SERVATING OF VALVE'S LIFE AND ITS DEVICE

PURPOSE:To obtain observating method and device of valve's life by which remaining life of a valve rod can be predicted with high precision, by correctly understanding occurrence of cracking of the valve rod and how cracking spreads. CONSTITUTION:A crack occurrence detector 23 and a crack spread detector 24 which can be switched to each other, are connected through lead wires 25a, 25b to a valve rod 2 being supplied with constant electromagnetism. So that the length of a crack and spreading speed thereof can be detected based on a voltage variation. An output signal from a displacement detector 25, of which detecting terminal 26 is installed at the valve rod 2, is input to a statistical processing computing unit 26, and is also input to a stress computing unit 27 together with an output signal from a crack spread detector 24. Displacement characteristics of the vlave rod 2 are operated in a statistical processing computing unit 26, and stress characteristics are operated in the stress computing unit 27, and temperature variation characteristics are operated in a temperature variation computing unit 30. The output signals after these operations are input into a stress variation computing unit 31, whose output signal is input into a life prediction computing unit 32. Its predicted value is output to an indicator 33.