The General method assumes the entire air demand must come from stored compressed air. This is the usable-capacity relation solved for required tank size, using the same pressure symbols as the Usable Capacity method.

\begin{equation}\label{eq:receiver-tank-general-size} V_{required} = V_{usable} \cdot \frac{P_{atm}}{P_{in} - P_{out}} \cdot k_{gal} \end{equation}

Equivalent form: \(V_{required} = Q_{demand} \cdot \frac{P_{atm}}{\Delta P} \cdot k_{gal}\), where \(Q_{demand} = V_{usable}\) and \(\Delta P = P_{in} - P_{out}\).

Symbols

\(V_{required}\)	Required receiver tank size \([\unit{ \gallon}]\)
\(V_{usable}\)	Required usable air drawn from the tank \([\unit{ \cubicFoot}]\)
\(P_{atm}\)	Atmospheric pressure \([\unit{ \psi}]\)
\(P_{in}\)	Initial tank pressure for drawdown \([\unit{ \psi}]\)
\(P_{out}\)	Final tank pressure for drawdown \([\unit{ \psi}]\)
\(\Delta P\)	Pressure drop, \(P_{in} - P_{out}\) \([\unit{ \psi}]\)
\(k_{gal}\)	Gallons per cubic foot (7.48) \([\unit{ \gallon\per\cubicFoot}]\)