Abstract: The reheat-stop-valve mechanism is a vital auxiliary machine in the steam turbine unit, which has specific requirements in dynamic performance, reliability and tightness. However, mechanical jamming often emerges in such mechanisms during cold start, and the trouble is greater and severer with higher steam parameters. Thus, the normal running requirement of the unit cannot be guaranteed. Abnormal variation of dynamic behavior of the reheat-stop-valve mechanism during cold boot is discussed in view of the failure phenomena and structure feature. Great physical property difference, for example coefficient of heat conductivity, leads to different transmission speed of heat in parts. Then, the radial and axial clearance varies greatly in the process of cold start, which influences dynamic behavior. Finite element method is used to quantitatively analyze the clearance variation from cold-boot to steady state, and dynamic performance is evaluated. The numerical results are consistent with the engineering problems, which are valuable to solving the problems in power plants. A concrete schemes is proposed in respect of improving tolerance design and manufacturing precision control, which has important theoretical value and realistic guiding significance to the solution of such engineering problems.

Key words: Dynamic behavior, Jamming, Mechanism, Thermal analysis