4 Control Valve

8/3/2019 4 Control Valve

1/91

CONTROL VALVE APPLICATION


2/91

What is a Control Valve ?

Control Valves are one type of the final control element

in a open or closed Control Loops.


3/91

Common Terms used in Control Valve

1. Flow Coefficient (Cv or Kv)

Cv is defined as Quantity of water in US GPM, at 60 Deg F, that will flow thru the valve

At specified travel with pressure drop of 1 psig.

Cv is the term used in US.

Kv is defined as Quantity of water in m3/Hr, at 5 Deg C and 40 Deg C, that will flow thru

the valve at specified travel with pressure drop of 1 barg.

Kv is the term used in Europe.

Relationship between Cv and Kv is :

Kv = 0.856 Cv


4/91


2. Dead Band

The range thru which an output signal can be varied, upon reversal of signal, without initiating

observable change in output.

For the valve assembly, controller output is input to valve assembly and process variable is

Output.

Dead band is expressed as percentage of input band.

3. Hysterisis

Maximum difference in output value for any single input value during a calibration cycle,

excluding errors due to dead band


5/91


4. Inherent Flow Characteristics

The relationship between Flow Coefficient and the closure member (disk) travel as it is moved

from closed position to rated valve travel with constant pressure drop across the valve.


6/91


4. Inherent Flow Characteristics

Linear Characteristics : Travel is linearly proportional to capacity and therefore the theoretical

Gain is constant at all loads.

Equal Percentage Characteristics : A unit change in lift will result in a change in flow rate, which is

Is a fixed percentage of the flow rate at that lift. E.g. each %age increase in lift will increase the

previous flow rate by about 3%.

Therefore, theoretical gain of equal percentage valves is directly proportional to flow rate and

increases as the flow rate increases

On logarithmic chart, the equal percentage characteristics correspond to a straight line having a

slope that corresponds to its fixed percentage.

Quick Opening Characteristics : The gain decreases with increase in flow rate.


7/91


5. Installed Flow Characteristics

When the valves are installed in process, the differential pressure is no longer constant, it varies

With flow.

The differential pressure drops as the flow increases, Valve gain also drops, this tends to shift the

Characteristics of the equal percentage valve to linear and installed linear valve to quick opening.

6. Rangeability

Ratio between maximum and minimum controllable flow thru the valve.

OR

Ratio of the Cv required at maximum flow (and minimum pressure drop) and the Cv required

at minimum flow (and maximum pressure drop).


8/91


7. Fast Process

Controlled process is considered fast if its period of oscillation is less than three times that of

positioned valve.

If the period of oscillation is three times or more that of positioned valve, then the process is

slow process.


9/91


8. Cavitation

7. Flashing

The high flow velocity at the vena contracta of the valve is reached by obtaining its energy

from the pressure energy of the stream. This causes localized pressure reduction, if it drops

below the fluids vapour pressure, results in temporary vaporization. Downstream of the vena

contracta the pressure recovers in the valve causes the temporary voids to collapse. This

procedure is called CAVITATION.

Cavitation generate extremely high pressure shock waves in the non-compressible stream.When these waves strike the solid metal surface of the valve or downstream piping, it may cause

damage to valve internals and piping. Cavitation is usually coupled with vibration and a sound

like rock fragments or gravel flowing through the valve.

Flashing begins in the same manner as Cavitation. In case of Flashing pressure downstreamremains at or below vapour pressure. This causes vapour to stay in vapour phase as fluid

leaves the valve and enters the downstream piping. The specific volume increases as liquid

changes to vapour, which in turn causes an increase in the fluid velocity. If enough vapour

is formed, the resulting high valve outlet or pipe velocities can erode metal.


10/91

Control Valve

Body

Bonnet

Actuator

Positioner


11/91

Different Components of Control Valves

Valve Body


12/91

Trim

Trim consists of internal parts contained within the body and wetted by the process fluid

The main components are Plug, Stem, Seat Rings, cage, seat retainers, spacers, guidebushing etc.

Trim parts create flow restriction or throttling action and is responsible for most of the pressureloss dissipated in the valve

Trim design serves to determine the inherent flow characteristics of the valve


13/91

Quiz No. 1

Define Flow Coefficient Cv of a valve.


14/91

Different types of Valves

1) Globe Valves

1) Ball Valves

2) Butterfly Valves

2) Gate Valves

3) Plug Valves

3) Saunders Diaphragm Valves

Linear Valves

Rotary Valves


15/91

Globe Valves

Type

Single Ported

withCharacteri-zed Plug

(A)

Single Ported

CageGuided

(B)

Single Ported

Split Body(C)

Double

Ported, top-bottom

guided orskirt guided

plug (D)

Angle

(E)

Y- Type

(F)

Three Way

(G)

Eccentric

Plug, RotaryGlobe

(H)

Sizes

Typically NPS to 16 (DN

15 to DN 400): Availableupto NPS 48(DN 1200)




15 to DN 250)


15 to DN 400)



Typically NPS1 to 16 (DN

25 to DN 400)



Typically NPS1 to 12 (DN

25 to DN 300)

