Faulty Control Valve Positioner Replacement Procedure with Checklist

In order to keep the system accurate and reliable, it is necessary to replace a control valve positioner that is malfunctioning. 

A comprehensive, step-by-step procedure for executing a replacement is provided in this guide. The technique includes verifications of safety, calibration, and specifications.

Step 1: Pre-Replacement Preparations

Gather Necessary Tools, Equipment, and Documentation

• Gather the positioner kit including the new positioner, compatible mounting brackets, screws, and fasteners, along with hand tools such as screwdrivers, adjustable wrenches, Allen keys, and hex wrenches. 
• Testing instruments like a multimeter for electrical checks and an air pressure gauge for pneumatic positioners will be needed, as well as calibration instruments like a handheld calibrator/ signal generator for input simulation. 
• Collect relevant documentation, including the positioner’s operation manual, wiring diagrams, and mounting instructions, the P&ID of the control loop, and manufacturer’s data sheets for the positioner and valve actuator.

Verify Positioner Compatibility

• Confirm the positioner’s model number, input signal range, and compatibility with the control valve type. 
• Check for the correct mounting orientation, bolt size, and alignment points, and verify that the positioner’s input signal type matches the system’s setup.

Inspect the Work Area and Plan for Access

• Identify any confined spaces, confirm adequate lighting, and prepare scaffolding or lifting mechanisms if needed.
• Obtain necessary permits if in a confined or hazardous area.

Step 2: Safety Considerations

Personal Protective Equipment (PPE)

• Ensure that personnel wear appropriate PPE, such as safety glasses, gloves, hard hats, steel-toe boots, and flame-resistant clothing in hazardous environments. 
• Additional PPE like hearing protection, face shields, or respirators may be required.

Lockout/Tagout (LOTO) Procedures

• For electrical isolation, disconnect power to the control valve circuit and tag disconnect switches. 
• Disable DCS or PLC control signals and interlock to prevent unintended valve movement, and turn off the main air supply while venting residual pressure to confirm zero pressure using an air gauge.

Depressurize and Vent the System

• Ensure the control valve line is depressurized. Open vent valves or drain the process line according to procedure to avoid leaks or spills during replacement.

Step 3: Specifications Verification for Positioner Installation

Input Signal Range

• Signal Type: Verify that the input signal matches the required range, typically 4-20 mA or 0-10V.
• Protocol Verification: Check for compatibility with communication protocols like HART, Foundation Fieldbus, or any other protocol specific to the control system.
• Impedance Ratings: Ensure the input impedance is compatible with the system’s requirements to avoid signal distortions or power issues.

Air Supply Requirements

• Supply Pressure Range: Confirm that the air pressure supplied to the positioner is within the manufacturer’s specified range, ensuring safe operation.
• Air Consumption Rate: Verify the air consumption rate to ensure the system maintains efficiency and does not cause unnecessary wear on air supply components.
• Air Quality Requirements: Check that the air meets filtration and dew point standards, as moisture or particulates can degrade performance.
• Port Connections: Confirm the port size and type are compatible with the air supply setup, avoiding leaks or misalignments.

Mechanical Specifications

• Mounting Type: Ensure the mounting pattern matches the valve, such as NAMUR, integral, or remote mounting configurations.
• Stroke Range Compatibility: Verify that the positioner can accommodate the full stroke of the valve for precise control.
• Feedback Configuration: Confirm that the feedback setup (lever, shaft, etc.) matches installation requirements for accurate positioning.
• Housing Material and Protection: Check the material and IP/NEMA ratings for suitability, especially in harsh or outdoor environments.
• Ambient Temperature Range: Ensure the positioner’s temperature range matches the conditions of the installation site.

Performance Specifications

• Accuracy and Linearity: Verify that the positioner meets accuracy and linearity specifications, as these affect the control loop performance.
• Hysteresis, Resolution, and Response Time: Check these specs to ensure the positioner delivers precise control, particularly in high-demand applications.
• Dead Band: Confirm that the dead band specification is acceptable for the application, preventing unwanted drift in control settings.

