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  • CFM/PSI VS length of air hose, question

    I know there is a simple formula or answer to this question.

    I have an air compressor that provides 9.6cfm at 90psi.

    I am running an a pneumatic tool that is rated 3cfm at 90psi.

    I have a hose reel with 100 feet of 3/8 hose. I notice the tool does not run at optimum and I must pause frequently. This morning I replaced the 100 feet of hose with a 20 foot piece of 3/8 hose and the tool worked very well.

    So here is my question:

    I know there is a formula or a calculation to determine the loss of CFM as the hose length increases. Can anyone enlighten me?

    Thank,
    Cactus Man

  • #2
    Re: CFM/PSI VS length of air hose, question

    Maybe you can try this

    Place a 1/4 NPT T fitting at the inlet to your air tool. Attach a 0-200 PSI pressure gauge to the side port of the T fitting and the tool to one end and the hose to the other. Set the regulator for 100 PSI with the trigger not pulled. Then pull the trigger and note the gauge reading at the tool inlet. You can then set the pressure for 90 PSI (most air tools) or whatever needed and note the gauge reading back at the pressure regulator when using that tool. Make notes and you'll be set for later on. What really matters is to get the right inlet pressure for each air tool when it's working. You can try this test with different hoses and note settings needed.

    I'm sure there are math formulas but it's nice to just take simple measurements and be sure. Do not leave the T with gauge attached. It's just for testing.

    Comment


    • #3
      Re: CFM/PSI VS length of air hose, question

      3/8" hose is good for about 20 cfm well beyond the capacity you require at 3 cfm. Is your 3 cfm intermittent use or full on use. Either way 3/8 is plenty for most home use applications. I have 100' of 3/8 hose and it runs all my tools easily. You may see issues if you have joined 2 50' hoses with a limiting connector or a hose real with small restrictive connectors. I changed all my quick connects to 3/8" T style, mostly because the 1/4 quick connects are crap and leak.

      Comment


      • #4
        Re: CFM/PSI VS length of air hose, question

        WB, where did you purchase those T style quick connects? I have a leak somewhere in my compressed air system and maybe those fittings will cure it. I'm currently using fittings that I bought at Harbor Freight so I'm guessing my problem is probably a case of "you get what you pay for".
        Teach your kids about taxes..........eat 30 percent of their ice cream.

        Comment


        • #5
          Re: CFM/PSI VS length of air hose, question

          Not big bucks either but I got them at HD

          Comment


          • #6
            Re: CFM/PSI VS length of air hose, question

            You should have no issue with a long hose..........it's not like a long extension cord. There is no real measurable drop in the distance. As has been stated...there could be restrictions in the connectors, but this is not a factor of the length of the hose. Leaks at the connectors can also cause pressure drops.

            Comment


            • #7
              Re: CFM/PSI VS length of air hose, question

              Originally posted by wbrooks View Post
              3/8" hose is good for about 20 cfm well beyond the capacity you require at 3 cfm. Is your 3 cfm intermittent use or full on use. Either way 3/8 is plenty for most home use applications. I have 100' of 3/8 hose and it runs all my tools easily. You may see issues if you have joined 2 50' hoses with a limiting connector or a hose real with small restrictive connectors. I changed all my quick connects to 3/8" T style, mostly because the 1/4 quick connects are crap and leak.
              you hit it on the button

              tools are typically listed/ rated at a 25% duty cycle. it's sort of like the h.p rating of air compressors use to be

              your tool is most likely 12cfm if used for a minute without stopping.

              length of hose defiantly will make a difference when the volume goes up. just pure physics/ friction.

              sure increasing the hose i.d will work or decreasing the length of hose will also work too. the real issue is you're not at 3cfm.

              plug the tool directly into the compressor and see if the compressor can keep up if it is truly 9.6cfm at 90 psi. chances are the compressor will not keep up with this tool

              rick.
              phoebe it is

              Comment


              • #8
                Re: CFM/PSI VS length of air hose, question

                Thanks for the replies...
                in a word.."oh crap!!"
                I have lots of dollars invested in a good quality quick disconnect connectors/couplers..auto type I think..and these are not of the Harbor Freight inventory. I am not using the "T" style couplers mentioned, but the other style.

                All my air tools use the husky swivel connector.
                I use a 3/8 air hose..the blue stuff . I actually have 250 feet, in 3 fifty foot rolls and a single 100 foot roll. The 100 foot roll is on a reel and used 90% of the time. There are times when I need to add additional hose and that's when the other 50 foot rolls are used.

