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Miniature air compressor
- Thread starter basalt
- Start date
I'm not sure the propriety of compressed air around lathe/mill work. I have heard many people come down on different sides of that argument. But, that being said... If you are looking for low pressure, skip the tank altogether and buy a good sized Aquarium pump. They are designed for continuous run. If that's enough pressure, then you shouldn't even be taxing it.
I'm a newbie, so take that for what it's worth... I just like to think outside the box.
I'm a newbie, so take that for what it's worth... I just like to think outside the box.
Home-made compressors never give me a warm fuzzy feeling, but if you want to give it a try then this might work:
http://www.aaroncake.net/projects/12vminicompressor.htm
http://www.aaroncake.net/projects/12vminicompressor.htm
If you can find an old refrigerator compressor, they will work, not high volume and I wouldn't think they would last forever but definitely cheap. Add a pressure switch and a check valve and a safety valve and you are ready to go.
- Joined
- Jan 25, 2013
- Messages
- 22
Thanks Guys, What I want to do is build the cylinder, piston etc. from scratch. I read somewhere that reed valves might work--basically a leaf shim covering a port. Either that or use 2 check valves. I plan to drive it with a sewing machine motor so it is not going to be very big. Other concerns are what material to use for the piston (rings) and cylinder wall to reduce friction. Any ideas or or other links would be much appreciated. Thank you for taking the time to read my post.
- Joined
- Nov 13, 2012
- Messages
- 165
Hello Basalt,
I don't have any plans for a miniature air compressor, but I can offer some "for whats its worth" comments.
You might be able to adapt a design from a model steam engine or gas engine. The air compressor only has to withstand the heat of compression, so materials for steam or gas will certainly work. Air compressors are all about volumetric efficiency - higher is better. Steel reed valves make it easier to get minimal clearance volume. Design for the smallest clearance volume you can get, and you will still have plenty of clearance left to pass any water droplets. You could also use small ball-check valves. I would go for oil-less design. Use an off-the-shelf sealed ball bearing for the connecting rod/crank pin joint. Likewise, I would use small, sealed ball bearings for the crank shaft bearings. Teflon rings are widely used in compressors these days - even large industrial compressors. This gets you oil-free air without having to worry about lubrication. You might be able to make the entire piston out of Teflon. If the design is belt driven, a flywheel will be necessary to smooth out the crank velocity. You didn't say what type of volume (cfm) you are looking for - that will determine the cylinder dimensions and operating speed. Single stage compression is easy in the 20 - 60 psig range. Single stage compression is possible up to 120 psig or so, above that, two stage compression is usually used to limit the temperature rise of the air per compression. A belted compressor makes it easy to match the motor power to the compressor demand. You can select pulley sizes to keep the compressor from overloading the motor. One problem with piston compressors is being able to start the compressor when under pressure (for example you want to re-start the compressor when the tank pressure has fallen to 30 psig). One solution is to have enough motor torque to do the job. I think this is the best design for a small, model type compressor. Otherwise, there are different schemes for "unloading" the compressor until the crank comes up to speed. For a quick and dirty estimate, lets say you have a 0.5" bore and a 1" stroke at 300 rpm = 60 cu in/min. Say you can get 50% vol eff = 30 cu in per min (measured as intake air). Say you are compressing to 60 psig into a 3" dia x 10" ln long = 200 cu inch tank. 60/15 * 200 = about 800 cu in of free air to fill the tank. At 30 cu in / min = 27 minutes to fill the tank. In reality, it goes a little faster since you are pumping against less than 60 psig for the first part of the cycle. The shaft horsepower required would be around 0.1 hp.
Might give you some idea if this is the scale you are looking for.
Terry S.
I don't have any plans for a miniature air compressor, but I can offer some "for whats its worth" comments.
You might be able to adapt a design from a model steam engine or gas engine. The air compressor only has to withstand the heat of compression, so materials for steam or gas will certainly work. Air compressors are all about volumetric efficiency - higher is better. Steel reed valves make it easier to get minimal clearance volume. Design for the smallest clearance volume you can get, and you will still have plenty of clearance left to pass any water droplets. You could also use small ball-check valves. I would go for oil-less design. Use an off-the-shelf sealed ball bearing for the connecting rod/crank pin joint. Likewise, I would use small, sealed ball bearings for the crank shaft bearings. Teflon rings are widely used in compressors these days - even large industrial compressors. This gets you oil-free air without having to worry about lubrication. You might be able to make the entire piston out of Teflon. If the design is belt driven, a flywheel will be necessary to smooth out the crank velocity. You didn't say what type of volume (cfm) you are looking for - that will determine the cylinder dimensions and operating speed. Single stage compression is easy in the 20 - 60 psig range. Single stage compression is possible up to 120 psig or so, above that, two stage compression is usually used to limit the temperature rise of the air per compression. A belted compressor makes it easy to match the motor power to the compressor demand. You can select pulley sizes to keep the compressor from overloading the motor. One problem with piston compressors is being able to start the compressor when under pressure (for example you want to re-start the compressor when the tank pressure has fallen to 30 psig). One solution is to have enough motor torque to do the job. I think this is the best design for a small, model type compressor. Otherwise, there are different schemes for "unloading" the compressor until the crank comes up to speed. For a quick and dirty estimate, lets say you have a 0.5" bore and a 1" stroke at 300 rpm = 60 cu in/min. Say you can get 50% vol eff = 30 cu in per min (measured as intake air). Say you are compressing to 60 psig into a 3" dia x 10" ln long = 200 cu inch tank. 60/15 * 200 = about 800 cu in of free air to fill the tank. At 30 cu in / min = 27 minutes to fill the tank. In reality, it goes a little faster since you are pumping against less than 60 psig for the first part of the cycle. The shaft horsepower required would be around 0.1 hp.
Might give you some idea if this is the scale you are looking for.
Terry S.