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Cubic Feet Per Minute (cfm)
Cubic feet per minute is a unit of measurement that represents volumetric airflow rate. Often abbreviated as cfm, this metric tells you the volume of air moved in one minute. Cfm is frequently described under standard conditions (scfm) for comparison purposes, but actual cfm (acfm) can vary based on environmental factors.
In air compression systems, the airflow rate measures the volume of air a machine can produce per minute. Cfm is one of the most important specifications when choosing a compressed air system. It can help determine whether an air compressor can adequately power your air-powered equipment or pneumatic tools.
The cfm rating indicates the device’s maximum airflow output. The higher the rating, the more air delivered. If your tools’ cfm demand exceeds the compressor’s cfm rating, the compressor may struggle to maintain adequate pressure, leading to interruptions in work.
FAQs
There are three important acronyms when measuring an air compressor’s airflow — cfm, scfm and acfm:
- Cfm (cubic feet per minute): Cfm is a general measurement of an air compressor’s flow rate.
- Scfm (standard cubic feet per minute): Scfm refers to a compressor’s airflow at standard temperature and pressure conditions, which showcases its capabilities under ideal conditions.
- Acfm (actual cubic feet per minute): Want to know a compressor’s real-world airflow? Acfm is a more precise measurement of airflow that considers specific environmental conditions.
Assessing compressor airflow is essential for determining whether you have enough to power all your tools and processes. A cfm calculation formula lets you determine the cfm output of an air compressor as follows:
- CFM = (V × ∆P) ÷ (T × 14.7)
Here’s what each of these variables stands for:
- V: Volume, typically listed on the air compressor tank
- ∆P: Change in pressure in psi (pounds per square inch), the difference between the ending pressure and starting pressure
- T: Time it takes for the air compressor to fill its tank in seconds, from desired starting pressure to ending pressure
- 14.7: The atmospheric pressure at sea level in psi
Cubic feet per minute and cubic meters per hour (m3/h) both measure the same thing — the volumetric flow rate of air. The difference is the units they use to measure volume and time:
- Cubic feet per minute measures volume in cubic feet and time in minutes.
- Cubic meters per hour measure volume in cubic meters and time in hours.
You might need to convert cfm to m3/h for several reasons:
- Comparing U.S. compressors using cfm to devices from other countries that use m3/h
- Communicating with international partners or suppliers to avoid misunderstandings
- Ensuring compliance with regulations or codes that specify m3/h when you’re used to working in cfm
There are two main specifications to consider when choosing an air compressor — cfm and psi. As we’ve discussed, cfm measures the volume of air flowing over time. Psi measures the pressure of the air. In air compression systems, pressure delivers the force. The air compressor must provide the right amount of pressure to complete specific applications.
Cfm and psi are inversely related. Increasing psi reduces the available cfm and vice versa. Squeezing air into a smaller space, thus increasing the pressure, requires more energy. This reduces the amount of air that can be moved in a given time — the airflow.
You must find a good balance between psi and cfm for your specific application to get the most from your air compressor.
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