Fresh water is one of the most basic conditions for human survival. Water scarcity and environmental pollution are the main factors restricting urban water supply. Water supply pipe leakage is a waste of valuable water. He not only increases the cost of clean water, but also increases the investment cost of water supply facilities, and also causes some secondary disasters. Therefore, protecting water sources, saving water, leaking and reducing damage has become the consensus of all mankind. Loss of water supply pipelines in China According to the statistics of the China Water Association 1998, the average leakage rate of China's urban water division is 12 to 13%. If the water leakage per unit time is counted, the leakage of China is far greater than that of developed countries. The specific figures are shown in Table 1: Table 1: Unit ratio leakage statistics National water leakage ratio China 2.85 Italy 2.5 Malaysia 1.2 Japan 1.0 United Kingdom 0.8 Germany 0.4 Singapore 0.3 Hungary 0.2 Unit ratio leakage Among them, the leakage rate = water leakage / water supply × 100%; Unit ratio leakage = annual leakage / (365 × 24 × pipe length), m3 / h / km, that is, the unit pipe length per unit time leakage. At present, most cities in China adopt the passive leak detection method or this method, while the law of underground pipeline leakage is from dark leakage to bright leakage. Sometimes the leaked water always flows into the river, sewer or cable trench, and therefore it is not clear. The potential of China's urban water division to reduce leakage is still quite large. Doing a good job of leak detection can greatly improve the effective water supply capacity, which is of great significance for saving water and improving the social and economic benefits of the Water Division. 1. Types and spread of water leakage sounds in water supply pipelines The task of the water supply pipeline is to deliver clean water to the users to meet the most basic needs of people. However, water leakage can also occur in the water supply pipe. When it occurs, the water sprayed from the pipe rubs against the leak port and collides with the surrounding medium, which generates vibrations of different frequencies, thereby generating a water leakage sound. The types of water leakage can usually be divided into three types: (1) Leakage friction sound: refers to the sound generated by the friction between the water and the leakage port of the discharge pipe. The frequency is usually 300~2500Hz, and it propagates along the pipeline to a distant place. The propagation distance is usually related to water pressure, pipe, pipe diameter, Interfaces, leaks, etc., within a certain range, can be detected at the exposed points such as gates, fire hydrants and so on. (2) Head impact sound: refers to the sound produced by the water ejected from the pipeline and the surrounding medium, and spreads through the soil to the ground in the form of a funnel. It can be heard on the ground with a leak detector. The frequency is usually 100-800. Between Hz. (3) Medium friction sound: refers to the sound produced by the water ejected from the pipeline to the surrounding particles (such as soil particles, sand particles, etc.), which has a low frequency. When the listening rod is inserted near the underground leak It is audible, which provides a basis for the final confirmation of the leak. Second, the main method of water supply pipeline leak detection Due to the consensus of humans on water leakage in water supply pipelines, some leak detection methods have been studied, and some instruments have been developed. For example, leak detection methods commonly used in economically developed countries such as Germany and the United Kingdom include: sound-sounding leak detection method and related leak detection method. , water leakage sound automatic monitoring method and partition leak detection method. The first three leak detection methods rely on the sound generated by the leak to detect the leak, which is no way for a silent leak. The zone leak detection method is to measure the presence or absence of water leakage by measuring the flow rate and pressure of the pipeline, which is the so-called minimum flow method. At present, China usually adopts passive leak detection method, audio-visual leak detection method or related leak detection method. Some water divisions also adopt automatic leakage sound monitoring method or district leak detection method. With the regulation of water supply pipe network management and technological progress, Many water divisions will gradually introduce the automatic sound leakage monitoring method or the regional leak detection method, which will play a positive role in quickly reducing leakage and controlling leakage. 