For example, at a waste water facility, in the basement, below a massive blower the audible sound was so loud no amount of yelling could be heard. You had to read a man’s lips and gesture to understand each other. But the SDT ultrasound detector heard only a single whistle coming from a blown seal on a regulator.
Repairing that one large leak took away the need for 1 of the 3 new compressors that had recently been installed.
If only they had performed an air leak survey before ordering the compressors.
If you have leaks you can hear, then there are many more leaks that just aren’t big enough to make an audible sound. If you don’t hear leaks, but your compressors run when demand is off peak. Then you have leaks.
Electrical arcing, tracking and corona generate ultrasonic sound immediately. You do not have to wait for the condition to worsen so excess heat brings a thermal difference that an IR camera can pick up.
Using contact probes or magnet sensors, you can perform structure borne ultrasound detection. This is used extensively for monitoring bearing conditions, traps, valves and to perform acoustic lubrication for proper grease application.