Design Pr.Rating

Typically all ratings are available from ANSI Class 150 (PN 20) to Class 2500 (PN 420) with special designs uptoClass 4500 ; Types C & H are limited to ANSI Class 600 (PN 100) ; DN = Nominal Diameter in mm, PN =Pressure, Nominal in Bar

MaximumPressure

Drop

Upto maximum allowed by body pressure rating depending on limitations of actuator size and trim design andmaterials

DesignTemperat-ure

Depends on material properties. Generally from -20 to 1200 Deg F (-29 to 538 Deg C). Cryogenic design fortemperature down to 423 Deg F )-253 Deg C). Special Valves have been designed for operation upto 1600Deg F (871 Deg C)


16/91

Globe Valves

Type

Single Ported

withCharacteri-zed Plug

(A)

Single Ported

CageGuided

(B)

Single Ported

Split Body(C)

Double

Ported, top-bottom

guided orskirt guided

plug (D)

Angle

(E)

Y- Type

(F)

Three Way

(G)

Eccentric

Plug, RotaryGlobe

(H)

Material OfConstruct-ion

Body and Bonnet Materials : Most cast and forged grades of carbon steel, low alloy steel, stainless steel, alloy20, duplex stainless steel, nickel and nickel alloy, bronze, titanium and zirconium. Fluropolymer lining also

available for corrosion protection.Trim Materials : Generally available in stainless steel, nickel, nickel alloys, bronze, titanium and zirconium. Hardfacing is available for erosive application.

Seal and soft seat materials : FEB, PFA, PTFE, PCTFE, ETFE, EPT / EPDM, Fluoroelastomers, Nitrile,Polyethylene, Polyurethane, UHMWPE, compressed graphite, and soft metals.

Leakage Metal seats in double ported design are Class II, while in single seated design they can meet Class IV and ClassV. Soft seats in double ported designs can meet ANSI Class IV and V, while in single seated globe valves theycan give Class VI performance

Character-istics

Available in all type of characteristics

Rangebility Based on ISA-75.11 or IEC 60534-2-4, it seldom exceeds 30 : 1. Special design can achieve 50 : 1 or higher byincreasing precision of control at small valve openings.

Capacity Cv = 10 d2 to 15 d2with single ported design closer to the bottom of the range and with double ported and

eccentric disc designs closer to the top of the range


17/91

Globe Valves

Advantages :

1. Simplicity of pneumatic actuator designs

2. Availability of a wide range of valve characteristics

3. Relatively low likelihood of cavitation and noise

4. Availability of wide variety of specialized designs for corrosive, abrasive and high temperature or

high pressure application

5. Relatively small amount of dead band and hysteresis


18/91

Globe Valves

Disadvantages :

1. Higher cost per unit of Cv

2. Greater weight and dimensional envelope relative to their flow capacity


19/91

Globe Valves

Body Forms :

1. Double Ported Valves

2. Single Seated Valves

3. Cage Valves

4. Pressure Balance Valves

5. Split Body Valves

6. Angle Valves

7. Y Type Valves

8. Eccentric Plug Rotary Globe Type

9. Three Way Valves


20/91

Globe Valves

1. Double Ported Valves

First Globe Valve developed during the early 20th century

Larger and heavier than single seated valves

Shut off is poor because it is not practical to have both plugs in

tight contact with seats at the same time

These are semi balanced i.e. the hydrostatic forces acting on the

upper plug partially cancels out the forces acting on the lower plug

Less actuator force required, hence smaller actuator can be used.


21/91

Globe Valves

2. Single Seated Valves

Most widely used Globe Valve Body Pattern

Available in wide variety configuration, including special purpose trims

Have good seating shut off capability

Less subject to vibration due to reduced plug mass

Easy to maintain


22/91

Globe Valves

Single Seated and Double Seated Valves has three general types of seat constructions :

1) Floating Seat Ring

2) Screwed Seat Ring

3) Integral Seat Ring

Seat ring sits in machined bore in the body with a gasket to seal the joint between the body

and seat ring. It must be retained in the body by cage or seat retainer to maintain gasket

tightness and concentricity with the plug. This can be replaced

Seat ring is threaded with a special tool ; a gasket may or may not be required. A separate

seat retainer is not required. This can be replaced.

The seating surface is machined directly into the body; This cannot be replaced.


23/91

Globe Valves

Single Seated and Double Ported valves has four different types of valve plug guides:

1) Post Guided

2) Top and Bottom Guided

3) Stem Guided

Provide more stream lined flow less subject to fouling in dirty service

Has similar limitation as Double Seated Valves

4) Cage Guided

Discussed under Cage Valves

Provide more stream lined flow less subject to fouling in dirty service Minimizes stagnant fluid cavities Better when dealing with fluids containing solids,

sticky or viscous fluids, or highly corrosive fluids.

Stem Guided

Post Guided

Top & Bottom Guided


24/91

Globe Valves

3. Cage Valves

It has rugged design

With proper selection of trim type and materials, these valve provide

relatively trouble free service for extended time period.

