Subject: Air tanks again.

From: [email-masked] (David Jenkins)
Date: 18 Oct 1993 14:57:54 GMT

There's been some discussion on this subject, so I thought I'd throw
my personal views in the ring - don'ttake these as gospel, use your own
intelligence and take guidance if unsure.  DONT take this as a recipe for
making an air tank (there isn't enough info here).  end disclaimer.

Yes, an air tank bursting is quite exciting for one lifetime, and usually
terminates at least one lifetime, if one is adjacent (according to pressure,
but see below).

The chances of a commercial air tank scrounged from something else and
working well within its original range actaully bursting are fairly remote,
*as long as it shows no sign of corrosion and has been hydraulically tested*.

Home made tanks are feasible for lower pressures (up to 100psi) as long as
they are tested (read a book on steam boiler manufacture and testing) and
follow guidelines for model boilers, e.g. use curved surfaces wherever
possible, and use stays for any flat surfaces.  Hydraulic test to twice
normal working pressure.

Use a tank made of a material unlikely to corrode, or be prepared to inspect
at frequent intervals.  Do hydraulic test at regular intervals anyway
(suggest following model steam boiler practice - 2 yearly for copper, 1
yearly for mild steel) to 1.5 times working pressure - no point in straining
the thing unduly.

Incorporate safety devices - one, preferably two, safety valves calibrated
against a known pressure gauge; use a pressure switch to stop the motor; and
fit a pressure gauge (which can be checked when the safety valve(s) are done.
Fit a drain cock to let out the condensate and to minimise corrosion.

I wouldn't run an air cylinder without these tests and safety devices - if
you don't know how to buy (or make) and fit these, then buy a commercial tank.

-- 

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] (John Cooper)
Date: Wed, 20 Oct 1993 16:49:35 GMT

In article <[email-masked]> [email-masked] writes:
>I notice a number of retailers and suppliers are selling kits to covert LPG 
>tanks- of which there seems to be a never ending supply- into air carry tanks. 
>(The kits are around $10.) Last night the new Northern Hydraulics catalog arrived
>and I see they carry them as well. As long as you stay under 120psi or thereabouts
>they should be safe, and as the former contents were quite volitile they should 
>be much easier to purge than tanks that held something heavier.
>
>--mike

I've been told that 'someone' sells conversion kits to convert a 20 (40?) LB
propane tank into a pressure feed sandblaster.  This sounds like a great idea
but I cannot find a source for the kit.  Can some kind soul provide a pointer?  Thanks.

-john

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From: [email-masked] (James W. Swonger)
Date: Thu, 21 Oct 1993 16:46:30 GMT

If you get the Eastwood (auto resto tools & stuff) they have nice 
pictures of their pressure feed blaster tanks. I followed the pictures
and made my own out of a spare compressor tank I had, some miscellanous 
fittings and tubing. Beats the hell out of siphon feed. 
-- 
##########################################################################
#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: [email-masked] (James W. Swonger)
Date: Thu, 21 Oct 1993 21:10:34 GMT

In article <[email-masked]> [email-masked] (Howard Rebel) writes:
>Why is the pressure feed sand blasters better?  I have only used
>gravity feed units.

 Gravity feed I take to be a small gun with a hopper above the nozzle.

 Siphon feed uses the suction from the air blast to pull in sand through a
long hose. The vacuum is not great, the maximum negative pressure is 14PSI,
the suction orifice gets plugged with wet sand (the water from the expanding
compressor air), and so on. I found that the sand feed was not very steady;
I'd get bursts of nothing but air.

 Pressure feed uses a tank of sand pressurized at some level up to the working
pressure of the compressor; typically I end up running about 20PSI to keep
the sand from dribbling out when the blast is off. This works out to maybe a
30PSI pressure differential, and gives a lot more sand delivery. I regulate 
to 60PSI at the gun because that gives adequate material removal rate; high
pressures may warp sheet metal locally, and draw down the tank faster. 
For high volume demand tools I have plumbed in a ball valve and garden hose
fitting into my garage air lines (1" PVC); the hose end fittings are readily
available and make decent quick couplings, plus I'm not flow limited by no
steenking 3/8" ID - try 3/4", for about 4X the flow. I get effective
material removal down to about 40PSI tank pressure, 50 ft from the garage -
a good place for sand, sez the wife.
-- 
##########################################################################
#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: [email-masked] (Howard Rebel)
Date: 21 Oct 1993 17:11:32 GMT

James W. Swonger ([email-masked]) wrote:
:  If you get the Eastwood (auto resto tools & stuff) they have nice 
: pictures of their pressure feed blaster tanks. I followed the pictures
: and made my own out of a spare compressor tank I had, some miscellanous 
: fittings and tubing. Beats the hell out of siphon feed. 
: -- 
: ##########################################################################
: #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!#

--
Howard Rebel [email-masked]
FAX: 719-590-5701