Part 1 - Getting to know the Basics
What do you need for leak detection? I often get asked this question by plumbers who wish to start out in leak detection, from those who might simply like to add it to their arsenal of tools, to those wishing to venture into the dedicated business of finding leaks for their customers.
No matter what level you wish to start out, and where you might end up, the good news is that you are unlikely to waste your money if you start with the basics. A basic “starters” kit should include a handheld leak detector like the SebaKMT HL50 and one or two microphones. Even if you start out small, and end up big, a good handheld leak detector never goes astray. It can often save you the need to haul your more complicated equipment around where it isn’t necessary.
Our HL50 meets that bill. It comes with 3 optional external microphones making it an extremely versatile unit. And if you decide to upgrade later down the track, then all the microphones are completely compatible with the entire range of SebaKMT equipment.
A unit such as a SebaKMT Hydrolux HL 50-BT in its most basic form incorporates an integrated sensor, and Bluetooth headphones. There are no cables or cords involved. It's a great unit for listening to valves, spindles, hydrants, and fittings, as well as hard surfaces (e.g. tile wall) in either a commercial or a domestic situation.
The PAM B-2 Multipurpose microphone allows you to listen to a broader range of surfaces, including soft ground, paved surfaces, softer walls (e.g. gyprock) as well as hard to reach pipes and fittings. You need to use this external microphone, coupled with one of the supplied adapters- Extension rod and tip, Magnet adapter or Tripod adapter.
The Pam W-2 Windproof ground microphone allows you to isolate external noises when taking a reading, making it easier to differentiate the noise of a leak, from the noise of the environment.
The PAM T-3-1 is a heavy-duty ground probe and can eliminate the need to create a “pilot” hole to insert the extension rod and tip for listening in softer ground. It also has a bracket to hold the HL 50 and an inbuilt mute function in the palm grip for easy single-handed use.
With just the HL 50-BT handheld unit and a B-2 Multipurpose microphone, you will have most domestic situations covered, whilst it is also a good start for commercial applications.
Part 2 - The Next Stage of Equipment
Following on from part one 'getting to know the basics', we are now going to look at what you need to get started in a more commercial/industrial situation. One of the pluses of the SebaKMT range is that a great deal of the ancillary equipment is common across the range of equipment, meaning that if you start small (with say an HL50 like we discussed in our last update), and decide to go bigger, you haven’t wasted any money. All of the microphones mentioned in last month’s feature are fully compatible with the next generations of equipment, which is outlined below.
Introducing the mainstay of the SebaKMT’s leak detection range, HL500, HL5000 and Correlux C3-HL.
The Hydrolux HL5000 Pro is a more robust unit than the HL50 which we touched on last month. It has a complete on-screen navigable menu which can be accessed via a “click and scroll” type button. It comes with a windproof ground microphone as standard. All other microphones are available as options. This means that if you started out with an HL50 and a suite of microphones, you are already well on your way.
Modern digital signal processing (DSP) technology allows the user to largely eliminate unwanted noises that may interfere with the actual leak noise via Dual Segment Analysis (DSP). In a normal noise spectrum, background noises from cars, wind, passers-by, etc. can drown out the actual sound of the leak.
The HL5000 Pro calculates and evaluates the background noise as explained above and displays it as a narrow bar in your noise graph. The actual sound of the leak is then identified and displayed as a wide bar in the graph. The nearer that you get to the leak, the higher this wide bar gets.
Unlike the basic filter settings of the HL50, the HL5000 is much more customisable. It has 9 pre-set filters to eliminate specific background noises. It also has user variable filter settings for even greater flexibility.
The HL500 can also be used to record and log leak noises over periods of time for later analysis and comparison as shown in the chart below.
It also features a pinpointing function with histogram measurement display to assist in marking the precise leak location.
The HL5000 further features a “line location” mode that can be used with specifically designed products to trace the location of unknown services, which can be a problem for accurate leak detection
The latest addition to the HL family is the Correlux C3-HL
This unit has all the features of the HL5000, but with a colour touchscreen display, making the unit incredibly simple to use.
One of the new features to add to the DSP and DSA function is the “Pitch” function, which allows the user to transfer low-frequency leak noises into more audible frequency range. The unit has a 16 hour operating time, as well as a handy car charger if you have multiple long days where you can't get back to the office.
