What happens if there is internal leakage in the check valve of a extraction-condensing steam turbine?

In extraction-condensing steam turbines, the check valve serves to prevent steam from flowing back from the extraction pipeline to the high-pressure section of the turbine when extraction is not required, or under certain conditions such as load shedding or shutdown. If there is internal leakage in the extraction check valve, under normal operation (assuming the pressure before the extraction valve is lower than the back pressure), the following phenomena may occur: 1. Control valve opening: Due to the internal leakage in the check valve, some steam may flow directly to the low-pressure side or the condenser without being utilized effectively, resulting in a reduced amount of steam that actually enters the turbine to do work. To maintain the desired power output, the turbine control system may attempt to increase the opening degree of the main steam control valve to compensate for the lost amount of steam. 2. Turbine hall pressure: If internal leakage in the check valve occurs after a certain stage of steam extraction, the pressure in the corresponding turbine hall may decrease due to the steam leakage. This can affect the steam flow rate in that stage and the stages following it, thereby impacting the overall efficiency and stability of the turbine. 3. Pressure before the extraction valve: • The pressure before the extraction valve should be relatively stable, but due to internal leakage in the check valve, this steam cannot be utilized effectively, and its pressure decreases as a result of the loss of steam. 4. Turbine power: • The actual power output of the turbine may decrease due to a reduced effective utilization of steam. At the same time, since the steam fails to convert its potential energy fully into mechanical energy, the heat consumption and steam consumption rates may increase, resulting in a poorer overall economic efficiency of the unit. 5. Safety and equipment condition: • Long-term internal leakage in check valves not only affects performance but can also have adverse effects on the internal components of the turbine, such as causing rotor imbalance, increasing wear, or triggering other safety issues. In summary, internal leakage in the check valve can lead to a decline in the turbine’s operating performance, increased energy consumption, and may pose a threat to the safe operation of the system; therefore, it is necessary to conduct timely inspections and repairs.