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Need help sizing an air compressor.

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  • Need help sizing an air compressor.

    The wiring on my outbuilding was finished yesterday. I had the electricians wire up a 220 circuit for an air compressor.

    After looking at Lowes and Home Depot this morning I'm not sure either of them have what I need.

    A couple of years ago I had a good idea on what I needed but now (and maybe for a quite a while longer than that) with HVLP paint guns being so popular I'm not so sure of what I need. (I'll primarily be working on my tractors and an old car but I'll be doing other things too like painting the metal patio set and reparing small to medium sized farm equipment.)

    Is an HVLP gun going to be the biggest user of air on my compressor? How many SCFM do they need and at what psi?

    Other things I'll be using are impact wrench, DA sander, cutoff tool, die grinder, etc.

    Will a good 60 gallon unit be plenty or should I go 80 gallon as one of the 'experts' suggested?

    Please recommend good brands of compressors or at least electric motors to look for.

    Also, I saw one compressor with 3 cylinders. I don't think I had ever seen one before. Is that something new?


  • #2
    DA sander, cutoff tool, die grinder, etc.
    An HVLP gun will run on most anything, but these are 'air loving'. A DA sander will really work a compressor trying to keep up with the air being pushed thru it --- air files, die grinders, impact wrench - these like lots of air.

    I'm kinda guessing here, but I think you would need to get above 15-16 cfm capability on your compressor to keep it from running constantly. And, thats not to say you cant get a lot of work done with the smaller units - heaven knows there are thounsands of pancakes & 10-20-30 gal ones out there running every day, - but if you can stand the finances now, its definately better to go ahead and get a good sized one.
    If everything seems to be going well, you have obviously overlooked something........


    • #3
      paint guns really dont use that much Psi or CFM, i have a CH paint gun that came wiht my compressor and never had an issue yet, also i recently gota breating machine, forma buddy long sorty but it puts out 15psi which i found is more then good enought for my paint gun or an airbrush kit, and the best part its 115 volt and no tank its 100% supply of non stop air, , as for the air tools you want to use id say for better performance 9 cfm at 90psi would be idea, 18 cfm is better but 9 is more then good at 90 psi and it would run higher cfm on lower psi no idea the numbers there but, its really boils down to your needs wants personal choice and budget ..

      its taken me over 4 years but now i can afford a 4 jow chuck for my lathe and a few other toys for my lathe longer story there any how

      all the best in your choice, but its still up to you in the end,i even use my 8 gallon ch machine for all my auto motive stuff and sandblasting now if your going to need to sand blast then get as much CFM as you can afford other wise it takes forever to blast anything big,,,

      ok thats my thoughts


      • #4
        Originally posted by Bill Pace
        I'm kinda guessing here, but I think you would need to get above 15-16 cfm capability on your compressor to keep it from running constantly.
        That sounds right. I have a single stage 3HP Ingersoll Rand that's 12.5 CFM that runs constantly when I'm using a die grinder or da sander.

        An HVLP gun uses very little air, by comparison.

        Whatever size compressor you pick, it's going to end up one size smaller than you need
        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


        • #5
          For the past several years I've been using an oilless, 25 gallon, 135 psi, porter cable compressor with a vertical tank on wheels. I love that little thing. It's light and portable. And since it's oilless I can lay it on its side in the back of the truck to haul it to where the work is. It will do everything so far but for some things it seems to take forever.

          The toughest task I've had it do is power my impact wrench to remove the 3 blades from my Gravely zero turn radius lawn mower. No way could I have loosened the nuts without an impact wrench. Even the guys at the shop where I bought the mower said it's a snap with an impact wrench but good luck trying to do it without one.

          Anyway, 80 gallons seems way too big but I've never done any really demanding work at home for an air compressor.

          Thanks for the replies and keep 'em coming. I'd still like to have some good brands listed.



          • #6
            Never buy 'oilless or maintence free' compressors, they are 10x noisyer and last 1/10th as long as oil filled. for painting you just get oil/water seperators and/or dessicators to put inline (need water seperation in an oilless compressor anyway)

            6cfm is the biggest you can get from 120v 15A circuit, or 7.5A at 240v (some are dual wired)
            Insure the compressor rating is 6cfm at 90psi or higher, some compressors cheat and spec 6cfm at 40psi and at 90psi its only like 4cfm. Ignore the HP ratings of 'small' compressors as they lie like shopvacs. 5hp from a 120v socket is never gonna happen.

            it will run HVLP paint guns all day long (well not all day long but painting is intermitant so it will catch up) Die grinders and cutoff tools are usable if you don't mind being intermitant (use of carbide burrs will greatly improved metal removed compaired to grinding stones) fine for light usage of impact wrench but id recommend 10gal tank min, idealy 20gal tank.

