A typical city centre – a challenging environment for leak detection
A city centre, such as that shown above, represents possibly the most challenging environment for a leakage team:

City centre distribution systems are extremely dynamic during daytime hours - and often at night

Multiple connection junctions provide a large number of possible routes for the leak noise, making it difficult to track down the source of the leak

Mains are often of large diameter, giving rise to low frequency leak noise being transmitted through the system. This type of leak noise is inaudible to the human ear

Ambient noise from traffic makes it difficult to concentrate and to discriminate differing levels of leak noise

Visual observations are often misleading due to the many underground services that can channel water leakage away from its source

The safety of pedestrians and motorists must be taken into account at all times

In the metropolitan environment there is an increased risk of equipment theft, particularly when correlating.

As a result of these problems, leak detection in the city centre is often time consuming, expensive and ineffective.

Sigma Hellas Ltd. offers a variety of leak detection equipment that can help the leakage team to meet any challenge.

Step Testing

The aim of step testing is to isolate lengths of the distribution system where leakage is measured quantitatively. The leakage can then be further investigated, usually by correlation and acoustic sounding

Leak Noise Correlation

Leak noise correlators are used to pinpoint the leak location.

A correlator works by detecting the sound from the leak when it arrives at two sensor points on the pipe, either side of the suspected leak position. The sound arrives at the closer of the two sensors first; then there is a "time delay" (Td) before the sound arrives at the farther sensor. This time delay, combined with knowledge of the distance (D) between the sensors and the velocity (V) of the sound in the pipe, enables the correlator to calculate the leak position (L).

This metod ensures that leaks are detected accurately and quickly, even under difficult site conditions.

Acoustic Logging

Probably the most significant advance in practical leak detection since the correlator, acoustic noise loggers enable leaks to be localised without disturbing the network. They are now replacing "stop tap bashing" as a routine survey tool, yielding significant benefits of cost efficiency - more leaks detected, more quickly and at lower cost.

Acoustic Leak Detection

Electronic listening sticks and ground microphones are increasingly used as routine tools to survey areas of suspected leakage. Ground microphones may also be used to confirm the precise position of a leak prior to excavation.