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PLANT UTILITYDKK2483

Chapter 3

VALVES

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ASSIGNMENT 1

Write a brief report on the following :

1- Relief Valves G6 4- Electrical Actuators G2

2 - Safety Valves G4 5- Pneumatic Actuators G1

3 - Automatic Valves G5 6- Air Release Valves G3

7- Pinch Valves G7

INCLUDE IN THE REPORT : (max. 5 Pages)

A- Introduction and description of the valve,

B- Valve Functions and Applications

C- Maintenance

D- General comments

Due Date : Wednesday 27th March 2013 during class

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Industrial Valves

Valve Application and Operation

Types of Valves

Valve Symbols

Valves

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Introduction

Classified as one of the most vital instrument in the industry, everyengineers, operators, and maintenance technicians should know

a basic knowledge of valve types and designs,

materials used to make valves, where various designs should and

should not be used,

factors to consider in specifying a valve for a specific application,how to calculate flow through valves,

valve maintenance and repair.

These are very important requirements as to ensure that the valve is

efficiently doing its job in producing and maintaining optimal results in

process, safety, economic and environment considerations. Valves

Valves

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The definitions may brief some useful understanding and concept when

we are dealing with valve.

Fluid : Any substance that can flow from one area to another when it

subjected to a normal and shear stress. Gases and liquids are both

considered fluids.

Valve : A mechanical device that is used in industrial piping to control

the flow of fluids.

On-Off Service : Valves that only operate in the fully open or fully

closed positions are said to provide on-off service.

Throttling Service : Valves that control flow by partially restricting the

passage of the fluid provide in what is called throttling service.

Valves

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Pressure Drop : The loss of energy that occurs when a fluid encounters

resistance passing through a valve.

The greater resistance, the higher the pressure drop for a given flow

rate.

A higher pressure drop means that more energy in the form of

pumping or compressing, must be used to move the fluid through the

piping.

Valves

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VALVE FUNCTIONS AND APPLICATIONS

The valves used for chemical processing plants can be divided into

two broad classes, depending on their primary function:

Shut-off valves (block valves), whose purpose is to close off the

flow.

Control valves, both manual and automatic, used to regulate flow.

A valve selected for shut-off purposes should give a positive seal in the

closed position and minimum resistance to flow when open.

Gate, plug and ball valves are most frequently used for this purpose.

Valves

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Pressure Drop : The loss of energy that occurs when a fluid encounters

resistance passing through a valve.

The greater resistance, the higher the pressure drop for a given flow

rate.

A higher pressure drop means that more energy in the form of

pumping or compressing, must be used to move the fluid through the

piping.

Valves

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A valve selected for shut-off purposes should give a positive seal in the

closed position and minimum resistance to flow when open. Gate, plugand ball valves are most frequently used for this purpose.

If flow control is required, the valve should be capable of giving smooth

control over the full range of flow, from fully open to closed. Globe valves

are normally used, though the other types can be used. Butterfly valves

are often used for the control of gas and vapour flows. Automatic controlvalves are basically globe valves with special trim designs.

The careful selection and design of control valves is important; good flow

control must be achieved, whilst keeping the pressure drop as low as

possible.

Valves

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The valve must also be sized to avoid the flashing of hot liquids and the

super-critical flow of gases and vapours.

Non-return valves are used to prevent back-flow of fluid in a process line.

They do not normally give an absolute shut-off of the reverse flow.

Valves

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Classification of Valve

Valve classified by :- flow control elements

- function

- operating condition (pressure, flow, temperature)

Flow control elements regulates the flow of fluid through

the devices.

Some valves have movable gates, balls, plugs, diaphragms, disc

etcValves

Valves

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Valves

Primary purpose of a valve is to direct and control the fluids flow bystarting, stopping and throttling flow.

Designed to withstand pressure, temperature and flow.

Common valves in manufacturing : gate valve, globe valve, ball valve

check valve, butterfly valve , etc.

Different types of valve designed for different purpose and specialty

Valves

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Valves

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Gate Valve

One of the most widely used in the industry is the gate valve.

A gate valve stops flow by placing a gate across the pipes opening.

When the valve is wide open, the gate is raised completely out of the

flow line.

