310104d Valve Positioners 2025 (TF) (1)

Valve Positioners Objectives

• Applications and Selection

  • Understand the various applications of valve positioners in industrial settings.

  • Criteria for selecting the appropriate valve positioner for specific tasks.

• Features of Positioners

  • Key characteristics that define valve positioners and their operational advantages.

• Servicing Procedures

  • Steps involved in maintaining and servicing valve positioners.

Valve Accessories

• Dead Band

  • Dead band refers to a range where the signal to the valve actuator changes but there is no change in valve plug position.

  • Can be caused by:

    • Packing friction

    • Looseness in linkages

    • Wear in mechanical parts of actuator/valve combination

  • Importance of Adding Positioners

    • Provides precise control over valve stem position.

Fisher Valve Positioners

• Models: Fisher 3610J, Fisher 3582, Fisher DVC 6020, and Fisher DVC 2000

• Functionality:

  • Accurately measures valve stem position via mechanical or magnetic connections.

  • Enhances accuracy of valve plug movement and reaction time.

Installation of Valve Positioner

• Method of Installation

  • Typically bolted to the yoke of the actuator.

• Requirements:

  • Instrument Air Supply (ISA) must be connected.

  • Feedback mechanism needed to convey valve stem position to the positioner.

  • Control signals are sent to the positioner; pneumatic outputs adjust the actuator to position the stem and plug accurately.

Advantages of Valve Positioners

• Overcome Differential Pressure Effects

  • Maintains plug position despite changes in process pressure.

• Quick Response Time

  • Larger output volume compared to other pneumatic devices.

• Reverse Acting Operation

  • Increasing input signal results in a decreasing output signal.

• Split Range Operation

  • Can control full output signal to a valve using only half the input signal.

• Adjustable Flow Characteristics

  • Changing output cam allows for varied flow characteristics: quick opening, linear, equal percentage.

• Operates Springless Actuators

  • Positions plug accurately without spring force impact.

Control Valve Accessories

• Cam Characteristic Flow Curves

  • In 3582 mechanical positioners, cams alter valve flow characteristics without changing valve trim.

  • Utilizes a force beam mechanism.

Types of Actuators

• Sliding Stem Valve Positioner

  • Springless double-acting piston sliding stem actuator.

• Rotary Actuator Positioner

  • Controls rotary actuator applications.

Force Balance Valve Positioner

• Main Functionality

  • Requires a reverse-acting actuator to ensure valve stem position is maintained.

Motion Balance Valve Positioner

• Similar operational principles as force balance positioners focusing on stem position.

Positioner Bypass Option

• Maintains control as if unmanaged by positioner.

• Can operate valves in manual mode if the positioner fails (e.g., reverse acting positioner in bypass).

I/P Transducer Overview

• Signal Conversion

  • Converts 4-20mA electrical signals into pneumatic signals affecting valve stem position.

Electro-Pneumatic Transducers

• Limitations

  • Do not function as true valve positioners due to lack of positional feedback mechanisms.

  • Examples: Old Style Fisher 546, Fisher 846.

Smart Valve Positioners

• Key Features

  • Operate on 4-20mA signals, compatible with HART communicators and Foundation Fieldbus.

  • Self-calibrating and self-diagnosing capabilities.

  • Use a potentiometer for sensing valve position; feedback arm connects to valve stem.

  • Requires a pneumatic relay for function.

Valve Positioner Servicing

• Indicators for Servicing

  • Notable abnormal conditions:

    • Delayed response time

    • Hysteresis

    • Dead band issues

    • Calibration discrepancies

    • Changes in opening range

  • Servicing Steps:

    • Troubleshooting and removing for inspection.

    • Replacing worn components and recalibrating.

Specific Servicing Notes

• Mechanical vs. Smart Positioners

  • Mechanical positioners typically need more frequent servicing than smart ones.

• Safety Protocols:

  • Follow specific manufacturer instructions for servicing.

  • Notify operations prior to work, isolate all forms of energy, and employ PPE for safety.

Conclusion

• These notes conclude the essential knowledge on valve positioners and highlight the importance of maintenance and appropriate selection based on operational needs.