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Part (2)

VALVES

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Chapter (1)

Introduction

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Introduction to Valves

Every piping system must have some means of controlling the amount

and direction of flow. This is accomplished with valves. Valves used in the

machinery space piping systems, and constructed with threaded valve stems,

must be right-hand closing (clockwise).

Valves are usually made of bronze, brass, cast iron, malleable iron, or

steel. Steel valves are either cast or forged, and are made of carbon steel, low

alloy steel, or stainless steel. Alloy steel valves are used in high pressure, high

temperature systems. The disks and seats of these valves are usually surfaced

with a chromium-cobalt alloy known as STELLITE. This material is extremely

hard.

Bronze and brass valves are not used in high temperature systems or

systems subject to high pressures, severe vibration and shock. Bronze valves

are widely used in salt water systems. Seats and disks of bronze valves used for

salt water service are often made ofMonel An alloy of nickel and copper and

other metals (such as iron and/or manganese and/or aluminum) which is highly

resistant to corrosion and erosion.

Many different types of valves are used to control the flow of liquids and

gases. There are two main groups of valves.

STOP VALVES - Stop valves are used to shut off or, in some cases, partially

shut off the flow of fluid. Stop valves are controlled by the movement of the

valve stem.

Stop valves can be divided into four general categories: globe, gate,

butterfly, and ball valves. Plug valves and needle valves may also be

considered stop valves.

CHECK VALVES - are used to permit the flow in only one direction. These

valves are controlled by the flow itself.

Valve designs vary greatly due to the demands of service. Some valves

are combinations of the basic types mentioned, and others such as pressure

reducing valves must be considered special valves. In general however we may

consider stop valves to include globe valves, gate valves, piston valves, plug

valves, needle valves, and butterfly valves.

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Check valves include swing-check and lift-check valves.

Excessive leakage and premature failure of valve packing is an

indication of a scored valve stem. There is another method for classification of

valves according to the function of valves as will be explained.

Functions of Valves

Each valve has a particular application for which it is best suited.

Although valves may appear the same, they are very sophisticated in some

cases and represent a great deal of research, engineering, and testing. Five

functions of valves listed below:

1- Starting and Stopping Flow:

This is the service for which valves are most generally used. Gate valves

are excellently suited for such service. Their seating design permits fluid to

move through the open valve in a straight line with minimum restriction of

flow and loss of pressure at the valve. The gate principle is not practical for

throttling.

2- Regulating or Throttling Flow:

Regulating throttling flow is done most efficiently with globe or angle

valves. Their seating design causes a change in direction of flow through the

valve body, thereby increasing resistance o flow at the vale. Globe and angle

valve disk construction permits closer regulation of flow. These valves are

seldom used in sizes above 12 inch due to the difficulty of opening and closing

the larger valves against line pressure.

3- Preventing Back Flow:

Check valves perform the single function of checking or preventing

reversal of flow in piping. They come in two basic types, swing check and lift

check. Flow keeps these valves open, and gravity and reversal of flow close

them automatically. As a general rule, swing checks are used with gate valves

and lift checks with globe valves.

4- Regulating pressure:

Pressure regulators are used in lines where it is necessary to reduce

incoming pressure to the required service pressure. They not only reduce

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pressure but also maintain it at the point desired. Reasonable fluctuations of

inlet pressure to a regulator valve do not affect the outlet pressure for which it

is set.

5- Reliving pressure:

Boilers and other equipment subject to damage from excessive pressures

should be equipped with safety valves or relief valves. They usually are spring-

loaded valves, which open automatically when pressure exceeds the limit for

which the valve is set. Safety valves are generally used for steam, air or other

gases. Relief valves are usually used for liquids.

Basic Types of Valves

There are dozens of different types of valves, but nine or so are perhaps

the most frequently used and could be considered the basic types. The basic

types of valves shown in the next figure can be classified as the following:

1- Globe Valve.

2- Angle Valve.

3- Gate Valve.

4- Plug Valve

5- Ball Valve.

6- Butterfly Valve.

7- Needle Valve.

8- Check Valve.

9- Relief Valve.

