expensive equipment. It consists in its most simple form of a U-tube dunked in liquid nitrogen. It is put in-line before the pump. This will condense most crap –even at the very low pressures at hand.

A water trap is also put in line with the to be evacuated system, but it is solely used for water aspirators. And it is NOT meant to condense or trap anything during normal operation.

Water traps are ideally empty!

They are there to avoid having your system filling up with water in the event of a nasty water-pressure drop.

And IF there is a bit of water in it, the construction is such that gases flow over –not through the water. Pulling a vacuum through a liquid in order to enhance it would be a non-starter. (Hydra mentioned the practice for use in analyses –high vacuum is not the objective.)

If you want to stop acid fumes coming into your pump, use perhaps a gas-washing bottle with NaOH pellets.

But if one worries about a possible, theoretical reduction of vacuum with very cold water feeding the aspirator, and with a warmer water trap, containing a bit of accidental water- put the trap in ice and salt. That will do it. (I.e. the ice is on the outside)

But the ice story makes one ponder…..

The principle of an aspirator’s action is that it uses the speeding water’s Venturi effect to “drag” the air out. (Bernoulli’s theorem)

However the most important limiting factor is the partial vapour pressure of the medium itself –and cold water has naturally a significantly lower partial vapour pressure than warmer water.
.
Hmmm, come to think of it: add a load of anti-freeze, salt, calcium chloride or what have you, and then a load of ice, a filter and also add an electric pump with an appropriate pressure -and rate of flow that re-circulates the solution. Then we would be really cooking!

For prolonged processes: drain part of diluted mixture and add salt and water to taste….

The advantage to any other sort of pump would be that we would have both a decent vacuum (could be roughly worked out at hand of partial vapour pressure of solution) and we could throw any mean and corrosive vapour at it without much harm. (Even membrane pumps suffer from some organic solvents at higher flow-rates)

Wouldn't be easier to build or buy a hydroaspirator? ..//...The beautiful thing about hydroaspirators is that they wash corrosive acid
fumes down the drain and in the case of a glass model, no damage to the
aspirator.

I second that. I have a very nice (bought new) rotary vane pump, but there are disadvantages! (Water vapour, other stuff crapping up your oil, acids, or fetching liquid N2 or dry ice and acetone)

So I use aspirators as well. But not having a re-circulating pump yet, the water consumption bothered me.

So I modified one; made the exciting and incoming orifices about three times smaller in diameter. Guess what –the vacuum is even better! The water consumption is a fraction of before. (Better design)

The drawback is: getting to attained vacuum takes longer

So now I start to think.

At the same water pressure, the rate of gas-removal must be (loosely) proportional to the CIRCUMFERENCE of the water-jet, whilst the rate of water consumption is proportional to the cross sectional AREA.

I.e half the diameter halves the rate of evacuation, but it reduces water consumption by four times.

So if we want to be efficient and have to pay for our water / are environmentally conscious, we use multiple small-diameter Venturi/jets!

I reckon however that there is a bit of a drawback or trade-off.

I happen to have very good water pressure; but it will not work with marginal pressures.

Then the greater circumference / water-mass ratio will result in too much “braking” of the water-jet, the reduced velocity will give poor performance.

At any rate, there is plenty of room for development with these humble, useful pumps.

[aliced25]

I just finished doing a bunch of searching and looking around on precisely this topic...

Below are a couple of the better results:

http://www.badger.rchomepage.com/vacbag.html

Here is what they look like on the inside:

http://www.steffbard.com/teory.php?subaction=showfull&id=1138908101&archive=&start_from=&ucat=2&

Also see:

http://myweb.cableone.net/bcanderson/Boatz/Vacuum/Vacuum.html

Of course, you don't have to take this apart... It is just those who are rather less trusting of electro-mechanical type equipment who would even consider doing so.