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Air Compressors... How to keep them quiet?


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12 replies to this topic

#1 Subarutex

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Posted 20 October 2009 - 03:45 PM

I have this compressor, http://www.craftsman...ors & Air Tools

It works great for what I need more or less. I wish it had a bit more CFM for running the die grinder, but it does OK.

I find it runs a lot when using the grinder, and its pretty loud. I'm looking for ideas on how to quiet it down.

Unfortunately, this is still a mobile tool, so I can't just put it in its own room, which most of the internet seems to do.

What have you done? Ideas?

#2 Turbone

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Posted 20 October 2009 - 05:06 PM

Did it come in a box?
If not, try and find a frig box and put styrofoam sheets in it to insulate it.

#3 nipper

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Posted 20 October 2009 - 05:07 PM

There isnt alot that you can do besides wearing ear protection. Air compressors are noisey by nature, especially in the potable range.


nipper

#4 GeneralDisorder

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Posted 20 October 2009 - 08:07 PM

The problems are:

1. It's a 3600 RPM motor. It's running those little pistons REALLY fast (probably @3600 RPM - which is totally insane).

2. It's an oil-free recip - it's totally open (exposed crank) and needs to be in order to properly cool it.

3. Being a tiny-piston, oil free, high RPM, aluminium/plastic machine - it makes a TON of heat and has to reject it somehow. Air compressors double as excelent heaters and anything you do has to keep in mind that your machine (especially) needs proper airflow or it's going to melt.

What you can do:

1. Slow it down. Change the belt shivs if that's possible with your machine's design. This will reduce the speed of the air-end and of course also reduce the noise. You will lose CFM.

2. Enclose the machine. Basically build an insulated enclosure for it to sit inside of - you will need to provide a fan (attic vent fan perhaps?) to circulate air through the enclosure. DO NOT underestimate how hot that thing will get. All that plastic shrouding hides the fact that at 100 psi the discharge temp of that little machine is easily 250-300* F.

3. Put it outside with a shed roof over it and plumb some copper through the wall for your air supply. Provide a quick disconnect for the machine so it's still portable. Chain it up or wheel it inside at night though.

4. Get a bigger, oil lubed recip. I know that's probably not an option for you but I just wanted to point out that larger machines that are oil-lubed, typically run at 1800 RPM and as such make less noise. They are also heavier and the noise they do make is usually devoid of the annoying "buzzing" of the smaller, lighter machines. It's more of a thump, thump, thump noise and not at all annoying (IMO).

I have a little machine that is my portable with a 30 gallon tank - it's an oil-lubed recip. The machine was made by Coleman and it's a few years old (I beleive they don't make them anymore). But the air-end was made by Briggs and Stratton (the engine manufacturer) and although it does have a 3600 RPM motor the air-end runs at about 1200 RPM. It's not bad at all for what it is. Puts out about 5 or 6 CFM.... I got it for $84 from work when a customer never came to pick it up after I fixed the thing. I would reccomend something like that (it was probably a $300 or $400 machine new) over an oil-free machine. Especially if you are just running air tools as the oil won't hurt them. If you are painting a coalescing filter and a drier would be needed anyway so I'm not sure what the draw is for the tiny oil-free recips. They don't fill any niche that I can think of although it does mean you never have to worry about changing the oil.

GD

Edited by GeneralDisorder, 20 October 2009 - 08:19 PM.


#5 markjw

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Posted 21 October 2009 - 11:28 AM

You can also put a intake muffler on it. Seems I read somewhere that thats where alot of the noise comes from. I think it would work on a direct drive as well as a belted compressor.

#6 GeneralDisorder

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Posted 22 October 2009 - 09:44 PM

Yeah - the type of air filter on the machine can make a difference. Typically they are a screwed-in NPT fitting but being a highly custom type of machine and fully enclosed it could very well be totally different. Try this - when it's running just put your hand over the intake to the compressor (do this before it starts getting hot). That will instantly tell you exactly how much of the "noise" is comming from the intake. It won't hurt you - that's actually how we test the bottom end on recips - block the intake and listen for the sound of rods knocking.....

GD

#7 Legacy777

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Posted 23 October 2009 - 11:04 AM

I've got a similar Craftsman AC. It works pretty well, however yes it is noisy.

GD made some excellent points. One thing to note, the plastic shrouding on the compressor is designed to provide cooling of the compressor and motor.

As for the intake, it's just an oiled piece of foam. I don't think doing anything with this will drastically reduce the noise.


Some other info. I've had mine since 2003. I do use it pretty well, and it does run quite a bit when using a die grinder. Since owning it, I have replaced the bottom drain valve and the poppet valve on the compressor discharge going into the tank. I do leave it pressured up, and had a slow leak. Finally tracked it down to the pressure gauge.

