kb14 valve types and application

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KB14 Valve Types and Application

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Valve Types and Application

Figure VTA-1 Knife Gate Valve

THE VALVES

By definition, a valve is a device that controls the flow of a fluid. Modern valves cancontrol not only the flow but also the rate, the volume, the pressure or the direction ofliquids, gases, slurries or dry materials through a pipeline, chute or similar passageway.They can turn on and turn off, regulate, modulate or isolate the flow. They can range insize from a fraction of an inch to as large as 30 feet in diameter and can vary in complexityfrom a simple brass water valve to a precision-designed, highly sophisticated coolantsystem control valve made of an exotic metal alloy.

Valves can control flow of all types, from the thinnest gas to highly corrosive chemicals,superheated steam, abrasive slurries, toxic gases and radio active materials. They canhandle temperatures from cryogenic region to molten metal, and pressures from high

vacuum to thousands of pounds per square inch.

The valve is one of the most basic and indispensable components of our modern

Figure VTA-2 A 3-way Gate Valve

COMMON TYPES OF POSITIONERS

q Pneumaticq Electronicq Electro-pneumaticq Digital

MULTI-TURN VALVES OR LINEAR MOTION VALVES

q The Gate Valve

The gate valve is a general service valve used primarily foron/off, non-throttling service. The valve is closed by a flatface, vertical disc, or gate that slides down through the

valve to block the flow.

Advantages:

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technological society. It is essential to virtually all manufacturing processes and everyenergy production and supply system. Yet it is one of the oldest products known to man,with a history of thousands of years.

COMMON TYPES OF VALVES

q Multi-turn Valves, or Linear Motion, Valves

q Quarter Turn, or Rotary, Valves

q

Self-Actuated Valvesq Control Valvesq Specialty Valves

COMMON TYPES OF ACTUATORS

q Manual Actuators

q Hydraulic and Pneumatic Actuators

q Electric Actuators

1. Virtually no pressure loss across the valve face2. Can be used when the fluid contains suspended solids

Disadvantage:

1. Poor to fair sealing characteristics

Recommendation:

1. Not for frequent valve opening/ closing service2. Not for when precise throttling control is required

KSY2007 Copyright 2006-8 by Gentec Systems Co., All Rights Reserved.

q The Globe Valve

The globe valve effects closure by a plug with a flat orconvex bottom lowered onto a matching horizontal seatlocated in the center of the valve. Raising the plug opensthe valve, allowing fluid flow. The direction of fluid flowthrough the valve changes several times, which increasesthe pressure drop across the valve.



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Figure VTA-3 Globe Valve: (1) Stem, (2) Packing, (3) Disc, (4) Body, (5)

Bonnet, (6) Flow Path, and (7) Seat

The globe valve is used for on/off service and throttlingapplications.

Advantages:

1. Good sealing characteristics

2. Can be used in frequent open/ closing service face

3. Quick change of trim without removing valve from line

4. High capacity5. God rangeability

6. Low-noise trim available

7. Smooth control

Disadvantage:

1. High-pressure losses due to contorted path through the

valve2. Low-noise trim reduces capacity

Recommendation:

1. For flow regulation2. When tight shut-off is required

q The Pinch Valve

The pinch valve is particularly suited for applications ofslurries or liquids with large amounts of suspended solids. It

seals by means of one or more flexible elements, such as arubber tube, that can be pinched to shut off flow.

Advantages:

1. Effectively control the flow of both abrasives and

corrosives2. No contact between metal parts and the transport

media

Disadvantage:

1. Limited operating pressure



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Figure VTA-4 A Pinch Valve

2. Limited temperature Range3. High wear and tear

Recommendation:

1. For situations where product purity is a high priority2. For medical applications, pharmaceutical processes,

and handling of wastewater , slurries, pulp, powder and

pellets3. Contraindicated for services that require high-pressureand/or high-temperature flow, and for use with gases


The Diaphragm Valve

The diaphragm valve closes by means of a flexiblediaphragm attached to a compressor. When the



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Figure VTA-5 Typical Diaphragm Valves (Gentec DV84, and

DV86 Ultra High Purity Gas Valve)

compressor is lowered by the valve stem onto a weir, thediaphragm seals and cuts off flow. The diaphragm valvehandles corrosive, erosive and dirty services.

