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Term Report: Final Control Element

Final control element, the last device in the control loop, is considered the muscles and sinews of automatic controls.

The final control element furnishes the necessary power amplification between the low energy levels of the controllers and the much higher energy levels of the process needed to perform their function.

For the scope of this term report, final control elements will be considered to be:

The report should work towards a logical presentation and development of the various sections.

Note: The report is summary in nature, not problem solving and will have illustrations integrated throughout body.

      1. Mechanical Positioning Devices

Illustrate and discuss the operation of the following actuators.

  1. Spring Diaphragm
    1. direct acting
    2. reverse acting
    3. long stroke (rolling diaphragm)
  2. Piston and Springless Actuators
  3. Electrohydraulic and Pneumohydraulic Actuators
  4. Electrical Driven
    1. solenoid
    2. motor - a.c. types
    3. motor - d.c. types
    4. stepper types

Under each actuator discuss:

  1. type of motion produced (rotary/reciprocating)
  2. mechanisms for conversation between rotary and reciprocating motion (or vice versa)
  3. motion characteristics
  4. thrust force considerations and characteristics
  5. application
  6. relative cost
  7. maintenance requirements

Within a general heading (discussion to pertain to all actuators) discuss the following:

  1. the sources and effects of unbalanced forces acting on the stem
  2. packing box styles
  3. packing box materials
  4. relationship between packing box styles, materials, and static/breakaway forces
  5. the requirements for sealing forces between valve body and seat ring
  6. the effect of dynamic forces on the throttling body and its ability to position
  7. effect of stem forces on the accuracy and repeatability of stem positioning
  8. valve auxiliary devices such as:
    1. stem position transmitters
    2. valve positions
    3. volume boosting relays
    4. fail-to-lock relays
    5. valve open/valve closed microswitches
    6. electrical solenoid valves for ON-OFF actuation of pneumatic actuated valves
      1. Mechanical Flow Throttling Devices

Valve types to be considered:

  1. Globe
    1. single ported versions (and sub types)
    2. dual ported versions
  2. Gate
    1. uncharacterized
    2. characterized
  3. Ball
    1. uncharacterized
    2. characterized
  4. Butterfly
    1. standard
    2. high performance
  5. Plug
    1. conventional
    2. segmental
  6. Rubber
    1. Saunders (and subtypes)
    2. Pinch (and subtypes)

Under each valve type please discuss:

  1. actuation motion and force requirements
  2. high recovery / low pressure recovery type
  3. throttling or ON-OFF applications
  4. flow characteristics available
  5. leakage characteristics
  6. size range
  7. operating force/torque, valve positioner requirement
  8. special areas of application

Under a general heading please discuss:

  1. what conditions make a high or low pressure recovery valve
  2. noise generation mechanism within a throttling valve
  3. techniques of noise reduction/cavitation reduction
  4. fire classification what it means and what makes a valve "fire safe"
  5. throttling control valve manifolding
  6. space requirements for on-line valve repair
      1. Variable Speed Pumping

Briefly describe the operation of centrifugal pumps along with the affinity laws.

Outline the concept of replacing a throttling control valve with variable speed centrifugal pumping.

Discuss the positive and negative aspects of the application of variable speed centrifugal pumping.