Hazardous Area Classification

• Explosion Proof Ratings: Confirm the positioner’s explosion-proof certification to meet safety standards in hazardous environments.
• Intrinsic Safety: Verify that the positioner has the necessary intrinsic safety certifications for installations where spark prevention is essential.
• Area Classification Compliance: Ensure the device is certified for the area classification where it will be installed (e.g., Class I, Div 2).

Operating Parameters

• Action Type: Verify if the positioner requires direct or reverse action based on the control strategy.
• Fail-Safe Position: Check the fail-safe position setting (e.g., open, close) to ensure it aligns with system safety requirements.
• Travel Limits and Characteristic Curves: Ensure the positioner can achieve the required travel limits and has a characteristic curve suitable for the application.

Physical Dimensions

• Confirm that the positioner’s physical size and weight fit within the available installation space.
• Ensure there is sufficient clearance and that the mounting bracket is compatible with the valve setup.

Step 4: Documentation to Reference

• Original Device Datasheet: Review for detailed specifications and model-specific details.
• Valve Specifications: Cross-reference to ensure compatibility between the valve and positioner.
• Plant Instrument Specifications: Ensure alignment with plant-specific requirements and standards.
• Area Classification Documents: Verify the positioner’s suitability for the hazardous location classification.

Step 3: Removing the Faulty Positioner

Disconnect Electrical Connections

• Label each wire to ensure correct reinstallation and use insulation caps to prevent short circuits.

Disconnect Air Supply Lines (for Pneumatic Positioners)

• Remove air tubing using quick-connect fittings if available, or loosen them with a wrench. Inspect air lines for wear or damage and replace as necessary.

Dismount the Faulty Positioner

• Loosen mounting hardware, carefully remove bolts, nuts, and brackets, and inspect the actuator for visible wear, corrosion, or damage.

Step 4: Installing the New Positioner

Mount the New Positioner

• Begin by following the manufacturer’s alignment guidelines carefully. These are crucial for ensuring that the positioner is mounted in the optimal position relative to the actuator. 
• Incorrect alignment can cause improper functioning or even damage the system.
• Once alignment is confirmed, secure the positioner to the mounting bracket or directly to the valve actuator, depending on the installation setup. 
• Use bolts as specified by the manufacturer and tighten them with the recommended torque setting. 
• Proper torque ensures stability without over-stressing the mounting hardware.

Reconnect Air Supply Lines (for Pneumatic Positioners)

• Attach the air supply tubing to the designated input port(s) on the positioner. 
• Be sure that all connections are secure to prevent leaks, which could affect positioner performance.
• Inspect the fittings and use a leak-detection solution if necessary to confirm there are no leaks in the air lines.
• Set the air supply pressure to within the manufacturer’s specified range. 
• Too high or too low pressure can impair the positioner’s responsiveness and may affect valve control accuracy.

Wire Electrical Connections

• For electrical or electro-pneumatic positioners, connect the signal wires to the input terminals. 
• Double-check the polarity for each wire to ensure that connections align with the control signal standard (e.g., 4-20mA, 0-10V).
• Confirm grounding at the designated ground terminal. Proper grounding is vital to avoid electrical noise interference, which could result in erratic positioner behavior.
• Secure the cables along the path to prevent them from accidental disconnection or movement, which could disrupt the signal. 
• Use cable ties or clamps where necessary for additional support and to maintain a neat wiring setup.

Step 5: Calibration and Testing

Configure Positioner Settings and Feedback Position Calibration

• Begin by setting the input signal range to match the control loop requirements, typically 4-20 mA for most industrial applications. (like Split range control)
• This ensures that the positioner interprets the input signal correctly, facilitating accurate control.
• Adjust the zero and span settings on the positioner. Zero adjustment sets the valve to fully close at the minimum input (e.g., 4 mA), while span adjustment ensures the valve fully opens at the maximum input (e.g., 20 mA). (feedback position calibration)
• Carefully calibrate these to cover the valve’s entire range, providing precise control over the valve’s travel from fully closed to fully open.
• Tune the sensitivity and response settings as per the manufacturer’s recommendations. 
• Sensitivity affects the responsiveness of the valve to small input changes, while response controls how quickly the valve adjusts to a signal change. 
• Proper tuning helps prevent overshoot and ensures smooth, stable operation without oscillations or delay.

