How to use this calculator
- Enter peak air demand. Enter the tool, cylinder group or process demand as free-air flow.
- Enter compressor delivery. Enter the compressor FAD that is available while the event is running.
- Set duration and pressure band. Use the demand event duration, receiver cut-in pressure and receiver cut-out pressure.
- Compare the selected receiver. Read the required volume, selected utilization, stored free air, reserve time and recharge time.
How it works
A receiver stores usable compressed air only across the pressure band you allow it to drop. For an isothermal first-pass screen, the equivalent free-air storage is: V_free = V_receiver · (P₂ − P₁) / P_atm where P₂ is cut-out pressure, P₁ is cut-in pressure and P_atm is atmospheric pressure.
The receiver only needs to cover the demand that the compressor cannot supply during the event. If demand is Qd and compressor delivery is Qc, the shortfall is Q_shortfall = max(Qd − Qc, 0) and the required stored free air is Q_shortfall times event duration and allowance.
Worked example
Verified against the live calculator
Suppose a process needs 1200 Nl/min for 30 seconds and the compressor can provide
800 Nl/min during that event. The shortfall is 400 Nl/min. With a 20% allowance,
required stored free air is 400 × 0.5 × 1.2 = 240 L. Between 5.5 bar
cut-in and 8.0 bar cut-out, the pressure band is 2.5 bar, so the minimum receiver is
about 97 L. A 500 L receiver stores about 1234 L
of free air over that band.
Frequently asked questions
How do you size a compressed air receiver?
For a short demand event, calculate the free-air shortfall between demand and compressor delivery, multiply by the event time and safety allowance, then convert that stored free air into receiver water volume using the usable pressure band. The calculator uses Vreceiver = Vfree × Patm / (Pcut-out − Pcut-in).
What is stored free air in a receiver?
Stored free air is the equivalent volume at atmospheric pressure. A receiver does not deliver its whole water volume as usable air; it delivers the pressure-band difference, so stored free air equals receiver volume times the gauge-pressure band divided by atmospheric pressure.
Should I use compressor CFM or tool CFM?
Use free-air values for both. Enter the tool or process peak demand as demand flow, and enter the compressor free-air delivery available during the event. The receiver covers only the shortfall between them.
Does this check receiver safety rules?
No. It is a storage and reserve-time screen. Final receiver selection still needs the receiver pressure rating, safety valve, inspection/code requirements, compressor duty cycle, dryer and condensate details checked from current product and local requirements.
Method & assumptions
- Demand and compressor flow are free-air rates: Nl/min or SCFM.
- Storage is estimated as isothermal ideal-gas storage over the entered pressure band.
- Receiver volume is the vessel water volume, not the free-air volume.
- Does not select ASME receiver class, safety valves, relief settings, pressure switches, dryers, drains, pipe drops, compressor duty cycle or inspection rules.