What storage can and cannot do
A receiver is a buffer between production and consumption. It changes when air is produced, not how much air the plant uses in a day. Its energy benefits come from what the compressors do differently once it is installed:
- A short peak is supplied from the receiver, so a standby compressor does not start.
- A load/unload compressor switches less often, so it spends less time in blowdown and can use auto-stop safely.
- Control systems get time to respond, so the station can run with a narrower, lower pressure band.
- A remote machine with a pulsing demand keeps its inlet pressure without the whole plant running higher.
Storage cannot supply a demand that lasts longer than the receiver can support, cannot overcome a restricted pipe between the receiver and the user, and cannot replace the compressor capacity needed for sustained demand.
Define the result the storage must deliver
State the purpose in operating terms before choosing a vessel. For example: “the 20-second purge on line 3 must finish with the machine inlet above 6 bar while the second compressor stays stopped.” That is far more useful than “we need a bigger tank”.
Keep emergency reserve separate from energy buffering. Air held for a safe shutdown or a critical actuator cannot also be counted as buffer for ordinary peaks. If one vessel serves both duties, define which comes first and how the controls protect the reserve. Safety-related duties need their own specification from the responsible engineer.
Measure the demand event
A storage calculation is only as good as the event data behind it. Log pressure at the compressor, the receiver and the user at a few seconds’ resolution, with compressor power or flow, over at least one full production week.
- Identify each event where pressure falls or a compressor starts.
- Record its duration, the peak flow, the minimum pressure reached and how often it repeats.
- Note what the compressors did: loaded, started a second machine, or failed to keep up.
- Note the time between events, which sets the recharge time available.
Our air demand profiling page describes the logging.
Calculating useful stored air
The air a receiver can deliver depends on its volume and on the pressure band it is allowed to use. The commonly used relationship is:
Free air delivered (m³) = receiver volume (m³) × (upper pressure − lower pressure) ÷ atmospheric pressure, with pressures in bar absolute and atmospheric pressure about 1.013 bar.
Rearranged for sizing:
Receiver volume (m³) = event duration (min) × air deficit (m³/min free air) × atmospheric pressure ÷ (upper pressure − lower pressure).
The air deficit is the difference between the peak demand and what the running compressors can supply during the event. The lower pressure is set by the user’s minimum requirement plus the pressure drop between the receiver and the user at peak flow. This formula assumes the air temperature in the receiver stays constant. During a fast discharge the air cools and delivers somewhat less than calculated, so allow a margin.
Worked example: receiver sizing and sensitivity
A machine draws 4 m³/min (free air) for 30 seconds, every few minutes. The running compressor can supply 2.5 m³/min of spare capacity during the event. The receiver operates between 7.0 bar(g) and a lower limit of 6.3 bar(g), set by the machine’s 6.0 bar requirement plus 0.3 bar of route loss.
- Air deficit: 4 − 2.5 = 1.5 m³/min, for 0.5 min = 0.75 m³ of free air.
- Usable pressure band: 7.0 − 6.3 = 0.7 bar.
- Receiver volume: 0.75 × 1.013 ÷ 0.7 ≈ 1.1 m³.
The sensitivity is the important part. If the route loss could be reduced from 0.3 to 0.1 bar, the usable band becomes 0.9 bar and the required volume falls to about 0.85 m³. If the plant instead raised the upper pressure to 7.5 bar to widen the band, it would pay about 3–4% more compressor power (about 7% per bar), all year. Reducing the route loss is usually the better investment. See our air receiver tank sizing page for further cases.
Recharge must fit the production rhythm
After an event, the receiver must be refilled before the next one. Recharge time is the stored air divided by the compressor’s spare capacity once the event ends. If spare capacity is small, recharge is slow and the next event starts from a lower pressure. In that case a larger receiver does not help; the plant needs more capacity, a smaller event or a different control arrangement. A metering valve on the receiver inlet can limit how fast a local receiver refills, so it does not create a new peak on the header.
