instrument training material control valve final control element most widely used other types of...
TRANSCRIPT
Instrument Training Material
Control ValveControl Valve
Control ValveControl Valve
Final Control ElementMost widely used
Other types of final control elements are Dampers or louvers
Variable pitch fan blades
Final Control ElementFinal Control Element
Considered as the muscle of automatic control.
They furnish the necessary power application between the low energy levels of controllers and the high energy level needed to perform their function in control of the process.
Final Control Element
Final Control Element
Final Control ElementFinal Control Element
Control ValveControl Valve A power operated device that manipulates
the fluid flow rate, temperature, level in a process control system.
It consists of a valve connected to an actuator mechanism that is capable of changing the position of a flow-controlling element within the valve in response to a signal from the controlling system.
Control ValvesControl Valves Functions as a variable resistance, creating
a variable pressure drop in a pipeline This pressure-drop process is often called
throttlingthrottling It is consists of three major sub-assemblies:
The valve body assembly The internal trim parts
An actuator assembly
Variety of additional valve accessories
Valve Body Assembly
Actuator Assembly
Valve Positioner
Control ValveControl Valve
ActuatorActuator
The power to drive the valve. Power source could be:
Manual. lever or gear box.
Pneumatic.
Hydraulic.
Electrical driven.
Valve PositionerValve Positioner
Control element determine the opening or closing position, action and characteristic of the valve.
It receive signal from controller. It converts the signal to the appropriate
opening or closing setting of the valve. It provides the accurate control of the valve.
Valve BodyValve Body
The part of a valve that is the main pressure boundary,
providing pipe connecting ends, the fluid flow passage way,
in some cases, the part that supports the seating surfaces and closure member.
Size varies from 1” to 36” valve
body!
Control ValveControl Valve
Control Valves Control Valves Components -Components -Although there are so many types and makes of control valves, this drawing can be used to illustrate the location and description of the different components of control valve. The main difference mainly will be the type of actuator used by different manufacturers.
Body ConstructionBody Construction In order to fulfill the
control valve function, the valve body must:
Withstand the maximum operating pressure.
Have adequate capacity in respect of flow area.
Have correct flow characteristic.
Be able to resist erosion and corrosion.
DN 100 . P13001 . 3 309Line Size in metric unitsPipeline NumberRating of the Piping Equipment Material Composition of Piping Equipment
Valve BodyValve Body
All wetted parts of the control valve, including external bolts/studs and nuts must be designed to the same rating or equivalent piping class.
On the PEFS’s you will find the following information:
Piping ClassPiping Class
The piping classes are divided in different sections and the International Standard ANSI B.16.34 are applicable with the exception of the Classes 125, 250 and 400
The following Classes are used and their abbreviations:
1 = Class 1503 = Class 3006 = Class 6009 = Class 90015 = Class 150025 = Class 2500
Body SizeBody Size
The control valve body size may have the same size as the calculated trim size, but oversized bodies, up to the size of the adjacent piping, may be required to reduce the outlet velocity of the fluid
The control valve body size shall be selected from the following series:
Metric Sizes: DN 25, 40, 50, 80, 100, 150, 200, 300, 400, 450, 500, 600, and largerImperial Sizes: 1”, 1-1/2”, 2”, 3”, 4”, 6”, 8”, 10”, 12”, 16”, 20”, and larger
Full trim means bore size = port size.
Reduced trim means bore size smaller than port size
Valve TrimValve Trim
Integral Flange
Separable Flange
End ConnectionsEnd Connections
The following are the possible connections for control valves. Normally, all control valves should have flanged ends.
Some types of control valves, such as Camflex Valves and Butterfly Valves do have flangeless valve bodies, which are less expensive.
Screwed
Socket-weldButt-weld
Threaded connections are not permitted for process fluids. Allowed only for instrument air regulators if flange type cannot be obtained
End ConnectionsEnd Connections
Globe ValvesGlobe Valves is the most widely used control valve in
process control provides tight shut off withstand high differential pressure changeable flow characteristic by using different plug style offers a wide
range of sizes, pressure ratings, and flow characteristics
Globe ValvesGlobe Valves
Single Seated Globe Valves:This is the most preferred type for all applications with the exception of very high flow rates in combination with low pressure drops
Globe ValvesGlobe Valves
Double Seated Globe Valves - provides large capacities and ideal for high pressure applications with dirty fluids
Disadvantages high leakage rate
very expensive
Globe ValvesGlobe Valves
Angle-Body Globe Valve -
This type of valve is designed specifically for erosive liquid and gas applications. Normally installed with the flow entering at the side and leaving at the bottom
Globe ValvesGlobe Valves
3-Way Globe Valves:
For combining or diverting flow applications; provide large flow with low-pressure recoveries.
