SCFM vs. CFM – What is SCFM in Air Compressor?
SCFM and CFM are important units and references for measuring the volume of air compressors according to Charles’ law (also known as the law of volumes).
Air compressors convert power (electricity to pump air) into potential energy in the form of compressed air and kinetic energy of the exhaust gas or air, providing an important energy supply for many industries. So what is the difference between SCFM and CFM for air compressors?
What is SCFM vs CFM in air compressor?
What does SCFM mean?
SCFM (Standard Cubic Feet per Minute) is a measure unit for the amount of air that an air compressor can deliver per minute under standard temperature and pressure conditions.
The standard ambient temperature range for calculating SCFM flow rate is 60ยฐF (15ยฐC) to 68ยฐF(20ยฐC), sea level pressure is 14.7 psi (760 mmHg), and relative humidity is 36%.
Since SCFM is the volume of airflow measured under standard conditions, it is an ideal value and is always higher than the CFM value of an air compressor.
What does CFM mean?
In contrast to SCFM, CFM (Cubic Feet per Minute) refers to the unit of measurement for the amount of air that an air compressor can deliver per minute under actual temperature and pressure conditions.
Because the temperature and pressure and other conditions for calculating the CFM value are obtained in a realistic environment, it can also be called ACFM (actual cubic feet per minute), so it may be lower than the SCFM value of the air compressor most of the time. (Extended learning: How to Convert CFM to m3/hr?)
What is the difference between SCFM and CFM for air compressors?
SCFM is the only way to compare air volume between similar air compressors because in SCFM, all measurements are calculated based on a set of standard conditions. Operating conditions can vary depending on where the air compressor airflow is measured. But CFM can be trickier.
It is affected by atmospheric conditions and the surrounding environment, which means that the CFM value of an air compressor can vary from location to location.
For example, the same air compressor may have a lower compressed air output on the top of a mountain than it does at sea level. So it is important to note that if your air compressor is operating under conditions that do not match standard conditions, your actual CFM output may not match the SCFM.
Under standard conditions, there is theoretically no efficiency loss and SCFM equals CFM. But when the actual operating conditions of the air compressor are different from standard conditions, you may need to consider whether your air compressor can still provide enough air for your tools and equipment to keep manufacturing running properly on the job site.
Under any of the following conditions, the air density will be relatively reduced, and the actual CFM requirements of the air compressor for pneumatic equipment may be higher:
- When the ambient air pressure is low (at high altitude)
- When the ambient humidity is high (when the rainy season comes)
- When the ambient temperature is high (when the summer comes)
In other words, as the environmental conditions at the work site deviate from standard conditions, your air compressor needs to work harder in exchange for enough actual CFM to provide sufficient power for pneumatic equipment.
Or you may need to select or replace an air compressor with a larger power and higher SCFM rating for your production line to generate enough actual CFM to enable pneumatic equipment and pneumatic tools to operate normally at the work site.
How to calculate the CFM for air compressor?
Step 1. Determine the volume of your air compressor tank. The manufacturer should clearly mark it on the tank itself.
Step 2. Divide the tank volume by 9 to get the tank volume in cubic meters.
Step 3. Release the air from the compressor.
Step 4. Begin filling the compressor with air. Record the time it takes to fill the tank, keeping a close eye on the pressure gauge on the compressor. You will need to record the psi at two different times during the filling process: once when the compressor starts and once when it stops.
Step 5. When you start the compressor, record the psi shown on the compressor tank gauge and subtract it from the gauge when you stopped the compressor. For example, if the compressor starts at 75 psi and stops at 100 psi, the pressure difference is 25 psi.
Step 6. Divide the difference between the two recorded psi by 14.7. The result will be in atm (atmospheric pressure), which is the amount of pressure your compressor tank increased during the fill cycle.
Step 7. Take the tank volume expressed in cubic meters (from step 2) and multiply it by the pressure calculated based on atmospheric pressure during the tank fill cycle (from step 2). Divide it by the time it takes your tank to fill (from step 2) and you have the cubic capacity of your compressor.
