Subject: Compresssor Tank Ideas?

From: [email-masked] (Bob Neidorff)
Date: Thu, 14 Oct 1993 15:13:17 GMT

I am looking for ideas for a cheap air tank for a home-brew compressor.

I am assembling an air compressor from junk parts.  I don't know if I
will succeed, but we'll see.  I bought an old 1.5HP Capacitor-Start
single-phase motor and put new bearings in it.  It seems fine.  I also
have an old Kellogg air compressor.  I think it needs rings, but I
am not sure.  The price was right.  I called the manufacturer and got
the right size for pulleys assuming a 1.5HP motor.  

Now I am looking for a good idea for a cheap air tank.  There is lots
of scrap metal at the recycling centers, but I don't know what is
appropriate for this sort of thing.  I am not set up to weld, either,
so I would prefer something cheap which is ready to use.  One friend
proposed an old airplane tire buried underground, but this is a bit
impractical for me.

Any other ideas?

-- 
Bob Neidorff; Unitrode I. C. Corp.  |  Internet: [email-masked]
7 Continental Blvd.                 |  Voice   : (US) 603-424-2410
Merrimack, NH  03054-0399 USA       |  FAX     : (US) 603-424-3460

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From: [email-masked] ()
Date: 14 Oct 93 19:51:18 GMT

Although I doubt that an air tank can level a house I agree that it is dangerous
enough that I wouldn't try cheating mother nature over it.  I am a capable
machinist with tools ect. and when I think about how I would build a tank, even
cheaply I come up with... I wouldn't do it.  You can buy one cheaper than you
can jerrey rig a safe one.
	Compressing air is a way of storing energy.  The more compressed air
there is the more energy there is stored.  When it finds a way to release that
energy it will.  Hopefully it will be within your control.

Safely

Dave Parsons

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From: [email-masked] (Michael Burlage)
Date: 15 Oct 1993 03:46:51 GMT

>Although I doubt that an air tank can level a house I agree that it is dangerous

In a previous article, [email-masked] () says:

^^^^^^^^^^^^^^^stuff dumped^^^^^^^^^^^^^
If you can't help, at least don't discourage people,
it's not your life...

I once made a air compressor from an air-conditioner compressor

I used an old propane tank for the air tank.
One from a grill, a 20 pounder.

Take off valve and fill to the TOP with water to purge all the
propane out. FILL TO THE TOP!!!!!

then either weld a smaller pipe coupling to the tank or bush the
valve hole down to 1/2" or what you need.

I only went up to 90 psi with this, as this is the vapor pressure
of propane at room temp.  I'm sure they can hold more pressure,
but I don't want to go over the working pressure of the tank.

it worked fine for me, but,

(my disclaimer) do at your own risk, there, I said it.

 I've gone through about 5 motors, but the tank is still fine.
-- 
"Onward through the fog"
                         - Power-Hitter
[email-masked]
[email-masked]

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From: [email-masked] (David Jenkins)
Date: 15 Oct 1993 09:25:20 GMT

In article <[email-masked]>, [email-masked] (Bob
Neidorff) writes:
|> 
|> 
|> Now I am looking for a good idea for a cheap air tank.  There is
|> lots
|> of scrap metal at the recycling centers, but I don't know what is
|> appropriate for this sort of thing.  I am not set up to weld,
|> either,
|> so I would prefer something cheap which is ready to use.  One friend
|> proposed an old airplane tire buried underground, but this is a bit
|> impractical for me.
|> 
|> Any other ideas?
|> 
|> -- 
|> Bob Neidorff; Unitrode I. C. Corp.  |  Internet: [email-masked]

The best suggestion I've heard in recent times is to use the reservoir
air tank from a truck - they're big, tough and (usually) made of
stainless steel.  I don't know at what pressure air brakes work, but
it is considerable.