I have also removed the pressure regulator. This helps dramatically to improve the CFM. It made a difference when using my 1/2" impact gun.

#8 ShawnW

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Posted 26 October 2009 - 06:55 PM

I have the same thing only horizantal unit and I put mine in a little lawnmower closet in the corner of the garage and it made a HUGE difference. Might help to put a piece of foam under the wheels and base as the noise seems to resonate thru the floor a lot. I find myself using my 3/8 cordless alot so I don't have to use it.

#9 porcupine73

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Posted 26 October 2009 - 07:01 PM

I've got a similar craftsman unit my dad gave me; the only quiet solution I could find was to put in an adjacent different building and pipe the air supply over. Otherwise it was making me flinch badly every time it kicked on.

#10 GeneralDisorder

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Posted 28 October 2009 - 11:04 AM

I have also removed the pressure regulator. This helps dramatically to improve the CFM. It made a difference when using my 1/2" impact gun.


Interesting that they would put a very restrictive regulator on them..... one thing to consider is the pressure you are running. Most air tools are designed for 90-100 psi but a lot of these small compressors are pushing out 175 psi just to cram more air into a smaller tank. The problem is, that at higher pressure, the compressor isn't as effecient so CFM output goes down. So regulating it (with a properly sized regulator) is beneficial if your are boderline with the size of your compressor for the tool you are running. Not that a compressor that size could ever keep up with a die-grinder, but regulating down to 90 psi sure will help it not to run as much.

It really sucks that no one can seem to make a decent sized compressor for a good price. Most folks are chained to a compressor that simply can't supply the air that most air tools really need. It seems like if you don't have at least $3000 to spend you can't own more than an oversized tire-inflator. I would like to see some of the scroll compressors come down in price and hit the consumer market. A 5 HP scroll would easily put out 15 CFM and they have a good 20,000 hour life before tip-seal replacement is needed. Too bad they are outragously expensive because they are marketed to the medical and high tech industrys :mad:. They are simple diecast housings with like 3 moving parts :rolleyes:

GD

#11 Legacy777

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Posted 29 October 2009 - 03:18 PM

Yeah, my compressor only goes up to about 150 psig. It hangs down around 125 mostly. I've bought an electric grinder I use more now than the air die grinder....so it saves the compressor a little bit. I rebuilt it not too long ago. Replaced the cylinder liner & piston, and valve assembly. It didn't really change things, so I think the old one was fine.

It works. I wouldn't mind a little bit bigger and oil lubricated one....but like you said....to get a good one, they're not cheap.

#12 GeneralDisorder

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Posted 29 October 2009 - 04:05 PM

There are good deals out there in the used market. Just about a week ago I saw a Quincy QR-240 on an 80 gallon horizontal tank - brand new Baldor 5 HP single phase motor - freshly serviced and painted. $650. That's the kind of machine you want. That's about a 15 CFM @ 100 psi unit. They don't make the 240 anymore, and that one was probably from the 60's or 70's but you can still get all the parts to rebuild them. Built like a heavy-duty truck engine with disc valves, cast iron crankcase, cylinder, rods, and crank, timken roller bearings for the mains, etc, etc.

I have a QR-325 that came into work after some electrician working down at a school district facility hooked up the 3-phase backward to the machine and walked away. They make air running backwards but there's no oil pressure. It seized and they had to buy a new one. Everyone that works at my former employer gets their own compressor eventually and that one was given to me. Just the pump - had to buy a tank and motor for it. But I got a deal on a used 80 gallon vertical and bought a new motor. I'm into it about $500 but it would be about a $6000 machine if you went out looking to buy a new one. Having completely gone through the pump and having a new motor I can safely say it will be good for the rest of my life. They often last 30+ years down in the bowels of ships or at saw mills, etc. I've personally rebuilt units from the 50's with 100,000+ hours on them.

Just do some craigslist searches for "Quincy" in your area. There are lots of them out there and very often they are being given away for almost nothing in need of a rebuild. Your local Quincy dealer can set you up with a rebuild kit - it's rather like rebuilding a gas engine - hone the cylinders, new rings, replace the rod inserts, lap the valve seats and install new discs, new gaskets, etc. The only tough part is running them for a good long break-in period to seat the rings. Usually about 10 hours straight @ 100 psi will do a pretty good job. Don't be afraid of 3-phase stuff - typically you can just pull off the motor and replace it with a single phase equivelent with a minimum of rewireing. If you can rebuild a car engine - why not a compressor? It's not that big of a learning curve really.

GD

#13 Legacy777

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Posted 01 November 2009 - 02:55 PM

Thanks for the info. I'll have to see what I can find.




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