Multiplies the cylinder volumetric intake (at cylinder conditions) by the compression ratio to obtain the equivalent volume of free air at atmospheric conditions that the compressor must supply. This result is in standard cubic feet per minute (scfm).

\begin{equation}\label{eq:pneumatic-air-requirement-free-air} Q_{free} = Q_{cyl} \cdot r_c \end{equation}

Symbols

\(Q_{free}\)	Free-air equivalent consumption \([\unit{ \standardCubicFeetPerMinute}]\)
\(Q_{cyl}\)	Cylinder air intake volume at cylinder conditions \([\unit{ \cubicFoot\per\minute}]\)
\(r_c\)	Compression ratio \([\unit{ \unitless}]\)

Note

The result \(Q_{free}\) is the quantity used when sizing a compressor or calculating the compressed air supply requirement for a system containing one or more pneumatic cylinders. Sum \(Q_{free}\) across all actuators to obtain the total free-air demand of the system.