Making my home made silent air compressor

beetlebug64 · May 9, 2013

Hi, today I have decided to make a silent air compressor using used A/C compressor that come from an excavator, and this is what I want to have once finished

First, I 've cut the clutch plate to keep only the center part and after I've machined a hub to fix the v-belt pulley by 3 M6 allen screws for the center, and 4 M8 hex bolts to fix the pulley with the hub

What do you think about this project? Does it works for you? Let me your critics and sorry for my bad english

adama · May 9, 2013

Ahh how are you lubricating it? The compressors in all air cons run a very open lube system and rely on the gas charge to flush the oil around - lube the pump. When used as a air compressor you have to take the oil out of the pressurised air and reintroduce it to the pump. Whilst dealing with the heat and moisture issues. What you have done won't run for long unless you have addressed that issue! Come up with a simple answer for that though and your akin to a legend :-)

Simply opening the input port to atmosphere and connecting output to the tank with a pulley to rotate it won't solve that bit!

CalG · May 9, 2013

Gast hyas been making pumps with "oil through" for many years, Though the oil less are taking over. Oil lubricator on the inlet, seperator on the out let, Swap 'em when they need it ;-)

I like this setup beetlebug 64. A great way to make something useful from a nicely made A/C compressor!

Is it really silent?

IS there a second compressor head mounted on the tank?

Rob F. · May 9, 2013

It is common in the us to convert A/C compressors for air comp use on 4x4 trucks. York makes A/C compressors with an oil pan that does not rely on the refrigerant to lube it. Otherwise it is a simple matter to add oil mist to the intake air, like calg said above. My jeep has a york on it for air use. Should be plenty of info in the off road groups if needed. I believe they are just sucking through a standard air line drip oiler.
The only thing that may be a problem is the size of your new pulley, could be to slow RPM. Otherwise it looks good
Rob

autofrite · May 9, 2013

my compressor is in the closet.i built it specially for the compressor,plenty of clearance inside,draws air fom outside through an air filter.by just routing the air intake to the great outdoors dramatically reduced noise.boxing it in makes it quiet enough to make a phone call right beside it.when running it for long periods,i simply open door and it wont overheat.

the automotive air compressors as mentioned above are great if you dont need a great deal of volume.
the oil shouldnt be an issue until a person decides to try autobody repairs.
oil and bodywork dont mix (especially painting).all the filters in the world arent worth the risk of getting one drop of oil in a paint job.

sicero · May 9, 2013

Another thing you might consider is to use two pressure tanks designed to use a very small
tank with shut offs to the main tank. My small shop tank is 6" X 36".
You can get high pressure quick for short use of air tools, blow nozzels or pump up a tire.
Only use the big tank when you need high volume.
The pressure tank on my truck is only a gallon and works fine for pumping up a tire
or blowing some dip sht out of the left lane with the air horn. Kenny

kapps · May 9, 2013

I messed with quieting my 5hp v-twin compressor down earlier this year. I have it inside my shop due to the fact that I'm in a neighborhood and don't want my neighbors to hear it. I made a wooden box to hold the largest automotive flat air filter I could find. Lined the box on the inside with scrap 2" foam. That got it down to around 80dB with the doors shut. I was still getting a peak so I made a helmholtz tuning pipe out of some PVC and cut it down until the peak was gone (used a spectrum analyzer on my iPhone to help). Now I'm sitting around 75dB with the door shut. With the doors open standing 10 feet outside, it sounds like a very well muffled bike idling.

Edster · May 9, 2013

Why not use a pump for a trucks air brake system instead?

My dad built a compressor years ago with one and it worked pretty good.

Garwood · May 9, 2013

that pulley will spin it too slow. I would spin it around 2000 RPM depending on the motor size you have. Compressors like that are usually driven about 20% faster than the crankshaft.

CalG · May 9, 2013

Garwood said:
that pulley will spin it too slow. I would spin it around 2000 RPM depending on the motor size you have. Compressors like that are usually driven about 20% faster than the crankshaft.

