Control valve basics…

I.S.A (The International Society ofAutomation) Defines Control Valve as a PowerOperated Device that Modulates the FluidFlow Rate in a Process Control System

Control Valve is an assembly that includes, at minimum, a valve body assembly (Globe, butterfly, ball) and an actuator (manual, pneumatic, hydraulic, electrical Etc).

Actuator

Valve assembly

Positioner

Control valve - Definition

CONTROLLER

P

PR XTR

4- 20 mA

Pneumatic

P1=20 bar.g P2=10 bar.g

Supply air

Simple control loop

Why Control Valve

Manual On/Off Valve Manual control valves

Valve Types

Linear action control valves Rotary action control valves

Globe valve

3 Way valve

Angle valve Ball valveButterfly valve

V-ball valveGate valve Plug valve

Valve Types

Linear action control valves Rotary action control valves

Ball valves

Butterfly valves

Globe valves

The flow path of Globe valve is relatively more complex than ball valve or

butterfly valve hence Globe valve Cv is lower than ball & butterfly valves

Valve Types

Piston Diaphragm

Linear Rotary

Pneumatic Hydraulic Electric

Actuators

Actuator Types

Actuator Types

Pneumatic actuators

Electrical actuators

Hydraulic actuators

100

80

60

40

20

020 40 60 80 100

Valve Plug travel

Flo

w r

ate

Trim characteristics

Quick opening

Linear

Equal percentage

Plug Types

Quick opening Linear Equal percentage

Leak path

Unbalanced design

The fluid pressure is not balanced undershut-off condition in unbalanced design.This force assumes major significance inlarge size valves.

-Advantage: Better shut-off

-Disadvantage: Higher actuator force.

Balanced design

The fluid pressure acting on the plug isbalanced as the effect of pressure actingbelow the plug (upward force) iscountered by the pressure acting abovethe plug head (downward force) .

-Advantage: Lower actuator force

-Disadvantage: Additional leak path isintroduced

Leak path

Trim Types

Contoured Trim Caged Trim

Top Guiding

Cage Guiding

Cage Types

Ported cageEqual percentage

Drilled hole cagesEqual percentage

Drilled hole cagesLinear characteristic

Drilled hole cages, Multiple cage designs

Variable resistance cage

Flow Coefficient (Cv)

Water Flow

Oil Flow

Honey Flow

→ Valve Flow coefficient (Cv) = The number of US gallons / minute of 60 deg.F water

that will flow through the valve with 1psi Pressure drop.

→ Basic equation :

→ Check for choked flow :

Pvc = FF x Pv

(Pv = Fluid Vapor Pressure, FF = Critical Pressure Ratio , FF = 0.96-0.28 Pv/Pc )

→ Compensate for the swage factors / Consider viscosity

Liquid sizing

PChoked = FL2 (P1-Pvc)

→ It is very vital to understand the Bernoulli's principle - to understand valve sizing- to understand Cavitation - to understand flashing

→ v is the the fluid flow velocity→ g is the acceleration due to gravity→ z is the elevation→ p is the pressure→ ρ is the density of the fluid

From the above equation we could infer that if the velocity increases the pressure would decrease and vice versa

Bernoulli’s principle

------ equation1

Bernoulli’s principle / Continuity equation→ The continuity equation is

Q (flow rate) = A1 X V1 = A2 X V2 (area X velocity) ------ equation2

By applying equations 1 & 2 in a control valve and taking into consideration the pressure loss due to flow turbulence we can infer the following…

area-A1

Pressure- P1

velocity -V1

area-A2

Pressure- P2

velocity -V2

area-Avc

Pressure- Pvc

velocity –Vvc

P1 Inlet Pressure

P2 Outlet Pressure

V2 Outlet VelocityV1 Inlet Velocity

PVc

VVc

Valve inlet Valve outlet

Pv Vapour Pressure

Single Stage Letdown

Liquid service – pressure recovery curve

P1

P2

V2V1

PVc

VVc

Outlet Velocity

Outlet Pressure

Valve inlet Valve outlet

Pv Vapour Pressure

Inlet Velocity

Inlet Pressure

Cavitating service

P1

P2

V2V1

PVc

VVc

Outlet Velocity

Outlet Pressure

Valve inlet Valve outlet

Pv Vapour Pressure

Inlet Velocity

Inlet Pressure

PVc

Flashing service

→ Cavitation & Flashing are liquid phenomena

→ There is bubble formation when the static pressure of the fluid falls below the vapour pressure.

→The bubbles formed collapse when the static pressure increases above the vapour pressure. This is cavitation.

→The bubbles formed are carried downstream if the outlet pressure is less than vapour pressure. This phenomena is flashing.

→Both Cavitation and Flashing can cause excessive erosion on Trim parts, body and downstream pipe.

→Cavitation can be fully eliminated by offering suitable trim but not flashing.

→Low recovery valves are less prone for cavitation

Cavitation and Flashing

Pressure

P1

P2

V2V1

VelocityPVc

FlashpointPv

VVc

VVc

VVc

PVc

PVc

3 cage pressure & velocity profile

Cavitation

Pressure & velocity profile in a 3 cage trim

1 cage pressure profile

Outer Cage

Mid Cage

Inner Cage

Valve Plug

Flow

P1

Pvc(P2)

Pvc(P2)

P?