These are of two basic design configurations :

1) One type uses cage solely as a seat retainer to clamp a floating

seat ring into the valve body. This design is usually stem guided

or post guided. The valve plug is characterized. Cage does not

guide or control flow.

2) Second type uses cage to guide plug and cage opening are

shaped to provide the desired flow characteristic. These are

called Cage Guided Valves.


25/91

Globe Valves

4. Pressure Balanced Valves

Provide better control for high pressure drops applications

Reduces the magnitude of unbalanced plug forces

Reduces the Actuator Size used

It degrades the valve shut-off capability to some degree

In these valves there is provision for a pressure path from the

upstream pressure side of the plug to the area above the plug,

allowing upstream pressure on the upper plug area, hence

balancing the plug.


26/91

Globe Valves

5. Split Body Type Valve

Designed for hard to handle services involving slurries, gummy liquid

corrosive service.

Seat ring is clamped between the body halves, and the body is easily

disassembled for maintenance.

Available with limited trim design.

Body flange is more prone for leakage.


27/91

Globe Valves

6. Angle Valves

Used in a flow to close direction for high pressure drop services

Tungsten carbide or ceramic can be selected to resist erosion due to

higher trim velocities.

Venturi style outlet has high pressure recovery and low vena contracta

pressures, which makes the trim and down stream piping highly

susceptible to cavitation on liquid service, even with moderate

pressure drops. In order to avoid damage of piping, these valves

are installed directly on vessels or with larger downstream pipe.


28/91

Globe Valves

7. Y-Type Valves

These are used where good drainage of body passage is required

or high flow capacity is required, such as in controlling molten metals

or polymers, cryogenic fluids and liquid slurries.

These valves can be installed in horizontal, vertical or angled piping.


29/91

Globe Valves

8. Eccentric Plug Rotary Globe Valve

Its design and performance combine features of conventional rotary

valves with conventional globe valves.

Compared to most rotary valves, the valves has the advantage of lower

torque requirement

The plug design uses the offset center to obtain contact at closure without

rubbing on the seat, like ball valves

It is capable of substantial seat contact loading for tight shut off

approaching that of conventional globe valves.

Flow characteristics approaches linear

Flow capacity is between double ported globe and a high performance,double offset butterfly valve.

Less likely to cavitate, as pressure recovery in the body is moderate.


30/91

Globe Valves

9. Three Way Valves

Specialized double seated globe valve

Available in two types : One is for mixing and other for diverting service

These valves are not used for high pressure drop service.

Has similar limitations as of double seated valves


31/91

Globe Valves

Valve Connections :

Flanged End

Screwed End

Welded End


32/91

Globe Valves

Valve Material of Construction:

Piping specification defines the Material of Construction


33/91

Ball Valves

Type

Conventional

(A)

Characterized

(D)

Cage

(C)

Sizes &Design

Pressure

to 42 (12 to 1180 mm) inANSI Class 150 to 12 (300mm) in ANSI Class 2500

1 to 24 (25 to 600 mm)in ANSI Class 150; to 16(400 mm) in ANSI Class300; to 12 (300 mm) inANSI Class 600

to 14 ( 6 to 350 mm), Up toANSI Class 2500

Design Temp.Rating

Varies with size and material,typically from -250 to 600 DegF (-155 to 315 Deg C) withspecial designs available from-300 to 1800 Deg F (-185 to1020 Deg C)

From -50 to 300 Deg F (-45 to 150 Deg C);special units availablefrom cryogenic to 1000Deg F (540 Deg C)

From 425 Deg F to 1800Deg F ( -255 to 980 Deg C)

Rangability Generally claimed to be about 50 : 1

Characteristics

Between Equal Percentage and Linear

Capacity Std. Ball : Cv = 30 d2 to Cv =

45 d2

Full Bore Ball : Cv = 35 d2

to Cv = 100 d2

Cv = 24 d2 to Cv = 30 d

2 Cv = 20 d2


34/91

Globe Valves

Type

Conventional

(A)

Charecterized

(B)

Cage

(C)

Material OfConstruct-ion

Body : Cast or bar stock brass or bronze, carbon steel , stainless steel, ductile iron, aluminium, monel titanium,Hastelloy C, plastics, glass; also hafnium free sirconium ( for nuclear applications) and ceramic for abrasives.

Ball : forged naval bronze, carbon steel ( also plated), stainless steel, plastics, glass, ceramics, alloy 20, Monel,Hastelloy C, aluminum, titanium.

Seats : Teflon, Kel-F (both tetrafluoroethylene), Delrin, buna-N, neoprene, perbunan, Hypalon, natural rubber,graphite.

Leakage Metal seats : ANSI IV to VI

Composition seats : ANSI V or better


35/91

Ball Valves

Advantages :

1. Lower Cost

2. Lower weight

3. Higher flow capacity (two to three times that of globe valve)

4. Tight shut off

5. Fire Safe Design

6. Low stem Leakage (make it easier to meet governmental regulator requirements from OSHA and

EPA in the US and the Pressure Equipment directive (PED) in the EEC.


