Hitachi Air Technology Group

Please see for Air Flow Definition

SCFM - Standard Cubic Feet per Minute

It is common to rate the compressed air consumption in Standard Cubic Feet per Minute - SCFM.

The SCFM - Standard Cubic Feet per Minute - determines the weight of air to fixed or "Standard" conditions. There are several definitions of SCFM. The most common used in the United States is with "sea-level" properties:

• 14.696 Pounds per Square Inch (psia)
• 60 Degrees Fahrenheit (^oF) (520^oR)
• 0% Relative Humidity (RH).

Europeans normally use one ata and 0^oC as SCFM.

ACFM - Actual Cubic Feet per Minute

Unfortunate real life "actual conditions" are seldom "standard conditions". Actual air volume flow is often termed ACFM - Actual Cubic Feet per Minute.

Actual Cubic Feet per Minute - ACFM, depends on the

• pressure
• temperature
• humidity

of the actual air.

The conversion from SCFM to ACFM can be expressed as

ACFM = SCFM [P_std / (P_act - P_sat Φ)](T_act / T_std) (1)

where

• ACFM = Actual Cubic Feet per Minute
• SCFM = Standard Cubic Feet per Minute
• P_std = Standard absolute air pressure (psia)
• P_act = Actual absolute barometric pressure (psia)
• P_sat = Saturation pressure (psi)
• Φ = Actual relative humidity
• T_act = Actual ambient air temperature (^oR)
• T_std = Standard temperature(^oR)

ICFM - Inlet Cubic Feet per Minute

Inlet Cubic Feet per Minute - ICFM, is used by compressor vendors to establish conditions in front of additional equipment like inlet filter, blower or booster.

When air passes through the filter there will be a pressure drop. The conversion from ICFM to ACFM can be expressed as

ACFM = ICFM (P_act / P_f) (T_f / T_act) (1)

where

• ICFM = Inlet Cubic Feet per Minute
• P_f = Pressure after filter or inlet equipment (psia)
• T_f = Temperature after filter or inlet equipment (^oR)

* - Information supplied by The Engineering Tool Box

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