Air receiver tank sizing: how big should your receiver be?

Why receiver size matters

A receiver that is too small makes the compressor cycle rapidly between load and unload, wears inlet valves, contactors and motors, and lets pressure dip every time a large user starts. Operators then raise the setpoint to compensate, and every extra bar costs about 7% more power.

A receiver that is far too large costs more to buy, takes floor space, adds inspection and testing work and may need a larger foundation. It also takes longer to pressurise after a shutdown. Beyond a certain size it adds little benefit. The right size follows from a clear understanding of the duty.

Three reasons to size a receiver

1. Cover a demand peak that is larger than the compressors can supply, for a known time.
2. Limit compressor cycling on load/unload or start/stop control, within the manufacturer’s limits.
3. Bridge a gap, such as the time a standby compressor needs to start and load after the running machine trips.

Calculate the volume for each reason that applies to your system and use the largest. Receivers also cool the air and let condensate settle out, but that is a secondary benefit rather than a sizing basis.

1. Covering a peak

The storage needed to supply extra air for a set time, while pressure falls from an upper to a lower limit, is:

V = t × Q × p_a ÷ (p₁ − p₂)

• V = receiver volume, m³ (× 1,000 for litres)
• t = duration of the peak, minutes
• Q = air needed above what the compressors supply, m³/min of free air (1 m³/min ≈ 35.3 cfm)
• p_a = atmospheric pressure, about 1.013 bar absolute
• p₁ − p₂ = allowable pressure drop during the peak, bar

Example: a blow-off uses 50 cfm more than the compressor can supply for 1 minute, and users can accept a drop from 7.0 to 6.0 bar (about 101 to 87 psig). Q = 50 ÷ 35.3 = 1.42 m³/min. V = 1 × 1.42 × 1.013 ÷ 1.0 = 1.44 m³, about 1,450 litres. Allowing only 0.5 bar of drop doubles the volume to about 2,900 litres.

The allowable pressure drop has as much influence on size as the peak itself. That is why it pays to know the true minimum pressure your users need, rather than assuming the setpoint is the requirement.

2. Limiting compressor cycling

A load/unload compressor needs enough storage to keep its cycles within the manufacturer’s limit. A widely used formula is:

V = 0.25 × q × p_a ÷ (f × Δp)

• V = receiver volume, litres
• q = compressor free air delivery, litres per second (1 cfm ≈ 0.472 l/s)
• f = maximum load cycles per second the machine allows (for example 1 cycle per 30 seconds = 0.033)
• Δp = difference between load and unload pressure, bar

The worst case occurs when demand is half the compressor’s output, which is where the 0.25 factor comes from.

Example: a 212 cfm (100 l/s) compressor, 1 cycle per 30 seconds allowed, 0.5 bar band: V = 0.25 × 100 × 1.013 ÷ (0.033 × 0.5) ≈ 1,535 litres. Widening the band to 1 bar halves this, but raises average pressure and energy use.

The cycle limit comes from the compressor maker. Piston compressors on start/stop control often have a limit on motor starts per hour, which can need more storage than a screw on load/unload.

3. Bridging a standby start

If the running compressor trips, how long does the standby need to start and load, and how far can pressure fall before production stops? Use the peak formula with Q equal to the full demand and t equal to the start-up time.

Example: a plant uses 10 m³/min (about 353 cfm). The standby needs about 30 seconds (0.5 min) to start and load, and the process can tolerate a fall of 1 bar. V = 0.5 × 10 × 1.013 ÷ 1.0 ≈ 5.1 m³, about 5,000 litres. If the process can only tolerate 0.5 bar, the volume doubles. In practice, an automatic sequencer that starts the standby on a pressure signal and a slightly higher operating band make this duty manageable.

Rough guide for a quick estimate

For a single load/unload screw compressor in an ordinary industrial system, a total receiver volume of very roughly 6 to 12 litres per cfm of compressor capacity is common. Piston compressors on start/stop control often need more. Treat these as a starting point only; use the formulas above where peaks, sensitive users or several compressors are involved.

Variable-speed compressors and receivers

A variable-speed (VSD) compressor matches output to demand by changing motor speed, so it needs less storage for cycling. It still benefits from a receiver near the machine: it smooths rapid demand changes that the drive cannot follow instantly, gives stable pressure for the controller, and helps the machine avoid stopping and starting when demand falls below its minimum speed. Too little storage on a VSD system often shows up as frequent stop-start at low demand.