36/91

Ball Valves

Disadvantages :

1. Valves high capacity results in either using oversized valves or installing small valves in large

pipes. This means a substantial waste of pumping energy caused by the reducer pressure

drop.

2. These valves has the characteristic of a high pressure recovery results in low vena contracta

pressure. This in turn increases probability of cavitation and noise.

3. In operating rotary valves, the linear movement of cylinder or spring / diaphragm type actuatorsmust be converted by linkages, which introduces hysteresis and dead band.

4. A non linear relationship exists between actuator movement and the resulting rotation. These

considerations make the use of positioners essential, which on fast processes can lower the

quality of control.

5. The torque charecteristics of these vavles are also highly non linear and because of the high

break torque requirement, the actuator is usually oversized for the operation in the throttlingrange


37/91

Ball Valves

Types of Ball Valves

1. Conventional Ball Valves

2. Characterized Ball Valves

3. Cage Type Ball Valves


38/91

Ball Valves

1. Conventional Ball Valves

Available as Full Bore or Reduced Bore and Trunnion mounted

or floating

Requires quarter turn (90o) to fully uncover or fully cover an

opening

Valve design is standard, they can be used with or with out

actuator, hence third party actuator can be used.

Available is configurations such as two-way, three-way or split body.

Available with metal seat, soft seat or combination of metal &

soft seat (Fire safe design)

Flow charectaristics of the ball valve approximate those of an equal

percentage plug


39/91

Ball Valves

2. Characterized Ball Valves

Available as V-Notched, U-Notched, parabolic design

The ball is modified so that only a portion of it is used. The edge

of partial ball can be notched or contoured or shaped to obtain

the desired valve characteristics

Limitation is, mechanically the notched partial ball can bend under

pressure and thus introducing movement into the shaft seals ordistort the shaft.

The characteristics of the notch and parabolic ball valve is near

to equal percentage. If the characteristics were evaluated using

compressible fluids at critical velocities, these curves would be

flatter, closer to linear.


40/91

Ball Valves

3. Ball and Cage Valves

Under this design the ball is positioned by cage, in relation to

a seat ring and discharge port.

The valve consists of a venturi ported body, two seat rings, a

ball that causes closure, a cage that positions the ball, and a

stem that positions the cage.

Seat rings are installed in both inlet and discharge, but only

the discharge ring is active.

The body can be reversed for utilization of the spare ring.

The flow coefficients (Cv) are consistently high. Rangability 50 : 1.

Tight shut off occurs over a long operating life due to the continual

rotation of the ball at each operation which offer a new seating

surface each time it is closed. Low opening force is required, hence the size of actuator

required is relatively small.


41/91

Ball Valves

3. Ball and Cage Valves

Minimizes cavitation effects because flow tends to follow the curve

of the ball, thus reducing turbulence. The cavitation tends to occur

in the venturi passage, not at the seat, allowing use of hardened

or replaceable throats.

The expanding venturi discharge assists in handling flashing liquids.


42/91

Butterfly Valves

TypeGeneral Purpose, aligned shaft High performance, offset shaft

Sizes 2 to 48 ( 51 mm to 1.22 m) are typical, but unitshave been made in sizes from 0.75 to 200 (19mmto 5 m)

4 to 16 ( 0.1 to 0.4 m) are common, but units are availablefrom 2 to 80 ( 50mm to 2 m)

DesignPressureRating

Most arfe available through ANSI Class 300 ratingsand for up to 200 psid ( 1.4 MPa) pressure drop.Special units have been designed for up to 6000PSIG design pressure

For installation purposes most are available through ANSI600 ratings and for up to 720 psid ( 5 MPa) pressure drop

Design Temp.Rating

-450 to 1000 Deg F ( -268 to 538 Deg C). Specialrefractory lined units have been made for up to2200 Deg F ( 1204 Deg C)

-320 to 450 Deg F ( -196 to 232 Deg C) for Teflon seatedvalves; 1200 Deg F (649 Deg C) for metal seated ones.Special units are available up to 1700 Deg F (927 Deg C)

Body / DiscMaterial

Iron, ductile iron, carbon or alloy steels, stainlesssteel (302 316), aluminum bronse, Alloy 20,

Monel, Hastelloy C, titanium, chrome plating, nickelplating, kynar, Nordel, Viton, EPDM, Buna-N,neoprene elastomer lining, TFE encapsulation

Steel, 316 SS, alloy steel, Durimet 20, aluminum bronze,Alloy 20, Monel, Hastelloy C, titanium, tungstem titanium

carbide (TTC) coating

Seat Material TFE, Kel-F, EPT, Polyethylene, PTFE with titanium, Inconel, or 316 stainless steel or other metals.


