Instrument Training Material Control Valve Final Control Element Most widely used Other types of final control elements are Dampers or louvers Variable

Instrument Training Material

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


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 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


Double Seated Globe Valves - provides large capacities and ideal for high pressure applications with dirty fluids

Disadvantages high leakage rate

very expensive


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


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.


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.


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

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Documents

Instrument Training Material Control Valve Final Control Element Most widely used Other types of final control elements are Dampers or louvers Variable