What artificial demand means
Many compressed-air users behave like a fixed opening. An open blow-off nozzle, a leak, a vortex cooler or an air knife passes more air when the pressure upstream rises, even though the job it does stays the same. If the header runs at 7.5 bar when 6 bar would do, those users quietly take more air every hour the plant runs. That extra flow is artificial demand: air supplied without any extra useful output.
The effect is easy to underestimate because nothing looks wrong. Production runs, gauges look healthy and the compressor simply loads a little longer. Yet the compressor must generate that extra flow, and at a higher discharge pressure, so the plant pays twice: once for more air and again for compressing all of it harder.
It helps to keep four things apart in records, even though their savings overlap:
- Pressure-driven excess: the same user consumes more because pressure is higher than needed.
- Unnecessary running time: air flows when the task is absent, such as a blow-off left open at break time.
- Physical leakage: air escaping through a defect, whose flow also rises with pressure.
- Unsuitable use: a task that a blower, a fan, an electric tool or a better nozzle could do with less energy.
A leak fixed and a pressure lowered are two different actions. Their separately estimated savings cannot simply be added, because the lower pressure also reduces the flow through any leak that remains.
Why artificial demand stays hidden
Pressure in many plants creeps up over years. A machine once tripped on low pressure, so someone raised the compressor setting by half a bar. A new line was added at the end of an undersized pipe, so the station pressure went up again. Each change made sense at the time; together they leave the whole network running well above what most users need.
Common reasons the header pressure is higher than necessary:
- One small high-pressure user, often a single press or test rig, setting the pressure for the whole plant.
- Pressure drop across clogged filters, undersized dryers or long, narrow pipes, made up by raising the compressor setting.
- Restrictive hoses, quick couplings and regulators at the machine, so the gauge at the header looks fine while the tool starves.
- Wide load–unload bands or poorly coordinated multi-compressor controls.
- Historical settings nobody has questioned since commissioning.
How much pressure does each user really need?
The starting point is the minimum dynamic pressure each important user needs at its inlet, while working, to do its job reliably. That is not the same as the gauge reading at the compressor or the static pressure when nothing is running. Machine makers’ manuals often state a working pressure for cylinders, tools and controls; where they do not, it can be established by a careful trial.
| User type | Responds to higher pressure? | Typical action |
|---|---|---|
| Open blow-off, air knife, nozzle without regulator | Yes, flow rises roughly in proportion to absolute pressure | Fit a regulator, engineered nozzle or timer; review if air is needed at all |
| Leaks | Yes, in the same way | Repair, then lower pressure to cut residual leak flow |
| Pneumatic cylinders without regulators | Yes, air per stroke rises with pressure | Regulate to the force actually needed |
| Regulated users with their own regulators | Little, as long as supply stays above the set point | Check regulator set points are not higher than needed |
| Process users with a fixed mass-flow need | No, consumption is set by the process | Leave alone; protect the minimum pressure |
A simple demand profile, logged over at least a typical production week, shows how much of the total flow is pressure-sensitive. Our air demand profiling and pressure profiling pages explain the measurements.
Use absolute pressure in the arithmetic
Flow through a fixed opening at choked conditions is roughly proportional to the absolute upstream pressure, not the gauge reading. At sea level, absolute pressure is gauge pressure plus about 1.013 bar.
Worked example: an open nozzle passes 20 m³/h of free air at 7.0 bar(g). Absolute pressure is about 8.0 bar(a). Reducing to 6.0 bar(g), about 7.0 bar(a), changes flow by roughly 7.0 ÷ 8.0, so the nozzle now takes about 17.5 m³/h. Using gauge figures (6 ÷ 7) would overstate the saving. This is a teaching estimate; real users differ, so the trial is what counts.
The compressor also gains. As a typical figure, a screw compressor uses about 7% more power for every extra bar of discharge pressure, so lowering generation pressure saves energy even on air that is not artificial demand.
