To prevent major safety issues, adding safety valves is a common safety method that plays a vital role in enterprise safety. The safety valve itself will be damaged due to the limitation of service life and the influence of the environment during use, so it is necessary to find problems in time to reduce the probability of causing harm.

At present, nuclear power plants are only used in nuclear islands, and are not used in the main steam system, but the main steam pilot safety valve has a good record of use in foreign nuclear power plants. Since the structure of the main steam pilot safety valve is quite different from that of the nuclear island pilot safety valve, the functional principle and use of the main steam pilot safety valve are introduced.

The safety discharge capacity of the safety valve, that is, the displacement, is an important indicator to measure the performance of the safety valve. Under the guidance of the professional technology of "safety valve with online function and its detection system", the problem of displacement detection in the dynamic opening process of safety valve and its related flow mechanism are studied.

The main research contents include: According to the basic flow equation of the flow characteristics of the nozzle and the isentropic flow of the ideal gas, the calculation formula of the discharge amount of the safety valve is deduced, and the various factors that affect the discharge capacity of the safety valve are systematically summarized. The interaction mechanism between the parameters of the overpressure opening flow field of the safety valve is proposed, especially the variation law of the aerodynamic parameters.

In terms of experimental research, the displacement and other related parameters were tested in the field test using the valve core detection sensor and the detection flange sensor. Comparing the two-dimensional and three-dimensional numerical displacement calculation values with the test results, the research shows that the results are consistent with the test results, which shows that the use of special sensors to detect and measure displacement has good operability. As long as the numerical calculation of displacement is handled properly, the discharge capacity of the safety valve can be predicted more accurately.