Correlators work by attaching probes to fittings on the water network, such as valves and hydrants. They then electronically ‘listen’ for the presence of leak noises.
Two separate sensors (red and blue, pictured) are placed either side of an area of suspected leakage and the handheld receiver is programmed with the following detail;
- Length of main between the two sensors.
- Diameter of the pipework.
- Substrate of the pipework (MDPE, Cast Iron, Ductile Iron etc)
Ground Microphones work by placing a concentrated microphone (often referred to as an ‘elephants foot’) directly on the surface of the ground, in proximity to the water main.
The ground microphone listens to all noises in the immediate area and can be easily and quickly picked up and relocated to interrogate increasing and decreasing levels of noise, to pinpoint an area for greater scrutiny.
Ground microphones use headphones to isolate ambient noise and/or handheld units to give a visual representation of the presence of noise.
Listening sticks are a fairly rudimentary staple of the leakage technicians armoury.
They work in a remarkably similar way to a doctors stethoscope. Instead of a doctor placing the stethoscope on a patients chest and listening for breathing irregularities, the leakage technician uses the listening stick, usually on fittings such as valves, hydrants, stoptaps or even the main itself, then listens for subtle leak noise signatures (tiny vibrations), created by the leak at the fracture in the pipework then transmitted along the main and through the listening stick.
Whilst the listening stick appears to be a very basic tool the accurate use of a listening stick is an absolute skill. The technician requires an ability to listen ‘through’ ambient noises and pick out the presence (or lack) of a leakage signature.
C.A.T & Genny
The C.A.T (short for cable avoidance tool) and Genny (or generator) are two discreet parts of a system used to ensure that below ground services are identified and mapped so that the area can be excavated safely to avoid striking gas, electric and other utilities or cables.
The Genny can either physically clip onto fittings on ferrous/conductive mains or switched to inductive mode to transmit a signal through the ground above and into the main. Although generally less accurate it is still a useful feature when the availability of network fittings is scarce or the accessibility is poor.
The C.A.T has a number of settings such as ‘Power’ (for picking up cables carrying an electrical load), and Radio, (for picking up a signal from various ferrous services and telecoms cables). These modes work independently of the Genny, however when the C.A.T is switched to ‘Generator Mode’ it will pick up the signal emitted by the Genny.
Acoustic Logging involves strategically deploying a number of small listening devices into a network to passively listen to the noises created by the movement on the water within the pipework. They work in a similar principle to the sensors of a correlator.
Loggers are pre-programmed, then attached to fittings on the network, before being left for a predetermined period of time.
Once that time has elapsed each unit is retrieved and downloaded.
The information is overlaid against a map of the area/network, highlighting specific areas of elevated levels of leak noise activity. This detail indicates areas for further investigation.
Leak-finder is a sophisticated piece of leak locating apparatus that does not require prior knowledge of the route of the supply and nor does it require the leak noise to be audible. It can accurately locate leaks on supplies up to 50mm in diameter, of any substrate, where the internal bore is smooth
The leak-finder is capable of locating leaks up to 50 metres from the point of insertion and works by feeding the sonde end into the pipework, then inflating the head bladder before repressurising the supply with air.
This equipment and method are particularly useful for MDPE (and non-ferrous) supplies which are virtually untraceable via non-intrusive methods.
Ferret Leak Locator
The Ferret leak locator is a clever piece of equipment that does not require prior knowledge of the route of the supply and nor does it require the leak noise to be audible. It can accurately locate leaks on supplies ranging from 10mm to 45mm in diameter.
It works by creating access into the supply pipe for the Ferret to be inserted into the pipework. The pipework is repressurised with water. The Ferret head is then inflated to the optimum point where the pressurisation propels the Ferret deeper into the supply. The Ferret stops as soon as the pressure drops due to the escape of water through the compromised area of the pipework.
The location of the Ferret can be determined via an optional sonde, which is subsequently traced. Alternatively, the distance of travel can be noted by observing the 1m markers on the Ferret umbilical.
This is particularly useful for MDPE (and non-ferrous) supplies which are virtually untraceable via non-intrusive methods.
Preparing the supply and commissioning the Ferret
Deploying the Ferret and repressurising the system
A Mole is so-called due to the way that it performs its task.
Chambers are dug at the entry and destination points. The pneumatically powered mole is lowered into the chamber where it begins to burrow below ground to create a void through which a new supply can be pulled.
Its an exceptionally clean and convenient option where conditions are appropriate to use it.
For particularly long stretches where supplies are installed or renewed, a method known as ‘moling by stitching’ can be adopted, whereby a series of excavations are created and the new supply is pulled through section by section in one single continuous piece of pipework.
The squeeze-off clamp is extremely self-explanatory.
Squeeze off clamps are available for a range of sizes for use on good condition plastic pipework, mainly MDPE and Alkathene. They can even be used effectively on large diameter water mains.
To deploy the squeeze-off clamp, the top jaw mechanism is wound high and the bottom jaw removed.
The pipework is then inserted into the frame before the bottom jaw is reintroduced to the assembly. The mechanism is then wound down to compress the pipework and stop the flow.