Lower the header pressure or regulate locally?
| Approach | When it suits | Watch out for |
|---|---|---|
| Lower the compressor discharge pressure | Most users can work at the lower pressure and the pipe system has little drop | Critical users at the far end of the network; pressure dips during peak demand |
| Regulate locally at the user | Only some users are pressure-sensitive, or a few need higher pressure | Regulators set too high, or sized too small and starving the tool |
| Fix the cause of pressure drop | Filters, dryers or pipes lose a large share of pressure | Needs a pressure-drop survey to find the restriction first |
| Separate supply for a high-pressure user | One small user forces the whole plant to run high | Cost and maintenance of a booster or dedicated compressor |
| Flow or pressure controller after storage | Large swings in demand with good receiver capacity upstream | Needs adequate storage and the right control band |
See pressure optimisation and artificial demand and working pressure and the system pressure budget for the full method.
Running a controlled pressure trial
Pressure should come down in steps, with production’s agreement and a way to step back quickly.
- Agree which users are critical and what minimum pressure each needs; record who can stop the trial.
- Log flow, pressure at the station and at key users, and compressor power for a baseline period of normal production.
- Lower the set point by a small step, typically 0.2–0.3 bar, and hold it through at least one full production cycle.
- Watch the critical users, reject rates, cycle times and any low-pressure alarms.
- Repeat the step until a user shows the first sign of trouble, then go back one step and add a working margin.
- Record the final settings, the reason for them, and lock or label the adjusted regulators.
Do not chase the lowest reading seen on a quiet day. A setting that works at night shift may fail at full load, and one that works in the cool season may not cope when the Hyderabad summer pushes compressor room temperatures up and capacity down.
Proving the saving
A lower gauge reading is not proof. The trial needs comparable flow and power data before and after, taken under similar production. Correct for changes in output, shifts and ambient temperature, or compare like-for-like periods. Then check that the compressor controls actually turned the lower demand into lower power: a machine that simply unloads more often, at a high unloaded power, may show a smaller saving than the air figures suggest.
- Use specific power, in kW per m³/min of delivered air, as the station’s efficiency measure.
- Report pressure reduction, leak repairs and running-time controls separately, with a combined measured figure.
- Avoid adding independently estimated savings, because they overlap.
Our power and flow logging and specific-power assessment pages describe the measurement set-up.
When results do not match expectations
| Observation | Likely explanation |
|---|---|
| Pressure lower, flow unchanged | Most demand is regulated or process-fixed; little pressure-sensitive demand existed |
| Flow lower, power barely changed | Compressor control wastes the gain in unload running; review controls or sequencing |
| A machine starts faulting | Local restriction at that machine, not low header pressure; fix the hose, coupling or regulator |
| Savings fade after months | Settings raised again, new users added, regulators tampered with |
Keeping the improvement
Once the right pressure is found, make it hard to drift. Record the agreed set points on the compressor panel and in the maintenance system. Lock or tag regulators. Require an engineering check before anyone raises station pressure, and ask first whether a local restriction is the real cause. Recheck the pressure profile after any major line addition and at the start of summer.
How Reddy Compressors helps
We carry out compressed-air audits following the ISO 11011 method, including demand and pressure profiling, pressure-drop surveys, power and flow logging and leak surveys. We do not issue conformity certificates; we give you measured findings and a clear action list. Our engineers can then run the pressure trial with your production team, adjust compressor controls, fit regulators and correct restrictions.
As an independent multi-brand specialist we service and supply ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other makes, so recommendations are not tied to one brand. Our office is at Tarnaka, Secunderabad, and our service teams cover the whole of Telangana and Andhra Pradesh, with project support elsewhere in India where feasible.
What to send us
- Compressor makes, models and pressure settings, with nameplate photos.
- A simple line diagram of the plant air network, if available.
- The users you believe need the highest pressure and why.
- Any existing pressure, flow or power records and electricity consumption data.
- Production pattern: shifts, weekends and seasonal changes.
Frequently asked questions
Is artificial demand the same as a compressed air leak?
No. Artificial demand is the extra air consumed because pressure is higher than needed. Leaks contribute to it, because leak flow rises with pressure, but a leak is a physical defect to repair. Lowering the pressure reduces both leak flow and the excess taken by open blow-offs and unregulated users. Record the leak repair and the pressure reduction as separate actions.
How much energy does reducing compressor pressure save?