Where to put the volume

• Primary (wet) receiver near the compressors, before the dryer: cools the air, drops out condensate, stabilises control and protects the dryer from flow surges.
• Dry receiver after the dryer: stores treated air for peaks without overloading the dryer.
• Secondary receivers near large intermittent users, such as blow-offs, test benches or blasting points, so their peaks do not pull down the whole plant.

Pipework also holds air and counts towards storage, though usually only a small amount. A pressure regulator downstream of a receiver stops it releasing stored air below the regulator setting, so the useful pressure band is between the receiver pressure and the regulated pressure, not down to zero.

Selection checklist beyond volume

• Design pressure above the highest pressure the compressors can deliver, with the safety valve set at or below it.
• Safety valve capacity sized to discharge the full output of all compressors feeding it.
• Drain – preferably an automatic, zero-air-loss type on the wet receiver.
• Inspection opening to allow internal examination.
• Documentation – nameplate, design code, test certificate and manufacturer details.
• Orientation and space – vertical receivers save floor area; horizontal ones suit low ceilings.
• Internal finish – galvanised or coated interiors resist corrosion where air quality matters.

See our receiver inspection and safety page for the care a receiver needs once installed.

Multiple compressors and sequencing

Where several compressors share one header, storage works with the sequencer. A central controller running machines within a narrow pressure band needs enough receiver volume so that the trim machine does not cycle rapidly and base machines are not started and stopped unnecessarily. Size the receiver on the trim compressor’s capacity for cycling, and on total demand for any standby duty. Locate the main receiver where the sequencer’s pressure sensor reads stable, representative pressure.

How Reddy Compressors helps

Reddy Compressors, from Tarnaka in Secunderabad, sizes and supplies air receivers alongside compressors, dryers and piping. We work across Telangana and Andhra Pradesh and supply equipment across India. As an independent multi-brand specialist, we match receivers to compressors of ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair, Doosan, Kirloskar and others.

• We calculate receiver volume from your compressor capacity, control mode and demand pattern.
• We use measured demand from power and flow logging where peaks are uncertain.
• We advise on primary, dry and secondary receiver locations.
• We install and commission receivers with new, used or rental compressors.

What to send us

• Compressor make, model, capacity (cfm or m³/min), pressure and control mode.
• The size and pressure rating of any existing receiver.
• Your largest intermittent users and how long they run.
• The minimum pressure your critical machines need.
• Whether a standby compressor is installed and how it starts.

Frequently asked questions

What size air receiver do I need for my compressor?

For a single load/unload screw compressor in an ordinary system, a common starting point is about 6 to 12 litres of receiver per cfm, so roughly 1,200 to 2,400 litres for a 200 cfm machine. Where you have large intermittent peaks, a standby to bridge, or a strict cycle limit, calculate the volume for each duty using the formulas on this page and choose the largest.

Can an air receiver be too big?

Yes. An oversized receiver costs more, takes more space, needs more inspection work and takes longer to pressurise after a shutdown. It does not hurt compressor efficiency, but the extra benefit falls away beyond what the peaks and cycling actually need. Size it from the duty, and place some storage near large intermittent users rather than putting everything in one oversized tank.

Does a bigger receiver save energy?

It can, when the existing receiver is too small. Adequate storage reduces rapid load/unload cycling, lets you use a narrower pressure band without excessive cycling and covers short peaks without raising the setpoint. Since each extra bar costs about 7% more power, avoiding a higher setpoint is where the saving comes from. Storage cannot fix leaks or overloaded piping.

Does a VSD compressor need an air receiver?

Yes, though usually a smaller one than a load/unload machine. The receiver smooths sudden demand changes that the drive cannot follow instantly, keeps pressure stable for the controller and reduces stop-start operation when demand falls below the machine’s minimum speed. It also cools the air and collects condensate before the dryer. Follow the compressor maker’s minimum recommended volume.

Should the receiver go before or after the dryer?

Many systems use both. A wet receiver before the dryer cools the air, separates condensate and protects the dryer from flow surges. A dry receiver after the dryer stores treated air for peaks without overloading the dryer. The best arrangement depends on demand pattern, dryer type and space. We review it as part of sizing.

How do I convert cfm to litres per second for receiver sizing?

One cfm is about 0.472 litres per second, and one m³/min is about 35.3 cfm. So a 212 cfm compressor delivers roughly 100 l/s or 6 m³/min. Always use free air delivery, the flow referred to inlet conditions, not the volume of compressed air. Pressures in the formulas are in bar; 1 bar is 14.5 psi.

Related pages

• Air receiver tank price guide
• Air receiver tanks
• Receiver storage calculator
• Receivers and storage engineering
• Storage for energy saving
• cfm, psi and bar conversion guide