STUDY ON VARIATION OF SETTING AND STOPPING PRESSURES OF SAFETY VALVE WITH STRUCTURAL MODIFICATION

摘要

The possibility of pressure control with the structural change of a safety valve is investigated. Safety valve is commonly used as safety devices for numerous applications which include boilers,ships,industrial plants,and piping.Setting and stopping pressures of a safety valve,pset and psto，are traditionally adjusted with a fine tuning of seat ring and valve ring heights, hsr and hvr. However, it is not easy to achieve the proper setting and stopping pressures of a safety valve in practice. The depth of inside and outside grooves in a valve, di and do are modified and their effects on setting and stopping pressures of a safety vlave are tested. The most appropriate values appear 1.0 mm in di and 0.5～1.0 mm in do,respectively. The valve ring height, hvr,shows that the best results can be achieved at 2.3 mm for setting pressures of 0.1～0.4 MPa and 1.0 mm for setting pressures of 0.5～1.0 MPa. The stopping pressures increases with the increase of seat ring height,hsr, upto certain hsr value and then becomes independent to the seat ring height. This implies that there exists the optimum hsr，which provides the largest flow rate and the proper stopping pressure. Stopping pressures of a safety valve are adjusted with the seat ring and valve ring heights. This study,however,demonstrated that the modification of value grooves also changes setting and stopping pressures of a safety valve.Therefore,the proper selection in dimensions of the inside and outside grooves should be considered for the safety valve design.