OT: Portable Air Compressor

wrote:


The jeep boys use heavywall large diameter tubing for their rear bumpers and pressurize them as an air storage tank - with an engine powered compressor (often a "york" style A/C compressor)
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snipped-for-privacy@snyder.on.ca wrote:

Bloody!
That'd make a nice bang in case of a rear-ender...
-- Jeff R.
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I have such a bumper made from 2"x5" square tubing, never use it. It holds a bit more than 1 gallon. Add in the front bumper and you have 2 gallons. Really worthless for an air tank. Works nice for mashing down alder brush though. :)

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wrote:

5 feet of 6" round tubing makes about a 3 gallon tank.
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.

But not useful on a 33" tires. Typical application on a Jeep is to take four 33" tires from the off road 8-10PSI to the on road 26-28PSI. A quicky calc shows 16 gallons of air space in the tire or 2 cubic feet. At 7.5 psi gage, that is 3 standard cubic feet. At 29 psi it is 6 standard cubic feet, needs 3 cubic feet to get it to full pressure. Your 6" pipe has about .4 cubic feet so it would hold 3.2 standard cubic feet at 102 psi (what my smaller compressor puts out) If I hook the tank to the tire, I get equilibrium at pretty close to the 28 psi I was looking for. So the huge bumper will inflate ONE tire. Still have 3 to go.
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wrote:

So get yerself a coupla big assed CO2 cylinders to be used as bumpers. Just be careful of the valves!!! Gerry :-)} London, Canada
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Gerald Miller wrote:

And don't install them in opposite directions, or you could go into a nasty spin! ;-)
--
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On Thu, 16 Jul 2009 21:17:56 -0400, "Michael A. Terrell"

Calculations are way off. a 5 foot long 6" pipe is just a hair under 1 cubic foot in volume.. A 7 footer is more like 1.35 cu ft. That's 10 US gallons of air. at 120psi that is enough air to inflate more than 2 tires to 28psi from flat. It will EASILY take 4 tires from 10 to 25psi. (a 5 gallon tank will do 4 30 inch mudders without too much trouble)
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snipped-for-privacy@snyder.on.ca wrote:

I was talking about a pair of CO2 tanks, with the valves on opposite sides of the vehicle. ;-)
--
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wrote:

Not a problem! Because as you were stopping to check the pressure on the first tire being filled, and then walking around the vehicle to get to the next tire, the compressor has been chugging away the whole time filling the bumper tank back up again.
The bumper is too small to do it without a compressor, but it also lets a smaller compressor do the work in a reasonable time frame.
--<< Bruce >>--
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I don't see the original post, so I'll just add some comments at this point in the thread.
I think most of the retail store 12V units are borderline junk, with varying degrees of reliability. Paying more for one of these doesn't mean it's a better designed unit, but more likely that it also serves as a flashlight or other feature. When looking at the internal motors and pumps in these units, one might ponder if they couldn't build a better quality air compressor/inflator with some parts thay might have laying around, such as a decent quality cordless power tool motor, a small pump, and a check valve.
Most good air compressors made for mobility are made with gasoline engines as the power source.
Real electric air compressors for automotive applications are probably limited specialty-type applications. I haven't seen any of these units in automotive supplier's stores or catalogs over the years.
Maybe the most commonly available compressors built with any quality would be the pumps made for air leveling systems in some of the bigger cars.
A number of years ago, someone posted a commercially-made mobile air compressor in the dropbox (12V or maybe 24V). It had a heavy duty motor driving a 2 cylinder, single stage air compressor pump by a belt. The switch was a HD engine starter relay, so the current demand of the motor was likely significant. There wasn't a storage vessel attached, although it could've been under the vehicle.
Another unit that I saw in an automotive painting book in the 1970s, was an improvised installation of a belt driven, 2 cylinder, single stage air compressor pump with a 12V clutch, that was fitted to the vehicle's engine. I think this installation was a project of fabricating custom brackets to mount the pump so it could be driven by adding an additional belt/pulley to the engine. This application definitely had a receiver tank mounted underneath the vehicle, and all the necessary pressure control devices in place. Taking a pressurized vessel out on highways would be unsafe, but venting the pressure before driving it would make it safe.
--
WB
.........
metalworking projects
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wrote:

Not going to work unless you are running a medium-truck diesel engine, they are too specialized - the truck air compressors are on a mechanical PTO from the engine accessory drive. And they often have a water cooling jacket that is connected to the radiator system, so if it can't be connected you'll have to make a seperate small cooling system. And the unloader system is an oddball.
If you can find a place to hang it and a spare sheave to drive it, a modified AC Compressor is the way to go. The old York style is best for that, simple single piston.
--<< Bruce >>--
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Bruce L. Bergman wrote:

Any of the old ones that have an oil sump. The GM A6 would also work.
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wrote:

Any of the old ones with an oil sump - that you can modify with a sight glass or dipstick to check the oil level, and add an oil fill port or plug of some sort.
And that is the right shape to bolt into the space available - the old GM Harrison A6 is the long skinny one from the 450's through 60's IIRC. ( If the space is short and tall, use the York.)
They used the same compressor on Cadillac Factory Stretch Limos and Corvairs, and with a properly operating system you had enough excess cooling capacity to hang beef in either.
Oh, and you might want to get a refrigeration style coalescent oil seperator for the output, in case you have excess oil carry-over you can direct it back to the compressor sump with a ball valve.
Refrigeration oil is not a problem getting out of the compressor, because in a sealed system it'll be back in a few minutes. Not on a compressed air system.
--<< Bruce >>--
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Had a 60's GM car with air shocks; it had a vacuum-driven compressor to inflate them.
It was slow on tires but it never burned out!
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Bob La Londe wrote:

I have an onboard set-up on my response rig. It is mounted under the hood of a 97 S-Blazer. I cheated a bit and mounted it on the drivers side and it is powered off a second pulley mounted to the power steering pump.
In my case it can air up tires or power rescue tools.
For the once in a few years use it would be overkill. For that I would suggest a standard SCBA cylinder and a regulator. 27 cubic feet at either 2215 or 4500 PSI.
--
Steve W.

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Paintball sized CO2 cylinder & regulator.
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wrote:

Both Gast and Thomas make some "real" 12V DC motor driven close coupled oil-free piston compressors in the 1/4 - 1/3 - 1/2 - 3/4 HP range, and they will do 100 - 125 PSI. Check the Grainger catalog, they list some of them.
But they are not cheap, you'll pay $300 to $800 for a new one, depending on size. But still less than the production models with a starter motor and an oil-lube compressor, or the "On Board Air" systems that hang a screw compressor off the transmission PTO - and if you don't have a PTO you need to add one...
The Harbor Freight ones look OK, but I would not use them on anything "Mission Critical". You don't want a 20-mile hike out to civilization if you get a flat tire and the compressor craps out.
Read the charts and decide what your max pressure needs are, then the CFM, then the space to mount it under the hood.
You can probably hook up a set of jumper cables, a 10' hose and chuck, and make legs with rubber feet if you need Portable.
--<< Bruce >>--
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On Wed, 15 Jul 2009 14:48:37 -0700 (PDT), Too_Many_Tools

Better to use a 12 volt Delco generator with the feild coils switched to starter coils. Was a common mod for driving electric go-carts in the sixties. Draws less power than a starter and has ball bearings and belt drive.
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On Wed, 15 Jul 2009 22:29:49 -0400, snipped-for-privacy@snyder.on.ca wrote:

Neither one is practical. Starter motors are only intermittent duty, run them more than thirty seconds on and 10 minutes off and it's going to melt down somewhere - if you're lucky it'll only throw the solder at the armature connections to the collector segments first.
And motoring a generator isn't that efficient. It works, but only.
They DO sell close-coupled compressor heads seperately and on belt-drive "pedestal mounts" if you want to Frankenstein your own...
But frankly I'd let them do all the work on the production line and be done with it. If you aren't in a big rush you could live with a real 1/4 HP 12V DC compressor and a big tank to do your air up.
--<< Bruce >>--
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