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  • Scfm To Cfm

    Should someone could help me what´s the difference between SCFM and CFM.

    Is there any conversion factor between both?

    Thanks

  • #2
    Re: Scfm To Cfm

    The S stands for Standard, and means it was measured at standard temperature and pressure.

    The volume of liquids and gases change with temperature, so the flow rate at one temperature will be different than the flow rate at another temperature.

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    • #3
      Re: Scfm To Cfm

      How do you convert scfm to cfm if I know temp and pressure?

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      • #4
        Re: Scfm To Cfm

        It is hard to nail down cfm in conversions as i am finding out. You can google "convert Scfm to cfm" and you will get several sites. One i found had an online calculator converting SCFM to ACFM (Actual Cubic Feet per Minute) but I am not sure if ACFM = cfm. I am trying to size a compressor to my tools and this is very hard because my tools require 3.4 cfm at 90 psi and compressors are rated at SCFM. I checked out a tool and it required 18.6 SCFM and 3.4 cfm at 90 psi. Go figure.

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        • #5
          Re: Scfm To Cfm

          Originally posted by Unregistered
          It is hard to nail down cfm in conversions as i am finding out. You can google "convert Scfm to cfm" and you will get several sites. One i found had an online calculator converting SCFM to ACFM (Actual Cubic Feet per Minute) but I am not sure if ACFM = cfm. I am trying to size a compressor to my tools and this is very hard because my tools require 3.4 cfm at 90 psi and compressors are rated at SCFM. I checked out a tool and it required 18.6 SCFM and 3.4 cfm at 90 psi. Go figure.
          Compressors are always rated in terms of free air "inhaled" at the inlet, whether or not those conditions are "standard," 101.325 kPa, 20 °C, 36% RH. If conditions ar non-standard, a correction is needed. On the ouput side, only pressure is measured. So tools are rated at pressure needed, and free air delivered (or released after expansion.

          If temperature is much higher, altitude much higher, your compressor will appear to have lower capacity.

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          • #6
            Re: Scfm To Cfm

            Hi all..

            for oil free screw air compressor in a tropical condition using 10 bar compressor, 35C, I usualy just multiply factor to 1.2 for scfm to cfm
            exp: 100 scfm is 120 cfm, but thats all work..hope it helps

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            • #7
              Re: Scfm To Cfm

              Originally posted by Unregistered View Post
              It is hard to nail down cfm in conversions as i am finding out. You can google "convert Scfm to cfm" and you will get several sites. One i found had an online calculator converting SCFM to ACFM (Actual Cubic Feet per Minute) but I am not sure if ACFM = cfm. I am trying to size a compressor to my tools and this is very hard because my tools require 3.4 cfm at 90 psi and compressors are rated at SCFM. I checked out a tool and it required 18.6 SCFM and 3.4 cfm at 90 psi. Go figure.
              relationship is Q1 = Q2(p2/p1)(T1/T2), Q1 is scfm of compressor, Q2 is cfm of tools/system, p2 is operating pressure of tools/system in absolute (psig + 14.7), p1 is inlet pressure to compressor (14.7 psia), T1 is temperature of air at inlet in rankine (fahrenheit + 460), T2 is temperature of air at tool/system in rankine. your case if temperature is constant:T1 = T2
              Q1=3.4(90+14.7/14.7) = 24.2 scfm

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              • #8
                Re: Scfm To Cfm

                scfm refers to cfm under standard conditions.

                Using P1*V1/T1 = P2*V2/T2 should work. The pressure must be in absolute.

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                • #9
                  Scfm To Cfm

                  Does anyone know how to figure what CFM carb you need W/ a motor you dont know how many HP its going to turn out? Its a 351w and if anyone knows how, I can tell you whats in it to help determin it. thanks

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                  • #10
                    Re: Scfm To Cfm

                    Originally posted by trereamurry View Post
                    Does anyone know how to figure what CFM carb you need W/ a motor you dont know how many HP its going to turn out? Its a 351w and if anyone knows how, I can tell you whats in it to help determin it. thanks
                    Well, you'd like to minimize the pressure drop across the carb and intake valves. To tremendously oversimplify, at 6000 rpm, you are ingesting the displacement 3000 times per minute.

                    351 in³ x 3000 x 1 ft³/1728 in³ = 609 ft³/min
                    You'd like to minimize the pressure drop at wide open throttle. Whatever pressure drop you have vs 14.7 psi absolute atmospheric pressure will diminish air mass ingested and power.

                    At the other end, can air flow be sufficiently restricted to control unloaded idle? In high performance, you may want ganged carbs that open progressively.

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                    • #11
                      Re: Scfm To Cfm

                      Best not try too many times to get 6000rpm out of a 351 windsor or the big bang theory will be experianced. That engine will make max hp and torque about 4000-4500 rpm and if its got a 600cfm or scfm 4 bbl, you should look towards 300hp at the wheels, maybe.

                      Thats why you use a real chassis dyno. Please see tracklab . biz

                      Ron Hagen

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                      • #12
                        Scfm To Cfm

                        Realmente estan desenfoncados la cuestion es la siguiente cuando hablamos de SCFM: es cuando el productor diseño una maquina a unas condiciones standard es decir a una presion de 14,7psi, temperatura 60°f Y una humedad relativa de 0%, cuando hablamos ACFM es la condicion que entrega actual en el sitio, es decir si quiero un compresor en canada, debo pasar los sfcm del diseñador a acfm a mis condiciones de ambiente, y asi puedo seleccionar bien el compresor, es por eso que debemos deratear nuestro sistema antes de seleccionar un equipo.

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                        • #13
                          Re: Scfm To Cfm

                          How to convert scfm to cfm
                          Originally posted by Unregistered View Post
                          How do you convert scfm to cfm if I know temp and pressure?

                          Comment


                          • #14
                            Re: Scfm To Cfm

                            First you need to know the base pressure and temperature. For natural gas in the united states, the base pressure is typically 14.73 psia and the base temperature is 60 °F. You also need to know your local atmposheric pressure which decreases with elevation. At an elevation of 1000' above sea level, the atmospheric pressure is approxmately 14.2 psia. The last parameter you need to know is the compressibility of the gas. For low pressures (<150 psig) and temperatures in the range of 30-100 °F, the compressibility will be close to 1.0. Outside of that range, you need an equation of state calculator to determine compressibility. The formula to convert standard cubic feet per minute (scfm) to actual cubic feet per minute (cfm) is:

                            cfm = scfm * compressibility * PressureBase / (GasPressure + LocalAtmosphericPressure) * (GasTemperature + 459.67) / (TemperatureBase + 459.67)

                            where all of the pressures are in the same units (psi) and the temperatures are in °F.

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                            • #15
                              Re: cfm to scfm

                              i have a comppressor that puts out 14.7 cfm max, what would be the scfm number?

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