Flow CharacteristicsFlow Characteristics Control valve Flow characteristics is the
relationship between flow rate through the valve and valve travel as the travel is varied from 0 to 100%
CV: The VALVE FLOW COEFFICIENT is the number of U.S. gallons per minute of 60 degree F water that will flow through a valve at a specified opening with a pressure drop of 1 psi across the valve.
Inherent flow characteristic: refers to the characteristic observed with at constant pressure drop across the valve
Flow CharacteristicsFlow Characteristics
The three most common types of flow characteristics are:
Equal percentageEqual percentage - The inherent flow characteristic, which, for equal increments of rated travel, will ideally give equal percentage changes of the existing flow Cv at constant Delta P.
LinearLinear - equal increments of travel provide equal increments of flow Cv at constant pressure drop.
Flow CharacteristicsFlow Characteristics
Cont….Quick openingQuick opening – Provides for maximum change in flow rate at low valve travels with a nearly linear relationship. Additional increases in valve travel give sharply reduced changes in flow rate. Quick open plugs are used for on-off applications designed to produce maximum flow quickly.
Flow characteristics of globe valves can be deter-mined by the shape of the plug head.
CavitationCavitation
A two-stage phenomenon of liquid flow The first stagefirst stage is the formation of cavities
(vapor bubbles) within the liquid stream The second stagesecond stage is the collapse or
implosion of those cavities (beyond the vena contracta) back into an all liquid state
The energy released by cavitating liquids can, under certain circumstances, cause physical damage of valve or piping components
CavitationCavitation
Pressure P1
P2
PVcLiquid Vapor pressure
VelocityPv V
eloc
ity
Pre
ssu
re
Anti-Cavitation Valves -Anti-Cavitation Valves - For liquid services in which high pressure drops occur, the application of a conventional trim with standard flow direction often results in very high velocities and cavitation. This type of application requires anti-cavitation valve.Low Noise Valves -Low Noise Valves - Liquid flow noise, cavitation noise, and flashing noise can be generated by the flow of a liquid through a valve and a piping system. Special design of control valve is necessary to reduced the noise level to acceptable value.
FlashingFlashingPressure P1
P2
PVcLiquid Vapor pressure
Velocity
Pv Vel
ocit
y
Pre
ssur
e
•The liquid pressure drops below the vapor pressure and remains as vapor until the downstream pressure recovers.
•Flashing will cause choke flow condition to occur.
•In addition the vapor bubbles can also cause mechanical damage to the valve and piping system.
Cavitation & FlashingCavitation & Flashing
Cavitation point
Recovery Point
Packing Box and Bellows Seal - Packing Box and Bellows Seal - The packing box or stuffing box is the most commonly used stem seal. The bellows seal is used only for highly toxic process fluid where leakage is not permissible. For services with fluid temperature outside the packing material temperature limits, an extended bonnet is used. Also for very low temperature service, an extended bonnet is selected to prevent ice formation on the stem.
Packing box contains a number of
compressed packing to
maintain seal.
Standard Bonnet
Extended BonnetPTFE Internal Lining
Bellows seal is used for corrosive
or highly toxic fluids.
Miniature Valves - Miniature Valves - are used for very small flows size DN 25 (1”) and smaller.
VariPak Control Valve made by Masoneilan
Advantages: Adjustable CvAdvantages: Adjustable Cv Can be adjusted from 100% to 40 % without any change of input signal and/or control valve components
Large Cv range is achieved by changing different plugs and different shape of seat.
Camflex Valve
Eccentric Rotary Plug Valve Eccentric Rotary Plug Valve (Camflex)(Camflex)
Can be substituted for globe-body control valve.
The seat portion of the plug has the form of a spherical segment which is rotated through 50 degrees for maximum opening.
The design eliminates high torque and rapid wear of seat ring.
The tight shut off is achieved through the flexing action of the plug legs.
Varimax Valve
Rotary Globe Valve (Varimax)Rotary Globe Valve (Varimax) Provide control of high pressure compressible fluids
without the erosion, vibration and high noise levels associated with conventionally designed rotary valves. Because of their relatively large flow passages they are particularly well suited for applications involving gases.
