How to Calculate SCFM for Compressed Air Sizing

Written by brian baer
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How to Calculate SCFM for Compressed Air Sizing
SCFM is a unit of volumetric flow needed for compressor system design. (Jupiterimages/Photos.com/Getty Images)

SCFM stands for standard cubic feet per minute and is a standard volumetric flow rate used in sizing compressible fluid pipelines such as in compressor air systems. For all gas systems, the velocity of the flow and the flow rate are related to the pipeline's internal diameter. If two of the three variables are known, then the third variable is easily calculated.

Skill level:
Moderate

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Instructions

  1. 1

    Determine the compressed air system pipe size and cross sectional area. Typical industrial compressed air systems use a 6-inch diameter pipe on the discharge of the compressor. The calculation of cross sectional area is performed using A = (d/12)^2 x 3.1416 / 4, where A is the cross sectional area in square feet and d is the diameter of the pipe in inches. If the diameter of the pipe is 6 inches, then the area is 0.196 square feet.

  2. 2

    Determine the optimum velocity of the compressed air in the pipe. Compressible fluids, such as air, should not exceed a 90 to 100 feet per second (fps) velocity. Assume 90 fps.

  3. 3

    Determine the compressed air pipeline volumetric flow. This is the velocity in feet per second (converted to feet per minute by multiplying by 60) multiplied by the cross sectional area of the pipe. 90 feet per second is 5,400 feet per minute. The SCFM flow rate is then 5,400 x 0.196, or 1,058 standard cubic feet per minute.

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