Compressors and air tools - CFM vs SCFM

[California]

I've been curious about the difference between air CFM vs SCFM, ever since I bought a Harbor Freight compressor some 15 years ago, rated 5.1 CFM, that couldn't keep up with a HF die grinder rated to need 4.7 CFM.

Oh well that's just HF's marketing.

But recently looking at something from HF:

"Air Consumption 21 SCFM (3.1 CFM @ 90 PSI)"

Huh? What does all that mean?

 

[mrmikey]

Google is your friend\.
Here's the link to the complete article: What is SCFM in Air Compressors – SCFM vs. CFM Explained

What’s the Difference Between SCFM vs. CFM?​

SCFM and CFM are both essential values that indicate the airflow rate in a compressor. SCFM measures this value based on ‘ideal’ temperature and pressure conditions, while CFM measures the ‘actual’ air flow rate. CFM is the recognized value for measuring the airflow rate in the United States.

CFM (Cubic feet per minute) measures the volume of air or gas that flows through a compressor in one minute. Sometimes, the CFM rating of an air compressor a manufacturer provides may have a margin of error. Therefore, the best way to determine your air compressor’s most accurate CFM value is to test it in your facility.

 

[Roadworthy]

There is a conversion factor to get from one to the other so one may be larger or smaller than the other. SCFM Vs CFM Explained: SCFM To CFM Calculator + Chart

 

[WranglerX]

According ChatGPT

SCFM (Standard Cubic Feet per Minute) and CFM (Cubic Feet per Minute) are both units of measurement used to describe the flow rate of a gas, usually air, through a system. The main difference between them lies in the conditions under which the measurement is taken.

1. SCFM (Standard Cubic Feet per Minute): SCFM is measured at standard conditions of temperature and pressure (usually 68°F or 20°C and 14.7 psi or 1 atm). SCFM takes into account the fact that air density changes with temperature and pressure. Therefore, SCFM provides a standardized measurement that allows for comparisons between different systems regardless of the conditions in which they operate. SCFM is often used when precise calculations and comparisons are needed, such as in HVAC systems or industrial processes.
2. CFM (Cubic Feet per Minute): CFM, on the other hand, does not account for variations in temperature and pressure. It simply measures the volume of air flowing through a system in a minute without specifying any particular conditions. CFM is a more general measurement and is often used in everyday contexts where standardization is not critical, such as in household fans or portable air compressors.

In summary, while both SCFM and CFM measure airflow rate, SCFM is a standardized measurement that accounts for variations in temperature and pressure, whereas CFM is a more general measurement that does not consider such variations.

 

[Chuck Fuller]

According ChatGPT

SCFM (Standard Cubic Feet per Minute) and CFM (Cubic Feet per Minute) are both units of measurement used to describe the flow rate of a gas, usually air, through a system. The main difference between them lies in the conditions under which the measurement is taken.

1. SCFM (Standard Cubic Feet per Minute): SCFM is measured at standard conditions of temperature and pressure (usually 68°F or 20°C and 14.7 psi or 1 atm). SCFM takes into account the fact that air density changes with temperature and pressure. Therefore, SCFM provides a standardized measurement that allows for comparisons between different systems regardless of the conditions in which they operate. SCFM is often used when precise calculations and comparisons are needed, such as in HVAC systems or industrial processes.
2. CFM (Cubic Feet per Minute): CFM, on the other hand, does not account for variations in temperature and pressure. It simply measures the volume of air flowing through a system in a minute without specifying any particular conditions. CFM is a more general measurement and is often used in everyday contexts where standardization is not critical, such as in household fans or portable air compressors.

In summary, while both SCFM and CFM measure airflow rate, SCFM is a standardized measurement that accounts for variations in temperature and pressure, whereas CFM is a more general measurement that does not consider such variations.

I've been curious about the difference between air CFM vs SCFM, ever since I bought a Harbor Freight compressor some 15 years ago, rated 5.1 CFM, that couldn't keep up with a HF die grinder rated to need 4.7 CFM.

Oh well that's just HF's marketing.

But recently looking at something from HF:

"Air Consumption 21 SCFM (3.1 CFM @ 90 PSI)"

Huh? What does all that mean?

This is a fair question. I get asked this all of the time, I work for an air compressor rental company.

The simple way to explain this that CFM is a measurement of the air entering the compressor at atmospheric pressure. Your HF compressor rated at 5.1.CFM is a measurement of the air entering the compressor. This can be effected by relative humidity, elevation above sea level, temperature (hotter, thinner air takes more to compress to the same volume).

SCFM is a measurement of the volume of air taken at a given pressure. We never get something for nothing. The 5.1 CFM is a constant volume coming into the compressor. However, the compressor's job is to…… compress the air and in doing so, the volume of the air shrinks in relation to the volume of the air entering the compressor. The measurement of SCFM is calculated or stated at a given pressure. This is why your air tool consumes more air than that compressor makes at 90 PSI. As the system goes up in pressure, the volume of air is less.
I hope this helps to answer your question.

 

[WranglerX]

According to Gemini AI...

Where is CFM of a air compressor measured?

CFM (Cubic Feet per Minute) of an air compressor is typically measured at the outlet port of the compressor, where the compressed air exits the machine. This measurement indicates the volume of air delivered by the compressor per minute at a specific pressure.


It's important to note that CFM ratings are often provided at different pressure levels. For example, a compressor might be rated at 4 CFM @ 90 PSI and 6 CFM @ 40 PSI. This means the compressor can deliver 4 cubic feet of air per minute at a pressure of 90 pounds per square inch, and 6 cubic feet per minute at 40 PSI.
To accurately measure CFM, you would need a flow meter specifically designed for air compressors. However, manufacturers typically provide CFM ratings for their products, which can be used to select the appropriate compressor for your needs.
https://fluidairedynamics.com/pages... in Compressed,coming out of your compressor.

 

[nyone]

I have found with most air tools PsI really matters. My kobalt 60gal shuts off at 155psi. Others 135psi. A few extra psi really wake up air tools.

 

[Kyle_in_Tex]

With more and more cordless tools, I find my compressor sitting a lot more.

 

[WranglerX]

There's a lot of Google experts on this site.

Knowledge is power, when was last time you cracked open an encyclopedia..

 

[sd455dan]

If you go off the CFM at 90 or 175PSI at least you are sure of what the compressor is putting out where the pump and motor are pushing against what air is already under pressure. I would not buy a compressor that did not list CFM @ at least 90 PSI.