1. Project Overview The project case for the transformation of a plant's water pipelines. The plant's water taken from the Xiangjiang River, from the waterfront to the water purification plant pumping station to install a new DN500 water supply pipelines, from the purification station to the secondary pressurization pump room, the secondary pump room to the production area to lay two DN500 Of the water supply pipe, the total length of about 3km. The transformation of the terrain and more undulating, water pipelines to cross the entire living area, with the continuous development of the scale of production, the water supply system security requirements are higher and higher, more difficult. 2 fault analysis and reconstruction project situation is more complex, in order to do a good job in the design of construction drawings, I have to the scene twice to reconnoitre, one to view the scene to determine the direction of the water pipeline; the second is to listen to the power plant comrades at the old Water pipelines in the process of using the problems and comments on the transformation, which one aroused my attention, in recent years, frequent pipe burst pipelines, an average of more than one month to burst a pipe, seriously affected the normal Production. I went to the day before there is a pipe burst pipe, the whole plant water repair, I asked to look at the scene, the pipe is cast iron pipe diameter DN300, burst pipe phenomenon for the socket cracks 1m long, occurred in two Pressurized pump room pressure pump operation by a small pump for large pump. Power Division comrades said that once a week ago burst tube, the last burst tube and the situation is similar to the entire plant overhaul to open pumping water. Exhaust valve on the water pipeline, a long time disrepair, did not replace the exhaust function has been lost in time, through the analysis of the burst pipe time and phenomenon, I think the pipeline is poor exhaust, there are a large number of airbags in the pipeline, Pump water hammer is the main reason for squib. The secondary pump room pump without frequency conversion equipment, direct start to open too fast, in the big pump for a small pump or pump just started, within seconds the pump will be able to achieve the rated pressure and flow, pressure and flow within the pipeline After the gas is compressed, the volume becomes smaller, the internal pressure rises, the pressure at the pump port decreases, the flow rate increases, and the internal pressure of the gas rises to a certain extent and then expands inversely. The momentum and impulse alternately change. A series of rapid pressure alternating hydraulic lift phenomenon, and the pressure wave in the form of transmission in the pipeline, causing the pump water hammer, eventually leading to squib. Pump starts, the flow velocity in the pipeline is much higher than the design flow rate, resulting in the pressure of the pump water hammer can be up to about 2MPa, much higher than the test pressure, the continuous dynamic pressure dynamic destructive pressure is several times the static pressure, the old pipe Longer service life, lower strength, prone to burst tube. In order to avoid the pump tube water hammer explosion caused by the recurrence of pipe, the design of the exhaust pipe is crucial. 3. Pipeline gas sources, operating characteristics and hazards of gas in the pipeline there are many gas sources are mainly two aspects: 1> Pipe network ups and downs, stop pump or water pipe local vacuum resulting in the pipeline from the row Air valve or high water intake; 2> suction natural water pump, the maximum volume of dissolved air gas content of about 2% (that is, the water containing dissolved gas is about 20L / m3), studies have shown that when the pressure is reduced To a certain value when the water dissolved gas will be in the form of micro-bubbles quickly precipitated, and run with the flow of water accumulated into large bubbles or air sac. In the longer distance pipeline, due to the design flow rate is generally not large, many of the gas pipeline in the form of airbags in the upper tube. In many undulating pipelines, the airbag mostly exists in the convex point of the pipeline. In the small gradient and flat pipeline, the gas disperses in many independent airbags. According to the research theory of Professor Martin, a famous waterhammer in the United States, flatter water supply lines show six states of gas-liquid two-phase flow during water filling and operation. The process of filling water and exhausting water pipelines is quite complicated. Generally speaking, when the water pipelines are filled with water, the pipe flow patterns are mostly stratified flow, wavy flow, slug flow or annular flow, and exhaust gas is relatively easy; Slug flow, air flow or foam flow state, the exhaust is difficult to exhaust ordinary. The size of the airbag present in the pipe depends on the complexity of the pipe, the size of the pipe, the speed and method of water filling, the venting measures, and the like. A large number of engineering practice shows that when the airbag in the pipeline flows with water, it brings great harm to the long-distance water transmission pipeline, mainly in the following two aspects: 1> Difficulty in passing water due to poor exhaust gas, water resistance Increase, the flow does not reach the design value. Slope is not very large water pipe in the first water or water again after maintenance, pipeline water and gas phase is inevitable, if the exhaust is not smooth, it caused a serious "gas blocking", the gas can not discharge, poor water flow , Water filling is extremely difficult, especially gravity flow, slope is smaller, larger diameter, more serious. There are airbags inside the pipe, air resistance increases, the formation of serious "gas blocking", reducing the cross-section, the flow rate of less than the design value. 2> poor ventilation caused by water and pipe burst during operation, water supply system can not be normal operation. The existing airbag in the pipeline will disperse and aggregate due to the change of the pipe slope and the wall roughness of the pipe when the water flows, as well as the pipe fittings of the elbow and the diameter reduction. The change of the flow velocity in the pipe will easily cause the pressure difference between the two ends of the airbag to change. Small differential pressure changes will not have any effect on the incompressible water, but the impact on the air is great, it can cause changes in water flow velocity and pressure drop in the pipeline, causing the water hammer to trigger squib. 4. Exhaust valve type Exhaust valve is a special product on the water pipeline, its performance is extremely poor. At present, the common domestic exhaust valve structure can be divided into two categories, float ball exhaust valve (including combined, complex, power compound) and cylinder exhaust valve. 