In the fully open position, the gate causes very little resistance to flow.

The low resistance to flow means that very little energy is lost or

wasted as fluids pass through the valve.

As the gate is the part of the valve that regulates flow, this is why it is

called the flow control element.

A gate valve is good choice for on-off service and infrequent operation.

Valves

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Types of Valves

Gate Valvescommon valve in industry

places a movable metal gate in the path of a process

flow in a pipeline

this type of valve is used where flow rate are not

restricted

should not used to throttle flow for extended periods

the largest part of the valve is the body which can be

connected to the process piping

three way connection: flanges, threaded connections

or welding.

design for various process condition such as corrosive,high and low temperature services

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Gate Valves Components

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Example of valve process conditions

# stainless steel gate valvecorrosive, high-low temperature# alloy gate valvehigh temperature, high pressure

# bronze gate valvelow temperature, low pressure

# brass gate valvelow temperature, low pressure

# cast iron gate valvewater, lubricant, low pressure steam

Maintenance

@ take care not to damage valve seats - when closing gate

valve

@ temperature changes, close too quickly, pipe expansion -

cause a valve to warp

@ never used a wrench to snug it downuse lubricant to

moving parts

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Globe Valve

In a globe valve, the flow path changes in direction compared to gatevalve that the flow through is in a straight line.

This change of flow causes turbulence, and also results in a higher

pressure drop across the valve.

The higher turbulence and pressure drop mean that more energy isrequired to move fluids through an open globe valve.

The disc of a globe valve does not slide along the seating surface.

Hence, all contact between the disc and the seat stops as soon as flow

begins.

Valves

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This globe valve is preferred to use for services that require frequent

valve operation.

Valves

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Globe Valves

places a movable metal gate in

the path of a process flow this type of valve is used for

throttling service

consist of a disc, body, seating

area, stem, bonnet, packing, hand

wheel, etc body can connect to the process

piping

process piping connection (flanges, welding and threaded

connections)

stainless steeluse in corrosive, high and low temp services. alloyhigh temp and high pressure services

globe valves have a much greater pressure drop across the

valve than a gate valve

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Globe Valve Components

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Ball Valves

ball valves are notdesigned for excessive

temperature

take their name from the ball shaped, movable element in the centreof the valve

doesnt lift the flow control device out of the process

provide little restriction to flow

come in variety of shapes and sizes

shouldnt be used for throttling services

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Ball Valve

A ball valve is similar in design and operation to a plug valve. The flowcontrol element, however, is in the shape of a ball.

The ball has an opening or port which allows fluids to pass through.

Ball valves, like plug valve are quick opening. The ball is highly

polished which makes it uniform and smooth.

As a result, there is very little friction between the ball and the seat

rings when the valve is operated.

Because friction is not a problem in ball valves, they do not require

lubrication.

Valves

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Ball Valves Components

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Check Valves

designed to prevent reverse flow and to avoid possible contaminationdamage to equipment

limits backflow but not considered tight shutoff

have flow direction stamping on the valve body

typical check valve design is the swing check valve

check valve operates by gravity

designed to be used in variety

process condition

@ stainless steelcorrosive

highlow temp

@ alloyhigh temp

high pressure

Swing Check Valve

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Check Valve

The only moving part is a disc assembly that is attached to the body bya pivot pin.

The pivot-pin mounting leaves the disc assembly free to swing toward

and away from the valve seat.

When there is no flow through the valve, the disc is positioned so thatthe valve is closed.

Valves

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Lift Check Valve

Ball Check Valve

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Butterfly Valves

commonly used for throttlingand on/off services

physically is smaller than the

other valves

during throttling process, it have

non-uniform flow characteristics

designed to be operated at low

temperature and low pressure.

commonly found in cooling water

and heat exchanger system

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Butterfly Valve Components

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Plug Valves

quick opening, very popular in the process industry

regulate flow and provide very little restriction come in variety shapes and design

commonly design for fuel gas piping system, low pressure

situation, slurry and lubrication services, on/off services, low

temperature services and multi-port operation

should never used in throttling most plug valve should be limited to temperature under 480F

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Plug Valve Components

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Diaphragm Valves

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Valve Symbols

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