How to Select and Design Power Station Globe Valves for Drainage Systems
Power station globe valves, also known as drain valves, are crucial components in thermal power plants. They manage critical drainage applications, including high-pressure heater drains, reheater drains, and superheater drains. These valves demand reliable sealing, fast actuation, and robust automatic control with fail-safe functionality. Pneumatically actuated globe valves are the industry-preferred solution, offering dependable performance, straightforward maintenance, and inherent safety during power or air supply loss.The main stop valve product names of China Stop Valve Network include:Pneumatic Flange Straight-through Globe Valve,ANSI Flange Straight-through Globe Valve,High Temperature and Pressure Power Station Electric Globe Valve,Flange Straight-through Throttle Emptying Globe Valve,GB Bellows Globe Valve,DIN Angle-type Bellows Globe Valve,Flange Straight-through Low Temperature Globe Valve,Self-sealing Straight-through Globe Valve.
Choosing the Correct Pneumatic Actuator
For on/off drainage control, valves are typically selected for full-port operation. While both globe and ball valves offer fast cycling and good sealing, pneumatically actuated globe valves are the established standard for superior long-term reliability in these demanding services.
The choice of actuator is fundamental. The two primary types are:
Single-Acting Actuators: Equipped with a return spring, these provide automatic fail-safe action (either fail-open or fail-close) upon air supply loss, making them essential for safety-critical applications.
Double-Acting Actuators: These provide higher output torque/thrust but require an external air supply to move in either direction and lack an intrinsic fail-safe position.
Selecting the Fail-Safe Configuration:
Your system's safety requirement dictates the actuator choice:
For a Fail-to-Open Valve: Specify a single-acting, direct-acting actuator. Note that a continuous air supply is required to keep the valve closed against the spring force.
For a Fail-to-Close Valve: Specify a single-acting, reverse-acting actuator. The durability and consistent force of the internal spring are critical for long-term reliability.
Critical Design Step: Cylinder Thrust Calculation
Proper actuator sizing is non-negotiable for high-pressure drainage services. Key design principles include:
Reverse Flow Design: Implementing an "inlet flow from above" (reverse flow) orientation utilizes system pressure to aid sealing, significantly reducing the actuator thrust required to close the valve. This allows for a smaller, more cost-effective actuator.
Sealing Surface: A tapered (cone) seat design increases the sealing specific pressure, ensuring a tight shut-off even against high differential pressure.
Accurate Thrust Calculation: A precise calculation must account for system operating pressure, valve size and design, seat orientation, stem packing friction, and safety factors. This ensures the selected actuator will reliably open and close the valve under all specified conditions.
Conclusion
Achieving optimal performance and safety in power plant drainage systems hinges on the correct selection and design of pneumatically actuated globe valves. By prioritizing the required fail-safe action, selecting the corresponding single-acting actuator, and performing rigorous thrust calculations, engineers can ensure dependable, long-term valve operation that enhances overall plant reliability.
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