Introduction to Control Introduction to Control valvevalve

Chapter TwoChapter Two

What is A control valve!What is A control valve!

• Process plants consist of hundreds, or ev en thousands, of control loops allnetwork ed toget her to produce a product (Power,

Petro, Oil gas)• Each of these control loops is designed to

keep some important process variable su ch as pressure, flow, level, temperature,

etc. within a required operating range to ensure the quality of the end product.

• Each of these loops receives and internally creat es disturbances that detrimentally affect the pro

cess variable, and interaction from other loops in the network provides disturbances that influence the processvariable.

• To reduce the effect of these load disturbances, sensors and transmitters collect information abo

ut the process variable and its relationship to so me desired set point. A controller then processes this information and decides what must be done

to get the process variable back to where it shoul d be after a load disturbance occurs. When all th e measuring, comparing, and calculating are don e, some type of final control element must imple

ment the strategy selected by the controller.

• The most common final control element in t he process control industries is the control v

alve• The control valve manipulates a flowing flui

d, such as gas, steam, water, or chemical co mpounds, to compensate for the load distur

bance and keep the regulated process varia ble as close as possible to the desired set po

int.• The control valve assembly typically consist

s of the valve body, the internal trim parts, a n actuator to provide the motive power to o

perate the valve, and a variety of additional valve accessories, which can include positio ners, transducers, supply pressure regulator

s, manual operators, snubbers, or limit switches.

Component of Control valveComponent of Control valve

• Valve body• Actuator• Bonnet• Yoke• Positioner• Mounting bracket• Volume booster• Lock-up valve

CONTROL VALVE CONTROL VALVE CLASSIFICATIONCLASSIFICATION

CONTROL VALVE

LINEAR MOTION

ROTARY MOTION

GLOBE

DIAPHRAGM

GATE

GLOBE

ANGLE

3 WAY

SINGLE SEAT

DOUBLE SEAT

SPLIT BODY

ECCENTRIC PLUG

BUTTERFLY

BALLECCENTRICFULLV-NOTCH

Linear Control Valve

Actuator Direct Type

Actuator Reverse Type

Valve body

Gate vale

Diaphragm valve

Linear Valve FeaturesTORTUOUS FLOW PATH LOW RECOVERY CAN THROTTLE SMALL FLOW RATES OFFERS VARIETY OF SPECIAL TRIM DESIGNS SUITED TO HIGH-PRESSURE APPLICATIONS USUALLY FLANGED OR THREADED SEPARABLE BONNET

Linear Valve Features

Terminological of Sliding CVTerminological of Sliding CV• Actuator Spring• Actuator Stem• Actuator Stem Extension• Actuator Stem Force• Angle Valve• Bonnet• Bellows Seal Bonnet• Bottom Flange• Bushing

• Cage• Cylinder• Cylinder Closure Seal• Diaphragm• Diaphragm Actuator• Diaphragm Case• Diaphragm Plate• Direct Actuator• Extension Bonnet• Globe Valve• Packing Box

• Piston Type Actuator• Plug• Port• Reverse Actuator• Seal Bushing• Seat• Seat Load• Seat Ring• Spring Adjustor• Spring Seat

• Stem Connector• Trim• -Trim, Soft Seated• Upper Valve Body• Valve Body• Valve Body Assembly• Valve Plug• Valve Stem• Yoke

- Rotary Shaft Control Valve

CONVENTIONA L DISK

BUTTERFLY VALVE

SEGMENTED BALL VALVE

ECCENTRIC DISK VALVE CONTOURED DISK BUTTERFLY VALVE

Rotary Valve Features

STREAMLINED FLOW PATH HIGH RECOVERY MORE CAPACITY LESS PACKING WEAR CAN HANDLE SLURRY AND ABRASIVES FLANGELESS INTEGRAL BONNET HIGH RANGEABILITY

Rotary Valve Features

Terminological of Rotary CVTerminological of Rotary CV• Actuator Lever• Ball, Full• Ball, Segmented• -Ball, V notch• Disk, Conventional• Disk, Dynamically Designed• Disk, Eccentric• Flangeless Valve

• Plug, Eccentric• Reverse Flow• - Rotary Shaft Control Valve• Seal Ring• Shaft• Standard Flow

Nominal Position of CVNominal Position of CV

• Normally close (Air to open)• Normally open (Air to close)

Normally Closed Control Val Normally Closed Control Valveve

Normally Open Control Valv Normally Open Control Valvee

CV Fail positionCV Fail position

• Fail safe position - Fail to close - Fail to open• Fail to last position (Fail lock)

* Both Air fail and electrical fail

Control Valve "Fail-Safe" Control Valve "Fail-Safe" PositionsPositions

CV in P&IDCV in P&ID

Control valveControl valve symbol in P&IDsymbol in P&ID