Application of emergency closing valve and emergen

2022-08-10
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Application of pressure relief valve, emergency shut-off valve and emergency open valve

pressure relief valve, emergency shut-off valve and emergency open valve are generally made of rolled round steel or forgings and applied in recent years, which have attracted the attention of the construction and fire water supply industry

1 pressure relief valve

the pressure relief valve is set on the outlet pipe of the fire pump, which is usually closed and automatically opened when the pressure of the fire water supply pipe exceeds the set value, so as to prevent damage to the water supply system due to overpressure

the overpressure of the fire water supply pipe is mainly due to the following reasons: ① the flow head curve of the pump selected according to the fire design flow is steep, and overpressure will occur during small flow operation (self inspection or early stage of fire); ② The water pump suddenly stopped for some reason (such as power failure), and the outlet pipe did not take corresponding technical measures, so the pump was stopped and the water hammer caused overpressure

the setting of pressure relief valve should pay attention to the location, diameter selection, pressure setting and corresponding accessory configuration

① the pressure relief valve can be set near the fire pump or the fire water tank. Article 10.3.3 of the revised version of code for design of sprinkler systems gbh84-1985 stipulates that "each group of water pumps... Outlet pipes should be equipped with control valves... And pressure relief valves should be set if necessary." This article was changed into: "... When necessary, measures should be taken to control the outlet pressure of the water supply pump." These measures include pressure relief valves

when the pressure relief valve is set on the outlet pipe of the fire pump, it can be set in front of and behind the check valve. It can eliminate the overpressure caused by the small flow operation of the water pump in front of the check valve, and it can eliminate the overpressure caused by the small flow operation of the water pump (along the water flow direction) and the overpressure caused by the water hammer when the pump is stopped. Even if the outlet pipe of the fire pump does not take other measures to eliminate the water hammer when the pump is stopped (quick closing check valve, slow closing check valve, buffer tank, etc.), it will not cause harm and loss

② there are two methods for the diameter of the pressure relief valve, one is the same diameter as the fire water supply main pipe or a smaller level, and the other is the pressure relief valve of DN100 or DN150

from the perspective of pressure relief, the larger the diameter of the pressure relief valve, the faster the pressure relief and the better the effect. As shown in Figure 1, q is the discharge flow. If the diameter of the pressure relief valve is large, the Q value will be large. The RBC curve will deviate to the right, and the intersection point m of R curve and H curve will also move to the right, and its pressure value will decrease. However, from an economic point of view, the larger the caliber, the higher the price of the pressure relief valve, which will inevitably increase the engineering construction cost. Therefore, from the perspective of reality, the pressure relief valve with fixed diameter is preferred at present. Even if the actual pressure value during pressure relief will be slightly greater than the actual pressure value of the pressure relief valve with large diameter, the comprehensive effect is still feasible. Therefore, the diameter of pressure relief valve can be specified as follows: if the diameter of fire water supply main pipe D ≤ 150mm, DN100 pressure relief valve is used; If the diameter of fire water supply main pipe d> 150mm, DN150 pressure relief valve shall be used

③ the pressure setting value of the pressure relief valve should be higher than the pressure setting value of the main fire pump and stabilized pressure pump. When there is a stabilized pressure pump, there are two pressure values for starting and closing the stabilized pressure pump (referring to the pressure value when the stabilized pressure pump is running). The pressure of the shut-down water hammer of the stabilized pressure pump is easy to cause the pressure relief valve to be opened by mistake. Therefore, for the stable high-pressure fire water supply system, there should be perfect and reliable technical measures to eliminate the shut-down water hammer, and the residual pressure of the fire water supply pipe after the water hammer is generated should be rechecked. If it is lower than the pressure setting value of the pressure relief valve, it can be ensured that it will not be opened by mistake

④ the pressure relief valve should be set on the branch pipe connected with the fire water supply main pipe. In order to facilitate the maintenance of the pressure relief valve and prevent the control valve from closing by mistake, a signal gate valve or a signal butterfly valve should be set in front of the pressure relief valve. In order to maintain the smooth flow of water during the maintenance of the pressure relief valve, a bypass pipe should be set

2 emergency shut-off valve

the emergency shut-off valve is usually opened and automatically closes when the pipe pressure exceeds the pressure setting value, so as to prevent the fire water from entering the water tank when the fire pump is running, and at the same time, it can prevent the domestic water supply accessories in the living fire water supply system from being damaged due to overpressure when the fire pump is running

China recommends a common water supply system for living and fire fighting. This kind of system usually starts the domestic water pump with a low pressure value and a long service life. The pressure value of starting the fire water pump in case of fire is much higher than that of starting the domestic water pump. According to the fourth paragraph of article 8.6.3 of the code for fire protection design of buildings, "after a fire, the fire water supplied by the fire water pump should not enter the fire water tank." To solve this problem, an emergency shut-off valve should be set on the pipeline entering the fire water tank (as shown in Figure 2). At the same time, in order to prevent overpressure of domestic water supply accessories when the fire pump is started, an emergency shut-off valve should be set on the domestic water supply main pipe

The problem with the emergency shut-off valve is the pressure setting. If the pressure is set too low, the emergency shut-off valve will also be closed when the domestic water pump is started; If the pressure is set too high, the emergency shut-off valve will not close when the fire pump is started. Generally, the pressure setting value should be higher than the pressure value of the domestic water pump at zero flow and lower than the pressure value of the fire pump at the design flow. At the same time, when realizing light weight, comfort and partial intellectualization, reliable technical measures must be taken on the main water supply pipe to prevent water hammer

3 emergency opening valve

emergency opening valve is applied to water spray fire extinguishing system, which has not been implemented in the project at present. The emergency opening valve is closed at ordinary times, and the water is automatically opened when the pipe pressure reaches the pressure setting value, in order to prevent the water spray fire extinguishing system from spraying water due to low pressure before the fire pump reaches the rated speed

most of the valves set in the fire water supply pipeline are normally open, while the emergency opening valve is required to be normally closed, that is, it will not be opened until the fire pump reaches the rated speed after starting and the pipe pressure reaches the pressure value required by the design, which requires the valve to be opened and closed normally and reliably. The nature of the emergency opening valve is similar to that of the pressure relief valve, both of which are opened when the pressure value is reached. The difference is that after the pressure relief valve is opened, the water is discharged or returned to the fire pool for pressure relief; After the emergency opening valve is opened, the water flows into the water spray fire extinguishing system for fire extinguishing. Both belong to the category of hydraulic control valves, and both are equipped with needle valves for pilots, which are easily blocked by impurities and cannot act; There are diaphragms used to control the action of the valve disc. The diaphragms are made of rubber, which are easy to aging and wear. The corresponding measures taken for these two parts are: ① set a multi-stage filter in front of the needle valve, and the filter hole is reduced step by step to intercept solid particle impurities; ② The rubber diaphragm adopts high-quality products, and the condition of the diaphragm and the spring in the hydraulic control valve are regularly checked

the load taken in the experiment is regarded as the sintering load If the repeated experiment does not produce sintering, at present, the pressure relief valve, emergency shut-off valve and emergency open valve are treated as general-purpose valves, and are not included in the category of special valves for fire protection, so they do not need to be tested by the fire product quality supervision, inspection and testing center. The author believes that this situation should be changed. The pressure relief valve, emergency shut-off valve and emergency open valve are only used in the fire water supply system, and they should be included in the category of special products for fire protection as soon as possible

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