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1. LEAK DETECTION
This section will cover airborne leak detection of pressure and vacuum systems. (For information concerned with internal leaks
such as in Valves and Steam Traps, refer to the appropriate sections).
What produces ultrasound in a leak? When a gas passes through a restricted orifice under pressure, it is going from a pressurized
laminar flow to low pressure turbulent flow. (Fig. 1). The turbulence generates a broad spectrum of sound called "white noise". There
are ultrasonic components in this white noise. Since the ultrasound will be loudest by the leak site, the detection of these signals is
usually quite simple.
A leak can be in a pressurized system or in a vacuum system. In both instances, the ultrasound will be produced in the manner
.
described above. The only difference between the two is that a vacuum leak will usually generate less ultrasonic amplitude than a
pressure leak of the same flow rate. The reason for this is that the turbulence produced by a vacuum leak is occurring within the
vacuum chamber while the turbulence of a pressure leak is generated in the atmosphere. (Figs.2/3).
What type of gas leak will be detected ultrasonically? Generally any gas, including air, will produce turbulence when it escapes
through a restricted orifice. Unlike gas specific sensors, the Ultraprobe is sound specific. A gas specific sensor is limited to the
particular gas it was designed to sense (e.g., helium). The Ultraprobe can sense any type of gas leak since it detects the ultrasound
produced by the turbulence of a leak.
A. HOW TO LOCATE LEAKS
1. Use the TRISONIC SCANNING MODULE.
2. Select the LOG setting on the meter selection dial.
3. Use "fixed-band" position on the Frequency selection dial. If too much background noise is present, try some of the shielding
methods listed below.
4. Start off with the sensitivity selection at 10 (Maximum).
5. Begin to scan by pointing the module towards the test area. The procedure is to go from the "gross" to the "fine" - more and more
subtle adjustments will be made as the leak is approached.
6. If there is too much ultrasound in the area, reduce the sensitivity setting and continue to scan.
7. If it is difficult to isolate the leak due to competing ultrasound, place the RUBBER FOCUSING PROBE over the scanning
module and proceed to scan the test area.
8. Listen for a "rushing" sound while observing the meter.
9. Follow the sound to the loudest point. The meter will show a higher reading as the leak is approached.
10. In order to focus in on the leak, keep reducing the sensitivity setting and move the instrument closer to the suspected leak site
until you are able to confirm a leak.
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ULTRAPROBE APPLICATIONS
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