The Real Cost of Air Leaks
Compressed air is the most expensive utility in most plants, costing approximately £0.02–0.03 per m³ at typical UK electricity prices. A single 3 mm leak at 7 bar gauge loses approximately 30 L/min (1.8 m³/h) of compressed air. At 8,000 operating hours per year and £0.025/m³:
3 mm leak cost ≈ 1.8 × 8,000 × £0.025 ≈ £360/year
Most plants have dozens of small leaks. Use our leak cost calculator to quantify total annual losses.
Leak Rates by Orifice Size at 7 Bar
| Orifice (mm) | Flow rate (L/min) | Annual cost* (£) | Severity |
|---|---|---|---|
| 0.5 | ~1.5 | ~18 | Minor — fix during next shutdown |
| 1.0 | ~6 | ~72 | Minor — tag and fix within 1 month |
| 1.5 | ~14 | ~168 | Moderate — fix within 2 weeks |
| 3.0 | ~55 | ~660 | Significant — fix immediately |
| 5.0 | ~152 | ~1,824 | Critical — emergency repair |
*Based on 8,000 h/year, £0.025/m³ compressed air cost
Detection Methods
1. Ultrasonic Detector (Recommended)
Compressed air leaks produce ultrasonic noise at approximately 40 kHz as air passes through the orifice. An ultrasonic detector (e.g. Fluke 805 or SDT 170) picks up this high-frequency signal even in noisy environments. The signal is converted to audible sound via headphones or displayed on a meter.
Method: Survey during production (machines running), move detector slowly along pipework and fittings. Flag leaks with numbered tags for repair scheduling. Log location, estimated size, and repair priority.
Range: Leaks are detectable at 1–3 m distance depending on leak size and background noise.
2. Soap Solution
Apply diluted leak-detection soap solution (or washing-up liquid) to connections, fittings, and hose joints during a static pressure test (plant shut down). Bubbles confirm a leak — useful for precise location before repair. Cannot be used on live plant near hot surfaces or electrical equipment.
3. Pressure Decay Test
With all demand isolated, monitor system pressure over 15–30 minutes. Pressure drop = total leak rate. Good for quantifying total leakage before and after a repair programme, but does not locate individual leaks.
Most Common Leak Locations
- Threaded connections (especially older BSP fittings without thread sealant)
- Quick-release couplings — worn seals, damaged body
- Flexible hose connections and crimped ends
- Condensate drain valves (stuck open or failed)
- Pneumatic cylinder seals and piston rod seals
- Air gun and tool connections
- Control valve stem seals
Running a Leak Detection Programme
A structured programme typically follows this process:
- Baseline measurement: Pressure decay test or compressor run-time analysis to quantify total leakage as % of total compressed air supply
- Ultrasonic survey: Survey entire distribution network, tag all leaks with numbered tags, log in repair register
- Prioritise repairs: Sort by annual cost — largest leaks first
- Repair: Schedule repairs during planned shutdowns; fix critical leaks immediately
- Post-repair verification: Repeat pressure decay test and ultrasonic spot-checks to confirm savings
- Ongoing: Quarterly surveys to catch new leaks