You just need to find a local truck dismantlers. ;-)

-- 

David Jenkins

"Oh dear, I think you'll find reality's on the blink again."
-- Marvin The Paranoid Android

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From: [email-masked] (Chris Kent Kantarjiev)
Date: Fri, 15 Oct 1993 20:26:04 GMT

The concern that I always have with reusing freon tanks is that they're not designed for
repeated filling and emptying. They might work for a while, but they might also fail all of
a sudden.

-- 
Chris Kent Kantarjiev, Xerox PARC, Palo Alto, CA USA 	<[email-masked]>
 "Eating chile peppers is like gustatory skydiving. More than just food, 
  these little hot pods give eating the kind of thrills and excitement 
  usually associated with reckless gambling, fast cars and strong liquor."

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From: [email-masked] (Marco Moreno)
Date: Fri, 15 Oct 1993 17:27:23 GMT

In a similar vein....  I have a small portable compressor (10-15 gal)
which is much too small for most work.  I was wondering if anyone has
ever tried adding a second tank to a compressor.  I was thinking of
simply running a regular air hose from my small compressor to a 50-60
gal tank and hook up a line to the bigger tank for my air.  It would
then be simple to disconnect the main tank make it portable again.

Anyone see any problems with a setup like this?

-- 

Marco Moreno
[email-masked]

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From: [email-masked] (Michael Burlage)
Date: 16 Oct 1993 17:08:02 GMT

In a previous article, [email-masked] (Marco Moreno) says:

It will take longer to fill.
If it is a wimpy compressor, it may over-heat due to the longer
cycle time.
other than that it will work!

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From: [email-masked] (Pat)
Date: 17 Oct 1993 12:34:49 -0400

try this.
call on the local scuba shops and ask for a bum scuba tank.
a tank designed for 3K psi should be okat at 100 psi.
just keep it in a sand can.

-- 
-----------------------------------------------------------------------------
The greatest mistake you can make in life is to be continually
fearing that you will make one -- Elbert Hubbard.

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From: [email-masked] (John De Armond)
Date: Mon, 18 Oct 93 07:33:48 GMT

[email-masked] () writes:

>enough that I wouldn't try cheating mother nature over it.  

Ignorance can be bliss (NOT!)  About 20 years ago one of my racing partners
lost his garage and much of his house to a jerry-rigged compressor
that used a 40 gal water heater for the tank.  The explosion lifted
the roof, blew the walls out and settled the roof down on what remained.

If you want to figure this stuff out yourself, compute the expansion
ratio of a 40 gal tank and a typical garage and see what the pressure
on the walls would be.  Then keep in mind that according to DOE,
about 0.2 psi will topple the walls of a wood frame house.

Not only would I not even think about making a tank at home, I won't
use one that isn't ASME certified and is within 5 years of a current
hydro test.  Just not worth the risk.

John

-- 
John De Armond, WD4OQC                   | For a free sample magazine, send
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Email to me may be published at my sole discretion.

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From: [email-masked] (James W. Swonger)
Date: Mon, 18 Oct 1993 17:47:58 GMT

It's not usually the tank that goes, so you can find tanks pretty easily
with dead lungs and burnt-out motors still attached.

 I think you'll find that there's more to building a compressor than the
three primary components. This is another good reason to rehabilitate a
dead one - you get the pressure switch, the unloader, etc. The first 
compressor I rigged up, similar to the way you plan, burnt up the motor
trying to start up the lung into a full pressure head. 

 Compressor tanks have handy features like draincocks too. 

-- 
##########################################################################
#Irresponsible rantings of the author alone. Any resemblance to persons  #
#living or dead then yer bummin. May cause drowsiness. Alcohol may inten-#
#sify this effect. Pay no attention to the man behind the curtain. Billy!#

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From: Jim Jaskie <[email-masked]>
Date: Mon, 18 Oct 1993 17:59:25 GMT

Subject: Re: Compresssor Tank Ideas?
From: John De Armond, [email-masked]
>hydro test.  Just not worth the risk.

I always read your postings John, because I have always found them
thought provoking, and generally right.