Central or local storage?
| Arrangement | Best for | Watch out for |
|---|---|---|
| Wet receiver before the dryer | Cooling air and dropping out condensate; buffering compressor cycling | Drain reliability; does not buffer dryer pressure drop |
| Dry receiver after treatment | Supplying peaks without overloading the dryer and filters | Treatment still sized for compressor output |
| Local receiver at a large user | Short, high-flow pulses at the end of a long line | Recharge rate; check valve and metering to protect the header |
| Separate high-pressure storage with a regulator | Critical events needing a large reserve in a small vessel | Higher generation pressure for that air; regulator capacity |
Many plants benefit from both a wet receiver at the compressor room and dry storage after treatment. A dry receiver protects the dryer from flow peaks that exceed its rating, which would otherwise push wet air downstream. See receivers and storage engineering.
Storage and compressor controls
For fixed-speed load/unload compressors, effective storage between the compressor and its pressure sensor sets how long each load and unload period lasts. Too little storage gives short cycles and frequent blowdown, which wastes energy and wears the inlet valve. Manufacturers often state a minimum receiver volume per unit of capacity for stable load/unload control; follow their guidance as the starting point.
VSD compressors need less storage for control stability, but they still benefit from it when demand falls below their minimum speed or when a fast peak arrives. In multi-compressor stations, storage gives the sequencer time to decide whether a peak is brief or sustained before starting another machine. Sensor location matters: a sequencer reading pressure at a point with large dynamic swings will start and stop machines unnecessarily. Our pages on base, trim and VSD optimisation and unload and idle loss reduction cover the control side.
Verify the complete energy balance
- Log compressor power, pressures and starts before and after installation over similar production periods.
- Count how often standby machines start and how long they run.
- Check that pressure at the critical user stays above its minimum through each event.
- Check whether the station pressure setting has been lowered as planned.
- Report kWh and specific power, not only the smoother pressure trace.
Safety and maintenance of receivers
Air receivers are pressure vessels. They must have a design pressure above the maximum system pressure, a correctly set and sized safety valve, a pressure gauge and a reliable drain. Inspection and testing must follow the applicable pressure-vessel rules and the manufacturer’s guidance. Corrosion from condensate is the main threat in humid Indian conditions, so automatic drains need regular checking. See air receiver inspection and safety.
How Reddy Compressors helps
Reddy Compressors has supplied, rented and serviced compressed-air equipment since 2002 from our office in Tarnaka, Secunderabad. As an independent multi-brand specialist working on ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and others, not an authorised dealer but with tie-ups with all major and reputed brands, we:
- Log pressure, power and demand events to define the storage requirement.
- Calculate receiver volume, location and pressure band from the measured events.
- Check the pipe route between the receiver and the user for restrictions that would waste the storage.
- Supply receivers, drains and safety fittings, and adjust compressor and sequencer settings to use them.
- Supply compressors, new, used or on rental, where storage alone cannot close the gap.
Our 20+ service engineers and technicians cover all of Telangana and Andhra Pradesh, and we supply equipment and spares across India.
What to send us
- Compressor details, control type and pressure settings.
- Existing receiver size, design pressure and location, with nameplate photos.
- A description of the demand event: which machine, how long, how often.
- Required minimum pressure at the affected user.
- Any logging data or alarm records showing pressure dips.
Frequently asked questions
How do I calculate the right air receiver size?
Measure the demand event: how much extra air is needed above what the compressors can supply, for how long, and the lowest acceptable pressure at the user. Then use receiver volume = duration × air deficit × atmospheric pressure ÷ usable pressure band, with pressures in bar. Add a margin for cooling during fast discharge. Rules of thumb are a starting point only.
Does a bigger air receiver save electricity?
Only if it changes how the compressors run. A bigger receiver can stop a standby machine starting for short peaks, reduce load/unload cycling and allow a lower pressure band. If none of these happen, the saving is negligible. A receiver behind a restricted pipe, or with too narrow a pressure band, may deliver little useful air at all.
Should the air receiver go before or after the dryer?
Both positions have a purpose. A wet receiver before the dryer cools the air, drops out condensate and steadies compressor cycling. A dry receiver after treatment supplies peaks without forcing more flow through the dryer and filters than they are rated for. Many plants benefit from both. The best arrangement depends on dryer type, peak flows and where the demand events occur.
Can storage replace a second compressor?
Storage can replace a second compressor only for short events, where the receiver can supply the deficit and then recharge before the next event. It cannot replace capacity for sustained demand. If logging shows the deficit lasts many minutes or recharge time is longer than the gap between events, the plant needs more compressor capacity or a smaller event.
Why does my compressor still cycle often after adding a receiver?