Special Types of Valves

Each manufacturer builds many valves that are considered special. By

special, we mean that the valve does a particular job, the design is patented by

hat manufacturer, and no one else builds one exactly like it. In order to show

even a portion of them it would take numerous pages and explanations.

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1- Globe Valve 2-Angle Valve. 3-Gate Valve.

4- Plug Valve. 5-

Ball Valve. 6 Butterfly Valve.

7- Needle Valve. 8- Check Valve. 9- Relief Valve

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Chapter (2)

Different Types of

Valves

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1- Gate Valves

Gate valves are one of the most common types of valves used in

industry. With a gate valve the direction of fluid flow does not change, and thediameter through which the process fluid passes is essentially equal to that of

the pipe. Hence, gate valves tend to have minimal pressure drop when opened

fully.

Gate valves are designed to minimize pressure drop across the valve in

the fully opened position and stop the flow of fluid completely. In general, gate

valves are not used to regulator fluid flow. A gate valve is closed when a

tapered disk of diameter slightly larger than that of the pipe is lowered into

position against the valve seats. The valve is fully open when the disk is pulledcompletely out of the path of the process fluid into the neck. There are two

types of gate valves: wedge-shaped-gate type with an inclined seat, Fig. (1)

and a double-disk parallel-seat type, Fig. (2).

The former is the type most commonly used in industry. The wedge gate

may be solid or split into halves by a plane perpendicular to the pipe, shown in

figure. Disk flexibility is inherent to the split wedge design. This flexibility

allows the split wedge to seal more easily and it reduces galling of the sealing

surface in cases where the valve seats are angularity misaligned.

In the double-disk parallel-seat type, the valve is closed by lowering the

disks from the valve neck to a height equal to that of the valve seats. Once so

positioned, an inclined-plane mounted between the two disks coverts

downward stem force into axial force and presses the parallel disks firmly

against the valve seats sealing the two openings. This type of valve design can

also accommodate nonsymmetrical or angularity misaligned valve seats. Also

there are two types of gate valve the first is rising stem and the second is non-

rising stem, Figs. (3, 4, 5 & 6).

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Fig. (1):Wedge-shaped-gate type with an inclined seat, Gate valve

Fig. (2) ) Double-disk parallel-seat type,Gate Valve.

Fig. (3) Rising Stem Gate Valve

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Fig. (4) Non rising stem Gate valve - 4" high pressure

Fig. (5) Rising Spindle Gate Valve Fig. (6) Fixedspindle Gate Valve

2- Globe valves

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Globe valves are widely used in industry to regulate fluid flow in both

on-off and throttling service. The amount of flow restriction observed with a

globe valve is a function of the valve disk (or globe) location relative to the

valve seat. As can be seen in the pictures above, the valve seat and stem arerotated 90 to the pipe, see Figs. (1 & 2)). The direction of fluid flow through

the valve changes several times, which increases the pressure drop across the

valve. In most cases, globe valves are installed with the stem vertical and the

higher pressure fluid stream connected to the pipe side above the disk, which

helps to maintain a tight seal when the valve is fully closed. Traditionally the

valve disk and seat were both metal, thought some modern designs use an

elastomeric disk seal. These valves are inexpensive and simple to repair.

Fig. (1) Globe valve Fig. (2) Globe valve

Functions of Globe Valve

A globe valve derives its name from the globular shape of its body. The

valve body must large enough to allow the full area to open when the valve is

in the open position. Globe valves are usually used for regulating flow;

however, they can also be used for complete shutoff. The seating in a globe

valve is parallel to the flow, whereas the seating in a gate valve is

perpendicular.

Advantages of a Globe Valve

The principle advantage of a globe valve over a gate valve is that:

1- Its close regulation is due to the proportional relation of the size of the

seat opening to the number of turns of the hand wheel, which is the distinctive

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feature of the plug type globe valve. An operator can gauge the rate of flow by

the number of turns applied to the hand wheel.

2- Time, work and wear are also saved because of the fewer turns required

to operate a globe valve as compared to a gate valve. Whenever wear occurs asthe result of frequent or severe operation that the globe presents less of a

maintenance problem than a gate valve.

