In combined-cycle power generation plants, the most common design for managing high-pressure steam is with cascading bypass systems. Balancing valves are used on the hot reheat line to respond to control loop demands. The application is difficult because of high pressures, high temperatures, and large valve sizes. The valves must shut off tightly and also be capable of precise throttling.
Outfitting these valves with pneumatic actuators is also difficult. Because of the valve size and valve design, actuators must have high torque output, without taking up vast amounts of space. The actuators must also act quickly and eliminate hysteresis.
Most pneumatic actuator designs simply cannot meet the operating and size restrictions; hydraulic actuators, with all of their associated maintenance problems, are used instead.
A Kinetrol distributor in the Southwest USA was asked to recommend a better alternative to a line where very large scotch-yoke actuators, controlling two (2) 18″ valves, were acting poorly and were consuming space.
The distributor’s challenge was to deliver very high torque output, provide as small a package as possible, and improve the actuators stability and reliability.
The solution was to apply Kinetrol model 30 vane actuators. The model 30’s deliver 168,000 lbf of torque in a compact envelope. Additionally, the Kinetrol Model 30’s, combined with third-party digital valve positioners, provided the precision and response the application required to eliminate oscillations and instability. The actuators cycle about 20 times per day and have been performing without problems for years.