As a typical figure, a screw compressor uses about 7% more power for each extra bar of discharge pressure, so lowering pressure saves compression energy. Unregulated users and leaks also take less air at lower pressure. The real saving depends on how much of your demand is pressure-sensitive and how well the compressor controls respond, so it should be measured, not assumed.
Will fitting a regulator always reduce air consumption?
Only for users whose consumption rises with pressure, such as open nozzles, air knives and unregulated cylinders. A regulator set too high saves nothing, and one that is too small can starve the tool so operators raise the header pressure. Process users that need a fixed mass of air will not use less. Size the regulator correctly and set it to the measured need.
Why is a gauge reading not enough to set the right pressure?
A static gauge shows pressure when little air is flowing. What matters is the dynamic pressure at the user while it works, during peak demand. Restrictive hoses, couplings and filters can drop pressure sharply under flow, so a header that looks fine may still starve a machine. Log pressure at the user under load before deciding on a lower setting.
Should one high-pressure machine have its own compressor?
Often, yes. If a single small user needs higher pressure than the rest of the plant, running the whole network high to serve it wastes energy every hour. A small booster or dedicated compressor for that user can let the main station run lower. Compare the extra equipment and maintenance against the measured saving before deciding.
Does a successful short trial prove the pressure is right all year?
Not on its own. Demand changes with production mix, shifts and season, and compressor capacity falls in hot weather. Repeat checks at peak production and during the summer, and keep a margin above the first point where any user struggles. Treat the agreed setting as monitored, not fixed for ever.
Related pages
Field guide
Artificial demand: Air you use only because pressure is high
Every open leak, unregulated blow-off and uncontrolled user consumes more air when system pressure is higher. This extra consumption is called artificial demand. Lowering pressure to what users actually need reduces it, on top of the saving at the compressor itself.
Where it comes from
- Leaks, whose flow rises with pressure.
- Open blowing nozzles and cleaning guns without regulators.
- Equipment supplied at full system pressure when it needs less.
How to reduce it
- Find the pressure each user actually needs, at the point of use.
- Fix pressure drops in filters and pipework so generation pressure can come down.
- Fit regulators on users that need less than system pressure.
- Use efficient nozzles and timer or sensor control on blow-offs.
- Lower generation pressure in steps, watching the most sensitive users.
Do not lower pressure blindly: one critical user may set the minimum. If only one user needs high pressure, a local booster may be cheaper than running the whole system high.
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.
Artificial demand after a pressure change
How the flow of pressure-sensitive users (leaks, open nozzles, unregulated cylinders) changes when the supply pressure changes, the compressor saving from the lower set point, and a combined estimate that does not double-count the two.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Present flow of pressure-sensitive users (free air, unit below): 20
- Flow unit: m³/h
- Present supply pressure (bar g): 7
- Proposed supply pressure (bar g): 6
- Atmospheric pressure (bar a): 1.013
- Compressor input power (kW; 0 to skip): 0
- Power saving per bar reduced (%): 7
- Running hours per year: 0
- Specific power (kW per m³/min; 0 to skip): 0
Result
- Absolute pressures: 8.01 → 7.01 bar a
- New flow of the pressure-sensitive users: 17.5 m³/h = 0.292 m³/min = 292 L/min = 10.3 cfm
- Air saved: 2.5 m³/h = 12.5% of that flow
- Gauge-ratio figure (do not use): 17.14 m³/h would claim 14.3%, overstating the change
- Energy: enter compressor kW and specific power for the power and combined figures
Method. Pressure-sensitive users behave like a fixed opening: at choked conditions free-air flow is proportional to absolute upstream pressure, so Q_new = Q_old × (p_new + p₀) ÷ (p_old + p₀). The gauge ratio p_new ÷ p_old overstates the change and is shown only as the pitfall. Compressor saving from the lower set point = input kW × Δp × saving per bar (about 7% per bar is typical; edit it). Energy of the air no longer used = air saved (m³/min) × specific power × hours. The two overlap; the combined estimate = kW − (kW − air saved × specific power) × (1 − saving per bar × Δp). Regulated users and process users with a fixed mass flow do not respond. Teaching estimate: prove the saving by a stepped trial with logged flow and power.
What to take from it. Lower pressure in small steps against the minimum each critical user needs, and report pressure reduction, leak repair and running-time controls separately with one measured combined figure.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.