Design of pre action and automatic fire extinguish

2022-10-16
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It is impossible to use traditional methods to repair the pre action and automatic fire extinguishing system design of animal flow warehouse

pre action automatic sprinkler system (referred to as pre action system) is mainly composed of closed sprinkler, pipe, pre action valve group, inflation equipment, water supply facilities, fire detection and alarm devices, etc. The spray intensity 4, treatment procedure, action area, continuous spray time, nozzle selection and layout, pipe hydraulic calculation and installation of the pre action system are the same as those of the wet automatic sprinkler system. The pre action system can replace the dry system to improve the fire extinguishing speed and efficiency, and can also replace the wet system to prevent water leakage or mistakenly spraying due to pipe and nozzle failure. It is suitable for buildings with high safety requirements for automatic sprinkler systems. The author expounds several problems in the design of the pre action system of elevated warehouse for the reference of colleagues

1 Classification of fire risk level in setting places

classification of fire risk level in setting places is one of the keys to the correct and reasonable design of automatic sprinkler system. Whether the qualitative is correct or not is related to whether the system setting can play a role reliably. In the design process, according to the specific conditions of the setting place, refer to Appendix A, B and 3 of code for design of automatic sprinkler system gb50084- 2001 (hereinafter referred to as "sprinkler code") 0. 1、3. 0. 2、3. 0.3 the article description determines the fire hazard level

the classification of fire risk level of buildings in the "spray code" is the same as that in Article 2 of the original code The modification of article 0.1 is easy to master. From the current situation of the instrument and meter industry, the classification of the fire risk level of the warehouse is comprehensively summarized and simplified into level I, level II and level III with reference to the relevant specifications and standards of the United States and in combination with China's national conditions. In document 2, according to the type and size of stored goods, the placement method (density, stacking height), packaging materials and packaging methods, shelf forms, etc., the warehouse fire risk levels are divided into level I, level II, level III, level IV and plastic rubber (a, B, c). There are many types listed in the attached table, which is easy to be determined by analogy in design. It is suggested that the classification of warehouse fire risk level should be more detailed when revising the "spray regulations" for practical operation

2 technical measures to be taken to ensure the water filling time of the pre action system specified in the specification

Article 8 of the "spray specification" Article 0.9 stipulates that the water filling time of the pre action sprinkler system should not be greater than 2 min. Document 2 stipulates that the sprinkler system and the nozzle configuration controlled by it should meet the time limit requirements, that is, from the action of the temperature sensing system, the time for water to reach the nozzle at the most unfavorable point through every 122 m long water distribution main pipe should not exceed 1 min, and the maximum total time should not exceed 3 min. How to ensure the specified water filling time? In the design, the author carefully analyzes the factors related to the water filling time. In view of these factors, the design adopts the following technical measures

    2. 1. Setting of exhaust valve

in order to accelerate the exhaust and turn the originally inflated pipe into a wet system full of pressurized water, it is necessary to set the exhaust valve, but the exhaust of the pre action system is mainly driven by the high-pressure water flow after the fire pump is started. Therefore, this purpose can be achieved by setting an automatic air release valve at the top of the system pipe. After the solenoid valve is opened, the automatic air release valve can exhaust automatically. When the gas is exhausted, the automatic air release valve will close automatically under the action of water pressure. If it is a multi-layer pre action system, it is impossible to exhaust all the gas in the system by setting an automatic vent valve at the top of the pipe. Even if an automatic vent valve is set at the end of each layer, it is also impossible to exhaust all the gas in the system. Too many vent valves will increase the leakage of the system and may affect the accuracy of low pressure alarm

    2. 2 reasonable arrangement of pipes

exhaust is one of the factors related to water filling time. The exhaust time is closely related to the pipe arrangement. As the pipeline of the system is usually full of gas, if it cannot be quickly removed in case of fire, the speed of water filling will be hindered. In view of the problem that the pipeline gas can be quickly removed and cleaned, the following technical measures have been taken in the design

(1) shorten the exhaust distance. The exhaust mainly depends on the exhaust valve on the top of the riser of the main water distribution pipe. Therefore, the setting of the riser of the main water distribution pipe is very important for the exhaust. The balanced pipe layout is adopted, and the double risers of the water distribution trunk are set to speed up the exhaust speed. Although setting the double risers of the water distribution trunk will increase the system volume and prolong the water filling time, it has little impact on the water filling time compared with the whole system

(2) the spray riser should be arranged in the center of the pipe as far as possible, and the length of the distribution pipe from the spray riser to the nozzle at the most unfavorable point can be shortened accordingly. Its effect is similar to adding the spray riser, especially when the shape of the spray pipe is long and narrow, it is not suitable to set the riser at the end of the pipe

(3) horizontal pipe laying shall avoid gas gathering section. Because the gas gathering section will produce gas plug, which is unfavorable to water filling. In principle, the main water distribution pipe, water distribution pipe and branch water distribution pipe shall be installed horizontally and straightly, and convex installation shall not occur due to avoidance. Therefore, in the design, attention should be paid to the coordination with various professional types of work, and the comprehensive pipeline entering the press molding immediately should be reasonably arranged, so that the installation of horizontal pipes can meet the design requirements

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