EngineerBenchSizing an air line or receiver buffer
An air line can lose pressure while still being connected to a compressor at the desired set pressure. The pipe calculation estimates loss from free-air delivery, equivalent length, inside bore, and inlet pressure. Use actual inside diameter rather than nominal pipe size.
Keep free-air flow distinct from compressed volume
Free-air delivery expresses flow at reference atmospheric conditions, not the smaller physical volume occupied in the pressurized pipe. The field for inlet pressure is gauge pressure; the model converts it to absolute pressure internally. Include fitting effects in the equivalent length you enter.
A receiver covers a shortfall, not unlimited demand
The receiver mode uses the difference between air demand and ongoing compressor delivery, together with the usable pressure range. It estimates buffer time under an isothermal model. Controls, transient temperature, and pressure-vessel requirements are separate; a larger receiver does not increase sustained compressor output.
Following receiver pressure through a demand event
A receiver supplies only the difference between demand and compressor delivery during the modeled event. If demand is 300 L/min at free-air conditions and delivery is 100 L/min, the receiver supplies a net 200 L/min. The usable stored amount depends on receiver volume and the difference between starting and minimum allowed pressure, not on the starting pressure alone.
The buffer relationship assumes an isothermal storage estimate and steady flows. Pressure switches, compressor response, regulator behavior, and temperature change can alter the actual event. For pipe sizing, the empirical drop relationship uses absolute pressure internally, while the form asks for inlet gauge pressure. Do not add atmospheric pressure manually before entering that field. A nominal pipe designation is not its internal bore, and restrictive couplings can contribute meaningful equivalent length. Check the pressure required at the equipment during demand rather than only the compressor's unloaded gauge reading. Neither pipe sizing nor buffer time establishes a pressure vessel's permitted operating rating.
Formula
Pipe: Δp(bar) = 450 q(L/s)^1.85 L(m) / [d(mm)^5 pabsolute(bar)]. Receiver: t = V × Δp / [net FAD × atmospheric pressure].