Industry new

Emergency shut-off valve should pay attention to the use of the problem

Emergency shut-off valves are new products that have been developed in recent years. Applications are increasing in the project. During the installation and debugging process, we also found some problems, some of which are construction problems, and some of which are design issues. A good product not only has a better quality of the product itself, but the most important thing is to let everyone understand it, become familiar with it, and use it reasonably, so that it can play its biggest role.

First, why use emergency shutdown valve
As we all know, the fire control network and the living pipe have traditionally been two water supply systems. The two pump units have separately supplied water, and the water from the second road has been supplied from the pump room to the building for a long distance. In this case, the construction of the second-line pipeline is heavy, the pipeline material is twice as many, and the identification of a certain pipeline during maintenance is also inconvenient. Second, fire-fighting pipelines do not use for many years and are prone to rust. Corrosion thinning, usually without pressure, and in the event of a fire, the sudden increase in pressure within the pipeline, prone to burst, resulting in the fire system can not supply water. Third, Shanghai promotes direct pumping of water from the municipal pipe network and no longer sets up underground water pools. This not only saves the cost of pool construction, but also avoids secondary pollution of water sources. Maintaining the cleanliness of water and ensuring the health of the people is the most important one. Because of these advantages, this product is gradually being welcomed by everyone.

Second, the emergency shut-off valve works
The emergency stop valve is one of the hydraulic control valves. It consists of main valves, throttle valves, pilot valves, pressure gauges, and take-overs and other 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 upper chamber of the main valve is equal to the outlet pressure of the main valve, there is a pressure difference between the inlet and the outlet, and water flows out of the outlet through the valve port. . When the fire pump starts, or when the pressure of the variable frequency pump rises and exceeds the set pressure of the pilot valve, the pressure of the control valve of the main valve inlet guide valve increases, the pressure acting on the spring increases, and the pressure is pressed downwards to drive the valve core. Move down, so that the pilot valve is closed, then the main valve inlet pressure continues to be added to the main valve bonnet cavity through the throttle valve, because the valve is under the downward pressure greater than the upward thrust, the main valve is closed. The key point to note is that the inlet pressure is less than the set pressure and the valve is always open. The inlet pressure is greater than the set pressure and the valve is closed. Many designers now mistakenly believe that as long as an emergency shut-off valve is installed, it will shut down. No matter what the conditions are, it will be wrong.

Third, the problems in the project
We encountered many unreasonable points in the actual installation and debugging process and proposed for discussion.
Located in a residential area on Yushan Road, Pudong, Shanghai. The water supply pipe network is shown in Figure 2. The pump room in this residential area is located in the ground floor, with three floors of 12 floors and two floors of eight floors, with a storey height of 2.8 meters. The live pump fire pumps are all DN80, the life pump head is 53 meters, and the fire pump head is lifted. 60 meters, flow rate 10L/S, water supply is divided into five ways, DN80 tube enters the roof water tank. The water pump of DN80 is supplied by the DN80's water pump at the same time, so the water pressure is not high and it can only enter the water tank. The emergency shut-off valve sets the pressure at 0.5 MPa, and at the same time supplies the five-way water, the pressure will not exceed 0.5 MPa, and only the water tank will be filled with water. However, if there are four tanks full, the level control valve on the rotor pump water tank is closed, and only one tank is full and the water is not full, the pressure will increase, and the pressure will rise above 0.5 MPa. The emergency shutoff valve will close. The remaining tank will not be able to make up water. In order to allow each tank to be replenished smoothly, it is necessary to stabilize the pressure at 0.45 MPa so that it is less than 0.5 MPa, and it will not cause closure. This requires a pressure relief valve on the life pump. Most units now have no pressure relief valve on the life pump. Some units use electrical contact pressure gauges, which automatically trip when the water pressure rises above 0.5 MPa, and the pumps stop running, which still cannot solve the problem of replenishing water in a single tank.

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

The third problem is that in the drainage system of the pump house, the water discharged from the pressure relief valve should be discharged into the fire pool or sewer, and should not be placed in a narrow open ditch. Or take the example described above. During commissioning, the five-way water pipe is gradually shut down all the way. As a result, the water pumped out is completely discharged from the pressure relief valve in the basement, the drainage pump is far smaller than the fire pump, and the underground pumping station is flooded. . The best solution is to use variable frequency pumps for life pumps and fire fighting. The constant water pressure during commissioning is not affected by the flow rate. Alternatively, it is also possible to use a fixed displacement pump and a pressure relief valve. However, the pressure relief valve must be connected to a pool or sewer using a water pipe. The sewer size is larger than the inlet pipe. It is better to pass the user directly after closing the valve. An anti-pollution cut-off valve should be added between the fire pipe network and the living pipe network to prevent fire water from flowing back to pollute domestic water.

The fourth problem is the choice of installation location. To date, most users have placed the emergency shut-off valve in the well. A user placed the emergency shut-off valve under the stairs. I think that it is reasonable under the stairs to facilitate debugging and maintenance. If there is enough maintenance space in the well, some wells will only have an area of 40×60 cm2 and there will be 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. If it is necessary to remove the repair, it cannot be installed. It is recommended that the area of the manhole is 60×80 cm2, and the depth should not be too deep. It is advisable not to touch the valve after capping the manhole cover. In addition, it is necessary to add a soft joint or valve with a connecting elbow.

The fifth problem is that the pipeline should be flushed before it is started. During the debugging process, we found that the emergency shut-off valve could not be closed. Excluding the pressure factor, there were suspected pebbles remaining in the valve body. After inspection, most of the 12 valves had pebbles stored, and there were two lower chamber plugs for the valve body. full. Therefore, the pipeline should be cleaned before installing the emergency shut-off valve to ensure that all valves work properly.

PREVIOUS：Application of fluorine-lined valveNEXT：Electric ball valve evolved from related prod