The safety valve is the overpressure protection device of process equipment and pipelines, the correct calculation of the safety valve discharge is a reasonable choice of the safety valve, and an important basis to judge the reliability of the. GB150-89 "steel pressure vessel", according to the state of different flow valve, puts forward the calculation formula, 2 kinds of discharge therefore, judge the safety valve is in a critical state of flow or subcritical flow state, is the prerequisite of the correct selection of capacity calculation formula.
At present, the safety valve critical pressure ratio value of 2 Views: ① codes are of the view that the safety valve critical pressure ratio and nozzle critical pressure ratio is the same, the value of which is 0.528 (1,2). ② many experts and researchers considered, the critical pressure ratio safety valve critical pressure ratio is less than the nozzle, the value of about 0.2 ~ 0.3 (3]. So far, no precise and accurate safety valve critical pressure ratio calculation method is confirmed. Therefore, to determine the safety valve critical pressure ratio to determine the safety and proper flow state, is still a pressing problem in the project, the current has not been reported. Through theoretical analysis and experimental research, discusses the safety valve flow state, the critical pressure ratio calculation formula of safety valve.
Because of the complexity of structure safety valve, it is difficult to determine the minimum flow valve cross-sectional area at the air flow, thus unable to closure according to the minimum flow area at the speed of sound and accurately determine whether the safety valve critical pressure ratio. At present, the safety valve to determine whether the critical flow state is to determine safety valve discharge coefficient, as long as the discharge coefficient does not change with the pressure ratio.
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