GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: jeff76 on February 06, 2014, 11:38:22 AM
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just bouncing ideas around in my head.
would it be feasible to use small gas engines to compress air?
maybe daisy chain 3 or 4 weedeater engines together. using an electic motor to drive the crankshafts? and fitting air connections to route the exaust ports to the intake of the next engine, and finally to a tank?
and if this might be possible, would the electric motor need to turn the crank of each engine, or would the air pressure alone turn all of them?
obviously a 4t woudlnt work, but a 2t might.
tell me why it wouldn't. im sure it wouldn't because I never come up with sound ideas
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The piston area on the high pressure stage would be too much, not to mention blowby past the rings at 3000 psi, I think the motor torque required would be off the chart.... There is a reason that large 3000 psi compressors cost so much....
Bob
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yeah im trying to figure out a way around that, before I plunge into the darkside. there are no fill stations around me
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I can get airgas to deliver nitrogen or argon though. maybe figure out a way to introduce no2 to a springer to create combustion plus pressurized air. I know this would be extremely dangerous but mayber if a gun was designed with these kind of forces in mind.
hypothetically of course
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The piston area on the high pressure stage would be too much, not to mention blowby past the rings at 3000 psi, I think the motor torque required would be off the chart.... There is a reason that large 3000 psi compressors cost so much....
Bob
from you particularly I was expecting some sort of equasion why it wouldn't work.
what is off the charts? maybe a larger internal combustion engine instead of an electric motor to drive the device?
and maybe the blowby could be negated by higher rpm. prototypes don't have to be efficient
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3k psi on a 36mm piston =4733 pounds of force, trying to remove the head. :o :o It could be done with a small auto 4 banger. But it requires a lathe to do it. I have a 2 liter Datsun engine that I have been making plans around. 4 stages, teflon rings and a steel plate head. Each follow-up stage must be smaller than the preceding one.
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BBB, what would you you power such a monster with ???
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This might be a much easier way to go. It is from a friend of mine in Mexico. He says he has it adjusted so that it doesn't bottom out on the strokes and that really helps the durability.
http://www.youtube.com/watch?v=Gv6atVZCg_c&list=LLRGRC7ud_b3nTHT9SWBUEQg&feature=share# (http://www.youtube.com/watch?v=Gv6atVZCg_c&list=LLRGRC7ud_b3nTHT9SWBUEQg&feature=share#)
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BBB, what would you you power such a monster with ???
A big hand crank. ;D ;D I am not looking for speedy filling. ::) ::)
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A 4-stage compressor would have quite low compression ratios, at 4:1 per stage that would be 256 bar (less losses).... Perhaps 3 stages with a higher compression ratio might have less overall friction and therefore a lower power requirement?.... Three stages at 6.5:1 would be 275 bar (again, less losses).... I'd do some research on that before you begin.... If you use one of the Datsun pistons for the first stage, you have a swept volume of 500 cc = 30.5 CI, and if you figure maybe 25% losses, that would give you a 22 CI output per revolution, which would fill an 80 CF SCUBA tank in 80 x 1728 / 23 = 6000 revolutions of the crankshaft.... At 100 RPM that would take an hour, so you just have to figure out how much power you would need to run the compressor at that speed....
Then, of course, you have the problem of how do you lubricate it without causing combustion at the temperatures and pressures in the third (and maybe even 2nd) stages.... For 6.5:1 compression per stage, the 2nd stage would be about 77 cc and the 3rd stage about 12 cc swept volume, and if the engine is a 3" stroke, that would give bores of about 3.6", 1.4", and 0.55", pressures of 100, 650, and 4200 psi, and piston loads (TDC) of about 1000 lbs. each.... Whoa, wait a minute, a 4 cylinder engine has a 2-plane crankshaft, so yeah, you would need 4 stages to level out the power requirement over the two strokes.... so back to 4:1 compression....
Cylinders 500, 125, 41, and 10 cc.... Pressures 60, 240, 960, 3840 psi.... Bores (3" stroke) 3.6", 1.8", 0.9", 0.45".... Loads 600 lbs. @ TDC each.... Still the same swept volume per rev, so still an hour at 100 RPM to fill a SCUBA tank.... What about the torque to turn it (neglecting friction)?.... When the crank is at 90* (worst case for leverage), it has compressed the volume at BDC to half, and the crank offset with a 3" stroke is 1.5" (0.125 ft.).... The load would be about 300 lbs. per piston, times 2 on each stroke, so 600 lbs. x 0.125 ft. = 75 ft.lb. torque x 100 RPM / 5252 = 1.43 HP.... So, it would take roughly 1.5 HP to overcome the load, plus friction, so maybe double that, a 3 HP motor?.... no idea, really....
To turn it over by hand, 75 ft.lb. torque required, you would need a 1.5 ft. crank (ie a 3 ft. diameter handwheel) and the load would be 50 lbs.... OR, gear it down of course.... All I can say is, better you be cranking it than me.... *LOL*....
Bob
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The lubrication is easy, as it has a built-in oil pump, only needs some ports blocked and the relief valve reset. With a flat plate head, there is no need for oil topside. All rings will be Teflon with an oil scraper for the bottom of the piston. The Z20 Datsun/Nissan engine is 85mm bore x 86mm stroke. The pistons will all have the same stroke of course. So I will have to make three sleeve and piston combo's. 4.5:1 compression gets me about where I would like to be. Which gives about 600 pounds load on each piston. 4500 psi tanks are more efficient for fills. :D
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Crank offset with an 86mm stroke is 1.69", so the torque requirement goes up (at 600 lbs. per pair at mid stroke) to about 85 ft.lb.... plus friction of course.... That is 1.61 HP at 100 RPM, or if hand-cranking (same 3 ft. handwheel) 57 lbs. load (plus friction)....
Bob
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Thanks, I've got a 2.5 HP motor from a golf cart that would not even get warm at that output. Plus I could go solar to charge the batteries. HHmmm cheap air. ;D ;D I'll also be adding an expansion cycle cooler and dryer. A small bleed off the high pressure side will handle those chores. So what if it takes 1.5 hours instead of 1 hr. ;D
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BBB,
More [crank] power to you! That would be one heck of a compressor, with a .45" piston in the final stage. That has 20 times the cross sectional area as the shoebox 1/8" piston.
I am pretty sure you will need to run the air, at least between stage one and two, thru a chiller or something to get the water out. Air flowing thru a cold tank full of glass BBs or marbles will give a lot of surface area and condense a lot of water out. You probably laready have something figured out on that, though. I think that is one reason the shoebox requires a seperate first stage compressor, because that traps a lot of the moisture in its tank and keeps it out of the shoebox. Then you still need a dessicant to finish the job on the shoebox.
If you can keep the last 2 stages from leaking too bad this could be pretty sweet.
Lloyd
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85mm first stage, 40mm 2nd, 18mm 3rd, 8.8mm 4th. 86mm stroke 4.5:1 ratio on all stages. 5900 psi possible output.