3- Seat and disk in most globe valves can be repaired without removing the

valve from the pipeline.

While they are not recommended where resistance to flow and pressure

drop would be objection able, globe valves are generally ideal for throttling.

They are also preferable where frequent operation is necessary.

Globe Valve Installation

A hand control valve, identified on a flow sheet with the letters H.C. is a

globe valve with an indicator attached to it. This indicator tells the operator

how high or low the steam is being lowered or raised.

For layout purposes the important dimensions, such as the face-to-face

height of stem opened and the diameter of the hand-wheel, may be found in any

valve manufactures catalog. The majority of valve manufactures has

standardized the face-to-face dimension, Fig. (3).

Fig. (3) Different types of Globe Valves

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Globe Valve Seatings

Globe valves may be provided with either metal seatings or soft seatings. In the

case of metal seatings, the seating stress must not only be high but also

circumferentially uniform to achieve the desired degree of fluid tightness.These requirements have led to a number of seating designs. The ones shown in

Figure 4 are common variations.

Figure 4. Seating Configurations Frequently

Employed in Globe Valves.

Flat seatings (see Figure 4a) have the advantage over other types of seatings in

that they align readily to each other without having to rely on close guiding ofthe disc. Also, if the disc is moved onto the seat without being rotated, the

seatings mate without friction. The resistance of the seating material to galling

is therefore unimportant in this case. Deformation of the roundness of the seat

due to pipeline stresses does not interfere with the sealability of the seatings as

long as the seat face remains flat. If flow is directed from above the seat, the

seating faces are protected from the direct impact of solids or liquid droplets

travelling in the fluid.

By tapering the seatings, as shown in Figure 4b, c, and d, the seating stress fora given seating load can be greatly increased. However, the seating load can be

translated into higher uniform seating stress only if the seatings are perfectly

mated; that is, they must not be mated with the disc in a cocked position. Thus,

tapered discs must be properly guided into the seat. Also, the faces of seat and

disc must be perfectly round. Such roundness is sometimes difficult to maintain

in larger valves where pipeline stresses may be able to distort the seat

roundness. Furthermore, as the seatings are tightened, the disc moves further

into the seat. Tapered seatings therefore tighten under friction even if the disc is

lowered into the seat without being rotated. Thus the construction material forseat and disc must be resistant to galling in this case. The tapered seatings

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shown in Figure 4b have a narrow contact face, so the seating stress is

particularly high for a given seating load. However, the narrow seat face is not

capable of guiding the disc squarely into the seat to achieve maximum sealing

performance. But if the disc is properly guided, such seatings can achieve an

extremely high degree of fluid tightness.

On the debit side, narrow-faced seatings are more readily damaged by solids or

liquid droplets than wide-faced seatings, so they are used mainly for gases free

of solids and liquid droplets. To improve the robustness of tapered seatings

without sacrificing seating stress, the seatings shown in Figure 4c are tapered

and provided with wide faces, which more readily guide the disc into the seat.

To achieve a high seating stress, the seat face in initial contact with the disc is

relatively narrow, about 3 mm (18 in.) wide. The remainder of the seat-bore is

tapered slightly steeper. As the seating load increases, the disc slips deeper intothe seat, thereby increasing the seating width. Seatings designed in this way are

not as readily damaged by erosion as the seatings in Figure 4b. In addition, the

long taper of the disc improves the throttling characteristic of the valve.

Figure 5. Seatings of Globe Valves Adapted

for Throttling Duty.

The performance of such seatings may be improved by hollowing out the disc

to impart some elasticity to the disc shell, as is done in the valve shown in

Figure 6. This elasticity permits the disc to adapt more readily to deviations of

the seatings from roundness. The seatings shown in Figure 4d are ball shaped

at the disc and tapered at the seat. The disc can therefore roll, to some extent,

on the seat until seat and disc are aligned. Because the contact between the

seatings approaches that of a line, the seating stress is very high. On the debit

side, the line contact is prone to damage from erosion. The ball-shaped seatings

are therefore used only for dry gases, which are also free of solids. This

construction is used mainly by U.S. manufacturers.

