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Tractor Talk Discussion Forum

Compressed Air Powered Air Compressor...Confused

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in-too-deep

02-23-2007 14:10:03




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The other day I was watching Future Cars on Discovery Channel. They had a car powered by compressed air. (Painfully simple, wish I would've thought of it.) But that's not where I'm going. They mentioned an air compressor that's powered by compressed air. They didn't say how it works so my mind started trying to figure it out. The problem is, you would be using more air to run the pump than you would be compressing. There can't be 100% or more efficiency in a machine. Perpetual motion doesn't seem possible here. If you had two cylinders the same size, one being cycled by compressed air, and the other connected to it to compress air, it wouldn't work because they would cancel each other out, and you couldn't have the driven cylinder bigger than the drive cylinder...but if you have the driven cylinder bigger than the drive cylinder, you'd be losing air...compressing less than you use to power the compressor. Gosh fellas...this one's got me beat. I sure hope someone can shed some light on my poor addled mind and I hope I'm making atleast a little sense in my question. I'm tired of losing sleep!!

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buickanddeere

02-24-2007 07:04:52




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
We use an air powered compressor at work on a test/calibration bench. It takes 115psi service air pressing on a large piston which is connected to another sepatate small piston. We can get over 5000psi if patient.



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in-too-deep

02-24-2007 09:11:43




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 Re: Compressed Air Powered Air Compressor...Confus in reply to buickanddeere, 02-24-2007 07:04:52  
So atleast it can be done. Thing is though, you're using a whole lot more air to produce 5,000 psi. I don't really think there is a way to make compressed air for free...



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cannonball

02-24-2007 05:52:45




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 hey guys check this out and yes i can see this wo in reply to in-too-deep, 02-23-2007 14:10:03  
Link

gets some use of the braking process ...

MAY GOD BLESS THE USA



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RustyFarmall

02-24-2007 05:06:59




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
Never say never. Some of the greatest inventions and discoveries have taken place simply because the inventor or scientist didn't listen to the naysayers who said it couldn't be done.



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two mile

02-23-2007 19:16:15




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
I've been scratching my head with this one for years. First, regulate pressure to conserve volume. Somehow recoup whatever percentage is possible of your exhaust. Exchanging pressure vessels until depleted. I'm sure there is an engineer somewhere working this out right now. I just enjoy thinking about it.



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dds-inc

02-23-2007 17:49:10




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
YOu know sir, I was thinking about how neat it would be to have an electric motor/generator run on itself (which it probably could for a little while) AND to have it to be able to drive something else!! Sounds remarkable, doesn't it, to defeat the law of energy!!

ALAS, this is impossible, it just goes along with the age-old adage that you can't get something for nothing!



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TomH in PA

02-23-2007 17:43:33




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
Sounds like maybe they were pulling someone's leg? Sorta like the guy who put a chainsaw motor on an axe.



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Janicholson

02-23-2007 16:35:25




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
I'll chime in with a bit of reason (maybe)
If a source of compressed air was available at 100 psi and 100 cfm (a lot) but to power the ""car"" compressed air was needed at 3500 psi to have enough to go to town and get back. The high volume air could run a compressor, that also took in the 100 psi air, and through several stages drive it to 3500 psi. A two stage compressor recompresses air to higher pressures. it would be inefficient Compressing air produces heat (Bowels law) and that heat is almost always either lost, or not wanted in the compressed air. The cooling reduces the pressure, but allows more dense compressed air (hence intercoolers on turbochargers). It (like many wool over the eyes projects) does little to reassure me. Where is power source that drives compressor for the original compressed air, and why did they only compress it a little? JimN

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paul

02-23-2007 16:24:55




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
I caught that show in the last 10 minutes, so didn't see the whole thing. Was thinking, what a good show.... And then _that_ part came on. Sheez. Made it one of the stupidest thing I've ever seen. What a crock, no science in that. Just gives alternative ideas a black eye when something so stupid is said.

--->Paul



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Davis In SC

02-23-2007 15:42:58




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
Kinda reminds me of a plan an old guy back home had.. There was a creek behind his house, he talked of putting in a waterwheel and generator, to run a big motor and generator, that would run an even bigger set.....



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in-too-deep

02-23-2007 15:54:01




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 Re: Compressed Air Powered Air Compressor...Confus in reply to Davis In SC, 02-23-2007 15:42:58  
Yep, same kind of idea. Problem is, you can't create energy. I wouldn't think the motor would be big enough to run a bigger generator that would run a bigger gen...grrr we need a physicist. One thing I was thinking about...this compressor could be made up of diaphragm and/or rotary vane an/or piston pumps...still can't wrap my mind around it though.



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Midwest redneck

02-23-2007 15:13:44




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
One way to see if efficiency is the same (which is not) is to use a formula. Fluid power Horsepower and mechanical horsepower from an engine is different because of efficiency losses. For instance If I have a 25Hp tractor the actual output at the drive wheels (if it is hydraulic drive) is about 2/3 of the 25HP of the engine. If that 25Hp tractor was gear drive you get about 90% efficency or so. (I dont feel like looking it up in my Hydraulic system manuals, I would spend 15 minutes looking for the books in a closet)

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RayP(MI)

02-23-2007 15:01:00




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
A while back, there was a discussion of a air compressor used to provide power for mining operations. Essentially, the compressor captured air dissolved in water falling over a dam. Water fell into a underground chamber, and air collected in the upper part of the chamber. It was then piped to the various mining operations. Since it was quite a fall, the water back-pressure provided a fair amount of air pressure. If we had something like that, air powered vehicles might be a possibility. However, did you ever see the steam powered switch engines they used in railyards? Had an absolutely huge steam tank, and had to be refilled regularly from the stationary steam boiler system. Not terribly efficient! Suspect that air powered would have the same shortcoming.

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John S-B

02-24-2007 03:10:20




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 Re: Compressed Air Powered Air Compressor...Confus in reply to RayP(MI), 02-23-2007 15:01:00  
Some of those "fireless" steam locomotives came about because of concerns about ignition sources in oil refineries and munitions plants.



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Eric SEI

02-23-2007 18:35:46




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 Re: Compressed Air Powered Air Compressor...Confus in reply to RayP(MI), 02-23-2007 15:01:00  
In railroad maintenance facilities they would put compressed air in the steam locomotives in order to move them short distances. Firing them to move short distances would require too much lead time, plus then they would need to cool down before repairs could be made. An inefficient energy source but a very efficient use of time.



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Wardner

02-23-2007 14:47:09




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
Compressed air is hugely inefficient. Why does it take a 40 hp portable air compressor to run two jack hammers? It's because most of the energy goes out the exhaust port. It has to be dumped so that there is no back pressure. It would take three or four stages to extract most of the energy. The same holds true with air motors.



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Aaron Ford

02-23-2007 14:21:55




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 Re: Compressed Air Powered Air Compressor...Confus in reply to in-too-deep, 02-23-2007 14:10:03  
Kinda like an electrical powered generator. Or a solar flashlight.... Got me whipped, too.

Aaron



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