Contents
Rated Capacity
Rated capacity is the volume of air a compressor delivers at a rated pressure in a set amount of time, measured in cubic feet per minute (CFM). CFM directly relates to the compressor’s ability to power air tools and equipment.
Knowing the required CFM for your application ensures reliable equipment performance, streamlines future scaling, prevents costly production bottlenecks, minimizes energy costs and avoids undersizing and oversizing. At Quincy Compressor, we stock diverse units to meet different needs. Our network of professional and knowledgeable air experts will help you identify the correct air compressor capacity to match your air demands.
What Is Rated Capacity in Different Conditions?
Several terms define air compressor capacity at different temperatures, pressures and humidities:
- Standard cubic feet per minute (SCFM): This is the airflow measured under a standardized set of specific, ideal conditions, allowing for a fair comparison between different compressor models.
- Actual cubic feet per minute (ACFM): This CFM rating measures the actual volume of air a compressor delivers under real-world, site-specific environmental conditions such as altitude, temperature and humidity. Because these factors impact air density, a compressor’s ACFM differs from the SCFM.
FAQs
The CFM rating helps you determine tool compatibility since each pneumatic tool requires a different CFM to operate effectively. It also allows you to ensure work efficiency and that a compressor can deliver sufficient air to multiple tools simultaneously.
An air compressor’s CFM rating is always tied to the specific pressure measured in pounds per square inch (PSI). The CFM is usually given at a certain PSI. For example, 18 CFM at 90 PSI. Their inverse relationship means that when the PSI rises, the CFM drops, and vice versa.
The compressor flow rate is a general term referring to the volume of air a compressor delivers over time. This flow rate changes depending on operating conditions and is used to compare compressors when shopping.
In contrast, the rated capacity is the official flow rate the manufacturer specifies, measured under precise set conditions. It is used to measure and manage the compressor’s performance at full load and at a specific discharge pressure.
SCFM is the typical unit for rated capacity, while compressor flow rate is measured as SCFM or ACFM.
Determine the air consumption of all your tools and equipment you will run simultaneously, and calculate the sum of their CFM ratings to determine the peak air demand. Next, add a buffer to account for leaks, system health and future requirements.
For instance, the sum of a sander (12 CFM) and a grinder (8 CFM) running at the same time is 20 CFM. This is your peak air demand.
No, the tank size does not determine a compressor’s rated capacity, but it affects how long it will take before the compressor needs to cycle again.
Higher altitudes and temperatures result in less dense air, which means the compressor must work harder to deliver the same amount of air, reducing its effective capacity.
Horsepower (hp) indicates the motor’s power, while CFM and PSI represent the actual work a compressor accomplishes. To find the right compressor that will meet the demands of your tools and applications, assess the CFM and PSI ratings, as they reflect the asset’s performance.
Manufacturers generally use standards like ISO 1217 to test displacement compressors to ensure comparable and consistent ratings. Free air delivery (FAD) is the standardized measure defined by ISO 1217.
FAD is the actual volume of delivered air, calculated as if it were at the same temperature and pressure as the air at the compressor’s inlet. Some also use third-party testing, such as that from the Compressed Air and Gas Institute (CAGI).
Additional Resources
At Quincy, our goal is to support you and true support means connecting you to resources that best fit your needs.