Butterfly ValveButterfly Valve High flow rate Low pressure drop Consists of a cylindrical body with a disk or
vane. Advantage - reduces the likelihood of
clogging. Disadvantages
Not tight shut-off
Flow characteristic cannot be change
Ball ValveBall Valve Similar to a butterfly valve except that its flow-
control element is a sphere instead of a disk, and thus has a greater seating area.
Because of this, ball valves allow higher differential pressures and better sealing.
Normally used for on-off service (like emergency shutdown application).
The ball valve is not ideal for throttling service.
Fail Open
Fail Close
Spring Diaphragm Actuator
Spring-Opposed Spring-Opposed Diaphragm ActuatorDiaphragm Actuator
Spring
Diaphragm
Fail OpenFail Close
Multi-Spring, Spring Diaphragm Actuator
Diaphragm
Set of Springs
ActuatorsActuators
Spring-Opposed Piston Spring-Opposed Piston ActuatorActuator Long-Stroke Long-Stroke
Piston Piston ActuatorActuator
Positioner Schematic Positioner Schematic for spring-diaphragm actuator or spring-opposed piston actuator.
Positioner Schematic - Two Output SignalPositioner Schematic - Two Output Signal
Control Valve AccessoriesControl Valve Accessories
Filter RegulatorsFilter Regulators - For control valves which cannot handle the maximum air supply pressure of up to 8 Bar, they are provided with Air Filter Regulator.
Filters Filters - For actuators which can handle the maximum air pressure, a Air Filters is used instead of Air Filter Regulator.
Control Valve AccessoriesControl Valve Accessories
HandwheelsHandwheels - For control valves which needs to be open manually, in most cases during plant start-up, require hand wheel. The hand wheel facility is designed such that one man can operate the valve.
Limit StopsLimit Stops are provided to prevent the control valve from fully closing or fully opening.
Control Valve AccessoriesControl Valve Accessories
Limit SwitchesLimit Switches are installed in control valves to electrically indicate open, closed, or intermediate position of the valve stroke
Limit switches can either bemicro-switches enclosed in an explosion proof box
or proximity sensors
Volume BoostersVolume Boosters are used on throttling control valves to provide fast stroking action with large input signal changes. Depending on the actuator size, packing set and the number used, boosters can decrease valve stroking times by as much as 90%. Quick-Quick-
Exhaust Exhaust ValvesValves are applied to achieve a specified
opening or closing time
Lock-up Valves Lock-up Valves are used for control
calves which must stay-put (remains at last
position) in case of an instrument air failure.
They are known also as Stay-Put Valves.Solenoid ValvesSolenoid Valves are used to interrupt or cut-
off air signal to the actuator. It is used to switch a particular control valve or ESD shut-off valve to their fail safe position (Fail Close or Fail Open).
Schematic of Control Valve Basic PipingSchematic of Control Valve Basic Piping
I
P
Pneumatic Positioner
Current to Pneumatic Transducer
Valve Actuator Output To
Actuator
Valve travel Feedback to Positioner
4 - 20 mAFrom DCS
Pneumatic Signal3 - 15 PsiG
Regulated Air Supply
Instrument Gauges
Setting dependent on Actuator operating pressure
Schematic of Double Acting Control Valve PipingSchematic of Double Acting Control Valve Piping
I
P
PneumaticPositioner
Current to Pneumatic Transducer
Valve Actuator Output
To Actuator
Valve travel Feedbackto Positioner
4 - 20 mAFrom DCS
Pneumatic Signal3 - 15 PsiG
Regulated Air Supply
Instrument Gauges
Setting dependent on Actuator operating pressure
Example of ControlValve Example of ControlValve Piping Piping Schematic Drawing Schematic Drawing
POSIT-IONER
A B C
D E F
Exh
Exh
Air RegulatorSet 3.8 Barg
Check Valve
Lock upValve
Set 3.4 Barg
Trip ValveSet 2.8 Barg
Volume Tank
Booster Relay
Signal
4-20mA
Air supply
The valve remains at last position incase of Air Failure.
Instrument StandardInstrument Standard ANSI – American National Standards
Institute API – American Petroleum Institute ASME – American Society of Mechanical
Engineers ASTM - American Society for Testing and
Materials BSI – British Standard Institute
Instrument StandardInstrument Standard DIN – The German Institute for Standardization ISO – International Organization for
Standardization NEMA – National Electrical Manufacturers
Association NIST – National Institute of Standards and
Technology CENELEC - European Committee for
Electrotechnical Standardization
Thank YouThank You
Next On….. Basic Control Theory..