# Creating a Vacuum



## Long Shot (Jul 30, 2014)

So has anyone ever heard of a swing motor?


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## butcher (Jul 30, 2014)

I have heard of them used in refrigeration as compressors, I cannot say I have learned much about them yet.


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## Silver Sliver (Jul 31, 2014)

I found this on them, it may be helpful.

http://www.sawafuji.co.jp/english/tech/shindou.html


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## g_axelsson (Jul 31, 2014)

It's the same principle as the small pumps in coffee makers use and in aquarium bubblers. I can't see any way to do a good vacuum pump based on that construction, the location of the piston would move depending on the pressure and could easily hit the end of the cylinder when the pressure is low (expanding springs).

What's your question?

Göran


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## solar_plasma (Jul 31, 2014)

Now this is interesting:

https://www.youtube.com/results?search_query=refrigerator+compressor+vacuum

I just wonder if it is allowed to dismantle newer refrigerator models. Older types in most countries definitely not. But it might be a possibility to ask a licensed scrap yard.... oO

edit: how to find out the wiring:
https://www.youtube.com/watch?v=k0p8v6wtVIE


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## Long Shot (Jul 31, 2014)

Okay - so part of my weekends are spent "dumpster diving" and what I found was a Sawafuji swing motor compressor on a disposed of fridge, presumably from a marine application. Solar - it had already had the refrigerant line damaged and all refrigerant had been lost. I worked for a large soda bottler for 15 years as a service tech so standard compressors are not news to me, the guy on YouTube gives a good presentation and I have been looking for a compressor of the size he has for awhile. Silver Silver - a little research Monday morning found that these work on low voltage AC about 30V. They are odd as they only have one lead entering the compressor the other is simply hooked to the casing which might indicate they work on DC but when I hooked it up to an emergency light battery I have around here it just went thunk, once. I also have an ample supply of 24V AC transformers around and when I hooked that to it it runs decent and doesn't knock, bang or get hot. It doesn't pull a huge vacuum but should be sufficient for the task if I don't blow it up! Göran - I do get what you are saying, allowed to free flow it may not like it but seems good on the brief test I ran. My understanding is that the control circuit that runs this does exactly as you propose, runs it on pressure which is directly related to temperature. I suppose the question, if any, was does anyone use one of these for the app I intend?

So the whole point of this is that I need a vacuum pump for pulling fluids off of precipitants. I have no dimes invested in the setup so if it goes south, nothing lost. I am going to go forth with it and build it as a vacuum station and so how it all works out. I will keep the post up with the progress if anyone is interested in seeing how it works out.

Thanks Guys for chipping in.

Jeff B


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## butcher (Jul 31, 2014)

Jeff, I can not say whether the compressor will work or not here, but most refrigeration compressors are not designed to handle acids or acidic gases, which can destroy them pretty quickly.

you could can probably try a trap, and scrubber in line with the vacuum pump to possibly trap some of these acidic gases, but even then you will have some of the gases that will not dissolve in water, or can be hard to scrub effectively before entering your vacuum pump.

I can not see this pump lasting long in this application, but being free, and a learning expierience, why not try, then when it dies tear it down to see how it used to tick. just be safe.


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## Long Shot (Jul 31, 2014)

Butcher - that is good, sensible advice and as you say, a learning experience with nothing invested. If it throws in the towel, oh well. And thanks for the scrubber idea. That is something I did not think about but will probably prolong the life of it somewhat. Do you think that if the trap/scrubber was a basic solution that it would capture more of the airborne acidic gases?

EDIT - slightly basic


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## butcher (Aug 1, 2014)

Several gases are water soluble, like HCl, and some of the NOx gases... 

Bubbling the gases through a cold water trap can capture some of these, they can also bubble through so fast you will not capture them all, what may help to capture a little more is, if you make them go through this trap as smaller gas bubbles, maybe you can take the tube from the filter vessel and melt the end of the hose that will go down into the water of the water trap vessel, and punch many small holes in the side of this tube with a hot needle, towards the bottom of the closed tube, or use a large air stone type bubbler so that the gases will have to pass through these small holes to create smaller bubbles to bubble up through the cold (ice) water, where more gas to water contact can help to .capture more of the gases flowing through the solution.
You may also need more than one trap.

