Control Valves

Control Valves 1

Presented by:Syed Waqas HaiderProcess EngineerDefinitionControl 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)2Control valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor changes in such conditionsControl valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response 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

Click to edit Master text stylesSecond levelThird levelFourth levelFifth levelTypes3Control ValvesRotary MotionButterfly valvesBall valesPlug valvesLinear MotionGlobe ValvesControl Valves PartsThree main parts

Valve's actuatorValve's positionerValve's body4

A control valve consists of three main parts in which each part exist in several types and designs:

Click to edit Master text stylesSecond levelThird levelFourth levelFifth levelActuatorThe purpose of the valve actuator is to accurately locate the valve plug in a position dictated by the control signal

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The actuator accepts a signal from the control system and, in response, moves the valve to a fully-open or fully-closed position, or a more open or a more closed position (depending on whether 'on / off' or 'continuous' control action is used).Click to edit Master text stylesSecond levelThird levelFourth levelFifth levelTypes 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 motion6according to their supplyTypes of ActuatorsMulti-turn actuatorgives torque for at least one full revolutionPart-turn actuatorgives torque for less than one full revolutionLinear actuatoropens and closes valves that can be operated via linear force--sometimes called rising stem valves7according to their movementPositionerPositioners are instruments that help improve control by accurately positioning a control valve actuator in response to a control signalPositioners receive an input signal either pneumatically or electronically and provide output power to an actuator8

Positioner WorkingSome of the mechanisms

Force Balance Positioners Motion balance Positioners Electronic Positioners9Force Balance Positioners10

Motion balance Positioners11

Electronic Positioners

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Sensor to detect valve position

Micro-Processor Error = Position - SignalValve Bodies

13Flow characteristics of Control valves14

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