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Emergency shutdown valve works and engineering problems
Emergency shut-off valve is a kind of hydraulic control valve. Is composed of the main valve, throttle, pilot valve, pressure gauge and take over and other pipe fittings. When the inlet pressure of the main valve is lower than the pressure set by the pilot valve, the pilot valve is in the open state at this time. The pressure in the main valve cavity of the main valve is equal to the outlet pressure of the main valve, and there is a pressure difference between the inlet and the outlet. . When the fire pump starts, or when the pressure pump pump pressure exceeds the set pressure of the pilot valve, the pressure of the control valve of the pilot valve is increased by the inlet of the main valve, the pressure acting on the spring is increased, the pressure is reduced and the spool Down, so that the pilot valve closed, then the main valve inlet pressure through the throttle valve constantly added to the main valve cover cavity, due to the downward pressure on the valve flap is greater than the upward thrust, the main valve is closed. Please note that the key point is that the inlet pressure is less than the set pressure The valve has been open, the inlet pressure is greater than the set pressure, the valve is closed. There are many designers mistakenly believe that as long as the installation of the emergency shut-off valve, it will shut, without saying what conditions, it was wrong. We encountered in the actual installation and commissioning of many unreasonable place, put forward for discussion. Is located in Shanghai Pudong Yu Shan Road has a residential area. Water supply network, this residential area pump room is located in the ground, three high-rise two and eight eight storeys, 2.8 meters high, life pump fire pumps are DN80, life pump lift 53 meters, fire pump lift 60 meters, Flow 10L / S, water supply five, DN80 pipe into the roof tank. DN80 by the pump at the same time for five DN80 pipe, so the water pressure is not high, only reluctantly into the water tank. Emergency shut-off valve to set the pressure at 0.5MPa, while for five-way water, the pressure will not exceed 0.5MPa, only to replenish the water tank. However, if four tanks are full, the liquid level control valve on the tank is closed and only one tank of water remains to be replenished. At this time, the pressure will increase. If it exceeds 0.5MPa, the emergency shut-off valve will be closed and the remaining Under a water tank can not make up. In order for each tank can be smooth water, you need to stabilize the pressure at 0.45MPa, so that less than 0.5MPa, it will not cause closure. This requires a relief valve in the life pump. Now most units, there is no pressure relief valve on life pump. Some units use the electric contact pressure gauge, when the water pressure exceeds 0.5MPa automatically trip, the pump stops running, so still can not solve the problem of a single tank replenishment. The second problem is that when the fire pump starts, all emergency shut-off valves are open. DN80 DN800 sub-pipe water pipes, water tank at this time if the water is not full, the water pressure does not go up, can not exceed 0.5MPa, until the tank is filled, liquid level control valve is closed, the pressure can be increased. Here designers should consider increasing the pump capacity, or reduce the caliber of the pipe, the difference between the two should be at least second gear, such as the pump to DN100, five pipe to DN65, the pressure at this time can exceed 0.5MPa, shut down The role of fire water can be sent to the building. For another example, there is a residential DN100 fire pump on Shanghai Jiangjiang Road, and the six-way water pipe DN80 can not be shut down yet, so the pump and multi-way water supply pipe should be different from the second gear. The third problem is that the drainage system of the pump house, the water discharged from the pressure relief valve should be discharged into the fire water tank or sewer and should not be arranged in a narrow ditch. Or cited the above example, debugging five water pipes, all the way to gradually shut down, the results of the water pump all the pressure out of the valve to vent in the basement, the drainage pump is much smaller than the fire pump, underground pump house results were flooded . The best solution is to use life pumps and fire pumps are variable frequency, constant water pressure is not affected by traffic flow. Or with a quantitative pump pressure relief valve can also be, but the pressure relief valve must be connected to the pool or sewer pipe, sewer diameter than the intake pipe freshman to second gear. Emergency shut-off valve through the user's program is better. In the fire pipe network and life pipe network should add an anti-fouling cut-off valve to prevent fire water back to polluting domestic water. The fourth question, the choice of installation location. So far, most users have placed the emergency shutdown valve in the well. One user set the emergency shut-off valve under the stairs. I think it is more reasonable to place it under the stairs for debugging and maintenance. If placed in the well should leave enough maintenance space, and some well area of ​​only 40 × 60cm2, and more than 1 meter deep, space is too small maintenance personnel simply can not be debugged. And there is no expansion joints or soft joints at both ends of the valve, which can not be installed if the need to remove the maintenance. Proposed well area of ​​60 × 80cm2, the depth should not be too deep, to cover the valve without cover after the cap is appropriate. In addition, the need to add soft joints or valves have an elbow. Fifth question, the pipeline should be washed before it is activated. We found in the process of debugging the emergency shut-off valve can not be closed, ruled out the pressure factor, there are suspect pebbles in the valve body to survive after checking 12 most of the valves have small stones, of which two lower body plug full. Therefore, the installation of emergency shut-off valve should be cleaned before the pipeline, in order to ensure the normal operation of all valves.