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Capacity
Capacity is the amount that something can produce. In the context of air compressors, this term refers to the amount of airflow the system delivers under specified conditions. It is usually expressed in cubic feet per minute (cfm) or liters per second (l/s).
When choosing an industrial air compressor, you must consider capacity because this value determines whether your equipment will function properly. Adequate sizing ensures operational efficiency, prevents equipment wear and avoids unnecessary energy spending. Sizing a compressor too small or too large could harm your operations.
FAQs
Depending on the application, you can measure air compressor capacity using various meters and gauges. Rotary screw compressors have a capacity gauge, which shows the amount of airflow a compressor delivers at a given time as a percentage of the rated capacity. Compressors may also use a flow meter installed in the compressed air line. It measures flow in cfm as it flows through the pipe.
You can determine air compressor capacity using tank pump-up time in the following formula:
CFM = (V × ∆P) ÷ (T × 14.7)
Here’s what each part means:
- CFM: The air compressor cfm, or output capacity in cubic feet per minute
- V: The air receiver (tank) volume in cubic feet
- ∆P: The increase in pressure during the pump-up time, measured in pounds per square inch (psi)
- T: The time in seconds it takes to fill the tank from the starting pressure to the ending pressure
- 14.7: The atmospheric pressure at sea level, measured in psi
Capacity is one of the significant values you should consider when sizing an air compressor for your operation. You can determine the air compressor capacity you need by considering the pneumatic tools you must run simultaneously. These tools typically have a manufacturer’s recommended capacity in cfm. Add the recommended capacity values to find the approximate capacity needed.
After adding these values, create an additional safety margin to maintain effective operations. You may also consider future expansion to confirm that a compressor will adapt to changes as you grow. The final value you determine is your required capacity.
Rated capacity is the airflow volume rate at a particular pressure measured at a specific point. Actual capacity is the quantity of compressed gas delivered at the rated speed under rated conditions, otherwise known as free air delivered (FAD).
The rated capacity is the value displayed by the manufacturer. It represents the theoretical maximum air volume that the system delivers under ideal conditions. Actual capacity is the air volume delivered under real-world conditions, making it a more effective metric for ensuring a compressor meets your needs.
Besides cfm for air compressors, you may come across these two other acronyms as you research air compressor capacity. Actual cubic feet per minute (ACFM) is the air mass flow that a compressor produces during real-life conditions. Surrounding environments and atmospheric conditions often impact this value.
Standard cubic feet per minute (SCFM) measures air mass flow according to a specific set of standardized conditions determined by the American Society of Mechanical Engineers (ASME). These standardized conditions include:
- Atmospheric pressure at sea level (14.7 psi)
- Relative humidity of 36%
- Ambient temperature of 68°F
ACFM measures the actual capacity that an air compressor delivers, while SCFM measures the rated capacity. You can use the SCFM for each unit you need to run to calculate the required inlet ACFM.
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