Analysis of the causes of water meter self-rotation and exploration of mitigation methods

    Before the Ministry of Construction required water supply companies to implement "one meter per household", most users were measured by the total meter and did not deal directly with water supply companies. In the early days, there were fewer indoor water-using sanitary ware in residential buildings and the layout of water supply pipes was relatively simple, so the possibility of water meters rotating was small. With the continuous improvement of people's living standards, the number of sanitary ware in homes has increased, the layout of pipes has become relatively complex, and the water consumption has increased. In addition, with the implementation of "one meter per household", water prices have also continued to rise, and users and water supply companies have directly settled water charges. Therefore, users have also begun to pay attention to the operation of their own water meters, and the problem of water meter rotation has become prominent.

　　1 Analysis of the causes of rotation

　　1.1 Pressure fluctuations

　　Since water is a liquid and has incompressible physical properties, but in the water pipe, the pipe pressure is high, and the water will show a certain compressibility. In the water pipe, pressure fluctuations are inevitable, and most of the water meters currently used in my country are mechanical meters, which rely on the kinetic energy generated by the flow of water to drive the gears to operate, thereby achieving the purpose of measuring the amount of water. When water is not used, there is high-pressure water with equal hydrostatic pressure in the pipes connected at both ends of the water meter; when the pressure of the municipal pipe network increases, the volume of tap water in the pipe behind the meter will shrink due to the increase in pressure, and at this time a small amount of water will pass through the water meter, resulting in positive rotation; when the pressure of the municipal pipe network decreases, the compressed water in the pipe behind the meter expands due to the decrease in pressure, and a small amount of water will also pass through the water meter, but the difference is that this time it is reverse. We all know that when a general mechanical meter is inlet, it is inlet from the bottom and outlet from the top, pushing the gears to rotate forward, while when it is inlet from the top and outlet from the bottom, pushing the gears to rotate reversely, the resistance of the two-phase water inlet is different, although the water inlet at the two ends is the same, the readings reflected on the water meter are very different. According to experimental statistics, when there is no air in the pipeline, the amount of water generated is relatively small, about 0.5~1m3/month. Among the reasons for the pressure fluctuation of the municipal pipe network, the water inlet of the low-level water tank (pool) of the secondary water supply of high-rise buildings is particularly prominent, because these water tanks (pools) mostly use float valves to control the water inlet. When the liquid level in the water tank (pool) drops to a certain height, the float valve suddenly opens, which will inevitably cause a sudden pressure relief in the primary pipe network. In this way, the pressure before and after the registered water meter on the primary pipe network in or near the high-rise building will have a considerable difference, and the water meter will reverse. After the pressure before and after the water meter is consistent, if the float valve is closed, the pressure of the primary pipe network will increase again, and the water will flow from the front of the water meter to the back of the meter again, and the water meter will rotate; the water meter rotation caused by this reason is also one of the most troublesome problems for water supply companies and users.

　　1.2 Airbag

　　The amount of water generated by this reason is relatively large. The production process of tap water companies is built in the open air. A large amount of gas will be dissolved in the water during the production process. At the same time, during the construction process, gas will be brought into the pipeline. If the exhaust valve on the pipeline is not set properly, the gas cannot be removed well. In this way, if the home does not use water for a long time or the pipeline design is unreasonable, air pockets will be generated at the highest point or protrusion of the pipeline in the home. As we all know, the compressibility of gas is very high. At this time, if there is pressure fluctuation on the pipeline network, the space expansion and contraction in the pipeline behind the meter will be large, and the water meter will rotate more. According to statistics, the amount of water generated is as little as 2~3m3/month, and as much as dozens of cubic meters of water will be generated per month.