I took up you challenge on this one.  I opened up MathCad and did the cal
on a forty gallon water heater, and in a garage of 20ft x 30ft x 10ft.  I
don't know if this is typical or not, but the calculation was instructive
nontheless.

After the water heater blows up ( I assumed it went at 100 psi) the new
*equilibrium* pressure increased by about 0.1 psi.  This is less than the
0.2 psi that you mention, but note two items:
	1.  I believe that you 0.2psi number refers to external pressure loading
(as in an explosion nearby), internal loading ability may be much less. 
Note how often houses near tornados explode rather than implode.

	2.  This equilibrium pressure ignores dynamic overpressures due to the
initial shock wave (we have gas expansion at 6 times ambient), and also
assumes that the tank is in the dead center (no pun intended).  Local
pressures may be much higher than the 14.7psi ambient, initiating damage,
which then propogates.

	3. Garages may be built to less rigorous standards than a house, and
withstand less pressure.

	4.  The tank may have blown at higher pressures (bad regulator) or the
garage may be smaller (my workshop certainly is).

CONCLUSION:  I think John is right.  It certainly seems possible for a
forty gallon tank to level a garage.  I agree with your decision to be
prudent with a large air tank, it is certainly equivalent to a small bomb.

Now this has raised a question for me, and maybe someone reading knows
the answer.  The above scenario assumes that the tank disappears
immediately, and all the compressed air is released instantaneously,
instead of leaking out slowly through a small opening.  Now the speed of
sound in steel is greater than it is in air.  This means that the steel
will rip faster than the air pressure can decrease.  However, unless the
failure mechanism is brittle failure, a lot of energy (PdV) in the air
will be consumed in failing the steel (brittle failure mechanisms are
more like zippers, once you have enough energy to start the opening, it
will continue without increasing the load) .  This would lead one to make
the tank out of ductile steel, so that it would fail consuming energy
from the tank and minimizing the final *Blow*.  However, these tanks
always seem to be proof tested.  This testing method generally assumes a
brittle material, i.e. if it won't blow (fracture) at 2*max pressure, it
won't ever blow.  Guns are tested this way.  Ductile materials typically
work harden and hence can't be proof tested, because they are effectively
weakened.  Proof testing it today can weaken it enough so that tomorrow
it will blow at a lower pressure, e.g. exposure to 2*max pressure
modifies the steel so that it might fail at 1*max pressure. (This doesn't
happen with brittle material)
So which is it?  Does ASME demand a brittle steel that can be proof
tested, or a ductile steel that will fail graciously?

"They have no right to put their hands in my pockets" - General George
Washington

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From: [email-masked] (Robert Mitchell)
Date: 18 Oct 93 21:46:10 GMT

> Compressor tanks have handy features like draincocks too. 

Not that we haven't beat this topic to death already, but I am curious about	
failure modes in older compressors.

I have a Sears 20 gallon, 120 PSI, that must be pushing 20 years old.
I am not about to hydro test it every couple of years.
Once every year or so, I do drain a little (< half cup) of water out.
It is used at best infrequently...

Eventually, I would expect it to rust through, probably in a small area
close to the drain plug.  I do not expect a catastrophic failure.
Has anyone ever seen anything worse with a similar unit,
at pressures < 120 lbs?

Side note on diving tanks: every shop I have seen drills holes in	
tanks which fail visual.  You never want a bad tank to accidently
get back in high pressure service...

 - Robert Mitchell

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From: [email-masked] (Lee S Wilfinger)
Date: 18 Oct 1993 22:55:37 GMT

>Note how often houses near tornados explode rather than implode.

While I agree with the concept that the internal loading capacity may
be much less, I'd have to question your example. As I understand it, a
tornado is a low pressure area; if it came near a house, the air
pressure inside the house would be greater that outside, and of course
the house would explode. Why should it implode at all?

Perhaps a better example might be the shape of dams - they are curved
such that the convex side faces the water, where the greatest pressure
is. The loading capacity is different, in different directions.

-Lee Wilfinger
[email-masked]