Receiver transient storage calculator

What this calculator works out

The receiver transient storage calculator answers two practical questions. First, how large a receiver do you need to carry a defined short event, such as a burst of demand, a compressor start delay or a changeover between machines? Second, if you already have a receiver, how long can it support a known deficit before pressure falls to the minimum your process can tolerate?

Both answers come from the same relationship. Stored air is released only as pressure falls, so the usable storage depends on the pressure band, not on the receiver’s full pressure. A tank charged to 8 bar(g) that must not fall below 7 bar(g) releases only the air in that 1 bar band.

The storage formula, explained

For a short event where the air in the receiver stays at roughly constant temperature, the relationship is:

V = Q × t × P_atm / (P1 − P2)

• V is the geometric volume of the receiver, in m³.
• Q is the net deficit in free air, in m³/min: transient demand minus the supply that continues to reach the protected area during the event.
• t is the event duration in minutes.
• P_atm is atmospheric pressure in bar absolute, about 1.013 bar a at sea level and slightly lower at higher sites.
• P1 and P2 are the upper and lower usable pressures, both in bar absolute.

Because P1 and P2 appear as a difference, using gauge pressures for both gives the same difference. Errors creep in when one value is gauge and the other absolute, or when psig and bar are mixed. Our pressure unit and gauge-absolute conversion tool removes that risk. Remember that 1 bar equals about 14.5 psi.

Rearranged, the same formula gives hold-up time: t = V × (P1 − P2) / (Q × P_atm).

Worked example: sizing for a start delay

A plant runs at about 7.5 bar(g) (about 109 psig). When demand rises, a second compressor starts, but it takes around 30 seconds to start and load. During that half-minute the plant draws 3 m³/min more than the running compressor supplies. The process must not see less than 6.5 bar(g) (about 94 psig).

1. Net deficit Q = 3 m³/min.
2. Duration t = 0.5 min.
3. Usable band P1 − P2 = 7.5 − 6.5 = 1.0 bar.
4. V = 3 × 0.5 × 1.013 / 1.0 ≈ 1.52 m³, or about 1,520 litres.

A standard 2,000 litre receiver would give margin. If the band could only be 0.5 bar, the volume would double to about 3 m³. That is the main lesson: a narrow pressure band demands a lot of storage, and running the whole plant at a higher pressure to create a band costs energy, typically about 7% more compressor power for every extra bar.

Worked example: checking an existing receiver

A workshop has a 1,000 litre (1 m³) receiver between 8 and 7 bar(g). A blasting job draws 4 m³/min more than the compressor supplies.

t = 1 × 1.0 / (4 × 1.013) ≈ 0.25 min, or about 15 seconds. The receiver will support that deficit for a quarter of a minute. If the event lasts several minutes, no realistic receiver will cover it: the answer is more compressor capacity, a hired compressor for the job, or lower demand.

Recovery time after the event

A receiver that has been drawn down must be refilled before it can protect the next event. Recovery time is t_r = V × (P1 − P2) / (Q_surplus × P_atm), where Q_surplus is the spare compressor capacity above normal demand. If the compressor has only a small surplus, recovery can take far longer than the event itself, and repeated events will walk the pressure down. Check recovery whenever events repeat within minutes.

Where storage helps and where it does not

Central receivers protect the compressor and the control system. A local receiver near a large intermittent user, such as a blast pot, a test bench or a press, protects that user from the pipework restriction between it and the compressor room. Local storage is often the more effective choice when the problem is a long, undersized line.

Limits of the calculation

• The formula assumes near-constant air temperature. Very fast discharges cool the air and release slightly less than calculated; slow events are close to the formula.
• Pressure drop between the receiver and the user is not included. If pipework loses 0.5 bar at high flow, the user sees that much less.
• The deficit must be net. Subtract compressor output that continues during the event.
• The calculation ignores condensate volume. A receiver half full of water stores much less air, so drains matter.
• Receiver selection must also respect design pressure, safety valve rating and inspection requirements. Read our air receiver inspection and safety page.

