Acoustic leak detection finds leaks in pressurised water pipes by listening for the noise escaping water makes and working out where it comes from.
Acoustic leak detection finds leaks in pressurised water pipes by listening for the noise that escaping water makes. Water forced out through a crack or joint under pressure creates vibration in the pipe wall and sound in the water. Sensors pick up this noise, and the operator or software works out where it comes from. There are three common methods. Listening sticks and ground microphones let a trained operator hear the leak at valves, hydrants or the ground above the main. Noise loggers are left on fittings overnight, when demand and traffic are low, and flag those that hear a steady sound. Leak noise correlators place two sensors on either side of a suspected leak. From the time lag, the distance between sensors and the speed of sound in the pipe, the correlator gives the leak position: x = (D - v·τ)/2, where x is the distance from the sensor that hears it first. Utilities use these methods for active leakage control, often inside a district metered area where high night flow shows that a leak exists. Permanent loggers with telemetry can watch a network and send alerts. Pipe material matters. Metal pipes carry leak noise far. Plastic pipes such as PVC and polyethylene damp the sound strongly, so sensors must be closer, and hydrophones in the water often work better than sensors on the pipe wall. Pumps, traffic, customer use and pressure reducing valves add false noise. The correlator needs the right pipe material and diameter to estimate sound speed. For example, sensors 200 m apart on a cast iron main, with a sound speed of 1,200 m/s and a time lag of 0.05 s, place the leak (200 - 60)/2 = 70 m from the sensor that heard it first. Strengths are finding hidden leaks without digging. Limits are plastic pipes, background noise and the need for skilled staff to confirm each find.