1. Sound and leak detection method The sound-sounding leak detection method is divided into two types: valve plug listening and ground listening. The former is used to find the lead and range of water leakage, which is referred to as the leaking point pre-positioning; the latter is used to determine the location of the leaking point, which is referred to as the precise positioning of the leaking point. The pre-dumping position refers to the method of detecting the water leakage of the water supply pipe by the leaking rod, the electronic leak detector and the automatic noise recorder. According to the different instruments used, the pre-positioning technology mainly includes the valve plug listening method and the noise automatic monitoring method. (1) valve plug listening method The valve plug listening method is to use the leaking rod or the electronic amplified leak detector to directly sense the leaking sound generated by the leaking point at the exposed points of the pipeline (such as fire hydrants, valves and exposed pipes, etc.) to determine the leaking pipeline and reduce the leak detection. range. The sound frequency of leakage of metal pipes is generally between 300 and 2500 Hz, and the frequency of leakage of non-metal pipes is between 100 and 700 Hz. The closer the listening point is to the leaking point, the louder the sound of the leak is detected; otherwise, the smaller. (2) Ground listening method After the leaky water pipe section is determined by the pre-positioning method, the leakage point of the underground pipe is sensed on the ground by an electronic magnifying leak detector, and precise positioning is performed. The listening method is to track and compare along the leakage pipeline at a certain interval. When the local surface pickup is close to the water leakage point, the sound of the leaked water is higher, and the maximum is above the water leakage point. The spacing between the pickups is related to the material of the pipe. Generally speaking, the spacing between the metal pipes is 1 to 2 meters, the spacing of the non-metallic pipes is 0.5 to 1 meters, the spacing between the cement roads is 1 to 2 meters, and the surface of the soil is 0.5 meters. (3) Development status of the leak detector From the development of the German SEBA leak detector, it has evolved from the original analog signal processing to modern digital signal processing. Due to the use of digital signal processing, the ability to withstand environmental noise is enhanced. Digital frequency analysis, digital filtering, instantaneous and minimum recording, and continuous water leakage and continuous monitoring of short-term water use can only be achieved with digital instruments such as the HL 400 and HL 4000 leak detectors from SEBA, Germany. 2. Automatic sound leakage monitoring method The automatic leakage noise recorder (such as GPL 99 of SEBA in Germany) is an integrated sound wave receiving system composed of multiple data recorders and one controller. When the computer with the dedicated software programs the data logger, just place the recorder in different positions of the pipe network, such as fire hydrants, valves and other pipe exposure points, etc., according to the preset time (such as 2:00~4 in the middle of the night) :00) Simultaneously turn on/off the recorder to record the leaking sound signal throughout the pipeline. The signal is automatically digitized and stored in the recorder, and processed on the computer through special software to quickly detect the recorder. Whether there is water leakage in the pipe network area. The human ear can usually reach more than 30dB of water leakage, and the leaking noise automatic recorder can detect more than 10dB of water leakage. The distance of the data logger is determined by the pipe, pipe diameter, etc. Generally speaking, the metal pipe can be spaced from 200 to 400 meters, and the non-metallic pipe should be within 100 meters. The basis for judging the water leakage is that each leaking point will produce a continuous leaking sound. According to the noise intensity and frequency recorded by the recorder, it is judged whether there is any water leakage near the recorder. The computer software automatically recognizes and makes two or three dimensions. Figure, The use of leak noise automatic recorder for leak detection has the following advantages: (1) Regularity of leak detection helps to find early signs of water leakage; (2) Reduce labor intensity and expense because it can automatically start and stop work without using people to listen to it; (3) The instrument is easy to operate and can be used to compile files. 3. Related leak detection method The related leak detection method is the most advanced and effective leak detection method at present, and is especially suitable for areas where the environmental interference noise is large, the pipeline is buried too deeply, or the ground leakage method is not suitable. The correlator can quickly and accurately measure the exact location of the leaking point of the underground pipeline. A complete set of correlators consists of a correlator host (composed of a radio receiver and microprocessor), two radio transmitters (with preamplifiers) and two high-sensitivity vibration sensors. The working principle is as follows: when the pipeline leaks, water leakage sound waves will be generated at the leakage port and propagate along the pipeline to the far side. When the sensor is placed at different positions of the pipeline or the connecting member, the relevant instrument main body can detect that the leak is generated by the leaking nozzle. The