4.1 Float type exhaust valve Float type exhaust valve has a float in the valve body casing, when the valve body is in the water, the float ball falls into the casing, the exhaust port opens the exhaust gas, when there is water, the float Ball float to block the exhaust port, seal the water flow. This type of exhaust valve is simple in structure, but has the following technical defects: 1> large exhaust port can only discharge the first section of gas, not continuous exhaust. Pipeline gradient is not large, the pipe is mostly a period of water gas slug flow state, the buoyancy of the float ball valve only a few kilograms of heavy, while the first row of gas discharge row, the water put the ball float up , The second paragraph of the gas that is pressure, assuming the pressure of 0.2PMa, gas float on the force equal to the exhaust area by the pipe pressure, calculate the available DN100 exhaust valve ball force of about 150kg, DN300 exhaust valve support Ball power of about 1400kg, so a large exhaust port can no longer automatically open the exhaust gas, in the slug flow state of the exhaust function. 2> Small exhaust port diameter is generally 3 ~ 5mm, only a small amount of exhaust If the exhaust port performance is not good, only microporous exhaust, for large diameter pipe is extremely dangerous. 3> Long-term operation does not move, easy to stick because of floating ball failure. 4.2 Cylinder Exhaust Valve Cylinder exhaust valve is the use of float lever and other pneumatic cylinder control cylinder action, so that the body of large and small exhaust port opening and closing, is full pressure high-speed exhaust valve, the valve in any Pressure and water flow, as long as the gas pipeline into the exhaust valve, the exhaust valve opens large and small exhaust vent. When the water into the exhaust valve, large and small exhaust port that is closed, watertight. Or the valve can be seen that the gas is discharged at high speed, see the water that is closed, can be a large number of consecutive exhaust. The main features of this type of exhaust valve structure is: large, small exhaust port or exhaust only effective exhaust port diameter of not less than 70% to 80% of the nominal diameter of the exhaust valve, exhaust diameter, exhaust Fast, and in all cases can be high-speed exhaust. The average designer in the choice of exhaust valve exhaust valve is based on the nominal diameter calculation of displacement. Cylinder exhaust valve is fully able to meet the design requirements, the real play to prevent pipe water hammer and burst pipe role. 5. Exhaust valve selection and installation of the project water pipeline pressure flow, gravity flow, a gradient, a gradient, the gas pipeline running more complicated, you should choose a valve in any State can effectively discharge the gas inside the pipeline. By comparing the cylinder exhaust valve. Purification station built on a hill, from the waterfront to the pump station to purify the station, the pipe length 800m, pressure flow, gradient, installed in the middle of the bulge point of the exhaust valve, in order to be able to evenly distributed into the treatment of water structures, Installed in the purification station before the ultrasonic time-flow meter, if the pipeline has a large number of airbags, easily lead to over-flow meter measurement or can not measure, so ultrasonic time-difference meter installed in front of more than 10 times the diameter of the exhaust valve , To ensure accurate measurement. From the purification station to the secondary pressurization pump room, the pipe length is 1600m. The gravity flow and the gradient of the downhill section are large. The slope of other pipelines is relatively flat. The gas in the down-hill pipeline can be directly discharged into the clear pool in the mountain. Exhaust valves are installed at three locations. In order to protect the pumps in the secondary pressurization pump room, an exhaust valve is installed in the pipe at the secondary pressurization pump room. From the secondary pressurization pump room to the production area, the pipe length is 600m, the pressure flow and the slope are relatively flat, and the exhaust valve is installed at the midlift point. A total of 6 pipeline exhaust valve installed on the pipeline, which can effectively discharge the gas inside the pipeline, to ensure that the pipeline will not have gas pipeline problems. 6. Conclusion As the smooth delivery of water pipelines is the most important indicator of its safe operation, engineering practice proves that not installed or installed exhaust valve performance does not meet the requirements, may result in pipe burst, stop production, resulting in A certain degree of economic loss. Therefore, the use of good exhaust performance exhaust valve and rational installation is the key to the safe operation of the pipeline. Exhaust valve to have good performance, especially when the pipeline gas is slug flow, air mass flow, not only can quickly discharge the first airbag, and can continue to discharge any one airbag. That is, under certain pressure conditions, the exhaust valve must be filled with air to open the size of the exhaust vent, the water into the body, the valve is closed without drainage. Exhaust valve to meet the above requirements, the large exhaust port diameter of not less than 70% to 80% of nominal diameter, small exhaust port diameter is not limited. Bidding companies must show the exhaust valve through their own or testing agencies to test qualified certificate. Exhaust valve diameter is generally 1/8 ~ 1/5 of the main pipe diameter. If you choose to use non-slow closing of the exhaust valve, it is best to install a big one small two exhaust valve. If you choose to use a slow closing of the exhaust valve, only installed at the top of the tube can be. If the pipe is flat, a degassing valve should be installed every 0.5 ~ 1.0km when the slope is ≤ D / 1000. If the gradient ≤ D / 100, it should be installed every 1.0 ~ 1.5km exhaust valve. When the slope is large, consider installing an exhaust valve every 1.5 ~ 3.0km. When the slope is greater than or equal to D / 10, consider installing the vent valve only at the high point (D is the pipe diameter). Multi-ups and downs of the pipeline, should be installed in the high exhaust valve. According to the relevant specifications and technical requirements, scientifically select the exhaust valve, the performance of the selected exhaust valve test to identify the performance of the exhaust valve, after passing the selection. Search Keyword: More Valve Product Information
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