Page 300 - Water Loss Control

Contr olling Real Losses in the Field—Pr oactive Leak Detection 269

lengths of pipe and fittings such as flanged tee’s, bends, and valves may also have a
coating hardened epoxy resin. This too will reduce quality and propagation of leak
noise.

Types of Leak Noises
Smaller fittings, valve packing, and pinhole leaks tend to produce higher frequency
leak noise than cracks, breaks, and some joint leaks. Smaller leaks often have a “hiss-
ing” sound and larger leaks have more of a “rumble.”

Surface Covering the Pipe
Sandy soils and asphalt conduct sound quite well as opposed to clay and concrete.
Backfill soils that have cavities diminish the transmission of leak sound. Sounding on
unpaved surfaces is more difficult and a probe rod may need to be rammed through the
ground, if possible, to make content with the pipe to transmit the sound. If this is not
possible a device known as a “thumb tack” (round metal plate with a rod attached
transversely) can be placed in the ground as a sounding surface.

Soil Moisture
The variation of soil moisture and the altitude of the water table effect the propagation
of leak noise. Increased water in the soil diminishes the leak sound transmission. A
saturated soil creates a backpressure against the leak origin.

Sources of Interference with Leak Noise
Noise generated by traffic, pressure reducing valves (PRVs), consumer consumption,
partially closed valves, aircrafts, leaf blowers, air conditioners, generators, trains, cable
cars, compressors, transformers, and the like, all can compete with leak noise in a given
location and make leak detection more difficult. Many of these noises, however, occur
at frequencies outside of the typical leak noise frequencies. Today’s modern electronic
sounding equipment (leak noise loggers, leak correlators) have filters that separate
sound outside of typical leakage frequencies, making the existing leak noise detectable.
Still, the existence of interfering noises should always be closely considered by the leak-
age inspector in attempting to discern and pinpoint leakage.

16.4 Leak Detection Equipment
Leak detection equipment is available in a wide range of technologies, capabilities, and
prices. Hence a good understanding of the nature and occurrence of real leakage losses
enables the water utility operator to select the most appropriate technology. It is very
important to note that even highly sophisticated and expensive leak detection equip-
ment does not represent an appropriate remedy for a utility’s leakage problem if the
utility does not yet understand the real extent and nature of leakage occurrences in its
distribution system. A reliable benefit to cost analysis should be conducted before mak-
ing a major investment in leak detection equipment.
The most important factor for success in detecting leaks using any type of equip-
ment is the experience of the leak detection team in using the available equipment and
interpreting the results received from the equipment. The operator must be trained to
understand not only how to use the acoustic sounding equipment but also its limita-
tions. Only then will he successfully tailor the leak survey procedure to match the capa-
bilities of his equipment to the distances that leak sounds typically travel in his