time difference Td of the leaking sound wave propagating to different sensors, as long as the actual length L of the pipe between the two sensors and the propagation velocity V of the sound wave in the pipe are given, the position Lx of the water leakage point can be calculated as follows. Lx=(LV×Td)/2 Where V depends on the pipe, pipe diameter and the medium in the pipe, the unit is m/ms, and all are stored in the main instrument host. The test process is shown in Figure 4. The correlator has also undergone a low-to-high-performance development process. Modern high-performance correlators have time-domain and frequency-domain (FFT) real-time processing functions with high resolution (0.1ms), spectrum analysis and notch , automatic filtering, measuring the sound speed and distance of the pipeline, such as the German SEBA related instrument DYNACORR has these functions. 4. Partition leak detection method When the pipeline is listening to the sound of leaking water, in general, the leaking sound generated by the large leaking point is larger than the leaking sound generated by the small leaking point, but the leaking point is so large that the leaking sound is small, so we cannot think that it is listening. When the leaking water is loud, the amount of water leakage is large, and sometimes the actual situation is just the opposite. The zone leak detection method makes it possible to classify the water leakage point according to the amount of water leakage, and therefore can do this: control the large water leakage point and first eliminate it. There are many small water leakage points and several large water leakage points in each pipe network. Experience has shown that 80% of the total leakage is caused by 20% large water leakage points. Therefore, as long as the large water leakage point is eliminated, the leakage loss can be better controlled, and the leakage rate can be reduced. At the same time, the zone leak detection can greatly improve the leak detection speed. When using a flowmeter for zone leak detection, first close the valve connected to the zone to separate the zone from other zones, then use one fire hose to connect one end to the fire hydrant in the isolated zone and the other end to the flowmeter test. On the device; one end of the second fire hose is connected to the fire hydrant in other areas, the other end is connected to the test device of the flow meter, and finally the fire hydrant is opened to supply water to the pipe network in the isolated area, as shown in Figure 5. By measuring the flow rate in this area by means of a flow meter, the amount of water leakage under a certain pressure can be obtained, as shown in Fig. 6. If there is water leakage, you can find out which section of the pipe is leaking by closing/opening the valve in this area. The German SEBA flowmeter TDM 10-60 is designed for zone leak detection. Advantages of using zoned leak detection to detect leaks: (1) can quickly eliminate large leak points; (2) Systematic testing, which can analyze the condition of the pipe network; (3) Using the measured flow rate compared with the normal flow rate, early signs of water leakage can be found. Third, the problem should be paid attention to in the process of water supply pipeline leak detection The leak detection method and instrument for the water supply pipeline are described above. The type of leak detection method selected by each water department depends on the geographical location and equipment used. Regardless of which type of leak detection method is used, before going to the site for leak detection, on the one hand, it is necessary to clearly understand the actual direction, material, pipe diameter, buried depth, water pressure and service life of the underground pipeline; Make a selection and which instruments to bring. Check the instrument to be checked in advance to see if there is any problem, such as whether the battery voltage meets the requirements; whether the wiring is correct; whether there is any fault. Are other leak detection tools available? In addition, you should also pay attention to the following issues: (1) If it is verified by the open fire of the manhole cover that has not been opened for many years, it is proved that there is no toxic gas in the well before the operation can be carried out. (2) Pay attention to traffic safety when detecting leaks in urban areas. Warning signs should be placed and warning vests should be put on. (3) When it is difficult to locate certain leaks, it is necessary to check whether there is a cable here. (4) Be careful to keep the pickup or sensor in good contact with the test point. In short, all types of leak detectors have their own characteristics and performance and scope of use. As far as the ground leak detector is concerned, most of the leaking pipes in the pipeline can hear the sound of leaking water and accurately find the leak. Location, but a small number of leaks are not clear to the test. The main reason for the analysis is that the sound of water leakage is not transmitted to the ground. The situation may be: 1 The pipeline is buried too deeply, and the sound energy of water leakage is absorbed by the soil; 2 The leak