                My air compressor is the porter cable 240vac 60gal model CPLC7060V
                7HP peak, 135psi, 9.7cfm@90psi [delivery].

                So.. If I understand all the replies..
                I do not have any air leaks.
                All my tools are in great shape and not defective or leaking.
                I am not using the "T" style couplers

                Now. I know [from experience] the 1/4" hose is essentially ok for nailers.
                The 3/8" hose is what I see as the standard for homeowner and contractors.

                I have seen 1/2" hose but I thought that would be overkill and be way too much for me to handle..but considering Plumber Rick's comments..perhaps I should have outfitted my pneumatics with 1/2" hose?

                All my air tools not including the nailers and staplers are rated at 3 to a maximum of 6 SCFM depending upon the air tool.
                Nowhere in any of their operating manuals do they imply that the operating SCFM stated is at 25% and and at 100% operating they are higher!

                I know some devices do that, such as generators. They give you the peak wattage and the 50% running wattage. The peak rating is only intended for brief periods like the surge when a device starts up....etc.


                I may look closer to the hook up between the hose reel and the compressor..perhaps this is an area I can increase the size of the supply hose? I do have the regulator and inline water trap at the compressor..I do not use an inline oiler.

                Keep the comments coming

                Cactus Man

                Comment


                • #9
                  Re: CFM/PSI VS length of air hose, question

                  Please try adding a few 0-200 PSI pressure gauges inline from the regulator to the inlet of the tools. 3/8 hose should work fine. Somewhere there's a restriction. Try the process of elimination if you can. Start with a short piece of hose at the regulator and a blow gun at the other end of the hose. Then add in the hose reel and another piece of hose. This is where it would be great to have the T with gauge on it. Check for pressure drop. Next try a different hose.

                  As for the air compressor, does it run all the time if you keep the trigger pulled on one of your larger air tools? Forget specs. It's easy to tell if you have enough compressor. Just run one the tools a minute or two non stop. Note the tank pressure and keep in mind it needs to be over 100 and hopefully it can stay above 120 PSI.

                  By the way other than for industrial duty motors on on industrial grade air compressors the H P ratings are a joke. A 5 HP serious air compressor can produce 18 CFM at 120 PSI and keep it up!!!

                  I have a gut feeling the problem is with the hose reel. All parts need to be 3/8" inside diameter or larger. Try checking everything along the way to be sure there isn't some restriction.

                  By the way try direct connecting the same hose you use with the hose reel but bypass the reel. Also check the fittings. Can you pass 3/8" rod through them?

                  When I refer to a T fitting, I mean the simple iron ones used for simple plumbing. The idea is just to have a gauge or two inline at several places so you can see where the pressure drops.

                  Do try what Rick said and connect air tools right at the pressure regulator using say a good 3/8 x 25 foot hose. I recommend leaving out all fittings that you can. This is to be 1000% sure your air compressor can keep up with the air demand. Then add things one at a time. You'll find the trouble maker and laugh once you find it, or maybe not depending on what it is.
                  Last edited by Woussko; 06-08-2007, 02:30 PM.

                  Comment


                  • #10
                    Re: CFM/PSI VS length of air hose, question

                    Originally posted by cactusman View Post
                    Thanks for the replies...
                    in a word.."oh crap!!"
                    I have lots of dollars invested in a good quality quick disconnect connectors/couplers..auto type I think..and these are not of the Harbor Freight inventory. I am not using the "T" style couplers mentioned, but the other style.

                    All my air tools use the husky swivel connector.
                    I use a 3/8 air hose..the blue stuff . I actually have 250 feet, in 3 fifty foot rolls and a single 100 foot roll. The 100 foot roll is on a reel and used 90% of the time. There are times when I need to add additional hose and that's when the other 50 foot rolls are used.

                    My air compressor is the porter cable 240vac 60gal model CPLC7060V
                    7HP peak, 135psi, 9.7cfm@90psi [delivery].

                    So.. If I understand all the replies..
                    I do not have any air leaks.
                    All my tools are in great shape and not defective or leaking.
                    I am not using the "T" style couplers

                    Now. I know [from experience] the 1/4" hose is essentially ok for nailers.
                    The 3/8" hose is what I see as the standard for homeowner and contractors.

                    I have seen 1/2" hose but I thought that would be overkill and be way too much for me to handle..but considering Plumber Rick's comments..perhaps I should have outfitted my pneumatics with 1/2" hose?