Measuring the inputs properly

The weakest input is usually the deficit. Guesses from tool ratings tend to be wrong. A short logging exercise, with a pressure logger on the receiver and power or flow logging on the compressors, shows the actual size and duration of events and how often they occur. That data also shows whether pressure falls because of storage, controls or leaks. Our pressure profiling and air demand profiling services gather it.

Practical checks before you add a receiver

Before buying storage, confirm that the problem really is a short transient. Look at a pressure trend over a full shift. If pressure dips sharply for seconds and recovers, storage is a strong candidate. If it sags slowly and stays low, storage will only delay the same result.

• Check that existing receivers drain properly; a tank holding condensate stores less air and sends water downstream.
• Check the pressure drop across the dryer and filters at peak flow; a blocked element can look like a storage shortage.
• Check compressor control settings; a narrow load and unload band on a small receiver causes rapid cycling.
• Check that the receiver inlet and outlet pipes are large enough to release air at the rate the event needs.
• Check the safety valve setting and the receiver’s design pressure before raising the upper pressure of the band.

A receiver is a pressure vessel. Its design pressure, safety valve, drain and inspection record matter as much as its volume, and adding or relocating one should follow the vessel maker’s rules and the applicable inspection requirements.

How Reddy Compressors helps

We supply new air receivers and compressors, used and refurbished machines, and rentals from our own fleet for short peaks and planned jobs. Our engineers log pressure and demand on site, size central and local storage from measured events, check drains and safety valves, and adjust load and unload settings so storage does its job. We work on all major makes, including ELGi, Atlas Copco, Ingersoll Rand, KAESER and Chicago Pneumatic, as an independent multi-brand specialist, not an authorised dealer. We have tie-ups with all major and reputed brands.

Our office is at Tarnaka, Secunderabad. Service teams cover the whole of Telangana and Andhra Pradesh, and we supply equipment and spares across India.

What to send us

• Receiver volume, design pressure and location in the system
• Normal and minimum acceptable pressure at the critical user
• Compressor make, model, capacity and control type
• Description of the event: what causes it, how long and how often
• Any pressure trend or logger data you already have

Frequently asked questions

How do I calculate the air receiver size I need?

Multiply the net air deficit in m³/min of free air by the event duration in minutes and by atmospheric pressure, about 1.013 bar a, then divide by the pressure drop you can accept in bar. A 3 m³/min deficit for 30 seconds across a 1 bar band needs about 1.5 m³. Always size from a real event and a real pressure band, not from a fixed litres-per-kW rule.

Will a bigger receiver fix low air pressure?

Only if the low pressure is caused by short peaks. A receiver releases air only while pressure falls, so it cannot cover demand that stays above compressor capacity for long. If pressure is low all shift, the cause is usually too little capacity, leaks, a blocked filter or dryer, or undersized pipework. Logging pressure and power shows which problem you have before you buy steel.

How long will my air receiver supply air?

Hold-up time equals receiver volume times the usable pressure band, divided by the net deficit times atmospheric pressure. A 1,000 litre tank between 8 and 7 bar(g) supplying a 4 m³/min deficit lasts about 15 seconds. That is enough to bridge a start delay, but not to run a job. For long events, add capacity or hire a compressor.

Should I use gauge or absolute pressure in the receiver formula?

The formula is written in absolute pressure, but because only the difference between upper and lower pressure is used, two gauge values give the same difference. Problems arise when one value is gauge and the other absolute, or when bar and psi are mixed. Convert both to the same unit and basis first. One bar equals about 14.5 psi.

Where should an air receiver be installed, near the compressor or near the user?

A receiver near the compressor steadies the control signal, reduces cycling and collects condensate. A receiver near a large intermittent user protects that user from pressure drop in the pipework. Many plants benefit from both. If the far end of the plant drops pressure during peaks while the compressor room looks fine, local storage or better pipework usually helps more than a bigger central tank.

Related pages

• Air receiver tank sizing
• Air receiver tanks
• Compressed-air receivers and storage engineering
• Compressed air storage for energy optimisation
• Load unload cycle energy calculator
• Compressed air knowledge and calculation centre