Control valves
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date post
11-Sep-2014 -
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Devices & Hardware
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Transcript of Control valves
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Control Valves
Presented by:Syed Waqas HaiderProcess Engineer
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Definition
Control Valves
control conditions (flow, pressure, temperature, and liquid level )
open or close in response to signals received from controllers
Controller compare a "setpoint" to a "process variable" (value provided by sensors)
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Types
Control Valves
Rotary Motion
Butterfly
valves
Ball vales
Plug valves
Linear Motion
Globe Valves
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Control Valves Parts
Three main parts
Valve's actuatorValve's positionerValve's body
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ActuatorThe purpose of the valve actuator is to
accurately locate the valve plug in a position dictated by the control signal
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Types of ActuatorsPneumatic Valve Actuators: Adjust the position of the valve by converting air pressure into rotary motion or linear motion. Piston and Diaphragm Actuators
are examples of Pneumatic Actuators
Electric Valve Actuators: An electric actuator is powered by motor that converts electrical energy to
mechanical torque
Hydraulic actuator: Consists of a cylinder or fluid motor that uses hydraulic power to facilitate
mechanical operation. The mechanical motion gives an output in terms of linear, rotary or oscillatory
motion
according to their supply
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Types of Actuators
Multi-turn actuatorgives torque for at least one full
revolutionPart-turn actuator
gives torque for less than one full revolutionLinear actuator
opens and closes valves that can be operated via linear force--sometimes called rising stem valves
according to their movement
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PositionerPositioners are instruments that help improve control by accurately positioning a control valve actuator in response to a control signal
Positioners receive an input signal either pneumatically or electronically and provide output power to an actuator
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Positioner Working
Some of the mechanisms
i. Force Balance Positionersii. Motion balance Positionersiii. Electronic Positioners
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Force Balance Positioners
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Motion balance Positioners
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Electronic Positioners
Sensor to detect valve position
Micro-Processor Error = Position - Signal
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Valve Bodies
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Flow characteristics of Control valves
Quick Opening: Quick open plugs are used for on-off applications designed to produce maximum flow quickly
Linear: produces equal changes in flow per unit of valve stroke regardless of plug position, used where valve pressure drop is a major portion of the total system pressure drop
Equal Percentage: change in flow per unit of valve stroke is directly proportional to the flow occurring just before the change is made, generally used for pressure control