                    All my air tools not including the nailers and staplers are rated at 3 to a maximum of 6 SCFM depending upon the air tool.
                    Nowhere in any of their operating manuals do they imply that the operating SCFM stated is at 25% and and at 100% operating they are higher!

                    I know some devices do that, such as generators. They give you the peak wattage and the 50% running wattage. The peak rating is only intended for brief periods like the surge when a device starts up....etc.


                    I may look closer to the hook up between the hose reel and the compressor..perhaps this is an area I can increase the size of the supply hose? I do have the regulator and inline water trap at the compressor..I do not use an inline oiler.

                    Keep the comments coming

                    Cactus Man

                    Hello, I have used air tools as a mechanic for years and I agree that you should put a tee with a pressure gauge in the fitting at the tool to make sure you don't have any restrictions in your air line that could be causing the reduced performance you are experiencing. I know that 3/8 hose up to 100 feet long will run a 4cfm (at 25% duty cycle) die grinder just fine with little noticable pressure drop. Connect your tool up and pull the trigger and take a reading on your gauge, it should drop a few p.s.i., like 10 p.s.i. , depending on your hose size but it should stabilize within about 2 seconds and not noticably drop any more, then immediatly rise back when you let off the trigger, (assuming this is an air tool that uses air continiously while the trigger is pulled). If it drops way down, withing the first couple of seconds then you probably have a restriction at your compressor, it could be a defective regulator or it may have debris in it, it could be your water filter seperator, make sure it's big enough and isn't restricting your air flow and check your air hose for restrictions. Once I had a water filter that used a roll of toilet paper to absorb any water that made it into the air line, and it worked fine until the paper got moist and started to shift in the housing, blocking off the outlet port cutting my air flow in half. The 7.5 horse power rating on your compressor is Peak H.P. (which is what it can produce in lab. conditions, running off like 440 volts for a few seconds before it burns up), and not running H.P. ,which is probably about 3 or 4 H.P. depending on the current draw of your motor I have a true 7.5 H.P. industrial 2 stage air compressor on an 80 gallon tank and It produces 32 C.F.M. at 175 psi and draws 29 amps on 240volts. You should be able to get at least a good minute of strong running and good performance with any tool tool that you can buy at home depot with a 60 gallon tank and 9.7 cfm@135 PSI. Hope this info helps. Good luck!
                    Last edited by Steve Klyce; 06-08-2007, 07:25 PM.

                    Comment


                    • #11
                      Re: CFM/PSI VS length of air hose, question

                      I want to thank all of you for your input to my query, The science experiment is complete.

                      I went to home Depot and purchased the "T" couplers you suggested. I installed them from the compressor to the hose reel and inside the hose reel.
                      I do notice an obvious difference in the size/hole compared to the 1/4" style.

                      I then tried the angle die grinder ....it is a Harbor Freight model rated at 4CFM @ 90PSI.

                      With the 100 foot 3/8 blue hose on the reel the die grinder pooped out within 30 seconds. I increased the PSI to 110 PSI and the die grinder ran a bit longer but really did not do very well.

                      I then tried the 100 foot air hose without the hose reel and experienced the same effect.

                      I then hooked up a black rubber 3/8 hose about 25 feet long and at 90 PSI the tool worked perfectly. It did not slow down and the compressor did not run continuously, it only kicked in when it needed to.

                      I also tried a 50 length of the blue air hose and again the tool pooped out.

                      I decided to add a "T" after the moisture trap and now I have two couplers.

                      One coupler is for the 100 foot air hose on the reel for pneumatic nailing, stapling, blowing dust off, some drilling.

                      I then use the other coupler 1/4" for the die grinder and cut off tool and only run a 25 foot hose. I kept the 1/4" coupler at the tool end of the hoses so I can keep the HUSKY swivel couplers on the air tools.

                      They are now permanently attached and easy to access.

                      I do agree there is a limitation with the hose reel, and for whatever reason when using the 100 foot air hose. I have no air leaks..I verified this using the soapy water trick.

                      I looked in my "Pocket Reference" by Thomas J. Glover and in the section discussing "air" they spoke about 1/2", 3/4" and 1" They spoke about air hose friction, recommended air line size etc.

                      Under the topic of air tool requirements they explained typically running 90 or 100 PSI. They did not discuss 3/8 air hose/line.

                      So....