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If the valve is required for fine throttling duty, the disc is frequently provided

with a needle-shaped extension, as in the valve shown in Figure 7; or with a V-

port skirt, as in the valve shown in Figure 8 and in the seatings shown in

Figure 5. In the latter design, the seating faces separate before theV-ports open.

The seating faces are, in this way, largely protected against erosion.

An example of soft seating design is the valve shown in Figure 9. The soft

seating insert is carried in this case by the disc, and may be renewed readily.

Figure 6. Globe Valve, Standard Pattern, Integral Bonnet,

Plug-Type Disc Integral with Non-Rotating Stem.

Figure 7. Globe Valve, Angle Pattern, Screwed-in Bonnet,

Internal Screw Needle Disc.

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Figure 8. Globe Valve, Angle Pattern, Bolted Bonnet, External Screw, PlugDisc with V-Port Skirt for Sensitive Throttling Control.

Figure 9. Globe Valve, Standard Pattern, Union Bonnet,

Internal Screw and Renewable Soft Disc.

Connection of Disc to Stem

The stem of a globe valve may be designed to rotate while raising or lowering

the disc, or be prevented from rotating while carrying out this task. These

modes of stem operation have a bearing on the design of the disc-to-stem

connection. Most globe valves incorporate a rotating stem because of simplicity

of design. If the disc is an integral component of the stem in this case, as it

frequently is in small needle valves such as those shown in Figure 7, the

seatings will mate while the disc rotates, possibly resulting in severe wear of

the seatings. Therefore, the main field of application of such valves is for

regulating duty with infrequent shut-off duty. For all other duties involving

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rotating stems, the disc is designed to swivel freely on the stem. However,

swivel discs should have minimum free axial play on the stem to prevent the

possibility of rapid reciprocating movements of the disc on the stem in the near

closed valve position.

Also, if the disc is guided by the stem, there should be little lateral play

between stem and disc to prevent the disc from landing on the seat in a cocked

position. In the case of nonrotating stems, as in the valves shown in Figures 10,

Figure 11, Figure 12, and Figure 6, the disc may be either an integral part of

the stem (see Figure 6) or a separate component from the stem (see Figure 10,

Figure 11, and Figure 12). Nonrotating stems are required in valves with

diaphragm or bellows valve stem seal, as in Figure 10 and Figure 11. They

are also used in high pressure valves such as those shown in Figure 12 and

Figure 6 to facilitate the incorporation of power operators.

Figure 10. Globe Valve, Standard Pattern, Welded Bonnet, External

Screw, Plug Disc, Bellows Stem Seal with

Auxiliary Compression packing.

Figure 11. Globe Valve, Oblique Pattern, Screwed-in

and Seal-Welded Bonnet, External Screw, Plug Disc.

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Figure 12. Globe Valve, Oblique Pattern, Pressure-Seal Bonnet, External

Screw, with Impact Handwheel, Plug Disc.

Stuffing Boxes and Back Seating

Figure 13 and Figure 15 show three types of stuffing boxes, which are typical

for valves with a rising stem. The stuffing box shown in Figure 13 is the basic

type in which an annular chamber contains the packing between the gland at

the top and a shoulder at the bottom. The underside of the stuffing box carries a

back seat which, in conjunction with a corresponding seat around the stem, is

used to isolate the packing from the system fluid when the valve is fully open.The stuffing box shown in Figure 14 is supplemented with a condensing

chamber at the bottom. The condensing chamber served originally as a cooling

chamber for condensable gases such as steam. In this particular case, the

condensing chamber has a test plug, which may be removed to test the back

seat for leak tightness.

A third variation of the stuffing box has a lantern ring mounted between two

packing sections, as shown in Figure 15. The lantern ring is used mainly in

conjunction with compression packings and may serve four different purposes:

1. As an injection chamber for a sealant or an extruded or leached-out lubricant.

2. As a pressure chamber in which an external fluid is pressurized to a pressure

equal to or slightly higher than the system pressure to prevent any leakage of

the system fluid to the outside. The external fluid must thereby be compatible

with the system fluid and harmless to the surroundings of the valve.

