Development And Test Of A New Modulating Pilot-operated Safety Valve

The Modulating Pilot-Operated safety valve studied in this thesis is a high-grade product in the product range of the safety valve.Its structure is complex,the principle of movement is not easy to understand,and the design and manufacturing requirements are very high.Therefore,there are few manufacturers at home and abroad to produce this type of safety valve,and there are few obvious structural forms.Research papers on such pilot valves are rare in publications.In this paper,a new Modulating Pilot-Operated safety valve was developed,its working principle and action process,structure,design method and so on basic theoretical knowledge were studied in detail.The stress change process of the moving parts in the initial state,before opening,blowdown state and after closing,as well as the change of chamber pressure are analyzed in detail,and the static mechanical equilibrium equations are given in detail.Through the analysis,combination and deduction of the static mechanical equilibrium equations,the relations between the combination of the pilot valve piston and the main valve piston are obtained,that is,the area ratio of the top piston and the down piston in the pilot valve d12/d22 is equal to 3.5,the area ratio of the seat and the piston in the main valve must be greater than or equal to 0.65.The piston size combination of three sets of different ratios was specially designed,and the simulation experiment was carried out to verify the above relationship was correct.The design structure,design dimension,design method and key points of the main parts of the new pilot valve and main valve are given in detail,and the outer diameters of the top piston and down piston in the pilot valve are defined as ?43mm and?23mm.The valve back pressure can be adjusted by increasing the adjustment lever to control the area of the inlet hole of the pilot valve.The calculation method of the selection of the main spring of the pilot valve is given in detail,and a simple and easy calculation table is formed,which is used for the selection of the main spring of the pilot valve under different setting pressures.The setting pressure and sealing test of the new Modulating Pilot-Operated safety was carried out.Setting pressure is accurate,sealing pressure can reach more than 95% of the setting pressure,the overpressure and blowdown is stable.Finally,by setting different working conditions,the performance test is performed on the new type pilot valve,and the valve can be steadily action and repeatable action At the same time,draw the curve of the piston height of the main valve of the valve and the overpressure.