Advantages:

1. Almost no leakage

2. Process fluid is isolated from valve stem

3. Self-cleaning

Disadvantage:

1. Limited operating pressure

2. Limited temperature range

3. High wear and tear4. Poor control over 50%-opening in general

Recommendation:

1. Water-treatment service

2. Chemical and abrasive service

q The Needle Valve

The needles valve is a volume-control valve that restrictsflow in small lines. The fluid going through the valve passesthrough an orifice that is the seat for a rod with a cone-shaped tip. The Size of the orifice is changes by positioning

the cone in relation to the seat.

Advantages:

1. Precise resistance to flow resulting in accurate controlof flow

2. Tight shut-off3. Small and compact

Disadvantage:

1. Smaller flow capacity2. Small rangeability



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Figure VTA-6 Needle Valve (Closed and Opened)

Figure VTA-7 A Small In-line Plug Valve

3. Large pressure drop

Recommendation:

1. Excellent for control and metering applications2. Not for applications where the media is viscous (sticky)3. Not for dispensation of slurries

QUARTER TURN, OR ROTARY, VALVES

q The Plug Valve

The plug valve is used primarily for on/off service and somethrottling services. It controls flow by means of a cylindricalor tapered plug with a hole in the center that lines up withthe flow path of the valve to permit flow. A quarter turn ineither direction blocks the flow path.

Advantages:

1. Virtually no pressure loss across the valve face2. Can be used when the fluid contains suspended solids3. Lightweight, compact design4. High capacity5. Good rangeability6. Tight shut-off

Disadvantage:

1. Poor sealing characteristics, sealability poor with metalseats used at high temperatures

2. Limited-temperature range with resilient seats3. Choke flow problems4. Cavitation problems5. Requires removal for maintenance

Recommendation:

1. Not for service with highly corrosive fluids

2. Most suitable VPH-for handling slurries



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Figure VTA-8 An In-Line Ball Valve


Figure VTA-9 Typical Ball Valves for High Purity Application

q The Ball Valve

The ball valve is similar in concept to the plug valve butuses a rotating ball with a hole through it that allowsstraight-through flow in the open position and shuts off flowwhen the ball is rotated 90 degrees to block the flowpassage. It is used for both on/off and throttling services,especially in situations where tight shut-off is required

Advantages:

1. Ease of operation

2. Can regulate high volume, high pressure and hightemperature flow

3. Rugged construction providing for a long service life at



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Figure VTA-10 Inside a Ball Valve

Figure VTA-11 Schematic of a Rotary Motion Disk Closure Member inside a

Butterfly Valve (Opened and Closed)

low cost4. Ease of maintenance

q The Butterfly Valve

The butterfly valve controls flow by using a circular disc orvane with its pivot axis at right angles to the direction offlow in the pipe. The butterfly valve is used both for on/offand throttling services.

Advantages:

1. Lightweight compact design2. Minimal pressure loss across valve3. Low cost4. High throughput capacity5. Smaller shaft and actuator

Disadvantage:

1. Poor sealing characteristics2. Tight shut-off requires special lining: plus over-sized

shaft and actuators

3. Lining imposes temperature limitations

Recommendation:

1. Low-pressure applications

SELF-ACTUATED VALVES

q The Check Valve

The check valve is designed to prevent backflow. Fluid flowin the desired direction opens the valve, while backflowforces the valve closed.

Most check valves contain a ball that sits freely above theseat, which has only one through-hole. The ball has a

slightly larger diameter than that of the through-hole. Whenthe pressure behind the seat exceeds that above the ball,fluid is allowed to flow through the valve; however, once the



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Figure VTA-12 A In-line Ball Check Valve

pressure above the ball exceeds the pressure below theseat, the ball returns to rest in the seat, forming a seal thatprevents backflow (see Figure VTA-12).


Single-disc swing valves are designed with the closureelement attached to the top of the cap. Double-disc or

wafer check-valves consist of two half-circle disks hingedtogether that fold together upon positive flow and retract toa full-circle to close against reverse flow (see Figure VTA-13).

A lift-check valve is a check valve in which the disc (lift) canbe lifted up off its seat by higher pressure of inlet orupstream fluid to allow flow to the outlet or downstreamside. A stop-check valve is a check valve with overridecontrol to stop flow regardless of flow direction or pressure.When the valve is open, it acts as a check valve, but thevalve can be deliberately shut to stop flow.

Spring-loaded devices can be mounted vertically orhorizontally (see Figure VTA-14).

q The Pressure Relief Valve

The pressure relief valve is designed to provide protectionfrom over-pressure in steam, gas, air and liquid lines. Thevalve lets off some fluid when safe pressures are

exceeded, and then closed again when pressure drops to apreset level.