is submerged by water, and the sound energy of the leak is absorbed by the water; 3 The water pressure is too low, causing the leakage of water at the leak to be weak; 4 There is a sewer pipe above the leakage port; 5 leakage at the pipe interface, almost no water leakage; 6 There are buildings or deposits on the ground, no leakage conditions. For leaks where water leakage cannot be transmitted to the ground, it is best to test with a correlator to quickly and accurately locate the leak and it is much faster than using a ground leak detector. In short, the leakage of underground pipelines is very complicated. Sometimes it depends on various leak detection instruments and people's experience to judge, and sometimes even with other aids to judge, in order to achieve the best results. The operator cannot memorize the procedure, and the procedure and instrument performance should be combined. It is very important to accumulate experience. Every time a leak is detected, there must be an original record. After the relevant data is recorded and the data is accumulated to a certain amount, statistical analysis can be used to find out its regularity, which can improve the efficiency of leak detection in the future. Fourth, several suggestions In order to effectively reduce the leakage, the leak detection equipment should be selected in a planned manner, and the passive leak detection should be the active leak detection. The leak detection team should be set up as soon as possible to minimize the leakage. 1. Leak detection team formation (1) Quality of leak detection personnel With the development of science and technology, leak detection technology and instruments are becoming more and more advanced. Therefore, the leak detector should have the following conditions: 1 The higher the level of knowledge, the better, should have high school strength; 2 should have the professionalism of hard work and hard work; 3 Be good at learning, constantly explore and practice, and actively summarize the experience of leak detection; 4 In the age structure, it is recommended to combine the old, the middle and the young (the ratio is about 1:3:5), and gradually transition to the young. (2) Number of leak detection teams Generally, every 20 to 100 kilometers of water supply pipes are equipped with 1 to 2 leak detection. (3) Leak detector duties 1 Familiar with the operation of pipelines in the region; 2 Proficiency in leak detection instruments and pipeline positioning instruments; 3 proficient in routine leak detection methods; 4 Responsible for the inspection of leakage in this area; 5 is responsible for the maintenance and maintenance of the instrument; 6 Do a good job of leak detection, fill out the report, and write a leak report (4) Leak detection indicators 1 The detection rate of dark leaks (the ratio of the detected dark leaks to the total number of leaks) should be greater than 85%; 2 The correct rate of leak detection (the ratio of the location of the leak detection personnel to the actual leak point within 1 meter) should be greater than 95%. 2. Effectively select leak detectors The geographical, economic and technical conditions of the water divisions are different, and the instruments used are different. They should be selected according to their specific conditions. From the geographical analysis, the southern pipeline is buried shallowly, and the leak detector can solve 70% of the water leakage; while the northern pipeline is buried deep, the sound of water leakage is difficult to pass to the ground, and it is better to use the correlation instrument. However, from the analysis of economic and technical conditions, water companies in municipalities, capital cities and economically developed cities can select advanced leak detection instruments, which provides a prerequisite for rapid reduction of leakage. 3. Strengthen the training of leak detection personnel Leak detection is a comprehensive work, equipped with leak detection equipment, and it is difficult to bring benefits without selecting the right personnel. This requires strengthening the training of the leak detection personnel in order to improve the leak detection skills and at the same time train the inspection. Leaking people's hard work and dedication. 4. Choose an effective leak detection method Although there are many methods for detecting leaks in the water supply industry, from the actual effect of leak detection, the sound-detection leak detection method, the related leak detection method, the automatic leak detection sound method or the district leak detection method should be selected. At present, many water companies have chosen these methods, which have played a role in controlling water leakage. 5. To fully mobilize the enthusiasm of the leak detectors Leak detection is a difficult outdoor task, and sometimes it needs to work at night. How to mobilize the enthusiasm of the leak detection personnel is a problem that every water department should pay attention to. Economic leverage should be used to create a management system with awards and penalties to greatly mobilize the enthusiasm of the leak detectors. 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