            12cfm is your typicaly 3hp~ compressor, 15A at 240v, it will run die grinders continiously, impact wrenchs as much as you'd want, most other tools

            16cfm is your typical 5hp compressor (20A~25A circuit, will brownout your house a little when it turns on), comes with a 60gal tank, the 80gal tank is just gonna waste more space IMO. the 150/175 psi diffrence of medium and high end compressors is a minor help.. 175psi can require you to buy more expensive regulator/filter however.

            16cfm will actualy start running small sandblasters (still not faster then sanders unless the area is highly detailed) and DA sanders continiously, as well as easily run die grinders and air drills (500rpm air drill + 16cfm compressor = AWSOME, you can use 6" holesaws through steel. or drive 3+" deck screws into solid wood at 300rpm and stop on a dime. also it has no stall kick, it just stalls with the same torque as it was running with)

            The common '3' cylinder air compressor ($900 avg cost).. im not sure if they are all like this, but mine is NOISY, super super noisy, even after removing the belt guard its so noisy I need to move it outside (try taping the belt guard on one before buying it, if it rattings with a good hit, it will make the compressor 2x as noisy)

            Iv seen one or two of the 2 cylinder 2 stage 16cfm/5hp compressors and they are MUCH quiter, but often go for $1600~2000 with tank (but usally 80gal 175psi vs 60gal 150psi of the other 16cfm compressor)
            Thinking of just buying one of those cylinder heads for my compressor.. but they are like $400 heh.

            As is, I run two compressors, a 6cfm 20gal 115psi thats so quite you can talk over it, it lives outside and is allways pumped up and its cutoff valve open. pumps up once or twice a day, its great for painting, casual die grinding or sheet metal cutting with the nibbler, anything thats not gonna take more then a few mins.

            And a 16cfm 60gal 150psi thats indoors.. and too friggen noisy to wanna ever use so I only turn its shutoff valve on when I need to use it, cause when it pumps up at 3am it wakes up everyone in the house. the 6cfm you can't even hear inside. Both compressors actualy share the same 20A 240v circuit
            Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


            • #7
              A couple of important things to look out for. One of Kobalt's compressors is called PEAK horsepower That is a marketing BS as you can only measure Peak HP for a mirco second at start up.

              Another thing to find out before buying is what exactly does SCFM mean for that compressors manufacturer's.

              The correct definition is STANDARD CUBIC FEET/MINUTE and only that.
              That is the amount of air @ a certain temperature over a period of time.
              No buzz words like sustaining, silenced or any thing else is hype.
              Same with the horse power rating of the motors Peak is bogus, start up or any other advertising hype they can come up with.

              Buy more compressor than you think you need. As much or more than you can afford. OR wait and save up for the next larger one.

              The HF assembled in the USA one's are assembled in Rock Hill SC. By the atlas copco company. They are from Italy and one of the largest mining and construction compressor makers.
              The tanks are ASME stamped made by Manchester tank company here in the USA. As are most of the others that are assembled

              Here is the 800 number for the parts warranty in Rock Hill SC. 1-866-869-3114

              They also make 7 other brands at the same site.

              By the way Husk Pro, some Campbell Hausfields and Kobalt are assemble in the same plant here in the states. They all all have the same parts warranty 800 number. 1-800-543-6400
              Any of the pumps that have a VH in front of the number on the id plate of the above compressors are China units.

              Ingersoll Rand @ Tractor supply are also made in the USA thier 800 number parts warranty is 1-800-AIR-SERV

              Pumps, motors, and hardware and electrical controls and assorted parts. Can be made in any country, Mexico, China,US,Italy, or other. All the ASME tanks are made in the USA and carry the stamp.

              The motors and other parts change the country of origin with each shipment.

              The other thing to look out for is at home Depot they were trying to pass off a rebuilt as new and at new prices. Somebody peeled the tape off that was applied over the engraved re built info. But they also left the paper work in the envelope from the company that did the work.

              Check the dates on the name plate. These were over 2 years old.

              Buy more compressor, than you need as it has been said you will need it tomorrow.
              Been there, probably broke it, doing that!
              I am not a lawyer, and never played one on TV!
              All the usual and standard disclaimers apply. Do not try this at home, use only as directed, No warranties express or implied, for the intended use or the suggested uses, Wear safety glasses, closed course, professionals only


              • #8
                If you are looking for a high quality compressor that will last I don't think the ones sold at Lowe's and Home Depot will do. Their's tend to be homeowner grade which is probably OK for casual use like pumping up tires and low volume spraying.

                I've owned a few compressors and, except for one I sold and shouldn't have, you almost never have enough air volume. I think the DA sander will be a tool that consumes alot of air followed by the die grinder and cutoff tool. The impact wrench is a very low volume tool. Although I don't own a HVLP spray gun, I think one could require a fair volume of air.

                My suggestion is to buy the best compressor you can afford. The brands I'd recommend are Ingersoll Rand, Quincy, Atlas, Champion. I'd get a two stage compressor with cast iron cylinders, a real 5 HP motor and a 80 Gal tank. Most good two stage units will produce about 15-20 cfm at 90 psi which is what you want.

