Compressed air leaks do not result in a one-off loss, but permanently increase air demand. The additional air must be generated by the compressor, dried, filtered and distributed throughout the network. This leads to increased electricity consumption, running times, pressure losses and maintenance costs. The base load is particularly critical: high consumption outside of production often indicates leaks or unnecessary venting.

Leak detection should therefore not be viewed as an isolated maintenance task, but as a demand-side measure. Only once consumption, base load and the proportion of air lost to leaks have been reduced can the supply side be meaningfully assessed in terms of compressor control, pressure band and specific output.

Example of a weekly measurement: base load and standstill losses become apparent and can be assessed from an economic perspective.

In industrial leak detection, the distinction between audible sound and ultrasound is crucial. Most production noises fall within the audible, low-frequency range. Leaks in compressed air and gas pipes generate broadband turbulence with high-frequency sound components at small leak openings. Large leaks often generate audible sound as well; however, in production environments, this is frequently masked by machine noise.

The ultrasound generated by a leak is not caused by the gas itself, but by the turbulence that occurs as the gas escapes. The pressure difference, the geometry of the leak and the shape of the outlet opening determine the sound intensity and the frequency spectrum of the ultrasonic waves generated.

Higher frequencies offer better spatial resolution due to their shorter wavelength. However, as the frequency increases, atmospheric attenuation also increases, thereby reducing the achievable detection range. The choice of measurement frequency therefore represents a trade-off between resolution, range and interference suppression. In many industrial applications, a frequency range around 40 kHz has proved to be favourable. In environments subject to interference, however, a different frequency window may yield better results.

Further reading: Leak detection despite interference

The advantage of the ultrasound camera lies in the combination of distance measurement and visual identification. Leaks can be localised whilst the plant is in operation, when it is operating under real-world pressure and load conditions. This also reveals leak points that would not occur if the plant were switched off.

• Pipes on hall ceilings: inspection from a safe distance, without the need for a ladder or aerial work platform, provided the leak is sufficiently severe.
• Machinery and pneumatic systems: Systematically check valves, cylinders, hoses, couplings, filters, regulators and maintenance units for leaks.
• Protective grilles and robotic cells: With acoustically transparent grilles, the sound source can also be localised behind the barrier.
• Hazard and logistics areas: Measurements can be carried out outside the range of photoelectric sensors, robotic cells or forklift routes.
• Hard-to-access areas of plant: The ultrasound camera enables leak detection even at points of measurement with restricted access. This requires sound to propagate as directly as possible between the leak and the camera.

Example: Hard-to-access factory ceiling: The hotspot indicates an ultrasonic source on a compressed air pipe.	Example: Protective grilles can be largely acoustically transparent to ultrasound. The hotspot remains visible when the sound waves pass through the grille.

Wire mesh and protective fences are often largely permeable to ultrasonic waves. In contrast, solid surfaces such as Plexiglas, sheet metal, concrete, glass or smooth machine casings act as strong reflectors. For reliable leak detection, there should therefore be a direct sound path between the leak and the microphone array.

In the example shown, this direct sound path is made possible by an open gap in the Plexiglas casing. The solid casing is not in the sound path and therefore does not affect the measurement.

Packaging machine with plexiglass casing: The measurement is carried out via an open gap providing a direct sound path to the leak.

The volume of water lost and the resulting costs are the key factors in prioritising repairs. As large leaks can mask the sound of smaller leaks, they should be documented and repaired first. A subsequent follow-up inspection often reveals further leaks that were previously hidden.

Prioritisation logic: A small proportion of leaks often accounts for the largest proportion of losses. Repair large, dominant leaks first.

Leak detection alone does not save energy. Savings are only achieved through repair, follow-up and monitoring of the new operating condition. Any leaks found should be documented, including their location, a photograph, the leak rate, a cost estimate, repair instructions and status. Consumption is then compared before and after the work has been carried out.