Page 299 - Water Loss Control

268 Cha pte r S i x tee n

Impact sound

Leak

FIGURE 16.8 Impact sound.
16.3.3 Factors Influencing the Quality of Leak Sound

Pressure
The audible volume, quality, and propagation of leak noise are pressure dependent.
The higher the pressure, the better the quality of the leak noise and vice versa. There
needs to be at least 30 psi (~21 mH) in a zone for effective direct sounding using a
listening stick. In many distribution systems pressure during the day is less than pres-
sure at night due to higher consumer demand during the day. If day pressure is less
then 30 psi (21 mH) sounding should be carried out at night when consumption is
reduced and pressure in the system is higher. The most effective time for sounding in
densely populated urban areas is generally expected to be between the hours of 2:00 and
4:00 a.m. when consumption is at its lowest and pressure is at its highest. This is also
a time when traffic and other above-ground noises are at a minimum.

Pipe Material and Pipe Size
The audible volume, quality, and propagation of leak noise are also dependent on pipe mate-
rial and pipe size. Generally, the harder the pipe material (i.e., steel) and the smaller the diam-
eter, the better the quality of leak noise and the further the noise will travel along the pipe wall.
Conversely, those pipes with softer material (i.e., PVC) and larger diameter, will attenuate leak
noise. The following is a guide to noise propagation values on varying pipe material:

Cast iron ⎫
⎪
Steel ⎬ Good (for leak noisse sounding)
Copper ⎪
⎭
Ductile iron ⎫ A Average
⎬
Asbestos cement ⎭
PVC ⎫
MDPE ⎪ ⎪
HDPE ⎬ Poor
Internally lined ⎪ ⎪
Externally wrapped ⎭

Some corrosion protection applied to metallic pipes can diminish quality and prop-
agation of leak noise as well. Steel pipes usually have an internal concrete lining and are
externally wrapped and/or coated in bitumen paint, both absorbing leak noise. Smaller