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Posted By: Hotrod Lincoln BIG compressed air tank? - Mon Sep 02 2019 11:24 PM
A local salvage place has a bunch of retired LP gas tanks for sale for $100.00 apiece. These are the average size residential tanks used to store gas, probably 350-500 gallon size. They're not damaged or anything, just out of date for use for flammable gas. I'm considering buying one and plumbing my air compressor to it as a big reservoir tank. Once the thing gets up to pressure the first time and the compressor cycles off, I believe the compressor would only have to run occasionally to maintain the pressure. Comments- - - -suggestions- - - -cheers- - - -jeers- - - -what's your opinion, O wise ones?
Jerry
Posted By: Justhorsenround Re: BIG compressed air tank? - Mon Sep 02 2019 11:57 PM
I would think that would be comparable to some of the commercial setups. Just a po boy version. Go for it.🛠
Posted By: 2ManyTrucks Re: BIG compressed air tank? - Tue Sep 03 2019 12:12 AM
i did just that years ago for a small compressor i built
just a detail about safety that i had been warned about

apparently LP and some components of natural gas will dissolve into the steel of the tank, just a few microns into imperfections
if the tank was recently used, even if you 100 percent flush the tank out with air, leaving it sit for a short period or even overnight can produce an explosive mix of gases freshly released from the steel
so don't make that mistake if you want to weld or braze on the tank
do a fresh air flush immediately before and during any hot work
basically treat it as you would a car gas tank and you will be fine
-s
Posted By: Hotrod Lincoln Re: BIG compressed air tank? - Tue Sep 03 2019 12:26 AM
I'd probably need to weld a threaded bung into the bottom of the tank for a condensate drain. I always purge a gas tank with CO2 or nitrogen before dong any welding- - - -no oxygen- - - -no boom!
Jerry
Posted By: Harold41 Re: BIG compressed air tank? - Tue Sep 03 2019 03:51 AM
Once the tank is up to pressure, the compressor will have to run to replace what you take out, so the overall compressor duty will be the same If you take out 100 cu ft the compressor will have to put in 100 cu ft. The potential advantage will be you could take out a large volume in a short period of time and then the compressor would take longer to refill. If you have times when you need higher air flow than your compressor will provide it's a good solution.
Posted By: Hotrod Lincoln Re: BIG compressed air tank? - Tue Sep 03 2019 05:02 AM
I've got a good-sized bead blast cabinet stored away, waiting for enough air capacity in the shop to support it. I'll probably run two medium-sized compressors in parallel, feeding the single big tank. One's a direct drive that's currently on a 20 gallon tank, and the other is a belt drive unit that's on a 15 gallon tank with a rust hole in it.
Jerry
Posted By: Harold41 Re: BIG compressed air tank? - Tue Sep 03 2019 05:18 AM
The other thing you'll see is the compressor off times will be longer and the compressor on times will be longer. Which will give you fewer starts. I've always thought the fewer starts and stops the better. Sounds less expensive than buying another compressor.

Mostly what soaks into the steel is the mercaptan odorant. You might get some rotten egg smell for a while. People who make smokers out of propane tanks burn them to get rid of the odor.

If I did the calculations correctly a 500 gal tank holds about 682 cu ft at 150 PSI. If your Blaster uses 20 CFM it would take about 6 min to lower the pressure to 125 PSI, 12 min to lower it to 100 PSI.
Posted By: Grigg Re: BIG compressed air tank? - Tue Sep 03 2019 01:10 PM
Driving around Amish country it's common to see several 500 or even 1000 gallon former propane tanks plumbed for compressed air out behind the barn.
Posted By: Hotrod Lincoln Re: BIG compressed air tank? - Tue Sep 03 2019 04:40 PM
I'm also considering doing a conversion of a 4 cylinder gasoline engine into a high volume medium-pressure air compressor. That process dates back to the days when the entire front end of a Model A Ford was used to power jackhammers, etc. by cutting the front of the car off at the cowling area, and modifying the engine to run on two cylinders and compress air on two. A large air tank was bracketed to the frame, and the front axle, radiator, and cowl-mounted fuel tank and a tow bar completed the setup. The engine was modified so that the #1 and #4 cylinders ran on gasoline, and the #2 and 3 cylinders would ingest fresh air, compress it, and push it into the tank through a one-way check valve. The engine speed was controlled by a governor, which was conveniently able to be installed by removing a bolt-on piece of the timing cover that exposed the camshaft gear. Something similar could be built by using a Chevy II or Mercruiser 4 cylinder engine set up to run on 2 cylinders. Pressures of 100 PSI or a little more could be expected, or more if higher-compression pistons or modified combustion chambers were incorporated into the "compressor" cylinders.
Jerry
Posted By: Detroit Iron Re: BIG compressed air tank? - Tue Sep 03 2019 05:28 PM
An excellent use of the old LP tanks. Little to no danger if you "purge" the tank(s) ahead of time with some inert gas. I used to push a fat rubber tube into the exhaust of the car I was working on. Start it up, and shove the other end into the filler neck of the gas tank. So I could weld up/patch the leak in the tank. It's just a matter of keeping the O2 out of the mix. I've also used retired hot water heaters for the same task. They make great compressor tanks. The leak(s) are easy to weld up ahead of time, and plumbing them for (water) drainage is simple. People always say "aren't you afraid those tired tanks will explode"? To which I say no. They might spring another leak. But they'll never explode into shrapnel. Sheesh! smile

Anyway, no jeers, just cheers. A great find indeed!