The exit tube from the water trap (taking gases from the top of this trap can go into another bubbler vessel.
Example, Hydrogen chloride gases will dissolve in cold water to form a solution of hydrochloric acid.
HCl (g) + H2O --> HCl acid 
Nitrogen dioxide gases NO2, will dissolve in cold water to form a solution of nitric acid.
NO2 + H2O --> HNO3

NO (nitric oxide) is one of the gases that is not water soluble, this clear gas can be converted to NO2 with oxygen (since this is in a vacuum stream introducing oxygen to the vessel, or system would lower your vacuum capability), an alternative would be to add the oxygen to the water using hydrogen peroxide.
NO (g) +O2 --> NO2 (g)
Then 
NO2 (g) + H2O à HNO3
Or
NO (g) + H2O2 à HNO3

Depending on what gases you are trying to capture, you can try and use a solution to help neutralize the gases, so to help to convert the gas to a more soluble form, this can be the scrubber vessel before the gases go to the inlet of your vacuum pump.

Example, acidic gases like HCl you can neutralize with a substance of dissolved sodium hydroxide to help to convert the gas to a soluble solution of NaCl salt water.
HCl (g) + NaOH --> NaCl + H2O

Some of the NOx gases can also be converted to nitrate salts, in the sodium hydroxide solution, which could help to keep them dissolved in solution as sodium nitrate.

Sodium hydroxide is not the only base that can be used in the scrubber, but it is one of the stronger solutions. 

Glassware can be etched by strong hydroxide solutions, so you may not want to use your nice lab ware, you can always use old lab ware or other types of old bottles, with corks drilled out for the hoses.
The taller the bottles the further the gases will have to travel to bubble up out of the solution.

I really do not believe the refrigeration pump would survive long but you can try it.

There can be several ways to create a vacuum, even without the use of mechanical vacuum pump, some f which you could make with a few odds and ends, like the 55 gallon barrel of water sitting on a stand, or on top of another barrel, with he vacuum tube coming off the top of the sealed drum, and a drain valve to drain the water, to create the vacuum it the top of your drum this water could be drained into a lower barrel, (two barrels one sitting on the other with boards between them and piping and valve between the two barrels), a small pump can be set up t return the water to the upper barrel later, many different ways of getting a vacuum have been discussed several times on the forum, One I am have thought about is take a plastic air pump (for airing up tires or tubes), or one of those river raft foot pumps (which would need a spring return, and change the valve operation (check valves) to make it into a vacuum pump.

I have several types of vacuum pumps (for different purposes) but I also like to tinker and build things, so I may build some things just to have some fun tinkering, even if they do not always work, it can be a fun way to learn some things, and its even more fun when it works as intended.


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## Long Shot (Aug 2, 2014)

Butcher - thank you very much, that is very useful information. I really like the 45 gal drum thing as I have several water pumps around here that would be ideal for that, just wish I had some more real estate! As you say, there are other ways to do this. I too like to build my own stuff - two fold, I have or can usually find ample junk to do so and if it falls on its face, oh well, no big loss as opposed to wrecking something I've bought by trying to get it to do something it wasn't meant for!

Thanks again,

Jeff B


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## gold4mike (Sep 5, 2014)

I've ended up with three drinking fountains to scrap over the years and have been using one of those small compressors for vacuum filtering for at least 3 years without it failing yet. I don't scrub the fumes that enter it, figuring I got it for free and still have two replacements when it does. 

The thing that has probably helped its survivability is the fact that I had to make a manifold to allow a lot of air to enter the suction tube in order to lessen the draw. When I first tried it my filter paper sucked through the holes in my Buchner Funnel. I made a manifold using plastic pipe and three valves. That way I can use it for suction with more than one Buchner at a time and leave one valve open partially for extra air flow. I need to find a plastic needle valve for finer adjustment of the air flow.


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