　　1.3 Installation method and installation quality

　　1) Since most of the water meters are now in one unit, all the household meters are concentrated in one meter well or meter box. Considering the winter cold and frost protection and convenient meter reading, 5 to 12 water meters are connected with a Φ40mm~Φ50mm water distributor. The distance between the meters is small, and the straight pipe section left for the water meter is also small. The water use of some water meters is actually the pressure relief of the pipe section before the meter. For other water meters connected to the water distributor, the pressure of the pipe section before the meter drops, which will cause a slight reversal of these water meters. After that, the pressure of the pipe section before the meter is restored, and the water meter that is not using water will have a certain degree of self-rotation. This will affect the normal measurement of the water meter, causing errors between the water volume measured by the water meter and the actual water consumption of the user.

　　2) Pipeline projects are basically buried underground or in walls, and are considered concealed projects. The national pipeline construction specifications stipulate the installation requirements, construction procedures, acceptance standards, and precautions for various pipe materials and pipeline construction. However, during on-site construction, some construction workers do not follow the specifications, and the skills of the construction workers vary, resulting in more or less installation quality problems in the pipes behind the water meter and water-using sanitary ware; in daily work, it is often found that the pipes behind the meter or sanitary ware are not installed properly and there are leakages.

    2 Methods to alleviate water meter rotation

　　2.1 For water compression caused by pressure fluctuations, consider installing a check valve before the water meter to prevent water from flowing back.

　　In this way, when the pressure in the pipe section before the meter increases, the water is compressed and the water meter rotates positively; when the pressure decreases, the check valve automatically closes and the water meter does not rotate. When the pressure increases again, as long as the pressure is not higher than the pressure in the check valve, the water meter will not rotate again; the water meter rotates mainly because the water meter measures back and forth many times to accumulate a large amount of water. Installing a check valve can reduce the frequency of the water meter's rotation, which can also solve the problem of the water meter's rotation caused by pressure fluctuations to a certain extent. However, due to the high frequency of domestic water use and the small fluctuation of pipeline pressure, the check valve is required to have a higher sensitivity and better quality. As for the pressure fluctuations in the primary pipe network caused by the inflow of water from the secondary water supply facilities, the float valve can be improved, an auxiliary water inlet pipe can be added, and the water inlet method of the water tank (pool) can be controlled by combining the secondary water supply remote transmission device; during peak water usage periods, the float valve uses a smaller-diameter auxiliary water inlet pipe to let water in, and during low water usage periods, the float valve uses the main water inlet pipe to let water in. This greatly reduces the pressure fluctuations of the secondary water supply tank (pool) on the primary pipe network, thereby reducing the probability of the water meter rotating and the amount of rotating water.

　　2.2 For water meter self-rotation caused by air pockets in the pipeline due to unreasonable or unqualified pipeline installation, the following points can be achieved during the pipeline construction process

　　1) When designing, the exhaust valve should be reasonably arranged according to the characteristics of the pipeline to promptly remove the gas released from the tap water; when a newly installed pipeline or a newly installed household meter is connected to water for the first time, exhaust the air first and then slowly open the valve to exhaust the air in the pipeline as much as possible to reduce the gas content in the water.

　　2) All water supply pipes should have fewer bends and folds; indoor pipes should be laid upward at a certain angle as much as possible, and the highest point of the pipe should be designed on a frequently used faucet to reduce the chance of air pockets in the pipe network.

　　3) When the water meter is installed in the house, no one lives there, and there is a lot of gas in the pipe. It is recommended to investigate the user's situation when the water meter is installed. When the water meter is installed and accepted, close the valve behind the water meter of the unoccupied user. If water is needed in the future, the valve behind the meter can be opened by yourself.

　　2.3 For the self-rotation caused by the quality problems of the installation of pipes and water-using sanitary ware, the management should be strengthened during the construction process, the construction should be strictly carried out in accordance with the installation specifications, and the acceptance should be strictly controlled to reduce leakage.

　　In short, for the self-rotation caused by subjective human factors, we can solve it by further optimizing the design and standardizing the construction; for the self-rotation of water meters caused by objective reasons such as the compressibility of water, the current technical level, and the characteristics of pipelines, it is still a difficult problem to completely solve in the water supply industry, and we need to continue to summarize and explore in our work. (end)