Pneumatic Control Valve Diagnosis Using a Positioner Model

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Solution Overview

Problem

Pneumatic control valves in power plants require effective diagnostic methods to prevent abnormal states and maintain optimal operation, as existing methods are inadequate for real-time monitoring and prediction of valve state changes.

Innovation Solution

A method and apparatus using a positioner model to establish a relational expression for a pneumatic control valve, determining parameters that indicate its state, and comparing these parameters in real-time with reference values to diagnose abnormalities before they occur, thereby preventing shutdowns and improving operational efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If regular maintenance and valve replacement are performed periodically, then the valve state is maintained in optimal condition, but the power plant operation is interrupted and maintenance costs increase

Engineering Contradiction:

Improvevalve state maintenanceVSAvoidpower plant operation interruption

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent establishes a positioner model that performs preliminary diagnosis by comparing real-time operational parameters with reference values from normal operation. This allows early detection of abnormal states before they lead to valve failure, enabling maintenance to be performed only when necessary rather than following a fixed schedule, thus avoiding unnecessary power plant interruptions

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements a feedback mechanism where operational parameters (control pressure, valve stem displacement) are continuously monitored and compared against the positioner model's reference values. When deviations exceed predetermined thresholds, the system generates diagnostic information indicating abnormal states, allowing operators to take corrective action before complete valve failure occurs, thereby maintaining reliability without scheduled interruptions

Inventive Principle:

Principle #23Feedback

2Difficulty of detecting and measuring

If valve diagnosing equipment is used to check abnormal states, then the valve state can be diagnosed, but the power plant must be stopped and diagnostic time is consumed

Engineering Contradiction:

Improvevalve state diagnosisVSAvoidpower plant shutdown time

Core Design Contradiction:

Difficulty of detecting and measuringVSLoss of time

Solution Approach 1:

The patent replaces the need for physical valve diagnosing equipment and manual inspection with an electronic positioner model that continuously monitors operational parameters. The model compares real-time data (control pressure Pc, valve stem displacement xs) with pre-established reference values from normal operation, automatically detecting abnormal states without requiring power plant shutdown or physical intervention

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent enables continuous diagnosis during normal power plant operation by implementing real-time parameter monitoring through the positioner model. The system continuously compares operational parameters with reference values and generates diagnostic information without interrupting the power plant, thereby maintaining continuous useful action while detecting valve abnormalities

Inventive Principle:

Principle #20Continuity of useful action

3Reliability

If a positioner model with real-time parameter comparison is implemented, then early detection of abnormal states is enabled, but the system complexity and implementation cost increase

Engineering Contradiction:

Improveearly detection capabilityVSAvoiddiagnosis system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent leverages the existing positioner device, which is already part of the pneumatic control valve system, to perform dual functions: both its original control function and the new diagnostic function. By establishing a positioner model that uses the same operational parameters (control pressure, valve stem displacement) already measured by the positioner, the system achieves early detection capability without adding separate diagnostic hardware, thereby limiting the increase in system complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11378108B2Method and apparatus for diagnosing pneumatic control valve by using positioner model

Publication Date: 2022.07.05 KOREA HYDRO & NUCLEAR POWER CO LTD

AI summary

Method for diagnosing a pneumatic control valve by using a positioner model includes: establishing relational expression for outputting valve stem displacement according to control pressure, the relational expression including parameters for the characteristics of a positioner, an actuator, and a valve, determining initial parameter value by adjusting the values of the parameters until the difference between a measured value for a normal operation of the pneumatic control valve and output value obtained by the relational expression is smaller than predetermined error limit, determining diagnostic parameter value by adjusting the values of the parameters until the difference between a measured value for a diagnostic operation of the pneumatic control valve and an output value obtained by the relational expression is smaller than a predetermined error limit, and comparing the initial parameter value and the diagnostic parameter value so as to determine whether the pneumatic control valve has abnormality.