PRT 140: Lesson 13 Control Loops, Control Valves, and Regulators

• Air enters under the diaphragm
• Spring is pushing down
• Air fails = spring pushes all the way down
• Determines position of the valve stem

Air to Close – Fail Up (Open)

• Air enters over the diaphragm
• Spring is pushing up
• Air Fails — spring pushes all the way up
• Determines position of the valve stem

ACTUATOR Action/Failure Conditions

• Electric motor actuators
• Piston actuators
• Double-acting positioners

Action Failure Position – How Do You Know?

• Location of air inlet to diaphragm actuator
• Labeled on the valve in the field
• Labeled on PIDs
• Equipment Data on specific valve
• Overall Valve Failure Position is dependent on the design/operation of both the actuator and the valve (‘valve assembly’)

Actuator /Valve Types

• Actuators and valves — both can be Direct Acting or Reverse Acting
• Combination of Actuator/Valve Actions possible:
  • Direct/Direct
  • Direct/Reverse
  • Reverse/Direct
  • Reverse/Reverse

  Actuators: Action Recap

  • Direct Acting:
    • Air enters on top of diaphragm
    • Increased pressure = extend stem = push down
    • ATC on Direct-Acting Valve
    • Fail Up (Fail Open on Direct-Acting valve)
    • Air enters underneath diaphragm
    • Increased pressure = retract stem = pull up
    • ATO on Direct-Acting Valve
    • Fail Down (Fail Closed on Direct-Acting Valve)

    Actuators – look at detail

    Direct Action — Air Extends (pushes down) the Stem – (ATC, Fail Up)

    Reverse Action — Air Retracts (pulls up) the Stem – (ATO, Fail Down)

    

    VALVES: Plug Action — New Level of Detail

    • Direct Acting = by far the most common
      • Push plug down to close
      • Closes as stem extends (as stem pushes down)
      • ATC with Direct-Acting Actuator
      • ATO with Reverse-Acting Actuator
      • Pull plug up to close
      • Closes as stem retracts (as stem pulls up)
      • ATO with Direct-Acting Actuator
      • ATC with Reverse-Acting Actuator

      Valve — Direct vs. Reverse Acting

      Direct Acting — Stem Down to Close

      Air Extends (pushes down) the Stem – (ATC, Fail Up)
      

      Reverse Acting — Stem Up to Close

      Air Extends (pushes down) the Stem – (ATC, Fail Up)
      

      

      Questions

      Why are there different actions for —

      • Actuators?
        • Failure positions needed
        • Control response needed
        • Better control of actuator pressure (vs process pressure)
        • System pressure
        • System fouling
        • Push-down-to-close (Direct) is most common

        Valve Action Discussion

        • Most important?
          • Overall Valve Failure Position — FO or FC
          • Air to Close (ATC) or Air to Open (ATO)
          • Actuator Direct (Air on Top) — “Fail Open’
          • Actuator Reverse (Air on Bottom) — “Fail Closed’
          • Valve Plug Direct (push down to close) — almost all valve plugs are direct. Actuator Failure = same as Overall Valve Failure. If Actuator failure doesn’t match Overall Valve Failure — then look at valve plug action
          • Valve Plug Reverse (pull up to close)

          

          Activity

          A direct acting controller sends a standard pneumatic signal to a control valve. The control valve has a direct-acting actuator, and the valve itself is reverse-acting. Fill in the information in this table:

          Controller output, % of span	Action dir/rev (if known)	0%	25%	50%	75%	100%
          Controller output, % in psig
          Stem Position - "all the way up" to " all the way down" (depending on the actuator action)
          Valve % open, or "fully open" to "fully closed" - (depending on the plug action)

          Check your answers on this table.

          Pneumatic Actuators

          

          Piston Actuators

          note that they can be hydraulic or pneumatic

          Piston actuator diagram [image 140-13-13]

          Valve Positioners

          • Positioners — make the valve position match the controller output signal
            • Position the valve
            • Reverse the action
            • Mimic a valve trim type —
              • not discussed much here
              • if valve must respond to only part of the signal
              • Can be changed at the I/P transducer
              • Can be changed at the Valve Positioner
              • Physically reconfigured to respond in reverse
              • NOTE: Actuator will still fail in position dictated by spring/air configuration
              • Why would you do these reversals?

              Valve positioner diagram [image 140-13-14]

              Activity

              The tag on a pneumatically actuated control valve identifies it as air-to-open. If the positioner has been configured to reverse the signal, then the valve will fail _____________ on loss of instrument air supply.

              C. In its last position prior to the loss of air

              D. None of the above

              Types of Control Valves

              • Globe
              • Three-Way
              • Butterfly
              • Ball/Segmented Ball

              Three Way Control Valve

              • Three ports
              • Mixing or diverting
              • As plug moves, one inlet closes while the other opens

              Butterfly Control Valve

              • Higher flow capacity
              • Rotary stem/motor
              • All types of fluids

              Ball, Segmented Ball Control Valve

              • Rotary valve
              • Spherical plug
              • Segmented has shaped plug — flow characteristics
              • Used in slurries

              Air Regulators

              

              Symbols for Mechanical Regulators

              

              • Note: small regulators on actuators, control valves are not normally shown on PIDs
              • In-line mechanical pressure regulators are shown:
              • Note direction of the angled line —
                • Indicates whether pressure is controlled upstream or downstream of valve…

              PID, PFD, Symbol Information

              • PIDs, PFDs will indicate 3-way valves
              • PIDs will normally indicate FO, FC of overall valve
                • Will not be specific about actuator vs valve action
                • If you need to know that, where do you look?

