The Definitive Guide to Acoustic Leak Detectors

Water supply professionals and organizations are in a constant battle with nature and the material constraints of their systems. All water supply systems eventually develop leaks. Identifying these losses before they become cost intensive is part of any water supply system maintenance regime.

Acoustic leak detection devices are a valuable part of the waterworks professional’s tool kit and are useful for performing leak surveys and pinpointing leak locations. These detection activities allow necessary work to be completed with efficiency and have the potential to save organizations significant time and materials as well as thousands of dollars per year.

Acoustic Leak Detectors: Solutions for a growing problem

City and municipal water supply systems are large and can encompass hundreds of miles of pipeline. At any given time, multiple leaks can be present on these systems. Sometimes, operators are immediately aware of leaks due to large drops in the system’s water pressure. Often, however, slow leaks appear and the gradual increase in water loss may go unnoticed.

These small leaks can increase in size over time to cause major damage to city infrastructure and to private property. Even if individual leaks remain small and cause relatively little damage, the cumulative monthly water loss can significantly impact an organization’s budget, the overall system water pressure, and contaminate the supply to customers.

Fortunately, a class of tools has been developed specifically for the water supply industry to identify which lines are leaking and to pinpoint the exact location of those leaks. These devices are known as acoustic leak detectors.

What are Acoustic Leak Detectors?

Acoustic leak detectors are devices which utilize sound waves for the detection of waterline breaks and leaks. Think of an acoustic leak detector as a “stethoscope” for listening for leaks in a water supply system.

How do Acoustic Leak Detectors Work?

Acoustic leak detectors can have a variety of additional or specialized features, but all acoustic detectors incorporate three main components: a microphone, an amplifier, and headphones.

The Microphone: The microphone is placed directly on the ground surface above a pipe to pinpoint leak locations. Many units are equipped with connections for contact rods or magnets which increase the range of listening locations to include below ground level, valves, and hydrants. Most microphones are integrated with piezoelectric crystals. When these crystals interact with sound waves, they generate a small amount of electricity which is passed through a cable into the amplifier.

The Amplifier: Amplifiers are an integral part of any acoustic water leak detection device. Even with extremely sensitive ground microphones, the sound of a leak can be well below the range of human hearing. Powerful amplifiers allow the signal received from the ground microphone to be multiplied hundreds of times and into the audible range.

Headphones: The amplified signal from an acoustic leak detector’s ground microphone is finally passed into headphones worn by the user. The use of headphones is critical to the successful use of these devices. Even after amplification, the sounds of leaks can still be very low and just within the audible range. Headphones also decrease distractions from noise in the surrounding environment such as traffic, footsteps, and construction.

While all acoustic leak detection devices have the basic components listed above, there are various additional features added by manufacturers to increase the utility of the device. These range from digital and analog meters to computers that can store readings. These additional features will be covered later in this article.

How to Use an Acoustic Leak Detector

Acoustic leak detectors are useful tools for water supply professionals, but like other tools, they are only as good as the operator’s skill set. It is important that new users become familiar with the equipment before using it in the field.

A good way to practice is to find a line where a leak location is already known and to walk up and down the line with the detector, listening to the sounds of the leak with the microphone. If no known pipeline leak is available, an artificial “leak” can be created by opening a valve or hydrant to create the “whooshing” sound of a leak on the line.

It is important to consider that environmental conditions will affect both the sound of the leak and the effectiveness of the ground microphone. Background noise such as traffic or heavy rain may make it difficult to hear the low sounds of deep, small, or distant leaks. Many models have frequency filters to help eliminate these background noises and it is important to experiment with those filters to find what works in a particular noise environment.

Operators of acoustic leak detectors should also note that sound travels more quickly through denser materials. For example, a leak may sound louder when heard through concrete, asphalt, or packed clay. The operator should always take the density of the medium into effect when pinpointing a leak location.

To demonstrate: In stepping from a grassy area onto a sidewalk, an operator notices an immediate increase in the noise volume. This does not necessarily mean that the leak is closer. It could simply mean that the concrete is conducting the noise better. Further readings along the top of the sidewalk can help to determine if the leak is closer or further away at that location.

What Do the Leaks sound like in an acoustic leak detector?

The ground microphone of an acoustic leak detector will pick up on a variety of sounds, not just the noise of a leaking pipeline. It is therefore important for an operator to be able to recognize the different sounds that a leaking pipe can make and how to differentiate between those sounds and the noise from the ambient environment.

Types of Leak Sounds Read by Acoustic Leak Detectors

• Whooshing or Hissing: This sound will always be present in leaking pipes over 30 psi. It may sound like radio static. If you hear this, you likely have a leak.
• Splashing or Gurgling: if the leak is in soil and has already carved a channel through which the water is flowing, you may hear the sound of the flow. It has been likened to the sound of flowing streams or creeks.
• Thumping or tapping: Water may be exiting the pipe in short bursts. Tapping or thumping sounds may result when the bursts strike the side of the cavity created by the leak.
• Clinking: If the leak is causing the pipeline to vibrate, it may strike small stones, pavement, or other buried lines, creating a “clinking” sound.

All of these sounds are indicative of a leak location but remember: only the whooshing/hissing is present on all leaks on lines above 30psi. This makes a “hiss” the definitive leak identification sound. All other sounds are ancillary and will only aid the operator in confirmation.

Primary Applications of Acoustic Leak Detectors

Water Leak Surveys: Water leak surveys are performed by utility professionals to determine which lines on their system are leaking. These are generally conducted on a street-by-street, or line-by-line basis. During these surveys, the ground microphone is put into direct contact with hydrants, valves, or pipelines.

