Instrumentation_ Valve Type

7/26/2019 Instrumentation_ Valve Type

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Type of Control valves


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Purpose of control valve

For throttling purposes and general flow

control

Control valve is classify into 2 categories:

Reciprocating stem

Rotating stem


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Reciprocating stem

globe valve

the most common valves in existence.

The globe valve derives its name fromthe globular shape of the valve body.

The essential principle of globe valve

operation is the perpendicular

movement of the disk away from theseat.

Valve is divided into 2 areas:

Actuatorconverts the energy

input into mechanical motion

Body


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Example of globe valve

Single seated sliding stem globe valve

Double seated sliding stem globe valve


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Reciprocating stem

Three way valves

Split one stream into two other stream

Blend two steam into one stream Y-style valves

Commonly used in molten metal or cryogenic service

Pinch or diaphragm valves

Consist of some kind of flexure that can be moved

together to open or close the area of flow.

Commonly used for highly corrosive fluids, slurries,

high-viscosity liquids, some food processing

Gate valves

Mainly used as block valve

Fully open or fully closed services.


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Rotating stem

Butterfly valve

consist of a disk rotating about a

shaft

A flat circular plate is positioned in

the center of the pipe

Require minimum space for

installation and provide high-capacity flow at low cost

- Ball valve

Valve that opens by turning a handle attached to a ball insidethe valve.

The ball has a hole, or port, through the middle so that when

the port is in line with both ends of the valve, flow will occur

provide high-capacity flow at low cost


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Control valve actuator

converts the energy input, either pneumatic or electrical

into mechanical motion to open or close the valve.

Working principle

pneumatic

signal pressure is sent to the air

chamber of diaphragm actuator.

The pressure act on the diaphragm

to produce a pressing force whichcompress a spring to cause the

movement of the rod and valve

stem.

Pneumatically operated diaphragm

actuators


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most common onesolenoid

actuator By making or breaking an electrical

current signal

When current flows through the coil, a

magnetic field forms around the coil. The magnetic field attracts the

armature toward the center of the

coil. As the armature moves upward,

the spring collapses and the valve

opens.

When the circuit is opened and current

stops flowing to the coil, the magnetic

field collapses. This allows the spring

to expand and shut the valve.

Electrohydraulic and electromechanical actuator


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Piston Actuators

Used when maximum thrust output is required

along with fast response

When the pressure of the supply air is high

enough, the actuator forces are higher than with

diaphragm actuators

Working against high process pressure

The compressed air is applied to a solid piston

contained within a solid cylinder.


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QuestionDetermine type of valve. FC or FO? Why?


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Other Final Control Element


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Metering pump

A metering pumpis a ump used to pump liquidsat adjustable flow rates which are precise when

averaged over time.

Delivery of fluids in precise adjustable flow ratesis sometimes called metering.

Although metering pumps can pump water, they

are often used to pump chemicals, solutions, or

other liquids.

Many metering pumps are rated to be able to

pump into a high discharge pressure.


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Piston pump

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Instrumentation_ Valve Type