The most common design for managing high-pressure steam in combined-cycle power generation plants is cascading bypass systems. Balancing valves are used on the hot reheat line to respond to loop control requirements. The application is difficult due to high pressures, high temperatures and large sizes of the valve (high torque). The valves must close tightly and be able to throttle precisely as well.
It is also difficult to equip these valves with pneumatic actuators. Due to the size of the valve and the design of the valve, the actuators must have a high torque output without taking up large amounts of space. Actuators also need to act quickly and eliminate hysteresis.
Most pneumatic actuator designs simply can not meet operating and size limitations, and hydraulic actuators, with all their associated maintenance problems, are used instead.
A better solution is to apply Kinetrol vane actuators. They deliver high torque in a relatively small package, and combined with state-of-the-art valve positioners, provide the precision and response the application requires to eliminate oscillations and instability.
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