High compressed-air use during downtime generally means air is still flowing somewhere: leakage, purge cycles, drains, blow-off nozzles or standby equipment. First verify that actual flow is high. A compressor running unloaded can consume significant electricity while delivering little useful air, so compressor runtime and compressed-air consumption are different measurements.
Separate standby air use from compressor electricity
A flow meter can show compressed air passing through a branch while the compressor is unloaded or off; motor runtime can also remain high when actual flow is low. Collect demand, power and pressure trends over the same downtime window. Only after identifying an unintended branch flow should estimated annual losses be calculated from its measured baseline and operating schedule. For related guidance, see Compressed Air Flow and Consumption: Units, Meters and Audits.
Identify which quantity is high
| Observed quantity | What it tells you | What it cannot prove |
|---|---|---|
| Header flow (standard m³/h) | Air crossing the meter boundary | Which branch wastes it |
| Totalized volume (standard m³) | Quantity delivered during a period | Compressor electrical cost by itself |
| Compressor runtime | How long the motor or machine runs | Useful air demand |
| Header pressure (bar, psi) | System pressure condition | Amount of air leaked without other data |
Downtime diagnostic sequence
- Record main-line flow, pressure and compressor load/unload state during normal production.
- Repeat during a representative scheduled production stop using the same meter location and flow units.
- List intentionally active systems: instrument air, safety actuators, dryer regeneration and known purges.
- With authorization, compare individual branches or controlled isolation periods to narrow the source.
- Inspect confirmed demand paths, including hoses, fittings, valves, air knives, blow-offs and drains.
- After repair, remeasure identical downtime conditions and verify whether consumption falls.
Worked example: what is really lost?
Hypothetical: a main-line meter averages 35 standard m³/h during a six-hour stop. Total delivered volume is 35 × 6 = 210 standard m³. A separately verified essential standby process accounts for 8 standard m³/h, leaving a 27 standard m³/h investigation baseline—not automatically 27 m³/h of leakage, because other legitimate consumers may remain.
Testo instrument for the measurement
The testo 6441 measures inline compressed-air flow and totals consumption in a correctly sized DN15 line. Its integrated totalizer supports before/after auditing. It does not locate leaks acoustically or directly report compressor kilowatt-hours. Its installation, flow range and reference conditions must match the pipe.
What to investigate after the air audit
If the measured demand is low but the compressor still runs, review load/unload control, pressure band, sequencing, storage and compressor sizing with qualified personnel. If actual idle flow remains high, prioritize demand-side leaks and unintended uses before changing compressor controls. Do not isolate controls or safety-related instrument-air circuits just to improve the reading. For related guidance, see Velocity Reading Isn’t Enough for Duct Flow—and How Traverses.
The U.S. DOE documents the economic significance of compressed-air leakage. However, any percentage reported for other systems is contextual information, not a measured loss rate at this site.