1. Session 6 - Agenda BREAK Activity Est. Time 1. Agenda
2. Introduction to Control Valves and Regulators (Chapter 11)
3. Component Purpose and Operation, operating scenarios
BREAK
6. Class activity and HWAs
Instrumentation I - Session 06

2. Chapter 11 Control Valves and Regulators
Instrumentation I - Session 06

3. Chapter 11 – Objectives (Page 1)
1. Given a drawing or actual device, identify the main components of a control valve:
body
bonnet
disc
actuator
stem
seat
spring
valve positioner
handwheel
I/P transducer
2. Given a drawing or actual device, identify and describe the following:
current to pneumatic transducer
indications of a sticking control valve.
Instrumentation I - Session 06

4. Chapter 11 – Objectives (Page 2)
3. Define terms associated with valves and other final control elements:
“air to close” (fail open)
“air to open” (fail closed)
fail last/in place/as is
4. Describe operating scenarios in which fail open, fail closed, and fail last positions are desirable.
5. Discuss the purpose of diaphragm valve actuators and piston valve actuators.
6. Compare and contrast a spring and diaphragm actuator to a cylinder actuator.
7. Explain why the action of a valve actuator may not correspond with the action of the valve.
Instrumentation I - Session 06

5. Chapter 11 – Objectives (Page 3)
8. Describe a valve positioner and explain three of its uses.
9. Explain the function of each of the three gauges located on a pneumatic valve positioner.
10. Given a pressure indication for each of the three gauges on a valve positioner, predict what the control valve movement will be.
11. Describe two ways a controller’s output signal can be reversed at the valve so the valve’s action is opposite of the controller output signal.
12. Describe a control scheme that utilizes reversing a controller’s output signal at the valve.
13. Explain how reversing a controller’s output signal at the valve affects the valve’s fail safe position upon loss of air.
Instrumentation I - Session 6

6. Chapter 11 – Objectives (Page 4)
14. Explain the purpose and operation of the following:
globe valves
three-way valve
butterfly valves
15. Given a drawing, picture, or actual device, identify and describe pressure regulators.
16. Define the following terms associated with regulators:
back pressure regulator (self-actuated)
pressure reducing regulator
17. Given a Process Flow Diagram and/or P&ID, locate and identify pressure regulators used in process control.
18. Given an instrument air pressure regulator, perform the following tasks:
blow down regulator to check for condensate or oil
set specific pressure for operating final control element.
Instrumentation I - Session 6

7. Control Valve Key Components
Control valves operate the process by producing a differential pressure drop across the valve.
A control valve has an actuating device or actuator. The actuator provides motion to a valve for controlling process.
This motion drives the flow controlling mechanism (e.g., plug or disc)
Instrumentation I - Session 6

8. Control Valve Key Components
The body is the housing component.
The valve bonnet is the top portion of the valve body
and connects the valve
body to the actuator.
The valve plug assembly that includes the valve stem moves to open or close the flow path through the valve.
The actuator is the device that provides motion to the valve using a spring diaphragm, spring piston, or double acting piston.
The stem is the pushing and pulling rod that transfers the motion of the actuator to the valve plug.(page 170)
Instrumentation I - Session 06

9. Control Valve Key Components
The seat in a valve is the stationary part of the valve trim connected to the body that comes in contact with the valve plug. When the plug is fully seated, the flow stops.
The spring provides the energy to move the valve in the opposite direction of the diaphragm loading motion to its fail-safe condition.
The diaphragm is the flexible member that creates a force to move the stem.
Instrumentation I - Session 06

10. Control Valve Key Components
A valve positioner is actually a proportional – only controller.
The position of the valve stem is sensed by a mechanical link that is directly connected to the positioner.
A handwheel is an actuator accessory that is used to manually override the actuator or to limit its motion.
An I/P or current to pneumatic transducer is a device that converts a milliampere signal into a pneumatic pressure.
The most common use for an I/P transducer is to provide the source of energy needed to drive a diaphragm or piston actuator.
A current to pneumatic transducer typically receives a 4-20 mA current signal and converts it to a 3-15 psig pneumatic signal.
Instrumentation I - Session 06

11. Fail Conditions
Control valves are responsible for regulating the movement of fluids in a process.
If there is a power or air failure, they should move to a safe position.
Instrumentation I - Session 06

12. Fail Conditions
If a plant loses power or air supply, the design engineers must recognize the required fail safe conditions during the design phase of a plant and choose each control valve response accordingly.
When an air to open control valve loses its instrument air signal or supply, the valve fails closed because a return spring provides more opposing force than the decreasing instrument air applied to the diaphragm.
Preventing overflowing a tank is a good example for this case.
Instrumentation I - Session 06

13. Fail Conditions
If a plant loses power or air supply, the valve fails open because the return spring provides more opposing force than the diminishing instrument air applied to the diaphragm and the force applied by the process.
Failing a pressure relief valve on a reactor in these conditions should be fail in the open position preventing a pressure buildup that may rupture the vessel.
Instrumentation I - Session 06

14. Fail Conditions
Actuators without a spring or other return mechanism usually fail in their last position just prior to loss of power unless the process pressure is high enough to change the valve position
Instrumentation I - Session 06