P?

Multiple stage letdown

FLOW Pvc(P2)

P1

P?

P?

Valve Inlet P1?

The Theory3 - Cages

V trimexit?

Multiple stage letdown

P1

V1 V2

P2

Inlet Outlet

VALVE

Pressure

Velocity

Flashpoint

Pv

InletPressure

Inlet Velocity

Outlet Velocity

Outlet Pressure

The TheoryDisk Stack

Multiple stage letdown

Multiple stage letdown

Pressure

P1

P2

V2V1

Velocity

FlashpointPVc

Flashing

VVc

InletPressure

InletVelocity

Vc =Vena Contracta

Outlet Velocity

Outlet Pressure

Inlet Outlet

Valve

Pv Vapour Pressure

Single StageLetdown

Flashing service – Pressure & velocity profile

Flow over + 1CC Satellite FC Angle valveSeat exit diffuser / baffles By choice of material Liner for the body Can also use 2cage / 3 cage or stack designEccentric rotary plug valve

Flashing service solution

Flo

w

Choked Flow

∆p

∆p allowable

∆p actual

Actual flow

Flow estimated with ∆p actual

Chocked flow

Cv = W

27.3 Fp Y (X P1g1)

W = Mass Flowrate (kg/hr)

Fp = Piping Geometry Factor

Y = Expansion Factor

X = Pressure Drop Ratio

P1 = Upstream Pressure (bar A)

g1 = Specific Weight (kg/m3)

Valve sizing coefficient (Cv) - Gas

Control valve noise

Noise is a random mixture of sound waves of varying amplitude and frequency

Rapid expansion of gases across the seat and turbulence is the primary source of the control valve noise.

Other sources of noise are …

Cavitation / Flashing in liquids, Resonance, Plug instability etc.

60

70

80

90

100

110

120

010

016

025

040

0

630H

z 11.

62.

5 46.

3 10

15KHz

LpA

in d

B

Frequency

Typical spectrum of control valve noise

dB

–“A

wei

ghti

ng

corr

ecti

on

Frequency in Hertz

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

20 50 100 200 500 1000 2000 5,000 10,000

Audible control valve noise

Source treatments

→Shifting control valve noise from audible frequency to high frequency by flowing through numerous small holes

→Creating flow turbulence and resistance

- dividing the flow into numerous flow streams

- changing the direction of flow / flowing through a torturous path

- allowing small streams to impinge against each other and lose energy

→By controlling fluid velocities

Path treatments

→ Sound transmission from the valve & pipe line to surrounding environment can be reduced by heavy pipe wall / insulation etc.

→ Proving in-line diffusers / baffle plates / silencers

→Proving vent silencers

Noise reduction techniques

Disk Stack Trim Designs

Noise control – source treatments

Multiple cage Trim Design

Noise control – path treatments

Vent silencer

Inline silencer

Diffuser

60

70

80

90

100

110

120

0 1 2 3 4 5 6 7 8

Allo

wab

le (

dB

A)

Permissible Exposure (Hours in a Day)

Duration of exposure Vs allowable noise

Control Valve Datasheet

Specification sheet

Windows Platform

Download via www.servernglocon.com

Sizing program

IEC 60534 - 8.3 Control valve aerodynamic noise predictionIEC 60534 - 8.4 Control valve hydrodynamic noise predictionANSI/ISA-75.01 Flow equations for sizing control valvesANSI/ISA-75.02 Control valve capacity test procedureANSI/ISA - 75.08.01 Face to Face Dimensions for Integral Flanged GlobeANSI/ISA - S75.19 Hydrostatic Testing of control valvesAPI Specification 6D Petroleum and Natural Gas Industries Pipeline ValvesAPI STANDARD 598 Valve Inspection and TestingASME B 16.34 Valves - Flanged Threaded , and Welding EndASME B16.10 Face to Face and End to End Dimensions of ValvesASME B16.20 Metallic Gaskets for Pipe FlangesASME B16.47 Larger Diameter Steel Flanges (NPS 26 Through NPS 60)ASME B16.5 Pipe Flanges and flanged fittings (NPS 1/2 Through NPS 24)ASME B16.9 Factory - Made Wrought Steel Butt welding FittingsASME QME-1 Qualification of Active Mechanical Equipment Used in Nuclear Power PlantBS 6364 Specification for Valves for cryogenic serviceISO 15848 Part 1 & 2 Fugitive Emmission - Proto Type Test / Production testMSS SP-55 Quality standard for Steel Castings for valvesNACE MR0175/ISO 15156 General Principles for selection of cracking-resistant materials ASME PBVC - Section II Part D Material PropertiesASME PBVC Section V NDE ASME PBVC Section VIII Pressure Vessels – Divisions 1 and 2ASME PBVC Section IX Welding & Brazing

Standards

Actuator Sizing

Noise Calculations

Velocity Calculations

Warning Alerts

Detailed Specification Build

Sizing program

SG Mobile App Sizing OutputsSizing Inputs

Severn Glocon Android Mobile App

CONTROLLER

P

PR XTR

4- 20 mA

Pneumatic

P1=20 bar.g P2=10 bar.g

Supply air

Simple control loop

Positioner:

Valve positioner delivers pressurized

air to the valve actuator so that the

position of the valve stem or shaft

corresponds to the set point from the

control system. Valve positioners are

typically pneumatic or analog I/P or

smart.

