Compare tool demand, delivered air and receiver storage
A farm workshop, repair bench or small production shop may need an impact tool only briefly but run another tool for several minutes.
A receiver stores air for a temporary demand surge; it does not increase the compressor’s delivered flow each minute.
Average demand below capacity can coexist with a shortfall while several tools run together.
This calculator compares both conditions so that you can review interruptions and recovery time before purchasing equipment.
Enter verified tool consumption, matching free-air delivery (FAD), receiver volume and documented operating pressures.
Results cover stored free air, buffer times with the compressor running or stopped, recovery and ideal average start/stop cycles.
Save the assumptions and evidence with your supplier worksheet.
This global engineering estimate assumes constant flow and temperature; it does not certify equipment performance or installation safety.
Match FAD and active tool consumption
Air actually delivered
Use delivered free-air flow at the documented working pressure.
Motor horsepower and piston displacement are not interchangeable with FAD.
Record the compressor model, specification revision, pressure and reference conditions.
Consumption while active
Enter the flow used by one tool while it is operating.
A catalog average may already incorporate a usage factor, so applying active time again would understate demand.
Ask whether the value is active or averaged consumption and which tool pressure it represents.
1 m³/min equals 1,000 L/min, and 1 L/s equals 60 L/min.
Converting units does not reconcile different free-air temperature, absolute reference pressure or humidity conventions.
FAD and normalized flow may use different references; reconcile them using manufacturer evidence before entering values.
Blank leakage means unknown, while entering zero explicitly models no leakage.
Average versus selected simultaneous demand
Two usage factors
For n units, simultaneity s is the proportion operating together.
Active time u is the percentage of the observation period for that group.
Use 100% simultaneity to test every registered unit together, and measure all active-time shares over the same period.
Tools with zero active time are excluded from both demands.
qpeak_i = qi × ni × si / 100
Qavg = Σ(qpeak_i × ui / 100) + Qleak
Qpeak = Σqpeak_i + Qleak
A 300 L/min tool active for 50% of the time averages 150 L/min, but it still needs 300 L/min while operating.
Selected simultaneous demand covers the combination defined by your simultaneity entries, rather than an automatically predicted maximum.
Reducing the entered percentage does not physically prevent tools from running together.
Review the 100% case as well; this model does not simulate tool sequences, independent probabilities or optimized scheduling.
Stored free air across a documented pressure band
Use only the available pressure difference
S = V × (P_hi − P_lo) / P_ref
V is receiver volume in L.
P_hi and P_lo are actual gauge pressures with the same datum; P_ref is the absolute free-air reference pressure used by the flow specifications.
All pressures must share the same unit, and changing the selector converts existing values.
The receiver is not assumed to discharge to zero pressure.
With a 100 L receiver, upper 8 bar, lower 6 bar and absolute reference 1 bar, usable stored free air is 200 L.
At a reference of 1.01325 bar, that volume is about 197.385 L.
Do not substitute local atmospheric pressure or 1 bar while retaining flow ratings stated at a different reference.
This is an isothermal approximation with receiver temperature equal to the free-air reference temperature.
Hot air after compression, cooling, condensation and rapid expansion can change the actual relation between pressure and usable air.
Running buffer, stopped buffer and recovery
From upper to lower pressure
t_off = S / Q
t_on_buffer = S / (Q − C)
With the compressor stopped throughout, divide storage by demand Q.
With full FAD C supplied from the beginning, use net consumption only when Q exceeds C.
Otherwise there is no drawdown by mass balance, which is not continuous-duty approval.
Zero demand has no finite stopped drawdown time.
From lower to upper pressure
t_recovery = S / (C − Q)
Recovery while continuing the same work requires supply above demand.
Equal supply and demand preserve the air balance but cannot refill the band.
The separate tools-off recovery estimate retains entered leakage, and recovery is impossible if that leakage meets or exceeds FAD.
Every buffer starts with the receiver at upper pressure.
An actual compressor that stops at the upper bound and restarts at the lower bound follows a different trajectory from already-running supply.
Do not treat a two-minute running buffer as a guaranteed real start/stop operating duration.
If tool pressure requirements or distribution losses make the lower bound unusable, useful operating time can be shorter.
Equivalent cycles and manufacturer limits
Assume constant average demand
t_cycle = t_off + t_recovery
starts/h = 60 / t_cycle
duty = 100 × Qavg / C
Cycle estimates require confirmation of actual start/stop control.
A finite repeating cycle exists only for average demand above zero and below FAD.
Zero demand produces zero repeating starts; demand at or above capacity cannot recover to upper pressure.
Required duty is the fraction of running time needed to produce average demand; requirements above 100% remain visible.
Enter verified manufacturer duty and hourly start limits to compare limit minus requirement.
Blank limits remain unknown rather than being replaced by a generic rule.
Observation windows, cooling requirements and minimum stopped time vary by machine.
These equivalent starts do not represent the motor starts of load/unload or variable-speed compressors.
Step-by-step use
- Verify active tool consumption and FAD references for pressure, temperature, humidity and working pressure.
Reconcile different references before comparing flows.
- Enter tool quantities, simultaneity and active-time shares for the same period.
Distinguish continuous work from brief events, and leave unknown numbers blank.
- Record receiver volume and actual upper/lower pressures from documentation.
Separately check tool pressure needs and distribution losses; field input limits are not equipment ratings.
