Five problems that should be paid attention to in

2022-09-23
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Five problems should be paid attention to when using shut-off valve

emergency shut-off valve is a new product developed in recent years. Its application in engineering is increasing. In the process of installation and commissioning, we also found some problems, some are construction problems, some are design problems. A good product is not only good in quality, but also the most important thing is to let everyone know it, get familiar with it and use it reasonably, so that it can play its greatest role. 1、 Why should we use the emergency shut-off valve?

as we all know, the fire pipe and living pipe have always been two water supply systems, which are supplied by two pump groups respectively, and the water is supplied by two pipelines for a long distance from the pump room to the building. In this way, due to the large construction workload of laying two-way pipelines, double the pipeline materials, and there are many inconveniences in identifying a certain pipeline during maintenance; Second, the fire-fighting pipeline is not used for many years, which is easy to rust. The pipe wall and interface are thinned due to corrosion, so there is no pressure at ordinary times. Once a fire alarm occurs, the pressure in the pipeline suddenly increases, which is easy to burst, causing the fire-fighting system to fail to supply water. Third, Shanghai advocates that pumps pump water directly from municipal pipes and no longer set up underground water tanks. This not only saves the cost of the construction of the pool, but also avoids the secondary pollution of the water source. The most important thing is to keep the water clean and ensure the health of the people. Because of these advantages, this product is gradually being welcomed by everyone

II. Working principle of emergency shutdown valve

emergency shutdown valve is one of hydraulic control valves. It is composed of main valve, throttle valve, pilot valve, pressure gauge, connecting pipe and other pipe fittings. When the inlet pressure of the main valve is lower than the set pressure of the pilot valve, the pilot valve is in the open state at this time, the pressure in the upper cover cavity of the main valve is equal to the outlet pressure of the main valve, there is a pressure difference between the inlet and outlet, and the water flows out of the outlet through the valve port. When the fire pump starts, or the pressure of the variable-frequency pump rises, which exceeds the set pressure of the pilot valve, the pressure from the main valve inlet to the pilot valve control pipe rises, the pressure acting on the spring increases, presses down, drives the valve core to move down, and closes the pilot valve. At this time, the main valve inlet pressure is continuously supplemented to the upper chamber of the main valve cover through the throttle valve. Because the downward pressure on the valve disc is greater than the upward thrust, the main valve closes. Please note that the key point is that the valve is always open when the inlet pressure is less than the set pressure, and closed when the inlet pressure is greater than the set pressure. Now many designers mistakenly think that as long as the emergency shut-off valve is installed, it will close, without any conditions, that is wrong

III. problems existing in the project

we encountered many unreasonable places in the actual installation and commissioning process, and put them forward for discussion. Located in Yushan Road, Pudong, Shanghai, there is a residential area. See Figure 2 for the water supply pipe, which promotes the electronic sampling box in Wuxi & nbsp; One million plastic bags can be used less each year. The pump room in the residential area is located on the ground floor. The building is 12 floors high in three buildings and 8 floors high in two buildings. The floor height is 2.8 meters. The life pump and fire pump are all DN80. The life pump lift is 53 meters, the fire pump lift is 60 meters, and the flow rate is 10l/s. The water supply is divided into five ways, and the DN80 pipe enters the roof water tank. Five DN80 water pipes are supplied by the DN80 water pump at the same time, so the water pressure is not high and can only barely enter the water tank. The emergency shut-off valve sets the pressure at 0.5MPa, and supplies five circuits of water at the same time. The pressure will not exceed 0.5MPa, so it can only replenish water to the water tank. However, if four water tanks are full, the liquid level control valve on the water tank is closed, and only one water tank needs to be replenished when the water is insufficient. At this time, the pressure will rise, exceeding 0.5MPa, the emergency shutdown valve will be closed, and the remaining water tank cannot be replenished. In order to make each water tank replenish water smoothly, it is necessary to stabilize the pressure at 0.45MPa and make it less than 0.5MPa, so as not to cause shutdown. This requires adding a pressure relief valve to the living pump. At present, most units do not have pressure relief valves on life pumps. Some units use electric contact pressure gauges, which automatically trip when the water pressure rises above 0.5MPa and the water pump stops running, which still can not solve the water replenishment problem of a single water tank

the second problem is that when the fire pump starts, all emergency shut-off valves are open. The DN80 water pump is divided into five DN80 water pipes. At this time, if the water in the water tank is insufficient, the water pressure cannot go up and cannot exceed 0.5MPa. The pressure can not rise until the pool is full and the liquid level control valve is closed. Here, the designer should consider increasing the capacity of the water pump or reducing the diameter of the water pipe. There should be at least a second gear difference between the two. For example, the water pump should be changed to DN100, and the five way water pipe should be changed to DN65. At this time, the pressure can exceed 0.5MPa, play a closing role, and send fire water to the building. For another example, there is a DN100 fire pump in a residential area on Kongjiang Road in Shanghai, and the six-way water pipe DN80 still cannot be closed, so the water pump and multi-way water supply pipe should be at a second gear difference

the third problem is that the water discharged from the drainage system of the water pump room and the pressure relief valve should be discharged into the fire pool or sewer, and should not be discharged into the narrow ditch of the operating steps of the Ming rubber fatigue testing machine, which is the Vice President/Professor of Nabing of Donghua University of technology. Take the example mentioned above. During commissioning, five water pipes were gradually closed under the action of the above-mentioned favorable factors. As a result, all the water in the water pump was pumped out and discharged into the basement by the pressure relief valve. The drainage pump was far smaller than the fire pump, and the underground pump room was flooded. The best solution is to use variable-frequency pumps for both domestic pumps and fire fighting, and the water pressure is constant during commissioning without being affected by flow. It is also possible to add a pressure relief valve with a quantitative pump, but the pressure relief valve must be connected to the pool or sewer with a water pipe, and the sewer diameter is one to two gears larger than the inlet pipe. The scheme of directly connecting users after emergency closing valve is better. An antifouling block valve should be added between the fire pipe and the living pipe to prevent the backflow of fire water from polluting the living water

the fourth problem is the selection of installation location. So far, most users have placed the installation position of the emergency shut-off valve in the dumb well. One user set the emergency shut-off valve under the stairs. I think it is more reasonable to put it under the stairs, which is convenient for debugging and maintenance. If it is placed in the dumb well, there should be enough maintenance space. Some dumb wells have an area of only 40 × 60cm2, and more than 1 meter deep, the space is too small for maintenance personnel to debug. And there are no expansion joints or soft joints at both ends of the valve, so it can't be installed again if it needs to be removed for maintenance. Recommended dumb well area 60 × 80cm2, the depth should not be too deep, and it is better not to touch the valve after the well cover is covered. In addition, it is necessary to add a soft joint or the valve has an elbow at one end

the fifth problem is that the pipeline should be flushed before use. During the commissioning, we found that the emergency shut-off valve could not be closed, excluding the pressure factor. It was suspected that there were pebbles in the valve body. After inspection, most of the 12 valves had pebbles, and two of them filled the lower chamber of the valve body. Therefore, before installing the emergency shut-off valve, the pipeline should be cleaned to ensure the normal operation of all valves

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