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To locate the leak area, gradually position the rod until the leak sound is heard at its loudest point. An
alternative to this is to use a flat metal disc or coin and drop it on the test area. Touch the disc and listen at
20 kHz. This is useful when testing concrete or asphalt to eliminate scratching sounds caused by slight
movements of the stethoscope module on these surfaces.
B. LEAKAGE BEHIND WALLS
1. Look for water or steam markings such as discoloration, spots in wall or ceiling, etc.
2. If steam, feel for warm spots in wall or ceiling or use a non-contact infrared thermometer.
3. Set Frequency to 20 kHz and use stethoscope probe.
4. Listen for leak sounds. The louder the signal the closer you are to the leak site.
PARTIAL BLOCKAGE:
When partial blockage exists, a condition similar to that of a bypassing valve is produced. The partial
blockage will generate ultrasonic signals (often produced by turbulence just down stream). If a partial
blockage is suspected, a section of piping should be inspected at various intervals. The ultrasound
generated within the piping will be greatest at the site of the partial blockage.
PROCEDURE:
1. Use stethoscope module.
2. Touch downstream side of suspected area and listen through headset.
3. Start test at 40 kHz. If the sound appears weak or confusing, change the frequency. As an example, try
to test at 30 kHz. then 20 kHz.
4. When necessary, if there is too much sound, reduce sensitivity.
5 Listen for an increase in ultrasound created by the turbulence of partial blockage.
FLOW DIRECTION
Flow in piping increases In intensity as it passes through a restriction or a bend in the piping. As flow
travels upstream, there is an increase in turbulence and therefore the intensity of the ultrasonic element of
that turbulence at the flow restriction. In testing flow direction, the ultrasonic levels will have greater
intensity in the DOWNSTREAM side than in the UPSTREAM side.
PROCEDURE:
1. Use stethoscope mode.
2. Start test in 40 kHz. If it is difficult hearing the flow signal, adjust the Frequency to 30 kHz or to 25 kHz.
3. Begin test at maximum sensitivity level.
4. Locate a bend in the pipe system (preferably 60 degrees or more).
5. Touch one side of bend and note dB reading.
6. Touch other side of bend and note dB reading.
7. The side with the higher (louder) reading should be the downstream side.
NOTE: Should it be difficult to observe a sound differential, reduce sensitivity and test as described until a
sonic difference is recognized.