Valve Closure Rate Control to Reduce Seat Impact Damage
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Solution Overview
Problem
Steam turbine valves suffer cumulative damage due to high closing velocities during shutdowns, and existing cushioning methods like impact, fluid, and shock absorbers are either ineffective or prone to leakage and mechanical complexity.
Innovation Solution
Implementing a valve control system that allows for variable closure rates, with a 'slow zone' near the valve seat where the closure velocity is reduced to prevent damage, using a configurable actuator to move the valve in two stages: quickly to a predetermined position and then slowly to full closure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple impact cushioning is used to decelerate the valve before it strikes the valve seat, then the mechanical complexity is reduced, but the valve components still experience high stresses and vibration transmitted to the machine structure
Solution Approach 1:
The patent employs fluid cushioning mechanisms where hydraulic or pneumatic pressure is used to decelerate the valve before impact with the valve seat. Fluid restrictors and cushioning chambers create a fluid barrier that absorbs impact energy, reducing stresses on valve components and vibration transmitted to the machine structure while maintaining relatively simple mechanical design.
2Object-affected harmful factors
If fluid cushioning with spring-loaded check valves is used to shunt pressure spikes, then the valve seat impact is reduced, but the mechanical complexity increases and leakage becomes prone
Solution Approach 1:
The patent uses hydraulic fluid cushioning systems with cushioning chambers and fluid restrictors that create a compliant fluid barrier. The hydraulic system absorbs pressure spikes and decelerates the valve through fluid resistance rather than mechanical check valves, reducing impact stresses while avoiding the complexity and leakage issues of spring-loaded check valve mechanisms.
3Object-affected harmful factors
If shock absorbers are installed to introduce mechanical compliance, then the valve seat impact is reduced, but the mechanical complexity increases
Solution Approach 1:
The patent replaces mechanical shock absorbers with hydraulic cushioning chambers that provide mechanical compliance through fluid elasticity. The hydraulic system introduces compliance between the valve and valve seat through fluid pressure dynamics rather than mechanical spring elements, reducing impact stresses while avoiding the added mechanical complexity of traditional shock absorber assemblies.
4Duration of action of stationary object
If hydraulic cushions that restrict hydraulic flow are used, then the service life is extended, but the cushions are not adjustable and do not protect valves if they close before the cylinder end of travel is reached
Solution Approach 1:
The patent employs dynamically adjustable hydraulic cushioning systems where the cushioning characteristics can be modified during operation. The system includes adjustable fluid restrictors and controllable cushioning chamber volumes that adapt to different valve closure scenarios, providing protection whether the valve closes at the end of travel or before, thereby extending service life while gaining adjustability and versatility.
Data Source
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AI summary
The subject matter of this specification can be embodied in, among other things, a method for controlling a valve includes providing a valve having an actuator configured to move a valve member between an open valve position and a closed valve position, moving by the actuator and at a first valve closure rate the valve member away from the open valve position and toward a threshold valve position away from the closed valve position, and moving by the actuator and at a second valve closure rate the valve member from the threshold valve position toward the closed valve position. A corresponding valve apparatus is also provided.