Air Compressor Formulas
 

Free air if volumetric efficiency (%) and piston displacement are known:

Free Air = piston displacement X eff. (%)


To find cubic feet of either compressed air or free air:

cu.ft. comp. air X (psig + 14.7) = cu.ft. free air X 14.7

  • cu.ft. comp. air [ Cubic Feet of Compressed Air ]
  • cu.ft. free air [ Cubic Feet of Free Air ]

To convert gallons (tank size) to cubic feet:

gallons X .134 =cu.ft.


Air Cylinders:

Total force in lbs. of air cylinder = area of the cylinder diameter (inē) x psi gauge pressure
CFM of Free Air req'd to Operate Air Cylinder (single acting)
= vol. of cyl. (in cu. ft.) x cycles per minute x (gauge psi + 14.7)/14.7
For double acting air cylinder multiple by 2


Compressor RPM:

motor pulley diameter x motor rpm
compressor pulley diameter


Motor Pulley Diameter:

compressor pulley diameter x compressor rpm
motor rpm


Compressor Pulley Diameter:

motor pulley diameter x motor rpm
compressor rpm


Motor RPM:

compressor pulley diameter x compressor rpm
motor pulley diameter


Required Piston Displacement:

free air
vol. eff.


Piston Displacement in Cu.Ft. Min.:

cyl. bor in in. x cyl. bore x stroke in in. x rpm
2200


Cu. Ft. Compressed Air:

cu. ft. free air x 14.7
(psig x 14.7)


Cu. Ft. Free Air:

cu. ft. compressed air x (psig + 14.7)
14.7


Gallons:

cyl. bor in in. x cyl. bore x stroke in in. x rpm
2200


Pump Up Time:

V (tank size in gallons) x (final tank press-initial tank press)
7.48 x atmos. press. (psia) x pump delivery (cfm)


Gallons:

cubic feet
.134