43/91

Globe Valves

TypeGeneral Purpose, aligned shaft High Performance, offset (eccentric) shaft

Characteristics

Linear to quick opening

Rangeability Generally claimed as 50 : 1

Leakage Unlined, 2 to 5%, lined, ANSI V Metal seat, ANSI IV; soft (toggle) seat, ANSI VI

Capacity With 60 Deg rotation, Cv = (17 to 20) d2. Typical forthrottling with 75o rotation, Cv = ( 25 to 30) d2; with 90orotation , Cv = ( 35 to 40) d2

Cv = (20 to 25) d2

Specialfeature

Reduced torque disc designs, fire tested seals, reduced noise disc, special disc seal designs


44/91

Butterfly Valves

Advantages :

1. Lower Cost

2. Lower weight

3. Higher flow capacity (two to three times that of globe valve)

4. Tight shut off

5. Fire Safe Design

6. Low stem Leakage (make it easier to meet governmental regulator requirements from OSHA

and EPA in the US and the Pressure Equipment directive (PED) in the EEC.


45/91

Butterfly Valves

Conventional ButterFly Valve :

One of the oldest type of valves

Dictionary defines the butterfly valve as a Damper or

throttle valve in a pipe consisting of a disc turning on a

diametral axis

Butterfly valve operation involves only rotating the vane,

disc, louver, or flapper by means of the shaft to which it isfastened to either manually or using actuator.

Butterfly valve are available in swing through design

Swing through designs have a symmetrical disc and

shaft design with a certain clearance required between

disc and body. The body is usually the solid ring type,

which is mounted between pipe flanges. It can be eitherthe wafer type or the single flange lug pattern, where flange

bolting goes thru body.


46/91

Butterfly Valves

Conventional ButterFly Valve :

The thickness of the disc and hub along with the diameter

of the shaft is a function of the maximum pressure drop

and torque required.

Swing thru designs are available with a variety of disc

shapes that serves to reduce the required torque and to

increase throttling angle range.

Swing thru designs are limited to a maximum throttling

of angle about 70 Deg open for the standard pattern and

60 Deg for heavy pattern due to their larger diameter shafts.


47/91

Butterfly Valves

High Performance ButterFly Valve :

The features include tight shut off, reduced operating

torque, excellent throttling capabilities, able to operate

with relatively high pressure drops, compact size, reduced

weight and lower cost.

There are many designs all have characteristics of

separable seat ring contained in the body and an

eccentric cammed disc.

The camming action enables the disc to back out of and

into the seat before and after the disc rotation when

throttling. This is accomplished by having the shaft offset

from both the centerlines of the disc and the valve body.

Tight shutoff is accomplished by two methods, one byproviding valve with an elestomer or plastic liner, in this

configuration the disc is also encapsulated in some cases

and the other is with cammed disc and a separate seal

ring clamped into the body.


48/91

Butterfly Valves

High Performance ButterFly Valve :

These valves are available with soft seal achieving ANSI

Class VI shut off and for high temp application metal

seat achieving ANSI Class IV. Some achieve ANSI

Class V also.

These are available in fire safe design i.e. soft seat

backed up with metal seat.

Various disc designs are available which improves the

noise reduction. Cambered and fishtail type disc

generated lesser noise than convention swing thru

type disc. Fluted type disc reduces the noise by another

10 dB on a weighted scale.


49/91

Plug Valves

Type V-ported, three way, Four Way, Five way, Fire Sealed

Sizes to 36 (12.5 to 0.96m)

DesignPressureRating

Typically from ANSI Class 125 to ANSI Class 300 ratings and up to 720 psig ( 5 MPa) pressure, with specialunits available for ANSI Class 2500. The retractable seat design is suited for 10,000 psig (69 MPa) service

Design Temp.Rating

Typically from -100 to 400 Deg F ( - 73 to 204 Deg C) with special units available from 250 to 600 Deg F ( -157 to315 Deg C)

Material ofConstruction

Iron, forged and alloy steel, chrome plating, 302 thrugh 316 SS, Alloy 20, Ni- resist, Monel, nickel, Hastelloy Band C, and zirconium, plug rubber or plastic, including PTFE linings

Characteristics

Equal Percentage, Modified parabolic, Modified linear

Capacity Cv = (25 to 35) d2

Rangability Generally 20 : 1

Leakage Metal seats ANSI Class IV, composition seats ANSI Class V


50/91

Plug Valves

6. Suited for corrosive, viscous, dirty fibrous or slurry services

7. Not recommended for applications where cavitation or flashing is expected

1. Lower Cost

2. Lower weight

3. Higher flow capacity (two to three times that of globe valve), high flow at low pressure drop

4. Tight shut off

5. Fire Safe Design

8. Low stem Leakage (make it easier to meet governmental regulator requirements from OSHA and

EPA in the US and the Pressure Equipment directive (PED) in the EEC.

9. The design using characterized or eccentric rotating plugs provide good control performance

and a self cleaning flow pattern, which also reduces noise and cavitation

10. These provide superior stem sealing capability, plug valves are also suited for such corrosive

applications as chlorine, phosgene, hydrofluoric acid, and hydrochloric acid. These are widely

used on lethal and toxic services and can be made fire safe by the use of grafoil packing and

meet the external leakage requirement limits of API 607


51/91

Plug Valves

11. These valves afford quick opening or closing with tight, leak proof closures under conditions ranging

from vacuum to pressures as high as 10,000 psig (69 MPa).

12. Plug valves are also designed with various characterized and Y-ported or diamond design, can

be used for throttling, while others, like the multiport, are used for diverting and bypass applications.

