Heath Consultants Aqua-Scop - Manual (Page 34)

(Figure 20)
Leakage on Asbestos-Cement and Plastic Pipe
The very poor transmission of sound on this material will make other
methods for detection necessary. The efficiency of using the Direct Contact
Microphone for the preliminary localization will be diminished by the lack
of sound transmission through the line. Also, if testing fittings with direct
contact with the Direct Contact Microphone no sound of flowing water is
heard, the presence of a leak cannot be excluded. It is recommended in all
cases to check over the mains with the Ground Microphone at distances
of 3 to 6 feet.
Other Sonics
Some highly sophisticated sonic instrumentation has been developed using
sound delay techniques, computer analysis, and analysis of sound waves
on the oscilloscope. These methods are quite expensive but should be
considered where conventional sonic methods are impractical.
G. Alternate Methods of Leakage Detection
Tracer Gases
For situations where sonic testing is completely impractical, the use
of tracer gases should be considered. There are several tracer gas
systems available and the following is a brief synopsis of advantages
and disadvantages of four of these systems:
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