Also available are optional power transmitters to turn the unit into a correlator that we will discuss next month.
Both of these units are ideally suited to the commercial and industrial spectrum, particularly where external noise may be an issue from industrial processes or just from run of the mill ambient noise.
Next month, we will discuss correlation and flow measurement, with a final chapter the month after to bring all of the information together.
Part 3 - Correlation
Following on from part one and two of the series we are now going to look at correlating equipment which is specifically used to locate leaks in water networks.
Water escaping under pressure at a leak location creates a noise. It disseminates in all directions across a pipe. When you attach a sensor, whether it is a piezo microphone or hydrophone, to the pipe network it picks up that sound. The sensor can be connected to a valve, a hydrant, the pipe itself, or directly connected into the water column via a tapping point.
The sensors wirelessly send what they hear to the "mothership', the correlator. It records, amplifies and analyses those sounds. The correlator then compares the two signals received and calculates the exact location of the leakage on the basis of how long it took to receive the sound signal from each sensor. It takes into account the sensor spacing and the sound velocity in the pipe based in pipe material and diameter entered even if they change within the measured section.
Attaching to the water column in large diameter trunk mains is typically the best method where possible. The correlator compares both signals and calculates the exact distance to the leakage on the basis of the delay time of the signals, sensor spacing and sound velocity in the pipe.
In order to detect the location of a leak, certain information must be available:
- The sound must be heard by a sensing microphone
- The diameter(s) and material(s) of the pipe must be known
- The velocity of sound in the pipe must be known
- From the inbuilt calculation table
- Physical measurements
- The distance between the monitoring points must be known
The more accurate this information is entered, the more accurate the location of the leak is determined. With good information the SebaKMT C3 correlator would normally locate leaks to within less than 1m.
The correlator in its most basic form, is a C3 standard unit, which is essentially a C3-HL from last months article, but equipped with two transmitters. These transmitters allow an acoustic signal, measured from either side of the suspected leak to be sent to the base unit, where the necessary calculations are performed. From this basic setup, various microphone sensors can be utilised to add additional functionality.
The piezo microphone is exactly the same unit as is used in leak detection, namely the PAM B-2 microphone as discussed in last month’s article.
Hydrophones are very sensitive sensors for correlation made especially for difficult circumstances of plastic pipes or large diameters. Hydrophones are directly connected to the water column, typically via hydrants and standpipes.
SebaKMT hydrophones feature a high sensitivity especially in the lower frequency band, making them highly suitable for correlation on plastic pipes, pipes with a long distance or larger diameter.
Specific audio filters are used, depending on the parameters of the pipe being measured, to isolate and detect the distinctive audio qualities of a leak.
If the measuring point is in an area which is difficult to access or if there is local interference, then an offline measurement can be performed at up to 8 points. Multi-sensors have a piezo microphone and recording logger combined in one easily deployable unit. The multi-sensors are programmed accordingly with the correlator and then deployed.
Following the measurement, the power transmitters and multi-sensors are collected and the data can be read and evaluated by the correlator.
The functions can be seen in the video link .https://youtu.be/PWPaHFFYuOM
If the exact material and diameter of the pipeline is not known, or local pipe anomalies result in pipe irregularities (and hence sound transmission velocity), the sound velocity propagation can be physically determined to eliminate the risk of incorrect pipe data and sound transmission velocity. This is done very simply be creating a “noise” in proximity to the measurement microphones. The sound transmission time, combined with the known distance from the noise to the microphone is used to determine the actual velocity of sound transmission.
After a leakage has been identified and pre-located by a correlation, the correlator can be used to pinpoint the leak position. In the area of the pre-located leak position, individual measurements are performed at a number of measuring points along the probable pipe run. The noise levels recorded are displayed on the correlator. The closer a measuring point is to the leak, the louder the recorded sound. To determine the leak position accurately, a number of pinpointing runs are carried out in succession. With each new run, a smaller distance between the measuring points ischosen, thereby narrowing down the exact leak location.
Correlating, followed by pinpointing has advantages over the process of simply “walking the line” in a number of ways; It removes some of the possibility of human error and subjectivity from the process, it removes external noises unrelated to the leak from the detection process, it can detect smaller leaks on larger diameter pipes that can otherwise be difficult to hear, and it allows relatively large areas to be initially monitored to quickly determine the worst areas.