Chris
Posted By: justmike Re: BIG compressed air tank? - Sat Feb 01 2020 09:41 PM
How do the Amish compress the air Grigg?
Posted By: klhansen Re: BIG compressed air tank? - Sat Feb 01 2020 10:18 PM
Originally Posted by justmike
How do the Amish compress the air Grigg?

A bicycle hooked to an air compressor?

Jerry's idea of a 4 cylinder engine/compressor reminds me of a gizmo my dad had with his shop truck (a '48 GMC 3/4 ton at the time). It was a thing that screwed into a spark plug hole and used that cylinder to compress air. It had an intake check valve arrangement (so that cylinder didn't pull as much fuel air mixture thru the intake) around a central output hose connection. We used it on a job to pump up a 1/4 mile long natural gas line for a leak test. I (as the plumber's assistant) would have been there for two days with a hand pump. It could be used for airing up tires on the road as well.
Posted By: John Milliman Re: BIG compressed air tank? - Sat Feb 01 2020 10:33 PM
Originally Posted by justmike
How do the Amish compress the air Grigg?

Can't speak for Virginia Plain communities, but around here, most of my Mennonite neighbors use Deutz air-cooled diesels to power their compressors and hydraulic pumps. Still a few Detroits in the 'Hood, but mostly, the two-cycle diesels have given way to the air-cooled 4-cycle engines as the Detroits wear out, become harder to maintain, use more fuel, etc.

Across from our (now former) farm, is (was) a furniture maker and he had a 2,000 gallon tank off on old propane delivery truck as his storage tank. His engine is a 3-cylinder Deutz. Powers both the air compressor and the hydraulic pump. The hydraulic pump powers his wood working equipment (lath, band saw, table saw, band sander, planer, etc). The air is for a few hand tools and the well pump. Most of the plain communities around here have drilled wells with a compressed air-powered well pump. It's pretty neat.
Posted By: Hotrod Lincoln Re: BIG compressed air tank? - Sat Feb 01 2020 11:09 PM
What impresses me around middle Tennessee is seeing the Mennonites bale hay- - - - - -they use a team of horses to pull the baler- - - -which is run by a Wisconsin V-4 air cooled engine. I guess spark plugs don't qualify as "electricity" to them for some reason. Some of the folks around our neighborhood also drive cars and trucks, but they paint over anything chromed, and only use vehicles for business purposes. The construction crew that installed our metal roof a couple of years ago drove about 40 miles to get here.
Jerry
Posted By: Justhorsenround Re: BIG compressed air tank? - Sat Feb 01 2020 11:35 PM
As with all styles of life some are more into it than others.
Posted By: John Milliman Re: BIG compressed air tank? - Sun Feb 02 2020 09:51 PM
It also depends upon which sect they are and what the local bishops/elders decide. It works for them so who are we to judge? It is fascinating to see how they work things out, though. I think they adhere to 1 Thess 4:11 ("Make it your life's ambition to live a quiet life, work with your hands and mind your own business."). As a community, they all work hard all day and sleep very well at night. Not a bad approach... smile
Posted By: 52Carl Re: BIG compressed air tank? - Mon Feb 03 2020 03:27 AM
A few years ago, I was at a friends farm where I had a storage shed to house my "precious" parts. I happened to notice some movement out in the half grown soybean field.
It was 3-4 grade school aged kids. They were sitting down in the bean field, playing some sort of game I guess. I noticed their clothing and lack of shoes and figured that they were the Mennonites from down the road.
My first knee jerk reaction was, "What are those weird kids doing playing outside in a bean field?!"
Then it dawned on me that they were doing exactly what we all did as grade school aged kids. Played outside barefoot.
Who are the weirdos now?
Posted By: coilover Re: BIG compressed air tank? - Tue Mar 17 2020 05:10 AM
The guys across the highway have a trailer mounted Smith compressor that has a 302 Ford that runs on 4 and pumps on 4. Has been out in a field with no faring so probably needs major work on the engine. The receiver tank, piping, compressor head on engine, and other bits and pieces are probably good. Could maybe be bought for near scrap price. I had a 1000g propane tank at my old shop with a hose hook up to my 600cfm International diesel powered sand blasting compressor. Took only a few minutes to bring the big tank up to 120psi. At the present shop I have a 4cyl John Deere diesel compressor with one outlet valve for a Milton air fitting where a hose can be run into the shop if air use is extremely high. Has a decal on it saying it is limited to 180cfm by OSHA standards. The noise level would be unsafe, according to Big Gov, if speed was increased for more cfm.
Posted By: Hotrod Lincoln Re: BIG compressed air tank? - Tue Mar 17 2020 06:20 PM
A friend out in California about 40 years ago used a converted flathead Ford V8 engine to power his portable sandblaster. When he needed more volume, I helped him install a 4" stroke Mercury crankshaft and pistons to replace the 3 3/4" Ford crankshaft. The Mercury engine from 1949-53 ran the longer stroke crank, which could also be offset-ground to 4 1/8" by using the 85 HP Ford rods from the late 1930's flathead V8's. 4 1/4" stroked shafts could be made by welding extra material onto the rod journals and setting up the crank grinder for the longer stroke. Those grasscutter strokers had a nasty habit of twisting the center main bearing in two at high RPM and hand-grenading the engine.
Jerry
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