Defect analysis and improvement of the MSIV pilot valve
                                                                                      HU Yinlong
                          (Jiangsu Nuclear Power Co., Ltd., China National Nuclear Power Co., Ltd., Lianyungang 222000, China)

Abstract: Aiming at the fail to open problem of the solenoid operated pilot valve of the MSIV in TNPS, the spring force of the pilot valve, the electromagnetic force of the electromagnetic actuator and other factors were researched. The relationship between the electromagnetic force and the working air gap of the electromagnetic actuator was obtained through the static characteristics of directacting electromagnet test, and some improvement work performance impact tests were done, combined with the mechanical stroke of the pilot valve and the adjust method of the working air gap of electromagnetic actuator, the temperature rise characteristics and the ambient temperature affect to the performance of the electromagnetic actuator, the temperature rise test and operation test under rated condition were done after the improvement .The results indicate that the opening reliability of the electromagnetic pilot valve can be greatly improved by reducing the air gap of electromagnetic actuator and the operating temperature of electromagnetic actuator, the improved electromagnetic pilot valve has not been unable to open or accidentally shut down after a period of time.

Key words: main steam isolation valve; solenoid operated pilot valve; spring force; electromagnetic force