Using an air tank for vacuum?

Can a typical "125 PSI air tank" be used as a "buffer" of vacuum? I have some applications in mind like desoldering, where I would use
vacuum intermittently, and it would be nice to use a tank to "store" vacuum. I was thinking about a use of an air tank. Not sure if regular portable air tanks can be used for vacuum, but my own feeling is that they should be OK. Just wanted to double check. Thanks
i
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On Sat, 04 Feb 2006 20:38:30 GMT, Ignoramus28190

In general, no. I have personally seen an ASME-rated small air tank (portable, probably 5 or 10 gallon) collapsed by pulling a vacuum in it.
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Hi,
Obviously it will depend on the design of the tank, and I'm not sure what these portable air tanks are like, so take Don's word here. The risk is that the walls of the tank will buckle under compression - it's much easier to buckle a metal sheet than it is to pull it apart in tension. You could look at small propane cylinders instead. I am pretty sure the smallest propane cylinders we have in England would be strong enough to take a vacuum. And if you don't mind destroying an air tank, you could try it. The energy storage wouldn't be huge, the steel wouldn't shatter, it would collapse slowly, and any bits would go inwards, so I think it would be a reasonably safe thing to try. Just pump it down slowly with a pump which can pull a good vacuum. It might be that you don't need a really good vacuum in your de-soldering application, anyway.
Best wishes,
Chris
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I wouldn't suggest trying it, especially after reading this post in this NG from "Steve" in May of 2000:
_____________________________________________
Someone passed the following message to me. I have no idea who originated it.
Good food for thought !!
------------------ Please share this visual with all of your employees in upcoming meetings. It is a great reminder that though many of our vessels are pressure-rated, many will not withstand significant vacuum. A vacuum can be created by simply draining a vessel without venting, or by steam cleaning and not venting --- the subsequent condensing of the steam is an extremely strong vacuum. The hotter or higher pressure of the steam, the stronger vacuum.
Even the condensing of a hot hydrocarbon, with low vapor pressure can have similar results if the system is not gas/N2 blanketed or equipped with a vacuum breaker.
The tank car in the linked photo is not one of ours. It is a general purpose PYGAS car that was being steam cleaned to prepare it for some maintenance work. The job was still in progress at the end of the shift, so the employee decided to block it in. Problem was there was no vacuum relief; the car cooled, the steam condensed and the car imploded."
http://www.metalworking.com/DropBox/_2000_retired_files/VacPwr.txt
http://www.metalworking.com/dropbox/_2000_retired_files/VacPwr1.jpg
http://www.metalworking.com/dropbox/_2000_retired_files/VacPwr2.jpg
_____________________
Note: the links have been "adjusted" to point to the current locations of the files.
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Wow. Amazing pictures. Thanks, Ram, Don, and Christopher. I will not use these cheap air tanks. I do indeed have a couple of propane tanks that are sitting here doing nothing (we now have a natural gas grill and electric stove/oven), so I think that I will simply convert one to vacuum. They should be good enuf. You are right that desoldering does not require deep vacuum, but it is good to "pool" vacuum so that it provides plenty of "pull" just at the right moment.
I do actually have a desoldering station, but I am not satisfied with its performance. It does not suck well enough, and yes, I did install a new tip. I have a heated compressed air gun RayChem HT-900B, which does a good job at desoldering, but splatters solder a little bit too much.
I recently bought a vacuum pump DV-142, similar to ebay item 7587026645, and want to hook it up sensibly. (I bought it from the military with a bunch of other stuff, like a box of machine belts. If anyone who participated on this thread has a need for a particular belt, let me know and I will check).
i

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"RAM" wrote:

That reminds me of the science experiment we did in junior high school many years ago.
Take a metal 1 gallon can like what acetone comes in. Put a little water in the bottom of it and then heat it up till it is boiling. Take it off the heat and quickly put the cap on it. The can will slowly start to be crushed by the atmospheric pressure when the steam condenses.
It looks like an invisible hand is squeezing it into a ball.
John
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The danger of tank collapse not withstanding, your idea should give some 'extra' vacuum. After all, don't they use vacuum storage in automobiles to assist wiper motors (old cars) etc.?
Ivan Vegvary

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Absolutely. By the way, here's another link to the story about collapsed rail tank car
http://www.delta.edu/slime/cancrush.html
i
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Yes.... some were standard tin cans. Size matters. I think you would be hard pressed to get a small propane tank to implode. Something the size of a railroad car is another story.
Mark

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wrote:

