CERAMIC VALVE RETAINING STRUCTURE

PURPOSE:To prevent the breakage of a stem of a valve due to a concentrated load, by forming a groove on the stem, forming a projection to be engaged with the groove on a cotter, and setting a contact length of the cotter contacting with the stem in a specific ratio. CONSTITUTION:A valve 1 consists of a valve member 1a and a stem 1b, and a cotter 3 is fitted to the stem 1b. The stem 1b is formed at its upper end portion with an annular groove 2, while the cotter 3 is integrally formed on its inner peripheral surface with a circular projection 3a located in the groove 2. A vertical length L of the cotter 3 is set to be 1.1-1.5 times an outer diameter d of the stem 1b, and a contact length of the cotter 3 contacting with the stem 1b is set to be substantially 0.6-1.1 times the outer diameter of the stem 1b. Accordingly, the inner peripheral surface of the cotter 3 is brought into generally uniform contact with the outer peripheral surface of the stem 1b, thereby dispersing a contact force of the cotter 3 with the stem 1b and preventing the breakage of the stem 1b.