Compressed air is often the most expensive utility in a factory, and leaks typically waste a significant portion of what is generated. Because a leak runs 24/7 and is invisible, it is easy to ignore, but every leak forces the compressor to work harder, burning electricity to replace air that never does useful work. Finding and fixing leaks, then measuring flow and air quality, is one of the fastest energy-saving wins in any plant.
Why leaks cost so much
A compressor converts a large amount of electrical energy into a relatively small amount of useful compressed air; the rest becomes heat. So every cubic metre of air lost to a leak is expensive. Worse, leaks lower system pressure, which tempts operators to raise the set point, and a higher pressure increases energy use and the leak rate. Fixing leaks lets you run at lower pressure, compounding the savings.
How to find leaks
- Ultrasonic leak detection: a leak emits ultrasound you cannot hear; an ultrasonic detector pinpoints it, even in a noisy plant and without shutting down.
- Walk the system under load: survey during production, tag each leak, and prioritise by size.
- Repeat regularly: leaks return as fittings and hoses age. A one-off survey decays, a routine programme keeps savings locked in.
Measure what matters: flow, pressure, dew point
| Measurement | Why it matters |
|---|---|
| Flow / consumption | Shows total demand and where it goes; quantifies leak load and verifies savings after repairs. |
| Pressure | Reveals pressure drops and lets you run at the lowest pressure that does the job. |
| Dew point | Confirms the air is dry enough; wet air corrodes pipes, damages tools and ruins product. |
| Oil / particles | Verifies air quality against the ISO 8573 class your application requires. |
Build the business case
Measure flow before and after a leak-repair campaign and the saving is concrete kilowatt-hours. Easy to put in front of management and to claim under energy-efficiency programmes. Continuous flow and dew-point monitoring then keeps the system honest and catches new problems early. This kind of measurement also supports ISO 50001 energy management.
Worked example: turning a leak survey into a number management approves
An ultrasonic survey across a plant's compressed air network typically tags each leak with an estimated flow loss (litres per minute at line pressure), calculated from the acoustic signature and, where practical, cross-checked with a flow meter. Say a survey identifies 40 leaks with a combined estimated loss of 150 l/min at 7 bar. Converting that continuous loss to compressor electrical demand (roughly, litres per minute of free air delivery translated through the compressor's specific power, typically in the region of 6 to 8 kW per 100 l/min for a well-run industrial screw compressor) gives a realistic estimate of the wasted electrical load running 24 hours a day, seven days a week, whether or not the plant is producing anything. That number, converted to an annual energy cost using the site's actual electricity tariff, is the business case: concrete, defensible, and directly tied to a fix (repair 40 fittings and hoses) with a payback typically measured in weeks, not years. Re-measuring total system flow after the repair campaign closes the loop and proves the saving actually happened, which is the evidence an energy-efficiency programme or management review will ask for.
Understanding ISO 8573 air quality classes
ISO 8573-1 defines air purity classes across three contaminant categories: solid particles, water (as a dew point or liquid content), and total oil content (including aerosol, liquid and vapour). Each category is rated on its own numeric scale, so a full air quality specification reads as three numbers together (for example, Class 1:4:1), not a single overall grade. The correct class depends entirely on the application: general pneumatic tools and cylinders can typically tolerate a relatively unfiltered supply, but food and beverage processing, pharmaceutical manufacturing, electronics assembly, and paint spraying all specify tighter classes, sometimes as strict as Class 1 for oil content where the compressed air contacts product directly or an ingredient stream. Getting the class wrong in either direction wastes money: over-specifying filtration and drying adds unnecessary capital and running cost, while under-specifying risks contaminated product, corroded piping, or damaged pneumatic components. Measuring your actual dew point, particle count and oil content against the class your process genuinely requires, rather than assuming a generic "clean and dry" standard is enough, is the only way to know where you stand.
Beyond leaks: artificial demand and system design
Leak repair captures the most visible and fastest-payback savings, but two other factors are worth measuring once a leak programme is underway. Artificial demand describes the effect where running the system at a higher pressure than necessary increases the flow consumed by every downstream device, not just leaks, because most pneumatic equipment consumes more air at higher pressure even when doing the same amount of useful work. Lowering system pressure to the minimum that satisfies the most pressure-sensitive point in the plant (rather than the historical "just in case" setting) reduces demand across the entire system, not only through the leaks. Second, poorly sized piping, undersized headers, and excessive pressure drop across filters and dryers all force the compressor to work at a higher discharge pressure than the point of use actually needs, compounding the artificial demand effect. A flow and pressure survey across the distribution system, not just a leak hunt, identifies these design-level losses, which a leak repair campaign alone will not fix.
Where to start
Survey for leaks with an ultrasonic detector, install flow and dew-point measurement on the main lines, fix the biggest leaks first, then lower the system pressure to the minimum the plant needs. Unitest Instruments supplies CS Instruments flow, pressure and dew-point measurement for compressed air, and can carry out a leak survey and air audit as a service; where a one-off audit or short-term monitoring campaign is a better fit than a purchase, instrument rental is also available.