3. As a sealant chamber in vacuum service into which an external fluid is fed to

serve as a sealant.

4. As a leakage collection chamber from which the leakage is piped to a safelocation.

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The inclusion of the lantern ring, however, increases the depth of the packing

column. Sidewall friction reduces the gland packing input load as the packing

depth increases, leading to an impairment of the seal integrity.37 Replacing the

lantern ring with a spring is used in rotating pump shaft seals

to improve the seal integrity.

Figure 13. Basic Stuffing Box.

Figure 14. Stuffing Box with Condensing Chamber.

Figure 15. Stuffing Box with Lantern Ring.

Direction of Flow Through Globe Valves

The question of direction of flow through globe valves has two answers. If the

possibility exists that flow from above the disc can remove either the disc from

the stem or a component from the disc, flow directed from below the disc is

mandatory. In this case, hand-operated globe valves with rotating stem and

metal seatings can be closed fluid-tight without undue effort, only if the fluid

load on the underside of the disc does not exceed about 4060 kN (9,000

13,000 lb).39 With a non-rotating stem and rollerbearing supported stem nut, as

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in the valves shown in Figure 12 and Figure 6, hand operated globe valves

with metal seatings may be closed fluid-tight against a fluid load of about 70

100 kN (16,00022,000 lb), depending on the leakage criterion and the

construction of the valve.

One particular advantage of flow directed from below the disc is that the

stuffing box of the closed valve is relieved from the upstream pressure. On the

debit side, if the valve has been closed against a hot fluid such as steam,

thermal contraction of the stem after the valve has been closed can be just

enough to induce seat leakage. If flow is directed from above the disc, the

closing force from the fluid acting on top of the disc supplements the closing

force from the stem. Thus, this direction of flow increases greatly the sealing

reliability of the valve. In this case, hand-operated globe valves with a rotating

stem may be opened without excessive effort, only if the fluid load acting ontop of the disc dose not exceed about 4060 kN (9,00013,000 lb).

If the stem is of the nonrotating type with a roller-bearing supported stem nut,

the globe valve may be opened by hand against a fluid load of about 70100

kN (16,00022,000 lb). If the fluid load on top of the disc is higher, a bypass

valve may have to be provided that permits the downstream system to be

pressurized before the globe valve is opened.

Standards Pertaining to Globe Valves

Appendix C provides a list of U.S. and British standards pertaining to globe

valves.

Applications

Duty:

Controlling flow

Stopping and starting flow

Frequent valve operation

Service:Gases essentially free of solids

Liquids essentially free of solids

Vacuum

Cryogenic

Two-Way Globe Valve

A two-way globe valve has one inlet port and one outlet port as shown in

the next figure in either a straight through or angle pattern. The valve can beeither push-down-to-close or push-down-to-open. Pneumatic and electric

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actuators with linear motion to operate globe valves are available for operation

with many control signals, Fig. (16) .

Fig. (16) Two-way globe valve

3- Piston Valves

Piston valves are closing-down valves in which a piston-shaped closure

member intrudes into or withdraws from the seat bore, as in the valves shown

in Figures (1, 2, 3,4 & 5). In these valves, the seat seal is achieved between the

lateral faces of the piston and the seat bore. When the valve is being opened,flow cannot start until the piston has been completely withdrawn from the seat

bore. Any erosive damage occurs, therefore, away from the seating surfaces.

When the valve is being closed, the piston tends to wipe away any solids,

which might have deposited themselves on the seat. Piston valves may thus

handle fluids that carry solids in suspension. When some damage occurs to the

seatings, the piston and the seat can be replaced in situ, and the valve is like

new without any machining. Like globe valves, piston valves permit good flow

control. If sensitive flow adjustment is required, the piston may be fitted with a

needle shaped extension. Piston valves are also used for stopping and startingflow when flow resistance due to the tortuous flow passage is accepted.

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Figure 1. Piston Valve, Standard Pattern, Seat Packing

Mounted in Valve Body, Piston Pressure Unbalanced.


Mounted in Valve Body, Piston Pressure Balanced.