13. Plug valves are used on gas, liquid and non abrasive slurry services.

14. Lubricated plug valves can also be used for abrasive slurries, and eccentric plugs are also used

on application involving sticky fluids.

15. Plug valves are also used for applications requiring the contamination free handling of foodsand pharmaceuticals.

16. Suitable for low flow control, Flow diversion, High or low temperature applications, vibration free

operation, Throttling control, only with eccentric and V ported characterized designs.

17. The conventional plug valves are generally undesirable for the following types of applications :

- Flow modulation or continuous, exact flow throttling

- Maintenance free operation (Occasional lubrication is usually required and plugs may wear)


52/91

Plug Valves


53/91

Saunders Diaphragm Valves

Type Weir, full-bore, straight through, dual - range

Application Slurries, corrosive fluids at low pressure drops

Sizes Standard units from to 12 (12 to 300 mm); special units upto 20 ( 500mm)

MaxOperatingPressure

In sizes up to 4 (100mm), 150 psig (10.3 bar); 6 (150mm), 125 psig (8.6 bar), 8 ( 200mm), 100 psig (6.9 bar)and 10 or 12 (250 or 300mm), 65 psig ( 4.5 bar)

VacuumLimits

Mechanical damage can occur when opening valve against process vacuum

TemperatureLimits

With most elastomer diaphragms from 10 to 15 Deg F (-12 to 65 Deg C); with PTFE diaphragm from -30 to 350Deg F ( - 34 to 175 Deg C)


Body materials : Iron, ductile iron, steel, 302 to 316 SS, Alloy 20, bronze, Monel, Hastelloy C, aluminum,titanium, graphite, plastic such as PTFE lining or solid plastics

Diaphragm materials : Teflon, Buna N, neoprene, hypalon

Characteristics

Linear and quick opening

Capacity Cv = 20 d2

Rangability About 10 : 1

Leakage ANSI Class IV and V


54/91

Saunders Diaphragm Valves

1. Lower Cost

3. Suitability for corrosive, dirty, viscous or slurry services

2. Tight shut off

Advantages :

Dis - Advantages :

1. Limited in their temperature (high and low) and pressure (high) ratings

2. Not suited for cavitating or flashing services


55/91

Conventional Saunders Diaphragm Valves

It utilises both diaphragm and weir for controlling the flow


56/91

Straight Through Saunders Diaphragm Valves

It has longer stroke length

Increased flexure requirement tends to shorten the life

of the diaphragm

Straight through design has smooth, self draining,

straight through flow pattern makes it applicable

to handle materials, such as slurry.

Flow characteristic of the straight through design

is more nearly linear than those of the conventional

Saunders valves


57/91

Full Bore Saunders Diaphragm Valves

The body of a full bore of a full bore Saunders valve is

modified to provide a special shape to the weir.

The opening of the internal flow path is fully rounded at

all points, permitting ball brush cleaning.

This an important feature in the food industry, where a

smooth, easy to clean interior surface is required.


58/91

Dual Range Design Saunders Diaphragm Valves

It is operated using two compressing members, hence

improving the control capability

The type of shape during the valve opening helps prevent

clogging, it also keeps abrasion at a minimum


59/91

Sliding Gate Valves

Type Knife gate V-Insert Plate and Disc (Multi orifice) Positioned disc

Sizes On / Off

2 to 120 ( 50mm to 3 m)

Throttling

to 24 (12 to 600mm)

Throttling

to 6 ( 12 to 150mm)

Throttling

1 to 2 ( 25 to 50mm)

DesignPressure

Up to ANSI Class 150; higher with wedge withinwedge design

Upto ANSI Class 300 Upto 10,000 psig (69 MPa)

VacuumLimits

DesignTemperature

Cryogenic to 500 Deg F ( 260 Deg C) -20 to 1125 Deg F (-29 to607 Deg C)


Ductile iron, cast iron, carbon steel, 304, 316, 317stainless steel, Alloy 20, Hastelloy. For V-Insert, seatingcan be metal to metal, nylon or RTFE

Body : Ductile iron, bronze,carbon steel, stainlesssteel, aluminum, Monel

Trim : SS, which can bechrome plated for hardness

or Teflon coated forcorrossion resistance;Monel and Hastolloy arealso available


60/91

Sliding Gate Valves

Type Knife gate V-Insert Plate and Disc (Multi orifice) Positioned disc

Charecteristics

Parabolic Linear Quick Opening

Capacity Cv = 45 d2 Cv = 30 d2 Cv = 6 - 10 d2

Leakages ANSI Class I or II with metal seat; better with soft seator lining

ANSI Class IV


61/91


62/91

V-Insert Type Gate Valves

Better control characteristics than knife edge gate valve.


63/91

Positioned Sliding Disc Gate Valves

Ideal for high pressure (upto 10,000 PSIG),

Can be used for cavitating, abrasive, or erosive services

Relatively expansive

Not suitable for sludge, slurry, viscous, or fibrous services


64/91

Quiz No. 2

What are the different types of Control Valves ?


