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  • Air compressor & spray gun compatibility

    I have a small 3HP air compressor that I'd like to use a gravity feed spray gun yet to be purchased. However when I read the specs on the spray gun they state that a certain CFM is required. My compressor indicates it has 2.4 SCFM at 95 PSI, so I don't know if a spray gun would work adequately in my situation is they require anywhere from 3 -8 CFM. Does someone have an answer for me. thanks.

  • #2
    Re: Air compressor & spray gun compatibility

    It should work fine. Generally I use my spray gun at 35 PSI and my compressor is smaller than yours. I have no problem.

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    • #3
      Re: Air compressor & spray gun compatibility

      Air compressors will have a higher SCFM rating at a lower PSI. They usually give another rating at 40PSI. Air tools use a high PSI, that's why that rating is given if only one is listed. As Pipestone Kid indicated, you never run a spray gun anywhere near the 95 PSI. Your compressor may have somewhere around a 3.5-4 SCFM at 40 PSI. You may have some difficulty spraying certain waterbornes, but only thing you can do is give it a try.

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      • #4
        Re: Air compressor & spray gun compatibility

        Thanks I will give it a try, reading specs that you don't really understand makes one apprehensive to a purchase that will not deliver the results you are looking for .

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        • #5
          Re: Air compressor & spray gun compatibility

          It will likely be fine. In addition to the above posts, keep in mind that the ratings are for the pump. Your spray gun is fed out of the tank, not the pump. When the tank pressure drops below the setpoint, your motor starts. In that case you are draining air from the tank (with the spray gun) and adding it to the tank with the pump. Your spray gun drains faster than the pump can add, so the tank pressure does, but it takes a while.

          You do have to be mindful of where the tank pressure is, though. It's not true that as long as it stays above the spray presure you're ok. Many (most) spray guns don't use a true regulator at the gun, they use a needle valve. The pressure at the air cap/tip will vary as the compressor tank pressure drops. Some guns use a regulator, but even those are single stage regulators, so the air cap / tip pressure does still drift downward as tank pressure drops (not near as bad as a needle valve) This can wreak havoc with certain finish materials - it's very frustrating when you have the gun adjusted for a good finish at the start but it degrades as you're working, since usually you need it at its best at the end of the shoot.

          To deal with this, just learn to check the gage (at the gun) and adjust the gun inlet needle or reg fairly often during a shoot, with the trigger pulled halfway (air on, fluid off). I also have several tips for my guns - using the right tip for the viscosity of the material makes the whole operation work better and be less sensitive to pressure change. For spraying urethane on cars I use a more complicated rig with two pumps and 70 gallons of reservoir. But for wood finishes I just use my old 3 HP Speedair with a 30 gallon tank, it works fine, with a Devilbiss "Plus" gun or a Binks 2001.
          Last edited by Andy_M; 09-16-2009, 03:01 PM.

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          • #6
            Re: Air compressor & spray gun compatibility

            If it is a constant bleeder gun (Bleeder guns have a constant discharge of air.) you will have problems,

            If the trigger shuts off the air as well as the paint flow, your probably OK if you don't try to paint extremely large surfaces.
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            • #7
              Re: Air compressor & spray gun compatibility

              RSTjean,

              You didn't say what the spec's required on the spray gun you are interested in or what your tank size and maximum working pressure are.

              I disagree with the few posts that state you will be fine. I have a 33-gal, 7 HP (running) NL compressor that I've used with my CH gun. The gun requires around 10 scfm at 40 psi and my compressor puts our about 9 scfm at 40 psi. As you can see, there's a negative difference.

              I can certainly use my gun, as spraying a finish is more a matter of short sweeping sprays. But, in a matter of a few minutes, my tank pressure will drop to a point where the compressor will come on, in an attempt to repressure the tank. If I get over zealous and attempt to run a continuous spray, the pressure would soon drop below 40 psi, and then, the gun would start to spit, rather than spray (thus ruining the finish)

              If you only have a small tank compressor, you will clearly see that you'll NOT have enough reserve air before the compressor will be required to turn on in an attempt to stay ahead of what the spray gun requires.

              Year's ago, I had and Ingersoll-Rand twin tank (wheel barrow-type) which put out about 4.5 cfm @ 40 psi. With that, I could use a small spotting gun (about a pint container with an overhead-index finger operated lever). With that particular set-up, the gun and tank were closely matched and I could spray finishes successfully... but, the only with short, sweeping bursts; and the compressor ran almost constantly.

              So, my experience has been that you really need to have a compressor that exceeds the spray gun's requirements; otherwise, you'll very limited in the frequency and duration of actual spray.

              I hope this helps,

              CWS

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              • #8
                Re: Air compressor & spray gun compatibility

                I agree with CWS. I use a Husky HDS790 gravity fed conversion HVLP requiring 9 cfm continuous on a 30 gal devilbis with a 13.5 CFM @ 40 PSI pump. My pump only shuts off briefly when I spray large cabinets even when doing smaller objects you do not use much less air as the idea is that the air runs continuously and you modulate the material on/off, the only time I release the trigger far enough to shut off the air is when my arm gets tired or I am changing positions. You will also want to get yourself a water separator/filter/trap. Humidity in the air is turned to water droplets in the tank/hose and will cause what is known as fish eyes in oil based finishes. The effect is lessened with water based material but it still produces a less than perfect finish.

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                • #9
                  Re: Air compressor & spray gun compatibility

                  Spray gun is modern tool to apply the finishing material. In this time, almost every finishing job is done with spray gun. Thanks.
                  Vacuum Systems | Industrial Pumps |Centrifugal Pumps

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