Sizing a compressed-air buffer (storage) receiver

A buffer receiver stores compressed air to ride through a short demand peak without collapsing network pressure. Its volume is found directly from four inputs: the peak flow, the compressor’s make-up during the peak, the duration, and the pressure drop you can tolerate:

V = (Q_net × t × P_atm) / (60 × ΔP)        with   Q_net = Q_demand − Q_makeup

Symbol	Meaning	Unit
V	Required receiver volume	ft³
Q_net	Net flow the receiver must supply (demand − make-up)	SCFM
t	Peak duration	s
P_atm	Reference atmospheric pressure ≈ 14.5 psia (1 bar, SCFM reference)	psia
ΔP	Allowable pressure drop = start pressure − lowest tolerable pressure	psi

When do you need a buffer receiver?

The compressor is sized on the average demand; the receiver absorbs the peaks. As soon as a station draws far more than the available capacity for a few seconds (blow-off, long-stroke cylinder, leak test, line start-up), the air must come from a reserve or pressure sags. The receiver decouples supply from demand: it “shaves” the peak and lets the compressor run smoothly.

Net flow: don’t forget the compressor’s make-up

During the peak the compressor doesn’t stop: it keeps feeding the network. So the receiver only has to make up the difference between what the event demands and what the compressor already supplies.

If make-up ≥ demand, the compressor keeps up on its own: no buffer receiver is needed for that event.
Otherwise, size on Q_net = Q_demand − Q_makeup. Ignoring make-up gives a needlessly large receiver.

Worked example

A blow-off station draws 100 SCFM for 20 seconds. The compressor supplies 30 SCFM during that time. Pressure starts at 110 psig and must not fall below 95 psig (ΔP = 15 psi).

Net flow: Q_net = 100 − 30 = 70 SCFM
V = (70 × 20 × 14.5) / (60 × 15) = 22.6 ft³, i.e. ≈ 169 US gallons (0.64 m³)

So you would pick a dedicated receiver of at least 200 gallons near the station. Ignoring make-up, you would have sized on 100 SCFM (≈ 242 gal), over 40 % too big.

ΔP is the decisive lever. Volume is inversely proportional to ΔP: if the equipment tolerates only a 5 psi drop (110 → 105) instead of 15, the required receiver triples. The first question to the process is therefore: what is the lowest acceptable pressure?

Local receiver or central receiver

A large central receiver smooths the whole plant; a receiver dedicated to the demanding station (as close to the peak as possible, with its own feed) is often more effective for an isolated, one-off demand. Placement relative to the dryer also matters: see Air receiver: before or after the dryer?.

Flow is reasoned in SCFM; to avoid confusing it with ACFM or standardised units, see Flow units.

With the Onyx M3 tools

Calculator: Receiver storage, enter the event flow, the compressor make-up, the duration and the two pressures: it computes the net flow and the required volume (gal, ft³, m³).
Calculator: Metered recovery, goes further: it checks that a given receiver rides through the peak and recharges in time before the next one.

References

CAGI, Compressed Air & Gas Handbook, Chapter 4 “Compressed Air System Design”: storage and demand management
Compressed Air Challenge, Best Practices for Compressed Air Systems: storage sizing and peak shaving
ISO 1217 / CAGI: SCFM reference (1 bar absolute, 20 °C) used as P_atm in the formula

Frequently asked questions

What is a buffer (storage) receiver for?

A buffer receiver stores compressed air to absorb short demand peaks (a blow-off burst, a large cylinder, a tool change) without dropping network pressure or forcing the compressor to react instantly. It decouples supply from demand: the compressor covers the average, the receiver covers the peak.

What is the formula for a buffer receiver volume?

V = (Q_net × t × P_atm) / (60 × ΔP), where Q_net is the net flow in SCFM (event demand minus compressor make-up during the event), t the event duration in seconds, P_atm ≈ 14.5 psia (1 bar, SCFM reference) and ΔP the allowable pressure drop in psi between the start pressure and the lowest tolerable pressure. The volume comes out in cubic feet.

Should I account for the compressor's make-up flow?

Yes. If the compressor keeps supplying air during the peak, the receiver only has to make up the difference: size on NET flow = demand − make-up. Ignoring make-up oversizes the receiver; if make-up already covers the demand, no buffer receiver is needed for that event.

Does a smaller allowable pressure drop mean a bigger receiver?

Exactly. Volume is inversely proportional to ΔP: tolerating a 5 psi drop instead of 15 psi triples the required volume. The lowest tolerable pressure (below which your equipment drops out) is what sets ΔP.