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:
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

spaco wrote:
If you've got the tank, try it.

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

On Sat, 04 Feb 2006 18:28:56 -0600, spaco
wrote:

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:
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

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.

On Sun, 05 Feb 2006 14:31:08 GMT, Ignoramus2963
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 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

Looks nice. 2x10-5 torr is the same as "20 microns", is that right?

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

Well?

Did the air tank collapse??

We're all waiting with bated breath!

According to Ignoramus19736 :

[ ... ]

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.

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.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH & Endowment Member
NRA Second Amendment Task Force Charter Founder



Chuck Sherwood wrote:
Looks nice. 2x10-5 torr is the same as "20 microns", is that right?


No.

20 microns is 20 milli-torr (2x10-3 torr)
Isn't it 20 mill-torr = 20x10-3 torr ?

1 torr = 1mm mercury.
Yep and 1 kilopascal = 1x10+3 pascals = 7.50062 torr.
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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