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Figure VTA-13 Dual Plate (Swing) Check Valve

Figure VTA-14 A Spring Loaded Ball Check Valve

Figure VTA-15 Inside a Typical Pressure Regulator

q Gas Pressure Regulator

Gas Pressure Regulators can also be considered as aspecial type of self-actuated valves. They are used tocontrol the downstream line pressure. They removefluctuations in the supply and the set points are adjustable.

CONTROL VALVES

The control valve is designed to ensure accurateproportioning control of flow. It automatically varies the rateof flow based signals it receives from sensing devices in acontinuous process. Some valves are designed specificallyas control valves. However, most types of valves can beused as control valves, both linear and rotary motion, bythe addition of power actuators, positioners and otheraccessories.

SPECIALTY VALVES

In addition to standard valve products, many valvemanufacturers produce custom-designed valves andactuators for specific applications. Valves are available in abroad spectrum of sizes and materials. Each design has itsown advantages, and selection of the proper valve forparticular application is critical. The factors generallyconsidered in the selection of a valve include:

q The substance to be handles and the required flow

rate.

q The requirement that the valve control and/or shutoff the flow in the manner demanded by the serviceconditions.

q The ability of the valve to withstand the maximumworking pressure and temperature.

q The ability of the valve to resist attack by corrosion

or erosion.

q Actuator requirements, if any.


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q Maintenance and repair requirements.


ACTUATORS

q Manual Actuators

A manual actuator employs levers, gears or wheels tofacilitate movement; while an automatic actuator has anexternal power source to provide the force and motion tooperate a valve remotely or automatically. Power actuatorsare a necessity on valves in pipelines located in remoteareas: they are also used on valves that are frequently

operated or throttled. Valves that are particularly large maybe impossible or impractical to operate manually simply bythe sheer horsepower requirements.

Some valves may be located in extremely hostile or toxicenvironments, which preclude manual operation.Additionally, as a safety feature, certain types of poweractuators may be required to operate quickly, shuttingdown a valve in case of emergency.

q Hydraulic and Pneumatic Actuators

The hydraulic and pneumatic actuators are often simpledevices with a minimum of mechanical parts, used on linearor quarter-turn valves. Sufficient air or fluid pressure actson a piston to provide thrust in a linear motion for gate orglobe valves. Alternatively, the thrust may be mechanicallyconverted to rotary motion to operate a quarter-turn valve.Most types of fluid power actuators can be supplied with fail-safe features to close or open a valve under emergencycircumstances.

q Electric Actuators


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Figure VTA-16 Components of a Typical Liquid Control Valve: (1) Seat, (2) body,

(3) pneumatic actuator, (4) spring, (5) bonnet, (6) stem, (7) cage, (8) plug, (9)

diaphragm, and (10) stem motion

The electric actuator has a motor drive that provides torqueto operate a valve. Electric actuators are frequently used onmulti-turn valves such as gate or globe valves. With theaddition of a quarter-turn gearbox, they can be utilized onball, plug, or other quarter-turn valves.

POSITIONERS

Valve positioners compare a control signal to a valve

actuators position and move the actuator accordingly. Theyare used with both linear valves and rotary valves. When acontrol signal differs from the valve actuators position, thevalve positioner sends the necessary power to move theactuator until the correct position is reached.

There are four basic types of valve positioners: pneumatic,electric, electro-pneumatic, and digital:

q Pneumatic

Pneumatic devices send and receive pneumatic signals.Single-acting or three-way pneumatic positioners send airto and exhaust air from only one side of a single-actingvalve actuator that is opposed by a range spring. Double-acting or four-way pneumatic positioners send and exhaustair from both sides of the actuator.

q Electric

Electric valve positioners send and receive electricalsignals. There are three electric actuation types: single-phase and three-phase alternating current (AC), and directcurrent (DC) voltage.





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q Electro-pneumatic

Electro-pneumatic valve positioners convert current control signals to equivalentpneumatic signals (or I/P operation).

q Digital

Digital or smart devices use a microprocessor to position the valve actuator andmonitor and record data.

Performance specifications for valve positioners vary by device type and includepneumatic input signal range, maximum supply pressure, milliampere input signalrange, split range, operating temperature, and output action. Common split rangesinclude 4-10 mA and 12-20 mA. Two-way, three-way, and four-way splits are available.

