Air Receiver Sizing Calculator

About Air Receiver Sizing Calculator (CAGI Formula)

The air receiver sizing calculator answers the two everyday storage questions with the standard receiver equation t = V(P1 − P2)/(Patm(Qd − Qs)). Time mode: given a tank, how long can it feed an intermittent demand — a blast cabinet, a large cylinder stroke, a pulse of tools — before pressure sags from the compressor cut-out P1 to the minimum acceptable P2? Volume mode: given the event duration, how many gallons (or liters) of receiver does it take?

The pressures enter as a band over atmospheric — that is what converts stored compressed volume into free air the tools actually consume — so the atmospheric pressure is an editable input for altitude. If the compressor keeps running during the event, its supply subtracts from the demand; and if supply meets or exceeds demand, the calculator says so plainly instead of reporting an infinite time. This is the event-storage formula only: real receivers are also sized for pulsation damping, condensate drop-out, and are pressure vessels under ASME Section VIII — preliminary sizing, not vessel design.

How It Works

1. Pick the mode: draw-down time from a known tank, or required volume for a known time. The unit toggle swaps the whole system — gallons/psi/cfm or liters/bar/m³-per-minute — converting your entries with round-then-clamp so nothing valid becomes an error.
2. Enter the pressure band: P1 is where the event starts (typically the compressor cut-out pressure) and P2 is the lowest pressure the demand tolerates (the regulator setpoint plus a margin). Only the band between them is usable storage — a 120 to 100 psi band stores far less than the tank's nameplate suggests.
3. Enter the demand of the event and any compressor supply that continues during it, both as free-air flow (cfm or m³/min). The net draw Qd − Qs is what the receiver must cover; a supply that equals the demand means the receiver only rides through regulation transients, and the tool reports the no-drawdown case explicitly.
4. Read the answer: time in minutes or volume in gallons/liters, plus the usable stored free air V(P1 − P2)/Patm — the cubic feet (or m³) of atmospheric-equivalent air the band holds. At altitude, lower Patm means each psi of band stores more free-air equivalents per tank volume; the editable atmospheric input handles that.
5. Sanity-check against practice: general-purpose plant rules run 3–5 gallons of receiver per cfm of compressor capacity, with event storage on top. And remember the excluded physics — this isothermal formula ignores temperature transients (fast blow-downs run cooler and deliver a little less), and says nothing about the vessel itself: relief valve setting, drain, and ASME VIII certification are separate requirements.

Worked Example

A 240-gallon receiver feeds a 50 cfm sandblast nozzle with the compressor off. Band: 125 psig cut-out down to 100 psig minimum, sea-level atmosphere 14.7 psia. V = 240/7.481 = 32.1 ft³. Usable free air = 32.1 × (125 − 100)/14.7 = 54.6 scf. Draw-down time t = 32.1 × 25 / (14.7 × 50) = 1.09 minutes. If a 25 cfm compressor keeps running during the blast, the net draw halves to 25 cfm and the time doubles to 2.18 min; at 50 cfm of supply the receiver never draws down at all. To ride out a full 5-minute event unaided, volume mode gives V = 5 × 14.7 × 50 / 25 = 147 ft³ ≈ 1,100 gallons — which is why long events get dedicated storage or a bigger compressor.

Formulas

Receiver time formula

t = V × (P1 − P2) / (Patm × (Qd − Qs))

Required volume

V = t × Patm × (Qd − Qs) / (P1 − P2)

Usable stored free air

Va = V × (P1 − P2) / Patm

Standards & References

• Compressed Air & Gas Institute (CAGI), Compressed Air and Gas Handbook — the receiver/storage time formula (also printed throughout compressor-manufacturer sizing literature)
• ASME Boiler and Pressure Vessel Code, Section VIII — the receiver as a pressure vessel (certification, relief, inspection) is OUTSIDE this calculator's scope; formula-only preliminary sizing

Frequently Asked Questions