Abstract: Upon the completion of 168-hour full load trial operation, the new type of domestic 1050MW unit was then put into operation. Unfortunately, main high pressure valves gradually became sticky and jammed, which caused action failure or in wrong position during operation and full stroke test. Through disassembly analysis, it is found that in addition to the damage and deformation of high pressure main steam valve sleeve seal ring, the narrow gap between valve stem and sleeve or main steam valve disc leads to the main steam valve sticking. In addition to adjusting the oil pressure of the oil pump and the operation of the valve as well as the switching time of the experiment to reduce the impact of the main steam valve stem on the sealing ring of the sleeve, the valve stem is reprocessed to increase the gap between the stem and the sleeve and the main steam valve disc, so as to resolve the problem of the main steam valve jam thoroughly. After the reinstallation, the main steam valve is back to normal place during the daily test and the switch process.

Key words: ultra supercritical, 1 050 MW generator unit, high pressure stop valve, jam, oil pressure, clearance, parameters optimization