15. Actuator Operation Figure 11-5 Actuator Operation
Instrumentation I - Session 06

16. Spring and Diaphragm Actuator
Very common
Low cost
High mechanical advantage
Instrumentation I - Session 06

17. Piston Type Actuator Can accept much higher input pressures
Single acting:
- spring opposed
the piston is opposed by a
spring
- the air cushion type
has a pressure trapped under
the piston and the air
compresses as the piston is
pushed down. Then, as the
instrument signal is reduced,
the trapped compressed air
pushes the piston back up
Instrumentation I - Session 06

18. Piston Type Actuator Double acting: - the instrument air pressure is
routed to both sides of the piston
Instrumentation I - Session 06

19. Valve Positioners
The function of a positioner is to make the valve position match the controller output signal.
The valve positioner manages the moving parts of a valve based on the instrument signal received from the controller in different ways.
Instrumentation I - Session 06

20. Valve Positioners
Position the valve: Adjust the position when the output controller signal is increasing or decreasing)
Reverse the action: For example, increasing the output pressure when the instrument controller signal is decreasing.
Instrumentation I - Session 06

21. Valve Positioners
Mimic a valve trim type (plug and seat) if output signal characteristics are changed by old style curves or new style programmed online methods, the valve positioner will imitate these changes
See page 175
Instrumentation I - Session 06

22. Valve Positioner Operation
Pneumatic valve positioners on spring and diaphragm actuators may have three gauges:
Instrument Pressure Gauge or input gauge:
(the output signal from
controller or I/P transducer)
Output Gauge:
(the pressure applied to the
actuator and can read the
pressure required for the
valve position.
Instrumentation I - Session 06

23. Valve Positioner Operation
Supply pressure gauge:
indicates instrument air
supply pressure.
Instrumentation I - Session 06

24. Output Signals
In some process control applications the output of the controller may need to be reversed at the control valve.
This can be accomplished by configuring the current to pneumatic transducer or the valve positioner to respond in reverse to the signal from the controller
Instrumentation I - Session 06

25. Globe Control Valve Has a globular shape appearance
Controls the flow with its plug and seat (trim) located inside the inner cavity (port)
A valve port is the orifice in a valve defined by the diameter of the seat.
Double ported valves can balance the high differential pressure acting on the single port valves and they have a higher flow capacity than a single port valves.
Instrumentation I - Session 06

26. Globe Control Valve
Instrumentation I - Session 6

27. Globe valve
Instrumentation I - Session 6

28. Three-Way Control Valve
Is a type of globe body valve
It has a three connecting ports instead of two
They either mix two flowing streams together or divert one flowing stream between two output ports
Instrumentation I - Session 06

29. What is going on here?
Instrumentation I - Session 06

30. Butterfly Control Valve
Instrumentation I - Session 06

31. Butterfly Control Valve
Also called rotary valves
Equipped with piston type actuators or spring and diaphragm actuators
Lower manufacturing costs and higher flow capacities than globe valves
The rotary stem has less wear on the packing than the sliding stem
Actuators used with butterfly valves use a rotary motor.
Non linear relationship between the % opening and the rate of flow through the opening
Instrumentation I - Session 06

32. Ball or segmented ball control valves
Is a rotary valve that contains a spherical plug
The control valve actuator rotates the plug to control the flow of fluid through the valve body
Convenient for slurries
Page 179
Instrumentation I - Session 06

33. Regulators
Are self contained and self actuating controlling device used to regulate variables such as pressure, flow, level, and temperature in a process
The important parts are:
- inlet: supplies pressure from a source
- outlet: regulates pressure
- diaphragm: senses the pressure on the
outlet side of the regulator
- pilot valve assembly: working part of the
regulator; entire mechanism works to
both supply pressure or relieve pressure
from outlet side
Instrumentation I - Session 06

34. Regulators An instrument air regulator action follows this sequence:
The handwheel is turned
The spring compresses
The diaphragm is pushed down
The pen and plug move from their seat
Air rushes in increasing downstream pressure (downstream of the regulator)
The output gauge responds accordingly
Equilibrium is established
Instrumentation I - Session 06

35. Regulators
Instrumentation I - Session 06

36.
Instrumentation I - Session 11

37. Backpressure Regulators
A back-pressure regulator is a device used to regulate and control the pressure of a process fluid upstream of the location of the regulator.
maintain the pressure in the vapor space of a vessel
Instrumentation I - Session 06

38. Symbols for Back Pressure Regulator
Instrumentation I - Session 06

39. Pressure Reducing Regulators
Instrumentation I - Session 06

40. Pressure Reducing Regulators
Control the pressure of a process fluid downstream of the location of the regulator
When steam leaves a boiler and could potentially have hundreds of pounds of pressure that need to be reduced to specific unit requirements that may only be 150 psi.
Instrumentation I - Session 06

41. Symbols for Pressure Reducing Regulator
Instrumentation I - Session 06

42. We will have a review for the whole chapters
for next week:
Please review chapters 10 and 11 and be ready for some review questions for our class activities
We will have a review for the whole chapters
Instrumentation I - Session 06