                      The bottom line is I cleaned up my air supply system. I now have the capability to properly and safely use my various air tools. I learned that the more air power demanding tools should not be used with anything longer than a 25 foot air hose.

                      I really can't change out to a 1/2" air hose system as I have 250 feet of the blue 3/8 hose; and for the majority of my needs even the 100 foot hose on the reel is just fine.

                      I hope those in the peanut gallery reading the posts were able to glean the useful input from those of you responding.

                      Thanks

                      Cactus Man

                      Comment


                      • #12
                        Re: CFM/PSI VS length of air hose, question

                        I have a feeling that your blue 3/8 hose is not really 3/8 or that the fittings on each end are restricting air flow. What would be a good test is to find steel balls in slightly under 1/4, 5/16 and 3/8 sizes and try to pass them through the hoses. Start with the 1/4 and work up. If it gets stuck, blast it out in reverse with a little blast of air. Put the end of the hose where the flying ball won't hit anyone and place a cinder block on it to keep it under control.

                        For the main testing, just use gravity. The little ball should roll along from one end to the other.

                        I have 50 feet of good 3/8 air hose and have no problems using a 1/2" impact wrench or a die grinder. My regulator is set so the gauge on it reads 90 - 95 PSI with the trigger pulled.

                        One last thought is that the blue hoses got crushed at some time. That would restrict the flow and it may be hard to see it, looking at the jacket. Try getting another 25 foot hose like your black one and connect them together. Then try the die grinder again.
                        Last edited by Woussko; 06-09-2007, 02:16 AM.

                        Comment


                        • #13
                          Re: CFM/PSI VS length of air hose, question

                          I know by now you hate the idea of more $$$, but please try this and post the results. I bet you'll be howling once you try it.

                          Get another 25 foot air hose just like your black one. Then connect them together so you have 50 feet. Next try your die grinder again like you have done.

                          I have a feeling you'll soon be selling all of your blue hose at a yard sale to help pay for more new better hoses.

                          I just connected up all of my good 3/8 hoses and have 75 feet now. I ran my die grinder and let it run for 2 minutes non stop. I then tried it with just one hose. This was with my pressure regulator set to 90 with grinder running. The only change was adding the additional hoses. In my case I have 3 that are 25 feet. I heard only a little drop in speed. With regulator set the 95 and all hoses in use it ran like a champ. Mine needs 4.5 CFM at 90 PSI at the inlet.

                          Time for Woussko's little ball test on the blue hoses.

                          With the hoses held out straight you might see if you can push (should be easy) a 5/16 steel rod a foot or more into the end (try both ends of the blue hoses. Then try it with the black hose. You should be able to find a 5/16 by 2 or 3 foot steel rod at a good hardware store. A 3/8 would be a tight fit if it would even go in through the fitting. You could use a 5/16 hardwood dowel that's say 2 feet or longer.

                          Comment


                          • #14
                            Re: CFM/PSI VS length of air hose, question

                            I think the problem is in the "blue hose". Grinding corrosion on acft, we used die-grinders with rotary files for a lot of the work, which was continuous. We used up to 150 feet of 3/8 hose and did not lose pressure (1/4" 25' long was the max. Longer would not hack it, as it would not carry enough volume). We also used the 3/8 hoses for our spray guns, which took 8.5 cfm+, and they also were under continuous use. We were using 1/4" id fittings. (We did have to go to the 5/16 ID fittings when we changed to HVLP spray guns).
                            One tip: when you are not using the hoses, make sure the ends are covered (I plug the male QD into the female on removable hoses). A lot of the 6 and 8-legged critters love to build nest and webs inside of air hose. Mud Dauber wasps love the little hollow in the female QD as well.

                            Go
                            Practicing at practical wood working

                            Comment


                            • #15
                              Re: CFM/PSI VS length of air hose, question

                              UNCLE!

                              ok, I will have to agree with the masses regarding the "blue air hose"

                              I'm sure many of you use this stuff and there are thousands of feet in use!

                              On the other hand, Harbor Freight has a sale right now on 1/2" air hose. I'm not sure about its color. The hose is either orange or black. I know they all have a pressure rating of 200PSI. I also know the different colors are not just to identify your hose. I think either will work in my case.

                              The orange is 25 feet item number 3107-3vga and it's $8.99

                              They also have a 3/8" black rubber air hose like what I'm now using successfully. item number 42185-6vga 50 feet for $12.99

                              So I'm not sure which way I'll go..perhaps I'll see what new comments follow this post.

                              Cactus Man

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