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#1
07-31-2006, 09:27 AM
 Unregistered Guest Posts: n/a
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
07-31-2006, 11:49 AM
 Robert Fogt Administrator Join Date: Dec 2005 Location: Seattle, WA Posts: 3,414 Rep Power: 12
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.
#3
05-21-2008, 07:16 AM
 Unregistered Guest Posts: n/a
Re: Scfm To Cfm

How do you convert scfm to cfm if I know temp and pressure?
#4
08-02-2008, 10:42 AM
 Unregistered Guest Posts: n/a
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.
#5
08-02-2008, 03:38 PM
 JohnS Double Ultimate Supreme Member Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,217 Rep Power: 18
Re: Scfm To Cfm

Quote:
 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.
#6
02-12-2009, 01:00 AM
 rotating engr Guest Posts: n/a
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
#7
12-08-2009, 04:57 PM
 Unregistered Guest Posts: n/a
Re: Scfm To Cfm

Quote:
 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.
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
#8
12-22-2009, 10:54 AM
 Unregistered Guest Posts: n/a
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.
#9
12-24-2009, 08:13 AM
 trereamurry Guest Posts: n/a
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
#10
12-24-2009, 12:15 PM
 JohnS Double Ultimate Supreme Member Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,217 Rep Power: 18
Re: Scfm To Cfm

Quote:
 Originally Posted by trereamurry 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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