- Confirm the shared reference and pressure conditions.
Use cycles only for verified start/stop control and enter manufacturer limits when available.
- Enter the target event duration and compare running and stopped storage needs.
Save TXT or print/PDF with the evidence and assumptions for supplier review.
Worked example: 100 L receiver and 300 L/min tool
These synthetic inputs are not product ratings or market benchmarks.
Use one 300 L/min tool, 100% simultaneity, 50% active time, 200 L/min FAD, zero leakage, a 100 L receiver, upper 8 bar, lower 6 bar and absolute reference 1 bar.
Synthetic compressed-air demand, timing and duty example| Metric | Result |
|---|
| Stored free air | 200 L |
| Average / simultaneous demand | 150 / 300 L/min |
| Simultaneous, already-running buffer | 2 min |
| Simultaneous, stopped buffer | 0.666667 min (40 s) |
| Average-demand stopped time | 1.333333 min |
| Average-demand recovery | 4 min |
| Equivalent average cycle / starts | 5.333333 min / 11.25 /h |
| Required average duty | 75% |
| Recovery with all tools off | 1 min |
| 90 s running storage needed / surplus | 150 / 50 L |
| 90 s stopped storage needed / shortfall | 450 / 250 L |
Average demand leaves flow surplus, yet the active tool consumes 100 L/min more than supply.
A fictional 60% duty limit is exceeded by 15 percentage points; a fictional limit of 10 starts/hour is exceeded by 1.25 starts/hour.
These example limits are not universal manufacturer limits and must be replaced with actual evidence.
Read shortfall, balance and pending states
Supply equals demand
With 200 L/min supply and 200 L/min demand, the mass balance is equal.
There is no surplus for recovery, so the result says balanced and cannot recover.
Additional leakage or consumption error can turn this condition into a shortfall.
Evidence is incomplete
Missing numbers or required confirmations keep the comparison pending.
Unknown values are not converted to zero to generate surplus or long runtime.
Upper pressure must exceed lower pressure; invalid units, quantities or ranges also stop calculation.
Negative target storage margin means insufficient stored air for that event under the selected supply state.
A margin of exactly zero reaches the lower bound at the end in theory, with no extra allowance for errors or losses.
Check status wording and signs alongside rounded numbers when margins are small.
Practical scenarios and measured checks
- Intermittent impact tools and longer-running tools need separate active-flow figures even if their average usage differs.
A whole-day average can hide a concentrated short event.
- If two operators take turns, save the planned simultaneity case and a 100% simultaneous case.
Discuss shortfalls when the planned sequence is not followed.
- Hoses, couplings, filters and dryers can limit pressure or flow at the tool.
Remaining receiver pressure does not establish matching pressure at the point of use.
- If observed recovery is slower, recheck FAD working pressure, leakage, averaging conventions, temperature changes and control response.
The calculation does not instruct you to raise a pressure setting.
Scope and exclusions
The model excludes pressure-dependent performance curves, rapid-discharge thermal changes, control response and actual tool scheduling.
It does not design piping, alter receivers or pressure controls, assess noise or electrical systems, or select air quality.
Flow surplus is not installation suitability or safety approval; review actual documentation and site conditions separately.
Frequently asked questions
Does equal horsepower mean equal air delivery?
Horsepower does not establish delivered flow.
Compare verified FAD at working pressure and matching reference conditions; using piston displacement can overstate supply.
Does doubling the receiver allow continuous use?
At the same pressure band, it doubles stored air and finite buffer/recovery times, but not FAD or required average duty.
Persistent demand above supply remains a flow shortfall.
Is reference pressure a gauge pressure?
The free-air reference is absolute.
Enter both receiver pressures on the same gauge datum and use their difference; do not mix gauge and absolute values or incompatible flow references.
Why is there no recovery time when supply equals demand?
Recovery needs supply left after consumption.
With C−Q equal to zero, the upper pressure cannot be restored, so the result remains balanced and cannot recover rather than inventing a finite time.
Are equivalent starts the actual motor starts?
They assume constant average demand and ideal start/stop control.
Concentrated usage, delays, minimum stopped time and pipe storage change actual cycles, and the count does not apply to load/unload or variable-speed machines.
Can I enter zero when leakage is unknown?
Zero can model a no-leakage assumption but does not verify that there is no actual leakage.
Obtain evidence for an actual capacity review and leave unknown values blank.
Is a two-minute running buffer guaranteed working time?
It starts at upper pressure with full FAD already supplied.
Actual stop-at-upper/start-at-lower control differs, and tool requirements, hose losses and temperature changes can shorten usable time.
Can I change pressure settings based on the saved result?
The worksheet communicates demand and storage for entered existing conditions.
It does not authorize pressure-control changes or receiver modifications; verify operating tables and requirements with the manufacturer and site personnel.
Sources and the next supplier check
Primary technical sources were checked on 2026-10-02.
Recheck current tool/compressor ratings, working pressures, FAD references and manufacturer duty/start limits whenever using the worksheet.
Build a review for your actual tools
Return to verified active consumption and FAD to review both average and simultaneous conditions.
TXT records units, evidence notes, confirmation states and whether the review began from a fictional example.
Check actual working pressure, distribution losses and manufacturer operating limits with the supplier before finalizing your purchase.
Enter tool and receiver conditions