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VALVES

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Contents

Introduction

Types of Control Valves

Control Valve Components Control Valve Accessories

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What is control valve Control valvesare valves used to control

conditions such as flow, pressure,

temperature, and liquid level by fully orpartially opening or closing in responce to

signals received from controllers that compare

a "setpoint" to a "process variable" whose

value is provided by sensors that monitor

changes in such conditions

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Control Valve

ACTUATOR

VALVE BODY

ASSEMBLY

BONNET

BODY

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Transmitter

Controller Sensor

ProcessControl Valve

Feedback Control Loop

Control Loop

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CONTROLLED

Basic Principle

OPEN

CLOSE

Inlet PressureOutlet Pressure

MINIMUM

MAXIMUM

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TYPES OF

CONTROL VALVES

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Control Valve Types

LINEAR MOTION ROTARY MOTION

GLOBE

GATE

DIAPHRAGM

BUTTERFLY

BALL

PLUG

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Linear and Rotary Motion

Tortuous Flow PathLow Recovery

Can Throttle Small Flow Rates

Suited to HP Applications

Usually Flanged or Threaded

Bonnet Separable

Streamlined Flow PathHigh Recovery

More Capacity

Can Handle Slurry / Abrasives

Flangeless

Integral Bonnet

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General Characteristics

Causing Turbulence & highP

Plug prone to wear/erosion Recommended for throttling

Used for unidirectional flow

Valves bore < pipe opening

Can be Single seated

Double seated

Globe Valve

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Single Seated Globe Valve

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Double Seated Globe Valve

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General Characteristics

Straight flow

Directionless valve Minimum pressure drop

Valve's bore pipe opening

Not recommended for throttling

Occupy less space as compare toGlobe

Gate Valve

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Diaphragm Valve

General Characteristics

No stuffing box packing

Not recommended for HP Used where tight closure is

important

Long life and friendly

maintenance valve Normally used for scale forming

or corrosive fluid

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Diaphragm Valve

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Butterfly Valve

General Characteristics

Reliable & long service life

Lines cannot be cleaned by pig Suitable for low pressure

service,10-20 bar

Easy to operate, both manually

& by remote control. Circular shaped disc used for

quick opening/closing

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Ball Valve

General Characteristics

LowP

Easy operation Quick opening

Two-way flow possible

Low maintenance costs

Ball is used for opening &closing

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Plug Valve

General Characteristics

Used for quick opening andclosing

Not recommended forthrottling

Used for more than oneinlet/outlet lines

Provides straight throughflow

Used for low pressure services

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CONTROL VALVE

COMPONENTS

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Parts of globe valves

BODY

Seat

Cage Plug

Plug seal

Gland paking Gaskets

stem

ACTUATOR Yoke

Actuator spring

Actuator stem

Diaphragm

Diaphragm casing Indicator scale

Indicator travel

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Packing

Bonnet

Body

Stem

Guide Bushing

Retainer or Cage

Plug

Seat Ring

Valve Body Components

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Body Assembly

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Actuator

Diaphragm

Material can be

Rubber

Neoprene

Can be Reinforced like Fibreglass, Nylon and Cotton.

Piston

Direct Acting

Reverse Acting

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Direct Action Diaphragm

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Reverse Action

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Common Applications

A positioner is a device put into a

valve to ensure that it is at acorrect position of opening as per

the control signal.

An I/P converter only sends the

opening/closing request to valvebut can not confirm its position.

Positioner

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Positioner senses the valve opening through a position

feedback link connected to valve stem

. I/P converter output is its set point input

positioner is a pneumatic feedback controller

Controlled external supply air to positioner provides power to

positioner to position a valve.

Reverse action

To change the control valve flow characteristics

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Input

3 to 15 PSI

Outputs

3 to 15 PSI

6 to 21 PSI

6 to 30 PSI

Depends upon Bench Set of the

valve

Positioner

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Valve Plug Types

Linear

(Conical)

Equal Percentage

(Tapered)

Quick Opening

(Flat)

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Cage

General Characteristics

A bit less hard material

According to the requirementof process

Guides the Plug

Reduces the noise (10 to 15 db)

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Types of Cages

Quick Opening Linear Equal Percentage

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Packing Box Assembly

The Packing Box Assembly consists of :

Packing Flange

Packing Follower (Bush) Lantern Ring

Equally spaced Packing Rings

Packing Material

Teflon

Graphite

Grafoil

Asbestos

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(Cond)

Equal percentage

equal increments in valve position result in equal relative or

percentage increment in the valve coefficient*

*valve coefficient

the flow in gallons per minute of water that flows through avalve at a pressure drop of 1 psi across the valve

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