Since solids such as metal or plastic conduct sound better than soils this direct connection is an effective way to listen for leaks along long stretches of pipeline. The connection is generally made with a contact rod threaded directly to the microphone, or with a powerful magnet that allows the microphone to attach to an iron or steel valve or hydrant.

Water Leak Pinpointing: Once a line has been identified with a suspected leak, it is time to find the exact leak location. The operator uses the microphone and walks the length of the leaking pipeline, placing the microphone on the ground every few feet. As the microphone gets closer to the leak location, the leak noises become louder. After passing the leak location, the sound will begin to decrease.

Useful Accessory Features on Acoustic Leak Detectors

All acoustic leak detectors include a ground microphone, amplifier, and headphones. However, manufacturers have added an array of additional features to increase the accuracy of the devices and the efficiency with which operators can identify leak locations.

• Sound Cut-Off Switches: The ground microphones and amplifiers on acoustic leak detectors are extremely powerful. This can cause wide swings in volume when traffic passes or if the ground microphone strikes a rock or pavement. By having a sound cut-off switch, users can regulate the connection to their headphones and can avoid hearing unnecessarily loud noises.
• Contact Rod Connections: Some leak detector ground microphones have threaded wells for attaching metal contact rods. These rods can be used for direct contact with hydrants or valves during leak surveys or can be used to push into soils for subsurface listening during pinpoints.
• Magnet Connections: Ground microphones can be equipped with detachable magnets. These magnets allow the microphone to be directly connected to steel or cast-iron fixtures during leak surveys.
• Frequency Filters: Many amplification systems for acoustic leak detectors have frequency filter options. These allow operators to “null” out some forms of unwanted background noise by cancelling all sounds within a certain frequency range. These filters are particularly useful in noisy urban areas or beneath electric transformers.
• Digital / Analog Meters: Leak pinpointing is conducted by listening for increases and decreases in the volume of leak sounds. Many amplifiers are equipped with digital readouts or analog meters to allow users to quantify the sounds that they are hearing. Sometimes small changes in sound can be difficult to detect by ear, but these meters allow the user to assign a numeric value to the signal and to more accurately pinpoint the leak location.
• Signal Recording: Many acoustic leak detectors have onboard computers that can record and graph signal strength. This allows operators to simply walk down the leaking pipeline, entering readings every few feet. The records and graphs can then be reviewed and analyzed to pinpoint the exact leak location.

What to Consider before choosing An Acoustic Leak Detector

An acoustic leak detector is an investment that can quickly pay dividends in saved water, repair time, and repair costs. When making the choice of which leak detector to purchase, it is important to consider what type of locating activities will be conducted, the type of environment they are likely to be used in, and the amount of training required for the operator.

If the lines with leaks are already identified, a leak pinpointing device may be adequate for the job. If leak survey and pinpointing functions are both necessary, a unit with both capabilities may be more appropriate.

Frequency filters are helpful in urban environments, but if the leak locating activities are primarily going to be focused in remote or rural areas, background noise filters may be unnecessary.

Basic acoustic only devices are straightforward to learn, but it may take extra practice or experience for an operator to become proficient. Units with more features or computer programing may require more orientation, but once learned, these features can save time and make for more accurate leak locations.

Unboxing/Setting up your Acoustic Leak detector

When you first receive your acoustic leak detector, it is important to check the delivery box for any signs of damage. Once this inspection is complete, remove your detector from the shipping container. They will usually be housed in a hard plastic carrying case with interior padding.

Open the case and locate the manual. Using the manual, ensure that all the components listed as part of the package have arrived. Check each piece for damage.

Once all parts have been confirmed as present and undamaged, begin assembly of the unit. Install the batteries in the amplifier and connect the headphones. Lastly, attach the ground microphone along with any contact rod or magnet that is appropriate for the test run.

Be careful with the ground microphone: the piezoelectric crystal inside the head is fragile and may be broken if the microphone is dropped. Be sure to always handle the microphone with care as the warranty generally does not cover damage to the crystal.

Once all the components are connected, your acoustic leak detector is ready to be turned on and used.

Caring for your Acoustic Leak Detector

Most acoustic leak detectors come standard with an ABS hard plastic case with interior padding. To preserve the life of the unit, always return the detector to the case after use. Before returning the unit to the case, be sure that it is dry, wiped of dust, and that the cables are disconnected and untangled. The headphones, amplifier, and ground microphone are all sensitive devices and can be damaged if stored wet or dirty. When storing your detector, the best practice is to place it in a dry environment at room temperature. Extreme heat or cold should be avoided.

Is an Acoustic Leak Detector Worth it?

If you are a Water Service Professional and expect to be locating and repairing leaks as part of your regular maintenance operations, an acoustic leak detector is an essential part of your tool kit. It can easily pay for itself in one or two jobs by saving man-hours, property damage, and frustration.

A misidentified leak location can turn what should be an easy fix into an expensive repair. The use of an acoustic leak detector can save the frustration and additional costs. Multiply this utility out over several weeks and months, and an acoustic leak detector can easily save you or your organization tens of thousands of dollars over its lifetime.

However, if you are expecting to locate only one or two leaks every five to ten years, an investment in an acoustic leak detector may not be the best option. If this is the case, there are numerous leak detection service companies throughout the United States such as American Leak Detection and Ground Penetrating Radar Services (GPRS). Leak location services and prices vary, but if you only expect to use them occasionally, then these may be the best option for your circumstances.

Contact us with your Acoustic Leak Detector Questions

If you or your organization are considering purchasing a leak detector, or if you already own one and have questions, please feel free to reach out to us at Precision Outdoor Tech and we will do our best to help you. We can be reached via our Contact Us Page or by completing the form listed at the link below for municipal employees.

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