controll valve presentaton

7/30/2019 Controll Valve Presentaton

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A PRESENTATION ON

CONTROL VALVES


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Control Valves

Control Valve: A power operated device, whichregulates the fluid flow rate in a process control

system.
http://en.wikipedia.org/wiki/Image:Pl_control_valve.GIF


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IMPORTANCE OF CONTROL VALVES

The most common final control element in the process

control industries is the control valve.

It manipulates a flowing fluid, such as gas, steam, water,or chemical compounds, to compensate for the load

disturbance

Thus, keeps the regulated process variable as close as

possible to the desired set point.


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A control valve consists of two main sub-assemblies

Valve body assembly:The main pressure boundary of

the valve that also provides the pipe connecting ends, thefluid flow passageway, and supports the seating surfacesand the valve closure member.

Actuator :An actuator is a fluid powered or electrically

powered device, which supplies force and motion to avalve closure member.

COMPONENTS OF A CONTROL VALVE


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PARTS OF AN ACTUATOR


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PARTS OF VALVE BODY ASSEMBLY


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TYPES OF CONTROL VALVES

.

SLIDING-STEM ROTARY

CONTROL VALVE

BALLBUTTERFLY

* THRU-BORE

* PARTIAL

GLOBE

PINCH

GATE

DIAPHRAGM


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GLOBE VALVEGlobe valve: A valve with a linear motion closure

member, one or more ports and a body distinguished by

a globular shaped cavity around the port region.


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Types of Globe Valve

Simple Globe Valve Angle Valve Three Way Globe Valve


11/26Double Ported Globe Valve


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BUTTERFLY VALVE BALL VALVE


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FLOWCHARACTERISTICS

0 10 20 30 40 50 60 70 80 90 100

908070

605040302010

00

Valve travel %Linear Rate of change of flowis same to rate of change ofvalve travel

Equal% -Rate of change of flow

due to change of valve travelis proportional to earlier flow

Quick opening -This produces

very high flow rate change ( 90%)for very small initial lifting (30%)

of valve plug.


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TYPES OF CAGES


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Selection of flow characteristicEqual percentage:

# For fast process# When high rangeability is required# When system dynamics are not well known

Quick opening :

# For On-Off control.# When max. valve capacity must be obtained quickly.

Linear :# For slow process.

# When more than 40% of the system pressure drop occursacross the valve.# When major process changes are a result of load changes.


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CONTROL VALVE FLOW COEFFICIENT (Cv)

Cv is the number of U.S. gallons per minute of water which will

pass through a given flow restriction with a pressure drop of 1

psi.Cv = Q ( p) (gpm/psi)

where Q = flow

p= differential pressure across the valve

Eg. : A control valve which has a Cv of 12 has an effective port area in the full

open position such that it passes 12gpm of water with 1 psi pressure drop.

PARAMETERS OF CONTROL VALVE


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The critical flow factor (Cf) is effectively an index of

pressure recovery in a control valve. High Cf values

indicate low pressure recovery where a low Cf value is an

indication of high pressure recovery.

It is to be noted that streamlined valves such as Ball

valves or Butterfly valves exhibit a high degree of

pressure recovery. Globe valve style, on the other hand,exhibits a much small amount of pressure recovery.

CRITICAL FLOW FACTOR(Cf)


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Cavitation

It is the phenomenon that occurs only in liquid service. Whenthe fluid accelerates to pass through the narrow restriction atthe vena contracta,the pr. may drop below the vapor pr. of thefluid. This causes vapor bubbles to form.

As the fluid continues past the vena contracta, as the flow areaexpands the the pressure builds again increasing the fluid pr.above the vapor pr. This pr. recovery causes the bubble toimplode. The implosion releases high amount of energy,damages the valve internals and the body.

This two stage process formation of bubble and its implosion iscalled cavitation.The release of the energy can easily be heardas a noise in the valve or in the downstream piping.


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CAVITATION DAMAGE


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CAVITATION CONTROLS

SYSTEM DESIGN

1. LOCATION OF VALVE

2. CASCADINGMATERIAL SELECTION

HARDEN MATERIAL,

LIKE 17-4 pH, 440C, 420SST HT

AND 316/COLMONOY 6 / ALLOY 6


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CAVITATION CONTROLS

ANTI - CAVITATION PRODUCTS

CCI DRAG DESIGN, UP TO 380 BAR PRESS. DROP.

FISHER CAVITROL - III DESIGN

CAVITROL - III WITH 1 STAGE- UP TO 99 BAR.

CAVITROL - III 2-3 STAGES- 99 TO 207 BAR.

CAVITROL -4 , ABOVE 200 BAR, SIZE LIMIT 2 TO 6.

ABB INTROL DESIGN


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FLASHING

Flashing is a process in which the pressure of the liquidfalls below the vapour pressure thus leading to the

formation of vapour bubbles. The subsequent flow will betwo phase consisting partly of liquid and partly vapour.

Flashing leads to high flow velocities which can damageboth the trims and the body (sand blasting effect).


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FLASHING DAMAGE


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Accessories

AFR : Air filter regulators are used to providea clean and regulated air.

Positioner :Applications on which theyshould be used include the following...

* When the best possible control is required.

* When max. loading pr.>20 psi is required.

* When reversing action is necessary.* For split range operation.

* For fast response.


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controll valve presentaton

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