The smooth exhaust of the water transmission and distribution system is an important technical indicator for its safe operation. Many problems in the pipeline are caused by the air and the airbag movement in the pipeline, which has been confirmed by many practices. In order to make more engineers and technicians understand this problem, the harms caused by improper exhaust measures of the water supply system are summarized as follows.
Caused a huge startup water hammer pressure rise in many high-lift, large pipe diameter, multi-undulation water pipelines, often using gas injection method to eliminate pump water hammer. Because this method is the most simple and economical, and effective. However, the gas injected into the pipeline during the pump stop caused trouble for starting the pump again. Because after the pump is stopped, the water pressure of the entire pipeline decreases and a large amount of gas is injected. When the pump is started again, the water flow rate is often higher. If the exhaust device in the pipeline is not good, the exhaust speed is lower than the water outlet speed of the pump. The airbag in will be in a compressed state, and this airbag is extremely unstable, constantly dispersing, accumulating quickly and suddenly, and crashing to stop, resulting in a rapid change in water flow speed. According to the relevant water hammer theory, the flow rate changes by 1m / s , Can reach the direct water hammer pressure rise of nearly 100 meters of water column. Changes in local water flow velocity due to airbag movement under higher pressure are generally difficult to predict and control, often reaching several meters per second. Due to the pump reversal and slow closing check valve control, the boost value can be limited. Therefore, the hazard of the pump start hammer due to poor exhaust is greater than that of the pump stop hammer. When this kind of pump-opening water hammer occurs at the pump outlet, it will crack the pump casing and flood the pump house, such as the water hammer accident in several large water intake pumping stations in southern and southwestern China. And when it occurs in the middle of the pipeline, it will burst, there are many examples of this.
Because some technicians have the tendency of "re-stop pump water hammer calculation, light start pump water hammer protection" in the calculation of water hammer protection, the exhaust device selected in the system is not analyzed, and the exhaust speed and reliability are considered Insufficient, thus exacerbating the probability of a tube explosion accident, which is not conducive to production safety.
Explosion of the city's water distribution and distribution network due to the fact that the city's water distribution and distribution network is generally flat, and the pipeline is long and has a mesh structure. Once a pipe section contains gas, if there is no nearby exhaust device on the pipe section, it is easy to cause explosion The damage continued to expand along the pipeline. Due to the inadequate exhaust facilities of most urban pipe networks in China, some have no exhaust devices originally; some have a few dozen kilometers of pipeline networks, but only a few are located at high points; The valve leaked and closed for no reason ... These improper measures exacerbated the occurrence of a tube explosion. According to statistics, a large city in North China has burst pipes more than 1,600 times a year, and a city in northwest China has burst pipes more than 900 times a year.
Causes pipeline vibration instability and serious leakage. Because the airbag in the pipeline is very easy to cause the pressure to rise and fall rapidly, the gas in the pipe for a long time cannot be discharged in time and cause the pipeline to vibrate locally. At the time, vibration for a long time may cause the socket pipe joint to loosen, thereby increasing the leakage of the pipeline. At the same time, because the airbag occupies a certain cross-section of the water, the local resistance coefficient of the pipeline is greatly increased, the pipeline is not smooth, and even severely blocks the water flow.
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