                Hope this helps.


                • #9
                  I would shoot for 15 cfm @ 90 psi as your minimum goal, compressors often are like building shops, once they're there you wish you went bigger, I've got a couple Devilbiss, one around 5 cfm, the other around 11cfm and have bought one of those triple pumps and a 60 gal reciever as a third unit. I've seem the triples configured as single and 2 stage and externally they look identical but maybe the valve internals on the 2nd stage head is different, anyway they rate them at 18.5 cfm. I would look for lubed cast iron pumps and the slower they run the longer they last, going bigger and slowing it down used to equal decades of longevity, a 60 gal tank should be lots.........
                  Opportunity knocks once, temptation leans on the doorbell.....


                  • #10
                    Originally posted by pgmrdan
                    Will a good 60 gallon unit be plenty or should I go 80 gallon as one of the 'experts' suggested?

                    All else being equal you will see exactly zero difference in whether your tools keep up or not between a 60 gallon and an 80 gallon tank, there will be a slight difference in the number of times it cycles during use but that's all. The size of the tank has next to nothing to do with how well a compressor keeps up in spite of common belief but a bigger tank will cut power consumption SLIGHTLY and Slightly reduce wear and tear, this is due to fewer high load start up cycles. A lot of guys think a bigger tank provides reserve air that will make a compressor perform better but it simply does not work that way, if your tool's air consumption exceeds the CFM rating of the pump you will still run out of air and a bigger tank will not help. An extra 20 gallons of storage will provide a little more time initially (usually just extra seconds however) but then that will be lost to the extra time it takes to refill the bigger tank so it is just a trade off and you will not gain anything. The bottom line is the size of the tank should be one of the last considerations (as long as it is reasonably sized of course) when selecting a compressor with CFM being the first along with pump size and type. Motor HP should be based on the AMP rating and never on what the manufacturer claims for HP, these HP numbers are almost always pure BS but that AMP rating is the required federal data and they will not lie about it. The CFM going into the tank is what really matters but people see the tank and a big tank may make a compressor LOOK big but this is one place where looks are deceiving. 60 gallons or 80 will be just fine and the 80 may offer some benefits in service life and power consumption, although power consumption reductions will be very small, but it will not make better performance.

                    NEVER pass up higher CFM for a bigger tank! For example a compressor with 15 CFM and a 60 gallon tank will handily outperform one with 13 CFM and an 80 gallon tank, the size of the tank simply does not make the difference that a lot of guys think it does.


                    • #11
                      With all these big compressors, how often do you drain condensation from the tanks? Do you fully depressure the tank when draining condensation?

                      I have a 5.7 cfm 20 gallon unit I drain daily(at least when I remember). I often leave it with the drain valve open and the power shut off for weeks at a time....
                      Design to 0.0001", measure to 1/32", cut with an axe, grind to fit


                      • #12
                        I allmost never drain mine yea I know, bad, but it only sees use once every week or so, so once a month and it spurts out a cup.. never let the entire tank depressurise.. infact I leave it at full pressure and just turn off the shutoff valve and it can go an entire week without turning on to pump up again.

                        But yea, tank size does not matter much unless your compressor can't keep up. I would never buy a smaller then 6cfm 20gal compressor though, as iv seen people use those small ones and they are lucky if they can get 1 bolt on/off with thier tiny impact gun before the tank is empty.
                        Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


                        • #13
                          I have a 3hp Emglo compressor that I have found to have the best specifications of any I have seen. Emglo was part of Davey Tree Service and has been sold to Dewalt, where they changed them into light duty, Home Depo kind of cheese. The old cast iron ones are now made by Steam Jenny corporation.
                          Anyhow, the specs are 3hp, 220v and 20 amps I think. 16 cfm at 90 psi. 4 cylinder, single stage. I set cutoff at 110 and cut-in at 90. This thing is quiet, due to the low pump rpm.


                          Last edited by Doozer; 10-28-2009, 09:17 PM.


                          • #14
                            Originally posted by coollx
                            My suggestion is to buy the best compressor you can afford. The brands I'd recommend are Ingersoll Rand, Quincy, Atlas, Champion.
                            Quincy and Champion are the Rolls-Royce of compressors, but Mike and I have the same 230V, 3HP Ingersoll Rand (12.5 CFM), and it's an Indian compressor with a Chinese motor.

                            Mine's been fine, despite abusive cycle times (i.e., running a DA sander constantly for hours on end), but Mike's had been busted at least twice that I know of...
                            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


                            • #15
                              I'm surprised radkins went that easy..........grin........I forgot to say or reconfirm my similar philosophy, watch out for the POS compressor motors that are overrated.........they take a light duty motor, spin them at 3450 and get some outrageous hp claims, I've got a real 1740 rpm 3 hp that will run the 18.5 pump and it weighs all of 80 lbs..............and best of all a low rpm pump for longevity.
                              Opportunity knocks once, temptation leans on the doorbell.....