65/91

Different types of Actuators

1) Linear

1a) Spring And Diaphragm

1b) Piston

2) Rotary

2a) Cylinder with Scotch yoke

2b) Cylinder with rack and pinion

3) Electric Actuators


66/91



These are pneumatically operated, uses air supply from controller, positioner or othersources.

These are of various types : direct acting (increasing air pressure pushes down diaphragm

and extends actuator stem) ; reverse acting (increasing air pressure pushes up diaphragm

and retracts actuator stem) ; reversible (actuators that can be assembled for either direct

or reverse action) ; direct acting unit for rotary valves (increasing air pressure pushes

down on diaphragm, which may either open or close the valve, depending on orientation

of the actuator lever on the valve shaft) Net output thrust is the difference between diaphragm force and opposing spring force

Molded diaphragms provide linear performance and increased travels

Output thrust required and supply air pressure available dictate size

Disphragm actuators are simple, dependable and econoical.


67/91




68/91


1b) Piston Actuator

Piston actuators are pneumatically operated using high pressure plant air to 150 psig,it eliminates the need for supply pressure regulator.

Piston actuators are double acting type to give maximum force in both direction, or spring

return to provide fail open or fail closed operation

Various accessories can be incororated to position a double acting piston in the event of

supply pressure failure. These include pneumatic trip valves and lock up systems.

Also available are hydraulic snubbers, handwheels, and units without yoke, which can be

used to operate butterfly valves, louvers, and similar industrial equipment.


69/91


2a) Cylinder with Scotch yoke


70/91


2a) Cylinder with Rack and Pinion Type


71/91


3) Electric Actuators

Electrical Actuators uses either reversible motor,servomotor drive or stepping motors.

Reversible motor can operate both linear or rotary

valves

Servo motor drives can position valves in rosponse

to feedback signals from linear or rotary encoders

Stepping Motors are well suited for direct digital

control and pulse feedback can be provided for

accurate closed loop positioning.


72/91

Different types of Accessories used with Control Valves

1) Positioners

2) I/P (Electropneumatic) Transducers

3) Booster Relays

4) Quick Exhaust Relays

5) Relays to lock up Valve position

6) Air Sets

7) Limit Switches

8) Solenoid Valves9) Hand Wheels

10) Limit Stop


73/91


1) Positioners

These are high gain plain proportional only controller. It measures valve stem position (towithin 0.1 mm), compares that measurement to its set point ( controller output signal), and if

there is diff. corrects it.

These are available in pneumatic and electronic (intelligent).

Purpose of positioner is to guarantee that, the valve does ,in fact, move to the position where

the controller wants it to be.

Advantages of positioner are :

corrects any variation due to packing friction due to dirt, corrosion,

lack of lubrication, variation to dynamic forces of the process, sloppy linkages (dead

band), non linearity of actuator. Split ranging the controller signal

Increases loop gain and hence loop response in slow process. Eliminates dead band and hysteresis


74/91


1) Positioners

Disadvantages of positioner are,

In case of fast loop, positioner are likely to degrade loop response, contribute to

proportional offsets, and cause limit cycling ( fast flow, Liquid pressure, small volume gas

pressure).

Types of positioners

Force Balance Positioner Motion Balance Positioner Electrohydraulic Positioners Digital to Pneumatic Positioners


75/91


2. I/P (Elecropneumatic) Transducer

It converts electrical signal ( 4 20mA) from controller to pneumatic signal (3 15 psig or 0.2

to 1 Barg). The most common application is the Interface between and electronic controller.

Most of the transducer design is Motion Balance Type.

3. Booster Relay

It amplifies pneumatic signals in volume (capacity) or in pressure, or both.

Large control valves and large actuators may require flow or pressure boosters installed

between the positioner and the actuator to achieve the required speed.


76/91


4. Quick Exhaust Relays

Also called quick exhaust dump valve, is a pilot valve that opens a high capacity vent when the

input pressure drops below a set pressure.

This is used when it is needed to quickly open a valve that vents a vessel

Or system during a shut-down.

5. Lock Up Valve Position Relay

It holds up the valve in its last position if the air supply is lost.


77/91


6. Air Set

It consists of air regulator with filter and drip pot. It is used to supply moisture free, oil free

and particle free (equal or above 5 micron) air supply to the positioner other instruments.

It is often purchased with the valve, mounted and tubed.

Regulator must have the pressure range to cover the spring range of the actuator, and it

should have built in overpressure vent to protect the Actuator.

A gauge is valuable to aid in setting the output pressure and for discovering a failed or

plugged supply.


78/91


79/91


9. Handwheel

Handwheels are used to provide manual control of the valve and to Override the actuator.

These are available as Top Mounted and Side Mounted.

10. Limit Stop

Limit stop is used to limit valve stem motion to either ensure a minimum opening or

limit a maximum opening.


80/91

Sizing of Control Valve

Sizing equation for control valve is based on Bernoullis theorem for the conservation of energy

and the continuity Equation for the conservation of mass.

The generally accepted valve capacity parameter called the valve coefficient is :

Cv = Q x sqrt (G / Press. Drop)

The equation is valid for turbulent and non choked (low pressure drop) liquid flows.

