Balance the shortfall during a burst
Net free-air demand = demand minus concurrent compressor supply, floored at zero. Multiply net demand in L/s by burst seconds to find the usable free air needed from storage. Isothermal minimum buffer volume in litres = usable free air × reference absolute pressure ÷ (high gauge pressure − low gauge pressure).
This is an isothermal ideal-air balance with receiver air and reference air at the same temperature. There is no temperature correction. A warmer receiver than the flow reference temperature needs a larger volume. Rapid bursts cool the air; the isothermal estimate is an optimistic minimum. Both flow figures must share the same reference conditions, and supply must be the amount actually available at that pressure during the burst after other running demand. Spare capacity is also needed after the burst to refill the receiver.
Worked example: a 30-second burst
With 1,000 L/min demand and no concurrent supply, a 30-second burst needs 500 litres of free air. Across an 8 to 6 bar gauge band, a reference pressure of 1 bar absolute gives 250 litres of receiver volume. At the calculator’s 1.01325 bar absolute default, the isothermal minimum is 253.3125 litres. This optimistic estimate is not a recommended vessel size: rapid bursts cool the air, so a larger receiver may be needed.
A buffer estimate, not a vessel specification
If supply equals or exceeds demand, the incremental buffer calculated for this burst is zero. That does not rule out the normal receiver needed by the installation. The model does not size load/unload cycling storage, choose a vessel, certify a design or recommend a starting pressure.
Use only a pressure band within all equipment ratings and process requirements. Actual selection needs the relevant engineering assessment, including pressure losses and the compressor’s response. Very small pressure bands can produce very large estimates; review the assumptions before using them.
Receiver fill-time mode
Net flow in L/min = effective compressor supply minus constant consumption at the same reference conditions. Fill time in seconds = 60 × receiver litres × (target − start pressure) ÷ (net L/min × reference absolute pressure). Supply must exceed consumption and target must exceed start. Both receiver pressures are gauge, so their difference is unchanged.
This rearranges the same isothermal ideal-air balance used for the burst buffer. Receiver and reference air temperatures are equal. The result is an isothermal (settled-temperature) fill estimate. Delivery varies with pressure, so use an effective available flow through the whole band and confirm the target stays within both compressor capability and receiver rated pressure. Both flow figures must use the entered reference pressure. Thermal transients and compressor controls are not modelled. It is not a certified FAD test, a vessel selection or a recommendation to exceed equipment ratings.
Worked example: filling 500 litres
Example fill inputs: a 500 L receiver from 0 to 8 bar gauge, 1,000 L/min effective supply, zero consumption and 1.01325 bar absolute reference. The isothermal (settled-temperature) estimate is 236.861584 seconds, or about 3.94769 minutes. These are example pressures, not operating advice.