Positioner require position feedback

from the valve stem or shaft and

deliver pneumatic pressure to the

actuator to open and close the valve

Positioner

Need for positioner:

• More accurate control: Since valve positioners know the valve’s exact position, they

provide more precise control.

• Faster control: Positioners help control valves respond faster to changes in the process

variable, minimizing the amount of time the system is operating above or below the set

point.

• Consistent valve position: A positioner is one solution to help stabilize valve position.

• More flexible configurations and functions:

• Minimize the effects of friction. Friction in the valve stem packing contributes to both

hysteresis and dead band, which reduce productivity

Positioner Need

Types

• Pneumatic devices send and receive pneumatic signals. They are intrinsically safe and can

provide a large amount of force to close a valve.

• Electro-pneumatic valve positioners convert current control signals to equivalent

pneumatic signals. They use a mixture of electricity and air.

• Digital or “smart” devices use a microprocessor to position the valve actuator and monitor

and record data. They are very accurate, use less air than analogue positioners, and allow

for online digital diagnostics

Type of Positioner

Electro-pneumatic positioner Digital or smart valve controllerPneumatic positioner

APS Actuator Positioning Sensor

SPS Spool Positioning Sensor

I2PCurrent to Pressure convertor

LUI Local User Interface

Ps,P1,P2 Pressure sensors

µC Microcontroller

S Supply pressure

Schematic of Digital Positioner

Actuator

Major position feed back sensor

Spool position feed back sensor

Primary controller

Secondary controller

SpoolI2P+-

+-

ActuatorSet point

SpoolSet point

Positioner Control Structure

What are the consequences of getting the Technical selection process

Wrong?

Control Valve (Trim) Erosion Damage

#1 Damage to Seat Ring

#3 Damage to Inner Cage

#2 Damage to Seat Ring /Cage interface

#5 Damage toInner Cage

#6 Damage to Plug

#4 Damage to Seat Diffuser

Control Valve (Trim) Cavitation Damage

#1 Damage to Seat Ring

#2 Damage to Cage /Seat Interface

#3 Damage toIntermediate Cage

#4 Damage to Inner Cage

#5 Damage to Plug

#6 Damage to Seat Ring

Choke Valve (Trim) Erosion Damage

#1- Erosion to Hardened Flow Sleeve

#3 - Erosion toStellite Cage

#2 - Erosion to Carbide Plug & Flow Sleeve

#4 - Erosion to CarbidePlug / Sleeve

#5 - Erosion to CarbideDisk Stack assembly

#6 - Erosion to CarbidePlug profile

Fatigue / Vibration Failure

#1 - Fracture failureof Carbide

Plug / Sleeve

#2 - Partial detachment of Carbide Plug nose

#5 - Fatigue failure of Plug Stem

#4 - Fatigue failure ofPlug ‘Balance Seal’

Ring#3 - Total detachment

of Carbide Plug / Sleeve

Valve SelectionValve Applications Required Specification

Compressor Anti-surge valves Quick Opening within the range of 0.5 to 2 seconds

Pump Recycle Valves Handle very High Pressure Drop & Cavitation Service

Separator Level control Valve Linear Flow characteristics, Erosive Process fluid, Hardened Trim Materials

Gas to Flare Valves High Aero Dynamic Noise, Source Treatment + Path Treatment

Seawater overboard dump valve

Very High Pressure drop and possibility of vacuum in downstream of valve

Pipeline Booster station valves Electro-Hydraulic Actuated Valves

Gaseous Oxygen Valves High Pressure Gaseous Oxygen, Fire retardant material

Cryogenic Valves LN, LOX, LNG Process fluids. Valves with extended bonnet design to avoid cold leakage.

Letdown valves Flashing Service & Angle Valves

Mixing & Diverting 3-Way Valves

Valve SelectionValve Applications Valve Type

High Cv & Low dP Butterfly Valves

High dP Globe Valves

Pulp & Slurry Applications Ball Valves & Plug Valves

Low Pressure drop Valves Globe & Top Guided Valves

Suspended Particles Globe & Top Guided Valves

High Pressure Drop Valves Globe & Cage guided Valves

Cavitation Service Globe & Multistage Trim Design

Aero Dynamic Noise service Globe & Multistage Trim Design

High Outlet Velocity Larger Globe valve with reduced Trim Size

High Rangeability in Flow Globe with Eq% or customized characteristics. Sometime two valves in split range to be offered

Constant Pressure drop Globe Valve with Linear Flow Characteristics

Liquid Level control Globe Valve with Linear Flow Characteristics

Globe ValvesEccentric

PlugBall Butterfly

GeneralService

HighPerformance

SevereService

Valve type vs Application category

Thank You