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What are ultrasonic leak detectors?

As the name implies, ultrasonic leak detectors detect the ultrasonic sound of a leak. You are probably familiar with the hissing sound a large leak makes. Smaller leaks also emit a sound, however the frequency is too high for our ears to detect it. An ultrasonic leak detector transforms the ultrasonic hissing sound to a sound that humans can hear, and thus leads to the source of the leak.

Some other information about ultrasonic leak detectors includes:

• Distance and access. Some leaks can be heard from a several meters away, therefore access to the leak is not always necessary. As long as the leak is turbulent, there will be enough sound that can be detected ultrasonically.
• Pressure. High pressure of leaks is not necessary. Ultrasonic can detect pinhole leaks with a pressure as low as 1 psi. However, the more pressure behind the leak, the easier it will be to locate.
• Sensitivity to sound. Ultrasonic leak detectors are very sensitive to sound. A good ultrasonic leak detector can actually let you hear the blink of the human eye. A leak test can be done in an enclosed area which is saturated with refrigerant, and the only indication an ultrasonic will give you is the sound of the leak. A good ultrasonic detector uses an electronic process called “heterodyning” to convert this high frequency leak sound to a lower range where the hissing of the leak can be heard through a set of headphones, and traced to its source. Any turbulent gas will generate ultrasound when it leaks, therefore it does not matter what refrigerant you are leak testing. Ultrasonic detectors will even detect air as it rushes into a system under vacuum.
• Background noises. Because the ultrasonic detector is focused on a specific band/frequency of sound, it will not detect wind, voices, traffic, and most normal operational sounds. However, larger systems with a multitude of pressure regulating valves and high velocity flow may produce hissing sounds at frequencies where ultrasonic detectors are mostsensitive. In this case it would be necessary to shut the system down, or use another method of detecting leaks.
• Choice of leak detector. Always consider the capabilities and the limitations of the leak detection method used. It is thereby important to consider more than just the sensitivity under laboratory / testing conditions when choosing a leak detector. For example, a highly sensitive “sniffer” type was able to detect a leak of 0.25oz. of refrigerant per year in a controlled laboratory setting. But the leak detector would give different results when used on the windy and dirty rooftop where you might be trying to find refrigerant leaks.

Where to use a leak detector?

Ultrasonic leak detectors are used to detect leaks of compressed air and other gases which are normally not possible to detect with the human ear.

No leak detector will find every leak, every time. It is often a combination of several available methods which will insure the highest rate of success.

How to operate a leak detector?

It is not easy to generalize the operating method of a leak detector. The reason is that there are many different kinds of leak detectors that require different ways of handling. However, some steps are the same:

• The probe of the ultrasonic leak detector instrument is placed near the gas/steam pipe line where a leak is suspected
• The headphone attached to the instrument is placed on the ears
• The probe is moved slowly until the person can hear a hissing sound through headphone, indicating a leak
• The position is marked to identify the location of the leakage

Precautions and safety measurements

The following measures should be taken when using ultrasonic leak detectors:

• Dust or smoke should not be coming out of the pipe, otherwise dust/smoke will choke the probe and leads to the instrument failure
• Avoid measurement at the places where sound levels are high
• Check the operating manual of the monitoring equipment for more detailed instructions on safety and precautions before using the equipment.