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Horsepower required to Compress Air

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The horsepower required to adiabatic compression of air can be calculated with the calculator below:

Theoretical horsepower required to compress one cubic foot of free air (atmospheric pressure) for single-staged, two-staged and three-staged compressors are indicated in the diagram below. In general - plus 15-20% friction.

  • 1 cfm (ft3 /min) = 1.7 m3 /h = 0.47 l/s = 28.3 l/min
  • 1 psi (lb/in2) = 6894.8 Pa (N/m2) =  6.895 10-2 bar
  • 1 hp = 745.7 W

The power required for adiabatic (process without transfer of heat) compression of air can be expressed as

HP = [144 N P1 V k / (33000 (k - 1))] [(P2/ P1 ) (k - 1)/(N k) - 1]                                (1)


HP = horsepower

N = number of compression stages

k = 1.41 = adiabatic expansion coefficient

P1 = absolute initial atmospheric pressure (psi) (14.7 psi at sea level)

P2= absolute final pressure after compression (psi)

V = volume of air at atmospheric pressure - standard or free air (scfm, ft3 /min)

  • adiabatic compression (or expansion) takes place without transmission of heat
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