Pressure relief valve, emergency shut-off valve and emergency opening valve settings

Abstract: Relief valves, emergency shut-off valves and emergency opening valves are the valves developed and applied in recent years. They have drawn much attention from the construction and fire water supply industries and talked about their own problems. Keywords: Pressure relief valve emergency shut-off valve emergency opening valve hydraulic control valve fire-specific 1 pressure relief valve relief valve set in the fire pump outlet pipe, usually closed, the fire water pipe network pressure exceeds the set value automatically opens to Prevent the water system from being damaged by overpressure. Overpressure of the fire water distribution network is mainly due to the following reasons: (1) The flow rate of the pump selected according to the fire design flow - the head curve is of a steep type, overpressure will occur during the low flow operation (self-test or early fire); Therefore (such as power outage) stalls, the outlet pipe has not taken the appropriate technical measures, stop pumping water hammer caused overpressure. Relief valve settings should pay attention to the location, caliber selection, pressure settings and the corresponding attachment configuration and other issues. ① relief valve can be located near the fire pump or fire water tank. Automatic sprinkler system design specifications "GBH84-1985 revised draft 10.3.3 of the draft request:" Each group of pumps ... ... outlet pipe should be set control valve ... ..., if necessary, should be set pressure relief valve. "The provisions of The draft for approval was changed to: "... Where necessary, measures should be taken to control the pressure at the outlet of the water supply pump." These measures include relief valves. When the relief valve is set in the fire pump outlet pipe, can be located in the check valve before and after. Set in the check valve before the pump to eliminate the small flow caused by overpressure, and located in the check valve (along the flow direction) not only to resolve the pump due to low flow operation caused by overpressure, but also digestion by the stop pump Water hammer caused by overpressure, even if the fire pump outlet pipe did not take any other measures to eliminate the stop water hammer (quick closed check valve, slow closing check valve, buffer tank, etc.), will not cause harm and loss. ② Pressure relief valve caliber has two kinds of practices, one is with the fire water main with the same diameter or smaller, the other is the use of DN100 or DN150 pressure relief valve. From the pressure relief point of view, the larger the pressure relief valve pressure relief faster, the better. As shown in Fig. 1, Q is the discharge capacity. The pressure relief valve is large in diameter. The Q value is large. The RBC curve is deviated to the right. The intersection point M between the R curve and the H curve also moves to the right and the pressure value decreases. However, from an economic point of view, the larger the caliber, the higher the pressure of the pressure relief valve will inevitably increase the construction cost. Therefore, from a practical standpoint, at present, the pressure relief valve with a fixed caliber tends to be adopted. Even though the actual pressure will be slightly larger than the actual relief pressure of the large-diameter relief valve, the combined effect is still feasible. Therefore, the relief valve caliber can be made as follows: If the fire water main pipe diameter D ≤ 150mm, the use of DN100 pressure relief valve; if the fire water supply pipe diameter D> 150mm, the use of DN150 pressure relief valve. ③ relief valve pressure setting should be higher than the main fire pump and pump pressure settings. When there is a regulator pump, there are two pressure values for the regulator pump on and off (refer to the pressure value when the regulator pump is running). Stabilization pump stop pump water hammer pressure easily lead to pressure relief valve open, so for a stable high-pressure fire water supply system should have sound and reliable technical measures to stop the pump to stop water hammer, and should review the fire water supply network after the water hammer Of the residual pressure, if lower than the pressure relief valve pressure set value, to ensure that does not accidentally open. ④ pressure relief valve should be set in the branch pipe and fire water supply pipe connection. In order to facilitate the relief valve overhaul and prevent the control valve from closing, the signal valve or signal butterfly valve should be set in front of the pressure relief valve. In order to maintain the water flow relief valve relief, bypass pipe should be set. 2 Emergency shut-off valve Emergency shut-off valve usually open in the pipeline pressure exceeds the pressure set value automatically shut down to prevent fire pump running fire water into the water tank at the same time to prevent fire pump operation, life - fire water supply system Water supply parts due to over-pressure damage. China's recommended life and fire water supply system. Such systems usually start the life of the pump pressure is low, fire start fire pump when the pressure is much higher than when starting the life of the pump pressure value, and according to "Building Code of Fire Protection," Section 8.6.3 fourth paragraph: "In the event of a fire, the fire fighting water supplied by the fire pump should not enter the fire water tank." To solve this problem, an emergency shut-off valve should be provided on the pipe into the fire water tank (Figure 2). At the same time to prevent fire pump start-up life water fittings over-pressure, should be set in the life of the water supply emergency shut-off valve. The problem with the emergency shut-off valve is the pressure setting. If the pressure is set too low, the life of the pump will be closed when the emergency shutdown valve; if the pressure is set too high, the fire pump start emergency shutdown valve does not close. In general, the pressure setting should be higher than the value of zero pressure when the pump life, fire pump design flow value is lower than the value of pressure. At the same time in the water mains must take reliable technical measures to prevent the production of water hammer. 3 Emergency opening valve Emergency opening valve used in water spray fire extinguishing system, has not yet implemented in the project. Emergency open the valve normally closed, the network pressure reaches the pressure set value automatically turns on the water, the purpose is to prevent the water spray fire extinguishing system before the fire pump reaches the rated speed due to low pressure water spray phenomenon. Fire water pipes to set the valve to normally open as much as the emergency valve to open normally closed, that is, after the start of the fire pump rated speed, pipe network pressure reaches the design requirements of the pressure value is turned on, which requires the valve opening and closing Normal and reliable. Emergency opening valve properties similar to the relief valve, are open when the pressure reaches the value, the difference is that after the relief valve is opened, the water discharge or return to the fire pool to relieve pressure; emergency open the valve open, the water into the water spray fire The system is used to extinguish fire. Both belong to the category of hydraulic control valves, are set for the pilot needle, and the needle valve easily clogged due to impurities and can not move; have used to control the valve disc action diaphragm, rubber diaphragm material, easy to aging, wear and tear. The corresponding measures for these two components are as follows: ① Multi-stage filter is installed in front of the needle valve, the mesh size of the filter screen is reduced step by step to trap solid particle impurities; ② The rubber diaphragm is made of high-quality products and the diaphragm and Hydraulic control valve in the case of spring. At present, relief valves, emergency shut-off valves and emergency opening valves are treated as general purpose valves, but not included in the scope of special fire-fighting valves, fire products without passing the Quality Supervision, Inspection and Testing Center. I believe that this situation should be changed, the relief valve, emergency shut-off valve and emergency opening valve are only used for fire water supply system, it should be included as soon as possible the scope of fire-specific products.