The above equation alone turned out to be inaccurate. This was corrected by adding variousfactors like Pressure Recovery Factor FL, Pressure Differential Factor Xt , Expansion factor Y,

Pipe Geometry FP, Reynolds No. Factor FR, Liquid Pressure Recovery Factor FF etc.

Using above factors, various formulas were developed for Non choked, tubulent flow in liquid,

Non choked vapour and gas, Choked Flow due to cavitation and flashing Liquids, Choked flow

due to sonic velocity in gases and vapours, nonturbulent (viscous) flow liquids.


81/91


Determine minimum and maximum Cv requirements for the valve, considering not only normal

but also start-up and emergency conditions.

Decide what type of valve will be used.

Select a valve with Cv within 10% to 80% of stroke range.

The size of valve selected will usually be turned out to be smaller than the line size. Never select

valve less than half the pipe size. It is ideal to select valve with one size smaller and if the required

Cv is still smaller then select reduced trim design.

From the manufacturer valve chart select a valve.

STEPS TO SIZE A VALVE :


82/91


Check the gain across applicable flow rate

Gain = Change in Flow / Change in valve stroke or travel

e.g. Min / Nor / Max Flow = x1 / x2 / x3

Cvmin / Cvnor / Cvmax / = Cv1, Cv2, Cv3

Corresponding stroke % = S1%, S2%, S3%

Gain #1 = (x2 x1) / (S2 S1) = Y1

Gain #2 = (x3 x2) / (S3 S2) = Y2

The difference between the Gains ( Y2 Y1) should be less than 50% of higher value between

Y1 and Y2.

Also note that the gain should never be less than 0.5.


83/91

Selection of Valve Characteristics

Selection of right characteristics is important because it is part of control loop, and the loop will be

Stable only if the products of all its gain components (the gains of the process, sensor, controller and

The valve gains) is constant.

Usually the controller is tuned so that this gain product is 0.5, in order to give quarter amplitude

Damping.

If the gain of loop do not vary with load, but is constant, the desirable choice is to use a constant gain

Valve (i.e. linear valve)

If the gain of the loop components (such as process) decreases with load (flow thru the valve), the

Proper choice is to use increasing gain valve (i.e. equal percentage valve).


84/91


There are different engineer who had developed different rules of thumb to be used in selecting valve

Characteristics, One of the engineers Lytles recommendations are as follows :

LIQUID LEVEL SYSTEM

Constant dP Linear

Decreasing dP with increasing load, dP at maximum load is greater than

20% of minimum load dP

Linear

Decreasing dP with increasing load, dP at maximum load is less than20% of minimum load dP

Equal Percentage

Increasing dP with increasing load, dP at maximum load is less than200% of minimum load dP

Linear

Increasing dP with increasing load, dP at maximum load is greater than200% of minimum load dP

Quick Opening


85/91


Liquid Process Equal Percentage

Gas Process, small volume, less than 10 ft of pipe between control valveand load valve

Equal Percentage

Gas Process, large volume (process has a receiver, distribution system,

or transmission line exceeding 100 ft of nominal pipe volume,decreasing dP with increasing load, dP at maximum load greater than20% of minimum load dP

Linear

Gas process, large volume, decreasing dP with increasing load dP atmaximum load less than 20% of minimum load dP

Equal Percentage

Pressure Control System


86/91


Flow Measurement Signal toController

Location of Control ValveRelation to Measuring

Element

Wide Range ofFlow Setpoint

Small Range of Flowbut Large dP Change

at Valve withIncreasing Load

Proportional to Q In series Linear Equal Percentage

Proportional to Q In bypass Linear Equal Percentage

Proportional to Q2 In series Linear Equal Percentage

Proportional to Q2

In bypass EqualPercentage Equal Percentage

Flow Control System


87/91


Temperature Control System

It is recommended to have Equal Percentage Control Valve.


88/91

Leakage Classes in Control Valve

As per ANSI FCI 70-2 ( earlier ANSI B 16.104), valves are categorized according to their allowable

Leakage into six classes. These leakage limits are applicable to unused valves only,

Class I Valve are neither tested nor guaranteed for leakage

Class II Valves are rated to have less than 0.5% of their capacity

Class III Valves are allowed up to 0.1% of their capacity

Class IV Valves must not leak more than 0.01% of their capacity

Class V Valves are specified to have a leakage of 5 x 10-4 ml/min water flow per inch of seat

diameter, per 1 psi (0.0685 bar) differential pressure

Class VI This is for soft seated valves, and leakage is expressed as volumetric air flow at rated

pressure drop of 50 psi (3.45 bar)


89/91

Standards :

IEC 60534, Part 1, 2, 3, 4, 5, Describes Terminology, Sizing, Test Procedures,

Dimensions, Inspection and routine testing and Marking

ISA S 75.01, 2000 Control Valve Sizing Equations

ISA S 75.02, 1996 Control Valve Capacity Test


90/91

Quiz No. 3

What are the different types of Accessories used with Control Valves ?


91/91

Thank You

Documents

4 Control Valve