What is SCFM in Air Compressors – SCFM vs. CFM Explained
Air compressors are practical applications of Charles’ Law. This process turns power (electric power that pumps air) into potential energy in the form of pressurized air and kinetic energy to expel the gas or air. Many industries require air compressors to carry out various processes in their plants.
What is SCFM in Air Compressors?
Standard Cubic Feet per Minute (SCFM) is the flow rate of a gas or air through a compressor at standard temperature and pressure conditions. The standard temperature for calculating SCFM flow rate ranges from 60°F to 68°F, at a pressure of 14.7 psi and relative humidity of 36%. Since SCFM measures volumetric airflow at standard conditions, it will always be higher than the CFM value for an air compressor.
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.
How to Calculate the CFM of an Air Compressor
You can find an air compressor’s CFM value using the following simple steps:
- Find the volume of the air compressor tank in gallons. Most manufacturers specify this on the product.
- Divide the value by 7.48. This value will be your tank volume.
- Release air from the compressor.
- Refill the air compressor with air, recording the time it takes to refill the tank while watching the gauge. Record the PSI (pounds per square inch) when the compressor kicks in and when it kicks out. You may call the first PSI measurement PSI 1 and PSI 2.
- Subtract PSI 1 from PSI 2 and divide the difference by 14.7. This value gives you the pressure in the compressor tank during refill (expressed in atmospheric pressure).
- Divide the tank volume you obtained earlier and multiply it with the pressure of the compressor tank during refill.
- Convert this value to minutes by dividing it by the number of seconds it took the compressor to pump that amount of air.
- Multiply the value by 60 to get the CFM of your air compressor.
Knowledge of SCFM is quite useful when working with air compressors. Once you understand how to convert units into SCFM, you can easily convert SCFM to psi and vice versa.
Additional Air Compressor Ratings to Consider
After identifying the SCFM or CFM values, there are some other essential ratings to consider when choosing an air compressor, such as:
PSI (Pounds Per Square Inch) indicates the amount of pressure forced through a compressor per square inch of area. Since pressure is inversely proportional to area, it increases as area decreases and vice versa. Applications such as cutting, sealing, painting, sanding, and pounding require high PSI. Factory tools having PSI ratings from 40-90 may be enough to carry out most of these processes.
Horsepower measures the motor efficiency of an air compressor at a given CFM and PSI. It describes the working capacity of the machine and is one of the most recognizable properties to look out for before completing a purchase. Depending on your application and for the optimum results, you can choose an air compressor rated sufficiently higher than your current CFM.
Air compressors perform rigorous amounts of work, so for efficient usage, they operate on an on/off cycle, also called a duty cycle. During its off-cycle, the compressor is not necessarily turned off but isn’t actively pressurizing any volume of air. Duty cycles are often specified as percentages, meaning that if a compressor has a duty cycle of 60/40, the compressor works for 60% of the time and is idled for the remaining 40%.
Gallons refer to the storage capacity of an air compressor’s tank. Usually, the larger the gallon size of the compressor, the longer the air compressor can perform. This consideration is crucial for projects that require a continuous stream of airflow.
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