The receiver may be connected through a restriction, isolated by a partly closed valve, or located away from the compressor’s pressure sensor, so the controls do not see its volume. The pressure band may also be very narrow. Check the connection size, valve positions and sensor location, then review the load and unload pressures against the manufacturer’s guidance.
How often should an air receiver be inspected?
Inspection and testing intervals are set by the applicable pressure-vessel regulations and the manufacturer’s recommendations, and they depend on the vessel and its duty. Between formal inspections, check the drain every shift or day, test the safety valve as recommended, and look for external corrosion, especially at the base and around the drain connection.
Related pages
Field guide
Storage: The cheapest way to stabilise a system
Receiver storage lets compressors run in longer, more efficient cycles, covers short peaks without starting another machine, and steadies pressure so the generation set point can be lower.
Where storage helps
- Short, high peaks such as blow-offs, test benches or batch processes.
- Fixed-speed machines cycling too often or idling for long periods.
- Sensitive users that trip when pressure dips.
- Covering the start-up time of a standby compressor after a trip.
Placement
A primary receiver near the compressors helps control and condensate removal. A secondary receiver near a large intermittent user supplies its peak locally, so the main system does not see it. Storage only works across a pressure difference: a receiver held at a tightly fixed pressure cannot release stored air.
See air receiver sizing and the receiver storage calculator.
What to send for a quotation
- Compressor make, model and rated power of each machine.
- Electricity tariff and annual running hours.
- Typical pressure at the compressor and at the furthest user.
- Any measurements you already have (power, flow, loaded hours).
Send it through find my part or the spare parts enquiry, or call +91 99590 60718 or +91 92468 88812.
Calculators and worked examples
These tools give indicative figures for screening, comparison and for preparing an enquiry. They run in your browser and send nothing. No prices or tariffs are assumed: enter your own to see costs. Efficiencies and other figures shown are example values: replace them with your own. Results are not a performance guarantee or a design certificate; final selection is confirmed by a service engineer against the machine data sheet and the site.
Receiver storage sizing
Estimate the receiver volume needed to ride through a short burst of demand without the pressure falling below the limit.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Burst demand above compressor output (m³/min free air): 5
- Burst duration (s): 20
- Allowed pressure fall (bar): 0.7
- Receiver volume you already have (litres; 0 to skip the hold-up check): 1520
Result
- Receiver volume needed: 2,412 litres
- 2.41 m³
- Practical size (with 25% margin): 3,016 litres
- Hold-up time of the receiver you have: 12.6 s before the pressure falls by 0.7 bar
Method. V = Q × t × P_atm / ΔP, where Q is the shortfall in free air (m³/min), t the time (min), ΔP the allowed pressure fall (bar) and P_atm = 1.013 bar. The same relation gives the hold-up time of an existing receiver: t = V × ΔP / (Q × P_atm). Isothermal; for a real system add a margin.
What to take from it. A receiver buys time. It does not create capacity: once it is spent the pressure keeps falling until the compressors catch up.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 7 November 2026. How our engineering content is reviewed.
Pressure budget and the cost of excess pressure
Add up the pressure that is lost between the compressor and the point of use, and see what a lower set-point would be worth.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Pressure needed at the point of use (bar g): 6
- Dryer and filter loss (bar): 0.5
- Piping loss (bar): 0.3
- Hose, fittings and regulator loss (bar): 0.3
- Control band and safety margin (bar): 0.3
- Current compressor set-point (bar g): 8
- Compressor input power (kW): 75
- Saving per bar reduced (%): 7
- Running hours per year: 6000
Result
- Total pressure losses: 1.1 bar
- Control band and safety margin: 0.3 bar
- Compressor pressure needed: 7.4 bar g (point of use + losses + band and margin)
- Possible reduction from current set-point: 0.6 bar
- Indicative energy saving: 18,900 kWh per year
- Indicative cost saving: Enter your electricity tariff (cost per kWh) above
Method. Required compressor pressure = point-of-use pressure + sum of losses. Savings = power × (reduction in bar) × saving per bar. A saving of roughly 6–8% of compressor power per bar of pressure is commonly quoted; it is indicative and varies with machine type and control, so edit it to suit.
What to take from it. The saving is real only if the farthest and most demanding point still works at the lower set-point. Prove it before you change the setting.