Pneumatic Trip Valve Partial Stroke Actuation
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Solution Overview
Problem
Steam turbine trip valves often bind due to scale and corrosion, requiring complete shutdown for maintenance, disrupting operation and posing safety risks due to infrequent testing.
Innovation Solution
A pneumatic trip system with partial stroke actuation using an electrically actuated pneumatic system that exercises the trip valve regularly, allowing for identification of binding issues without interfering with turbine operation, and includes an actuator assembly with a cylinder, piston, and biasing element to move the valve between open and closed positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the trip valve is tested by complete closure, then the operational status of the trip valve can be determined, but the turbine and driven equipment must be completely shut down, disrupting operation
Solution Approach 1:
The patent implements partial stroke actuation that moves the trip valve only a predetermined distance (e.g., 1/4 to 3/4 of full stroke) rather than complete closure. This partial action is sufficient to exercise the valve mechanism and detect binding issues while allowing the turbine to continue operating, thus resolving the contradiction between reliability testing and productivity maintenance
Solution Approach 2:
The testing function is segmented from the full valve closure operation. Instead of requiring complete closure for testing, the system separates the diagnostic function into a partial stroke movement that can be performed independently during normal operation, allowing reliability assessment without full shutdown
2Productivity
If the trip valve remains in the open position for an extended period, then the turbine can operate continuously, but scale and corrosion build up between the valve stem and bushings, binding the valve
Solution Approach 1:
The system performs periodic partial stroke actuations at predetermined intervals during normal turbine operation. This periodic movement exercises the valve mechanism regularly, preventing scale and corrosion from binding the valve stem and bushings, thus maintaining reliability while allowing continuous operation
Solution Approach 2:
The partial stroke actuation serves as a preliminary maintenance action that prevents binding before it occurs. By periodically moving the valve during normal operation, the system preemptively clears scale and corrosion buildup, ensuring the valve remains operational without requiring shutdown for maintenance
3Reliability
If the trip valve is exercised frequently to prevent binding, then the valve remains operational, but the testing process may interfere with the primary operation of the trip valve system
Solution Approach 1:
The partial stroke movement performs the diagnostic function without executing the full valve closure sequence. This partial action is sufficient to detect binding issues while leaving the valve in its normal operational state, thus maintaining ease of operation while ensuring reliability
Solution Approach 2:
The system uses an intermediary partial stroke position that allows diagnostic testing without triggering the full trip sequence. This intermediate state enables reliability assessment while maintaining the valve's readiness for primary operation, resolving the conflict between testing and operational readiness
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Ensures the trip valve is operational, prevents binding, and allows for timely maintenance, enhancing safety and reliability with minimal maintenance impact and cost-effectiveness.
Implementation Method 1
The pneumatic circuit is configured to pressurize the second chamber of the cylinder to actuate the piston to move the valve stem to an intermediate position
Implementation Method 2
a biasing element disposed in the second chamber of the cylinder, the biasing element engaging the piston to bias piston toward the second position
Implementation Method 3
The pneumatic mechanism is configured to pressurize the first chamber of the cylinder to cause the piston to hold the valve stem in the open position
Data Source
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AI summary
A pneumatic trip system for a turbine includes a valve member; a valve stem connected to the valve member; and an actuator assembly connected to the valve stem. The actuator assembly includes a cylinder; a piston connected to the valve stem, the piston dividing the cylinder into a first chamber and a second chamber; a biasing element disposed in the second chamber of the cylinder; and a pneumatic circuit in communication with the second chamber of the cylinder. The pneumatic circuit is configured to pressurize the second chamber of the cylinder to actuate the piston to move the valve stem and the valve member to an exercised position between the open position and the closed position while the first chamber is pressurized.