Refer the below link for the calibration of control valve positioner

Perform Calibration Check

• Use a handheld loop signal calibrator to simulate a 4-20 mA signal input to the positioner. Increment the signal at various points within the range (e.g., 4, 8, 12, 16, and 20 mA) and observe the positioner’s response.
• Confirm that the valve’s movement accurately corresponds to each signal level. For example, at 4 mA, the valve should be fully closed; at 20 mA, it should be fully open, and intermediate signals should position the valve proportionally.
• Make fine adjustments to correct any drift, inaccuracy, or hysteresis detected during this check. 
• Drift occurs when the valve doesn’t maintain the correct position over time, while hysteresis refers to discrepancies in response when signals are applied in increasing versus decreasing sequences.

Refer the below link for the calibration of control valve

Verify Full Stroke and Position Feedback in Control System

• Conduct a full-stroke test by moving the valve from 0 percent (fully closed) to 100 percent (fully open). This test ensures that the valve travels smoothly through its entire range without any binding or obstruction.
• As the valve moves, observe any position feedback provided by the positioner, whether an analog signal or digital indicator, to confirm it accurately reflects the valve’s real-time position in control system. Accurate feedback is crucial for process control, as it allows operators and automated systems to monitor valve positions reliably.
• If discrepancies appear between the actual valve position and feedback signal, further fine-tune the positioner’s feedback settings or recalibrate as necessary to ensure alignment. Completing this verification step ensures that the valve and positioner will operate with high accuracy in the control loop.

Refer the below link for Refer the below link for the stroke checking of control valve

Final Quality Checks and Documentation

Perform Functional Testing

• Simulate typical and extreme operational conditions to verify the control valve’s response accuracy. 
• Adjust the control signals across different settings, and observe the valve’s movement to ensure it matches expected parameters and reacts promptly to commands from the control system. 
• For control valves with position feedback, ensure the feedback signal aligns with the valve’s actual position.

Inspect for Leaks and Loose Connections

• If the control valve uses a pneumatic positioner, apply a soapy solution around air fittings, connectors, and seams to identify any air leaks. 
• Watch for bubbles indicating leaks and address any detected issues by tightening or replacing the connections. 
• Additionally, ensure all bolts, nuts, and fasteners on the valve assembly are tightened according to torque specifications. 
• Verify that tubing and wiring are secure to prevent vibration-induced loosening during operation.

Click here for the How to do maintenance on struck control valve?

Complete Documentation and Update Records

• Document the installation details, including the model number, serial number, calibration settings, and installation date of the new positioner. 
• Update loop drawings, piping and instrumentation diagrams (P&IDs), and maintenance logs to reflect the new configuration. 
• Additionally, record any calibration or adjustment procedures performed during installation for future reference, including any modifications made to the control system settings.

Remove Lockout/Tagout (LOTO)

• Following final checks, ensure the area is clear and it’s safe to restore power. 
• Carefully remove all Lockout/Tagout (LOTO) tags, locks, and barriers that were applied during installation to isolate the system. 
• Confirm that power, control signals, and instrument air supply (if applicable) are fully restored. 
• Test the system under observation to ensure it transitions smoothly into operational status, without any additional safety barriers, and that all devices function correctly.

Click here for How to do Control Valve Preventive Maintenance?

Checklist for Faulty Control Valve Positioner Replacement – Downloadable

Replacing a malfunctioning control valve positioner is crucial for ensuring precise control and reliability in industrial systems. This checklist offers a step-by-step guide to execute a successful replacement, from preparing tools and documentation to calibration and final quality checks.

For a downloadable checklist in Excel table format, click here to download. This below  link provides easy access to a detailed version that you can use in the field or digitally log your steps and status.

Click here for more Essential Instrumentation activities Checklists.

Quiz on Control Valve Positioners

Understanding control valve positioners is crucial for instrumentation professionals as it forms a significant part of the control system in various industries. The following Multiple Choice Questions (MCQs) with answers and explanations will help you prepare for interviews and enhance your knowledge of control valve positioners.