Design Theory And Dynamic Test Method For Large Flow Fast Response Safety Valve

The powered support is the core equipment of the fully mechanized mining face,and is coupled with the surrounding rock around the working face as a dynamic balance system to provide safe working space for the fully mechanized mining face.Its adaptability and reliability determine whether the working face can be safe and efficient.The safety valve is one of the important components of the powered support and is used to control the maximum working resistance of the powered support so that it does not exceed the allowable pressure value.Its performance directly affects the safety factor of the powered support,and affects the performance of the powered support.As the ratio of large mining height and large working resistance powered support in China's mines is getting higher,the cylinder bore of the leg is also getting larger,and the coal mining intensity,the mining depth is increased,the mining conditions are deteriorated,the hydraulic pressure and the flow rate of the powered support system is continuous increase?the pressure is up to 37.5MPa,the flow rate is up to2000L/min?,the requirements for powered support leg and safety valve system are also getting higher.Through the analysis of the rock stratum structure and movement law of the mining face overburden.based on the theory of voussoir beam,S-R stability theory and Key stratum theory,the coupling mechanism between powered support and surrounding rock is analyzed.The general law of mine pressure appearance in mining face is analyzed.The force situation of the stable structure when the working face is pressed and clarified when the initial pressure and the periodic pressure.The force of the powered support during the pressure of the working face comes from the weight of the immediate roof and the breakage of the main roof through the immediate roof.The calculation method of static load and impact dynamic load when the initial pressure and the periodic pressure in coal face is given.The load on the powered support is mainly applied to the leg.The dynamic characteristics of the double telescopic leg under impact load are obtained by theoretical calculation and computer simulation;this method provided the basis for the design and calibration of the leg.According to the coupling mechanism between the powered support and the surrounding rock,the load on the powered support is analyzed and calculated.The new test method for the combined dynamic and static loading of high pressure and large flow safety valve based on the combined loading of accumulator and gas explosion is proposed?the accumulator loading is simulated static Load,the gas explosion is simulated impact load?,the test device components and dynamic test system is designed.Finally,the corresponding high pressure and large flow safety valve test device is built.The explosion characteristics of the premixed gas in the explosion tank?Cylindrical vessel with ignition at the top center?were studied to provide a basis for the safety valve test.The results show:the maximum explosion pressure p_max,maximum explosion pressure rise rate?dp/dt?_max,and deflagration index K_G increase as the initial pressure p₀ increases.They are all linearly related to p₀.By selecting different initial pressures of the premixed gas and gas volume fractions,different explosion loads can be obtained to simulate different impact dynamic loads of the mining face.Based on the analysis of the basic requirements of the powered support safety valve,the static and dynamic characteristics and flow characteristics of the 1000L/min direct-acting mechanical spring-type safety valve that commonly used in coal mines are theoretically analyzed and computer simulated.The results show:Regardless of the opening degree of the direct-acting safety valve spool,a large part of emulsion overflows from the first and second discharge orifices;the maximum flow rate of emulsion is at the first row of overflow holes;when the safety valve is opened and overflowed,a negative pressure zone is generated.Based on the shortage of 1000L/min direct-acting safety valve,two new structural safety valves are developed.The gas safety valve used high pressure nitrogen as gas spring,and a reliable gas sealing device is designed;the pilot stage of the two-stage safety valve is the mature 100L/min safety valve,and the main valve core adopted the cone valve structure.The two-stage safety valve provided two conditions,that is,the small flow condition when the working face is normally propelled and the large flow condition when the impact pressure on the working face is appeared.The prototype for testing was also produced.The high-pressure and large-flow safety valve test device was used to test the impact characteristics of three high-pressure and high-flow safety valves.The results show:Under the given test conditions,the three structural safety valves work well and the pressure overshoot are almost the same;the gas safety valve had the shortest opening time,with an average of 0.277s.The opening time of the direct-acting safety valve was second,with an average of 0.288s.The two-stage safety valve had the longest opening time,with an average of 0.2949s.In the case of almost the same amount of overshoot,the gas safety valve had the strongest unloading ability,during the test;the total amount of emulsion discharged was about15.895L.The unloading capacity of the direct-acting safety valve was the second,the average emulsion discharged was 10.814L,the unloading capacity of the two-stage safety valve was the worst,and the average emulsion discharged was only 3.928L.In summary,the perform of gas safety valve was best,followed by direct-acting safety valve,and two-stage safety valves had the worst performance.