Is that 20% faster than 3450? or 1725?

Just checking.....

Rob F. · May 10, 2013

CalG said:
Is that 20% faster than 3450? or 1725?

Just checking.....

Check the rpm of the engine on the equipment it came off. Not the motor running it now.
Rob

Garwood · May 10, 2013

CalG said:
Is that 20% faster than 3450? or 1725?

Just checking.....

Those compressors are used on engines in vehicles, not electric driven. Say your pickup cruises at 1800 RPM then your AC compressor is spinning 2160.

CalG · May 10, 2013

Rob and Garwood, My bad, I was being facitious and pointing out the difficulty of using "Crankshaft RPM +20%" for the determination of compressor speeds.

I know the A/C pumps in my cars work even if I drive in a low gear at say 3800rpm or if I run in economy mode at 1300rpm.

With a 3:1 spread, those A/C compressors would seem to be relatively accomodating. Certainly I would try the present configuration before jumping to any "remakes".

I recently considered just the O.P. set up. I want a silent pump in the lab to provide air for actuators. (Very low volume, 70 psi) The A/C pump was rejected due to the oil issues. The lab is optics and vacuum coating , so oil in the air would be not in best interests.

That, and by the time the controls and fittings were assembled, there would be more $$ tied up than just buying a small unit. So that is what I did....Noisy though ;-(

beetlebug64 · May 12, 2013

Thanks everybody for your interests and your reply, well I have check the motor and is running at 2840 tr/min for 2 hp at 380 V. The outer diameter of the compressor pulley is 226mm approx 8.9 inch, and the outer diameter of the motor is 100mm approx 3.94 inch, so what size do I need for the motor pulley? I have found a ratio of 0.44.
With this ratio, when the motor run at 2840 tr/min, the compressor run at 1250 tr/min. If I increase the motor pulley diameter 20% more, the compressor should run at 1500 tr/min. Am I in the right way?

beetlebug64 · May 13, 2013

No more ideas? Am I alone feature my problem? HELP!!!!

Garwood · May 13, 2013

So you have a 2HP motor.

You need to know-

Pump displacement/rev

desired system pressure

Then you do the math to determine the maximum flow 2HP can deliver at that pressure and you drive the pump to just under that RPM.

If you don't know this stuff then the backyard method would be to run it as is and measure the motor amps at desired pressure. Compare the juice the motor is pulling with what it's rated for and adjust the pulley size accordingly.

Rob F. · May 13, 2013

Most of the A/C compressors I have seen use a pulley that is close in size to the crankshaft pulley. Calg is probably right about the 20% speed change on the pulley ratio, and as said the pump will work over a broad RPM range- it hat to due to changes in engine RPM. I would run the thing as is and see how it works. Check to see if you are getting enough air volume and also check the amp load on the motor. Reduce the size of the compressor pulley until the amp draw is just under the rated load on motor
Rob

GregSY · May 13, 2013

kapps said:
I messed with quieting my 5hp v-twin compressor down earlier this year. I have it inside my shop due to the fact that I'm in a neighborhood and don't want my neighbors to hear it. I made a wooden box to hold the largest automotive flat air filter I could find. Lined the box on the inside with scrap 2" foam. That got it down to around 80dB with the doors shut. I was still getting a peak so I made a helmholtz tuning pipe out of some PVC and cut it down until the peak was gone (used a spectrum analyzer on my iPhone to help). Now I'm sitting around 75dB with the door shut. With the doors open standing 10 feet outside, it sounds like a very well muffled bike idling.

Sp you have the whole compressor in a box? How do you get the heat out?

Doozer · May 14, 2013

Why doesn't someone make a compressor where the pump in inside the tank,
and the only feeds in are for the power and the intake air?
The whole pump and motor would be pressurized.
Might make for a quiet unit.

-Doozer

Making my home made silent air compressor

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