                Program Overview

                This program is made possible by a TAACCCT grant, which provides community colleges and other eligible institutions of higher education with funds to expand and improve their ability to deliver education and career training programs that can be completed in two years or less, are suited for workers who are eligible for training under the TAA for Workers program, and prepare program participants for employment in high-wage, high-skill occupations.

                Courses

                • PRT 110: Introduction to Occupational Safety, Health and Environmental Awareness
                  • PRT 110 Syllabus
                  • PRT 110 Course Schedule
                  • PRT 110: Lesson 1 Introduction to Process Safety
                  • PRT 110: Lesson 2 Hazard Classification
                  • PRT 110: Lesson 3 Routes of Entry and Environmental Effects
                  • PRT 110: Lesson 4 Gases, Vapors, Particles, and Toxic Metals
                  • PRT 110: Lesson 5 Hazards of Liquids
                  • PRT 110: Lesson 6 Hazardous Chemical Identification: HAZCOM, Toxicology, and DOT
                  • PRT 110: Lesson 7 Fire and Explosion
                  • PRT 110: Lesson 8 Electrical Noise, Heat, Radiation, Ergonomic, and Biological Hazards
                  • PRT 110: Lesson 9 Safety Permit Systems
                  • PRT 110: Lesson 10 Personal Protective Equipment (PPE)
                  • PRT 110: Lesson 11 Engineering Controls
                  • PRT 110: Lesson 12 Administrative Controls
                  • PRT 110: Lesson 13 Regulatory Overview: OSHA, PSM, EPA, NFDA, DOT
                  • PRT 110: Lesson 14 HAZWOPER
                  • AMIT 129: Syllabus
                  • AMIT 129 Course Schedule
                  • AMIT 129: Lesson 1 Intro
                  • AMIT 129: Lesson 2 Open Pit and PPE
                  • AMIT 129: Lesson 3 Mine Entering
                  • AMIT 129: Lesson 4 Clean Housekeeping
                  • AMIT 129: Lesson 5 Hazard Recognition
                  • AMIT 129: Lesson 6 Conveyor System
                  • AMIT 129: Lesson 7 Mine Explosives and Blasting
                  • AMIT 129: Lesson 8 Mine Maps, Emergency Evacuation, Barricading
                  • AMIT 129: Lesson 9 Mine Fires and Fire Fighting
                  • AMIT 129: Lesson 10 Mine Ground Control
                  • AMIT 129: Lesson 11 Mine Electrical Hazards
                  • AMIT 129: Lesson 12 Crusher and Mill Operation Safety
                  • AMIT 129: Lesson 13 Chemical Hazards
                  • AMIT 129: Lesson 14 General Hazards
                  • AMIT 130: Syllabus
                  • AMIT 130: Course Schedule
                  • AMIT 130: Class 1
                  • AMIT 130: Class 2
                  • AMIT 130: Class 3
                  • AMIT 130: Class 4
                  • AMIT 130: Class 5
                  • AMIT 130: Class 6
                  • AMIT 130: Class 7
                  • AMIT 130: Class 8
                  • AMIT 130: Class 9
                  • AMIT 130: Class 10
                  • AMIT F135: Syllabus
                  • AMIT F135: Course Schedule
                  • AMIT 135: Lesson 1 Introduction
                  • AMIT 135: Lesson 2 Circuit Mass Balancing
                  • AMIT 135: Lesson 3 Particle Size Distribution
                  • AMIT 135: Lesson 4 Performance Modeling & Assessment
                  • AMIT 135: Lesson 5 Crushing
                  • AMIT 135: Lesson 6 Grinding Circuit
                  • AMIT 135: Lesson 7 Ball Mills & Circuits
                  • AMIT 135: Lesson 8 Rod Mills
                  • PRT 140: Syllabus
                  • PRT 140: Course Schedule
                  • PRT 140: Lesson 1 Introduction
                  • PRT 140: Lesson 2 Pressure
                  • PRT 140: Lesson 3 Temperature
                  • PRT 140: Lesson 4 Level
                  • PRT 140: Lesson 6 Flow Measurement
                  • PRT 140: Lesson 7 Analytics and Miscellaneous Measurement
                  • PRT 140: Lesson 8 Introduction to Control Loops
                  • PRT 140: Lesson 10 Control Loops, Sensors, and Transmitters
                  • PRT 140: Lesson 12 Control Loops, Control Elements
                  • PRT 140: Lesson 13 Control Loops, Control Valves, and Regulators
                  • PRT 140: Lesson 14 Symbology and Course Review
                  • AMIT 145: Syllabus
                  • AMIT 145: Course Schedule
                  • AMIT 145: Lesson 1 Industrial Screens
                  • AMIT 145: Lesson 2 Classifying Cyclones
                  • AMIT 145: Lesson 3 Dense Medium Separation
                  • AMIT 145: Lesson 4 Gravity Separation
                  • AMIT 145: Lesson 5 Froth Flotation
                  • AMIT 145: Lesson 6 Dewatering & Clarification
                  • AMIT 145: Lesson 7 Leaching