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The definition of a sealed cylinder refers to isolating the steam engine cylinder; after shutdown, all drain valves connected to the cylinder are closed in order to maintain a temperature difference between the upper and lower cylinders. The rotor is manually rotated 180 degrees every 30 minutes to keep it aligned, thereby preventing permanent bending of the rotor. “The origin of the \"stuck cylinder\" phenomenon: After a steam turbine is stopped, for some reason, the turning device cannot be activated (including manual turning; at such times, the plant’s electrical power is usually completely cut off, and neither the lubrication oil pump nor the thrust oil pump can operate). Since the cylinder temperature is still high right after shutdown, if the turning device isn’t activated in time, the main shaft may bend due to the temperature difference between the upper and lower cylinders. This is explained in the safety regulations regarding the prevention of large shaft bending. Measures to be taken: 1. Seal tightly all steam supply lines leading to the turbine ； 2. After draining the water from the cylinder, close the drain valve tightly ； 3. At the shaft seals of each cylinder, use insulation material to seal them in order to prevent cold air from entering ； 4. When the temperatures of the high and medium pressure cylinders reach the rotor’s brittle transition temperature, manually rotate the rotor 180 degrees as a measure to seal the cylinders. 1. Reduce the vacuum to 0 kPa ； 2. Close all steam traps connected to the cylinder block ； 3. Stop steam supply to the shaft seal ； 4. Unless there are situations such as a loss of plant power or a fire in the oil system, the jacking oil pump and the lubricating oil pump should be kept in operation as much as possible ； 5. The main shaft is not turned. At this time, attention should be paid to the temperature difference between the upper and lower cylinders (which generally should not exceed 20°C; units with a capacity of over 600 MW require an even smaller difference). Under normal circumstances, no action is needed; however, if the temperature difference is too large or increases too rapidly, it is necessary to suspect the possibility of water or cold air entering the system, and the system should be inspected promptly to eliminate any abnormalities. The above conditions can be maintained until the cylinder temperature drops below 150°C, after which timely action should be taken. When the conditions during the cylinder sealing process improve, it is possible to try to start the turntable, but the following conditions must be met: 1. The oil pump and the top shaft oil pump are operating properly, with the maximum bearing temperature not exceeding 90℃ ； 2. The temperature difference between the upper and lower cylinders should not exceed 50°C. 3. The turntable can be manually tested, and any abnormal noises should disappear ； 4. The equipment related to the turning gear is operating normally, and the conditions for starting the turning gear are met. Preventive measures require that cold water or cold steam not enter the turbine. To this end, the following steps must be taken: 1. Closely monitor the temperature changes in various parts of the turbine cylinder, paying special attention to the temperature difference between the upper and lower cylinders. In the event of any abnormalities, the cause must be identified promptly and resolved right away ； 2. High and low pressure shaft seals should be supplied with steam separately, and their steam supply pipes must have adequate drainage measures. If there are issues with the drainage system, it should be modified at an appropriate time to eliminate potential hazards ； 3. During shutdown, the operators must verify, in accordance with the procedures, that the drain valves are open, ensuring unobstructed drainage ； 4. Pay attention to monitoring the water levels in the steam drum, condenser, and deaerator. The water level protection systems must be able to function properly; any abnormalities detected should be promptly investigated and addressed. Accidents such as a full condenser must be prevented at all costs ； 5. During operation, it is necessary to strengthen the monitoring and control of the water levels in the high- and low-pressure heaters, ensure that the water level protection systems for each heater are functioning properly, and take strict precautions against accidents involving water entering the cylinder due to leaks in the heater tubes or improper operation (such as inadequate control of the heater water levels) ； 6. It is necessary to strengthen the testing and maintenance of the high-pressure discharge check valves and all the extraction steam check valves, to ensure that they close quickly during shutdown and prevent steam from flowing into the cylinders. Measures to prevent cold steam and cold water from entering the turbine during and after shutdown (1) Check the condenser water level and ensure that the make-up water valve is closed. (2) Check and verify the shutdown status of the high and low pressure bypasses as well as the desuperheating water. (3) Check the closing status of the intermediate tap of the feed water pump. (4) Check and verify the closed status of the deaerator feed steam electric valve, the high-pressure heater drain to deaerator electric valve, the deaerator to shaft seal steam supply valve, and the stem leakage steam to deaerator isolation valve. (5) Check and verify the closed status of the isolation valves for the main steam, reheat steam, and auxiliary steam sources leading to the shaft seal steam supply. (6) Check and verify the closed status of the main steam inlet valve and the control valve of the cylinder and flange heating header. (7) Check and verify the opening status of the drain valves on the cylinder body, as well as those in the cold and hot sections of the reheat steam, and those located after the high-pressure bypass and before the low-pressure bypass. (8) After the turbine is shut down, the operators should regularly check whether the isolation measures for the turbine have been properly implemented, whether the cylinder temperature has dropped, and whether the temperature difference between the upper and lower cylinders of the turbine exceeds the allowable limits.