In the case of compressed air and gas leaks, the medium flows out of the system. In the case of a vacuum, the flow direction is reversed: ambient air flows into the system. Here, too, turbulent flows can develop at small openings, seal seats, flanges, or valves, generating ultrasonic signals.
The ultrasound camera therefore does not detect “vacuum” as a medium, but rather the acoustic energy of the inflowing air at the leak site. The method remains passive and requires no test gas. However, the focus of the evaluation shifts: Vacuum stability, pump load, process quality, evacuation time, and contamination risk take center stage.
| Aspect | compressed air leak | Vacuum leak |
| flow direction | The medium flows out of the system. | Ambient air flows into the system. |
| Typical assessment | Energy loss, base load, compressor work, media costs. | Vacuum stability, pump load, evacuation time, process quality, contamination. |
| Acoustic signal | Often stable and distinct when pressure is sufficient. | Often weaker and more dependent on geometry, distance, and access. |
| Measurement strategy | Start from a distance, check large leaks first, then move closer to smaller sources. | Short distance, quiet frequency window, multiple viewing angles, and targeted inspection of sealed areas. |
Since the absolute pressure difference in many vacuum applications is smaller than in compressed air networks, a weaker ultrasonic signal often occurs at the leak site. In addition, the geometry of the leak has a significant influence on sound radiation. Small gaps or seal seats often produce less directional ultrasound than nozzle-like outlet openings in compressed air applications.
For practical leak detection, short measurement distances, low-interference frequency windows, stable process conditions, and measurements from multiple angles are particularly crucial. For microleaks, the limiting factor is usually not the system’s theoretical sensitivity, but rather the signal-to-noise ratio at the microphone array. The key factor is whether the leak signal stands out sufficiently from the background ultrasound.
Leak in a vacuum pump in a utility room
| 1. | Perform the measurement under actual operating conditions if the leak occurs only under vacuum. |
| 2. | Start at a short distance, because the signal is often weaker than with compressed air leaks. |
| 3. | Use FFT or a frequency window to reduce interference in the ultrasonic range. |
| 4. | Scan for leaks from multiple angles, as gaps and cracks can emit sound in specific directions. |
| 5. | For enclosed panels, use open areas or gaps; do not measure through Plexiglas or solid surfaces. |
| 6. | Always evaluate hotspots in the context of the system: Prioritize vacuum components and sealing areas, and critically assess reflective surfaces. |
Differential pressure determines the signal strength. The greater the pressure difference relative to the ambient pressure, the stronger the ultrasonic signal at the leak. As a practical lower limit, the pressure should be approximately −300 mbar relative (approx. 700 mbar absolute); below this level, the leak becomes more difficult to detect acoustically.
Material transport can cause interference. If the vacuum system conveys solids such as injection-molding pellets, the impact of the particles against the pipe wall can generate broadband ultrasound that masks the leak signal. Since this ultrasonic noise lies within the same frequency range, shifting the frequency window is only of limited help—therefore, testing should be performed under vacuum without simultaneous material transport.
Very small leaks may fall below the acoustic detection limit—or be masked by spatially close, stronger ultrasonic sources. If this cannot be resolved even by reducing the measurement distance, supplementary leak testing methods may be necessary.
Ultrasonic measurement quickly locates typical leaks during operation, but does not replace every highly sensitive leak test in the micro-range.
In-Depth:Compressed Air Leak Detection Despite Ultrasonic Interference Sources
| Problem | Ultrasonic Solution | Advantage |
| Vacuum Reaches Setpoint Only Slowly | Systematically inspect sealing areas with ultrasound. | Faster identification of potential sources of external air ingress. |
| Pump load increases | Locate and prioritize leak points. | Lower pump load and more stable operation. |
| Process quality fluctuates | Test seals and chambers under actual operating conditions. | Less external air ingress and more stable process conditions. |
| Leak is difficult to access | Measurement from a safe position or across open areas. | Less disassembly required and faster inspection. |
Detects multiple leakages simultaneously with globally unique Power Beam Forming. 4th generation technology - also suitable for other gases. Helps to locate and repair leaks - including cost estimation and ISO 50001 documentation.
uses 30 MEMS microphones for Calculation and visualization of the ultrasound image. The device also makes inaudible ultrasound audible.
Due to the integrated camera and the available accessories our starter kit for leak detection enables reliable leak detection as well as compressed air leakage calculation and reporting according to ISO 50001.