Step 8. Finally, convert this number to minutes by multiplying the result by 60 to get the CFM of your air compressor.
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What does SCFM mean for air compressors?
1. Knowing SCFM is very useful when working with air compressors. Once you understand how to convert the units to SCFM, you can easily convert SCFM to psi and vice versa.
2. Air compressors are often rated lower in CFM than in SCFM because most manufacturers measure CFM at air pressures less than or equal to 90 PSI. To properly compare different compressors, it is best to use SCFM ratings rather than CFM ratings because in SCFM, all measurements are calculated based on a set of standard conditions.
If you purchase an air compressor in an area where the environmental conditions are different from standard conditions, you may find that your air compressor may not be able to meet your air consumption needs.
What do the numbers on air compressors mean?
There are other numbers and ratings that reflect different capabilities of air compressors, but their names can be confusing. How do we know what they mean?
PSI: Pounds per square inch. This is the unit of pressure that an air compressor delivers. Most air tools require 40 or 90 psi to do their job.
HP (horsepower): Horsepower is a measure of the power of the motor or engine that drives the compressor. While horsepower is the rating most consumers are most familiar with, it is also the most misleading. Generally speaking, the higher the horsepower, the greater the CFM output of the air compressor.
Gallons: This is a unit of measurement for the size of the air tank, which is an important consideration when using tools that require a continuous air flow, such as spray guns or sanders. The larger the air tank, the longer the air tool can operate at its rated pressure before it must stop to rebuild the tank pressure.
Duty cycle: Many air compressors are designed to run in cycles, most of which occur on fixed-frequency air compressors. The ratio of their on-time to off-time is called the duty cycle. All compressors have a specific rated duty cycle, such as 50/50 or 75/25.
An air compressor with a 50/50 duty cycle runs 50% of the total working time, and the machine will inevitably be shut down 50% of the time to ensure that the air compressor does not damage or stop working due to problems such as high temperature. An air compressor with a 75/25 duty cycle runs 75% of the total working time and is shut down about 25% of the time.
SCFM vs. CFM FAQ
- What is the difference between air compressor pressure, CFM, and SCFM?
Air compressor pressure refers to the force with which the compressor outputs compressed air. CFM (cubic feet per minute) is a unit of measurement for the amount of air that a compressor can deliver per minute. SCFM (standard cubic feet per minute) takes into account temperature, humidity, and atmospheric pressure to provide a standardized measurement of the amount of air delivered.
- What is the relationship between CFM and SCFM?
Both CFM and SCFM are units of measurement for the amount of air delivered by air compressors. However, SCFM is generally a standard value measured by air compressor manufacturers under standard conditions, while CFM represents the amount of compressed air delivered by the air compressor under actual working conditions. Under standard conditions, a compressor with a higher SCFM rating will deliver more air than a compressor with the same CFM rating.
- How do air compressor pressure and CFM affect the air tools used?
Air compressor pressure and CFM affect the performance of air tools in different ways. Higher pressure can provide more power to the tools that need it, while higher CFM can allow air tools to be used longer. It is important to understand that pressure vs. CFM helps in selecting an air compressor specification that matches the requirements of the specific air tool being used.
- Can the pressure and CFM of an air compressor be adjusted?
Yes, many air compressors are able to adjust the pressure and CFM to meet the specific needs of the user. This can be achieved through the use of regulators and other control devices.
- What does 6SCFM 90 PSI mean?
It means that under standard conditions and the air compressor pressure is 90psi, the compressed air delivery is 2.6 cubic feet per minute.
- What is a good CFM at 90 psi?
An air compressor with a power of 10 horsepower or more should produce about 3 or 4 cubic feet of compressed air per minute at 90 PSI.
- How do I choose CFM for my compressor?
For best results, consider the air tool you are using with the highest SCFMrating and purchase an air compressor with a compressed air output greater than that rating. For example, if you plan to use an impact wrench that requires 5.8 SCFM, you will need to purchase an air compressor with an output of at least 6 CFM. If you plan to provide compressed air to multiple tools at the same time, add up the SCFM requirements for all of your air tools.
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