Yes, and those vacuum storage vessels on later model GM cars are molded in the shape of a sphere for maximum strength, and manifold vacuum from an engine is partial.
If you start getting down into a fairly hard vacuum like that tank car failure with condensed steam, the integrity of the vessel starts being a serious issue. A sphere is the best shape for that job, anything cylindrical or square is going to need serious internal bracing to survive.
--<< Bruce >>--
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If you've got the tank, try it. Tie a piece of copper wire around the girth and watch it for looseness as you evacuate it for the first time. It the wire gets significantly loose, then the tank is too weak. I don't think the posts about the railroad tank car are applicable to your situation. If you get to 26" Hg, then most of the air pressure that can be applied already is. If somebody used a rusted out air tank or one that already had a dent, and it "gave in", I wouldn't be surprised. If you are worried, put a box around it while you test it. We used a 1 lb propane bottle as a vacuum reservior for years on a machine sold and none of them ever gave up. If you don't know what implosion looks like in-process, boil some water in a one gallon paint can, take it off the heat, then put the cap on. Pretty dramatic, but look at the wall thickness.
Pete Stanaitis ----------------
Ignoramus28190 wrote:

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spaco wrote:

Absolutely..... ..
I have used MANY conventional Air Tanks without any issue.
Your worst possible case disaster is it folds up on itself. (NEVER seen it happen)
Propane tanks STINK inside and will smell for a long time... Remember, your pump will evacuate that stink all the time.
Grummy
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wrote:

The ASME tank I saw collapsed by vacuum was brand new from Grainger. We saved that crumpled wreck to give to Noel when he retired. He was the engineer that had specified it for purchase. Seemed like a good idea at the time.....
That said, don't be afraid to try it. If the tank fails, all it does is collapse, no big deal other than the cost of the tank. It just goes "crump".
I don't know if a 20 lb propane tank would collapse or not, but it'd be interesting to find out. They're not far from spherical so I'd expect that they'd work OK.
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wrote:

I saw a webpage from a rec.crafts.metalworking poster where he described making a vacuum accumulator made from a propane tank. The opening in it (after removing the valve) is supposed to be 1" NPT, so it will be easy to step down to 1/4" NPT. I already have some vacuum gauges from two broken vacuum pumps that I had to take apart a while ago.
So, I think, it makes little sense to buy a air tank if I can make something good out of a propane tank.
i
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On Sun, 05 Feb 2006 14:31:08 GMT, Ignoramus2963

I chopped a propane tank up to make my first vacuum chamber for coating telescope mirrors. Worked fine at 2x10-5 torr (a pretty good vacuum, at least good enough for my needs).
http://lerch.no-ip.com/atm/Vac/system_Medium.jpg
More information on my web-site,
Take Care, James Lerch http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site) http://lerch.no-ip.com/ChangFa_Gen (My 15Kw generator project) Press on: nothing in the world can take the place of perseverance. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent. Calvin Coolidge
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wrote:

Looks nice. 2x10-5 torr is the same as "20 microns", is that right?
The pump that I will soon pick up, is supposedly able to get 25 microns. I am aware that I do not need that for solder sucking, but it may be helpful in other instances.
i
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No.
20 microns is 20 milli-torr (2x10-3 torr) 1 torr = 1mm mercury. 760mm mercury = 1 atm.
You can't measure it anyway unless you have a thermocouple vacuum gauge.
I have two welch (1400 & 1405) two stage pumps. Getting down to under 10 milli-torr with a mechanical pump is a challenge no matter what the specs are.
Rule #1. Everything leaks below 1 torr Rule #2. Everything leaks even more below 50 milli-torr
For example, I hooked up a short length of 3/8 automotive hose to the 1400 pump. It could easily get to 100 milli-torr but not much lower. Dead headed either pump will get a litle under 10 milli-torr even though the spec is closer to 1.
Getting vacuum down in the 10-5 torr range is getting pretty fancy requiring a diffusion pump (or turbo pump) and maybe even a cold trap. Now you need yet another vacuum gauge to measure levels this low.
Everything you ever wanted to know can be found with a google search for sam's laser and vacuum page.
chuck
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Well?
Did the air tank collapse??
We're all waiting with bated breath!
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Thanks Chuck. It was educational and I saved your post. Practically speaking, I doubt that I would need vacuum beyond 25 microns, and for now I would be satisfied with much lower vacuum, like 20 inches HG for desoldering. I may play with making freeze dried food, and there I likely need a vacuum that is not particularly deep.
i
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    [ ... ]

    And you *don't* want to use the same pump for food freeze drying that you use for desoldering.
    The desoldering will get at least some microscopic bits of lead into the plumbing.
    Bleeding back to atmospheric after freeze drying may transport those into the food.
    And I really think that using the kind of pump which you have purchased (and not yet received, I believe) for de-soldering will lead to contamination of the pump oil. I would suggest a Gast rotary vane style pump for that, It runs dry, and doesn't have oil to get contaminated.
    Good Luck,         DoN.
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