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Currently, the standard for determining internal leakage in valves is that, after the valve has been closed for 6 hours, there is an obvious sound of leakage, or when using an infrared temperature gauge to measure the temperature of the valve stem (near the valve body) or at a distance of 150 mm downstream from the valve body, if the temperature is above 70°C, it is considered to be an instance of internal leakage. This method of judgment is applicable to most valves with internal leakage, but in practical work we have encountered the following special cases: 1. Due to the location of pipe installation, there is high-temperature steam present in front of or behind some valves, such as the start-up vent valves for the high-pressure bypass, low-pressure bypass, and high-temperature superheaters. Even if these valves are airtight and do not leak, the temperature of their valve stems can still exceed 70°C. Therefore, other methods must be used to determine internal leakage in these valves. For example, the temperature after the high-pressure bypass valve can be compared with the exhaust temperature to determine whether there is internal leakage in that valve; the temperature after the low-pressure bypass valve can be compared with the exhaust temperature of the turbine’s low-pressure cylinder to check for internal leakage in that valve; and it is possible to determine whether there is internal leakage in the exhaust valve of the high-temperature heater by observing whether steam is emitted from its exhaust port. 2. Drain valves or blowdown valves connected side by side to the drain and release pipes; when the location of the last valve is close to the main pipe, if there is a leak in any of the valves in the pipeline, the temperature of the other valves will rise to above 70°C, as is the case with boiler blowdown valves and superheated steam drains. Therefore, other methods must be used to determine internal leakage in these valves; generally, the temperature of the pipe wall in front of the valve or the temperature of the valve stem in front of the valve is measured to assess internal leakage.