There are three types of output actions: direct, reversible,and field reversible. Direct action devices increase theoutput signal as the input signal increases. Conversely,reversible action devices decrease the output signal as theinput signal increases. With field reversible products,devices can be switched between direct and reversibleaction.

Valve positioners differ in terms of applications, features

and approvals. Some products are designed forautomotive, aerospace, marine, medical or militaryapplications. Other products are suitable for foodprocessing or pharmaceutical applications. General-purpose devices are commonly available. Intrinsically safe(IS) valve positioners do not produce sparks or otherthermal effects that would ignite a specified gas mixture.Devices that are made from stainless steel are used incorrosive or high temperature environments. Commonapprovals for valve positioners include marks from theCanadian Standards Association (CSA) and Underwriters

Laboratories (UL), an independent testing organization.

Table VTA-1 Typical Flow Coefficient, Cv, for Ball Valves (Full Bore)

VALVE SIZE

Inches 1/2 3/4 1 1 1/2 2 2 1/2 3 4 6 8 10 12 14 16 18

mm 12 19 25 37.5 50 62.5 75 100 150 200 250 300 350 400 450

FlowCoefficient C

v26 50 94 260 480 750 1300 2300 5400 10000 16000 24000 31400 43000 57000

Table VTA-2 Typical Flow Coefficient, Cv, for Ball Valves (Reduced Bore)

VALVE SIZE

Inches 3 4 6 8 10 12 14 16 18 20

mm 75 100 150 200 250 300 350 400 450 500

Flow Coefficient Cv 420 770 1800 2500 4500 8000 12000 14000 18000 22000





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Table VTA-3 Typical Flow Coefficient, Cv, for Butterfly Valves

FLOW COEFFICIENT Cv

Size Disc Angle - Openness Maximum flow velocity (ft/sec)

inches mm90 deg (wide

open)70 deg 50 deg 30 deg ANSI 150 ANSI 300

2 50 85 65 35 15 90 90

2 65 160 120 65 29 80 90

3 80 260 195 104 47 80 804 100 475 356 190 86 80 80

5 125 770 577 308 139 80 80

6 150 1125 844 450 203 75 80

8 200 2110 1583 844 380 70 75

10 250 3350 2513 1340 603 60 70

12 300 4800 3600 1920 864 50 60

14 350 6900 5175 2760 1224 50

16 400 9000 6750 3600 1620 50

18 450 11800 8850 4720 2124 50

20 500 14300 10725 5720 2574 50

Table VTA-4 Typical Flow Coefficients and Flow Factors for Straight-through Diaphragm Valves

FLOW COEFFICIENT AND FLOW FACTOR Cv and Kv

Valve Size Unlined Rubber Lined Glass/Plastic Lined

DN Inch Cv Kv Cv Kv Cv Kv

15 9 7 9 8

25 1 38 33 31 26 39 34

32 1 56 48 46 39 58 50

40 1 75 65 66 57 79 68

50 2 128 110 107 92 138 119

65 2 238 205 195 168 254 219

80 3 330 284 264 228 342 295

100 4 588 507 480 414 618 533

125 5 924 797 720 621 960 828

150 6 1680 1448 1260 1086 1800 1552

200 8 2580 2224 2196 1893 2724 2348

250 10 4020 3466 3420 2948 4296 3703

300 12 6060 5224 4884 4210

350 14 10300 8879 9950 8578

Table VTA-5 Typical Flow Coefficients and Flow Factors of Weir Diaphragm Valves




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FLOW COEFFICIENT AND FLOW FACTOR Cv and Kv

Valve Size Unlined Rubber Lined Glass/Plastic Lined Plastic Lined

DN Inch CvK

vC

vK

vC

vK

vC

vK

v

15 6 5 6 5

20 12 10 9 8 12 10 7 6

25 1 18 15 14 12 18 16 11 10

32 1 28 24 22 19 28 24 17 14

40 1 43 37 35 30 45 39 31 27

50 2 80 69 64 55 88 76 59 51

65 2 127 109 102 88 132 114 83 7280 3 185 159 148 128 186 160 148 128

100 4 315 272 252 217 336 290 270 233

125 5 420 362 363 313 440 379

150 6 605 522 484 417 630 543 505 435

200 8 1300 1121 1309 1128 1320 1138

225 9 1630 1405 1320 1138 1680 1448

250 10 1980 1707 2000 1724 2 100 1 810

300 12 2550 2198 2600 2241 2700 2328

350 14 3700 3190 3750 3233 3880 3345

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