Figure 3. Piston Valve, Adapted for Draining Vessels,

Seat Packing Mounted in Valve Body.

Construction

The seatings of piston valves are formed by the lateral faces of the valve bore

and the piston. A fluid-tight contact between these faces is achieved by a

packing that either forms part of the valve bore, as in the valves shown in

Figure 2 through Figure 3, or part of the piston, as in the valves shown inFigure 4 and Figure 5. Packings commonly used for this purpose are

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compression packings based on compressed asbestos or PTFE and O-ring

packings.

In the case of the piston valve shown in Figure 2, the piston moves in two

packings that are separated by a lantern ring. The lower packing represents theseat packing, while the upper packing seals the piston to the atmosphere. The

bonnet serves thereby as the gland that permits both packings to be tightened

through tightening of the cover bolts. Disc springs under the nuts of the cover

bolts minimize variations in packing stress due to thermal contraction and

expansion of the valve parts. When one of the packings leaks, the fluid seal can

be restored by retightening the bolts. Retightening must be carried out while the

valve is closed to prevent an unrestrained expansion of the seat packing into the

valve bore. The valve shown in Figure 2 differs from the one in Figure 3 only

in that the piston is pressure balanced. The two packings around the piston areboth seat packings, and a separate packing is provided for the stem.

The purpose of balancing the piston is to minimize the operating effort in large

valves operating against high fluid pressures. The packing train of the valve

shown in Figure 3 is likewise stressed through the bonnet in conjunction with

springs under the nuts of the cover bolts, or with a spring between the bonnet

and the packing. However, as the piston moves into the final closing position, a

shoulder on the piston contacts a compression ring on top of the packing so that

any further progression of the piston tightens the packing still further.

The piston valve shown in Figure 4 carries the seat packing on the end of the

piston instead of in the valve bore. The packing is supported thereby on its

underside by a loose compression ring. When the piston moves into the final

closing position, the compression ring comes to rest on a shoulder in the seat

bore so that any further progression of the piston causes the compression ring

to tighten the packing. Because the packing establishes interference with the

seat in the last closing stages only, the operating effort of the valve is lower

over a portion of the piston travel than that of the foregoing valves.

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Figure 4. Piston Valve Adapted for Draining Vessels, Seat Packing

Mounted on Piston; the Ram-Seal Principle.


Mounted on Piston.

The piston valve shown in Figure 5 also carries the seat packing on the piston.However, the loose compression ring is replaced by a friction ring that acts as a

spring element and, as such, pre-stresses the packing. When the piston moves

into the seat, the friction ring comes to rest in the seat bore, and any

progression of the piston increases the packing stress. National standards that

apply specifically to piston valves do not exist.

Applications

Duty:

Controlling flow & Stopping and starting flow

Service: Gases, Liquids, Fluids with solids in suspension & Vacuum

4- Angle Valve

Angle valves operate in a manner similar to that of a globe valve. Avalve stem raises and lowers a disk to control fluid flow through the valve. The

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90 angle between the inlet and outlet pipes greatly reduces the pressure drop

across the valve as compared to a globe valve, Fig. (1) .

These valves have been used for flow control especially in systems

where valve geometry or pressure drop were a concern. When flange facingsare used, this design allows for easy removal and replacement of the valve.

Fig. (1) Angle Valves

Function of Globe and Angle Valve

Globe and angle valves are compact and light in weight, and they can be

installed in less space than required for conventional valves. Their pressure-seal

bonnet assures freedom from bonnet-joint leakage and maintenance.

The globe and angle valve has a swivel plug type disk. These valves are

used in high pressure service. The end-to-end dimensions are different from

those of flanged valves.

Function of Angle Valve

The internal parts of an angle valve are very similar to those of a globe

valve. The angle valve derives its name from the fact that the outlet flow leaves

the valve 90-degree from the inlet.

The Advantage of the Angle Valve

1- The angle valve has considerably less turbulence, restriction of flow, and

pressure drop than a globe valve because flow makes one less change of

direction.

2- Angle valves also cut down on the piping installation time, labor andmaterials.

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3- An angle valve reduces the number of joints or potential leaks by serving

as both a valve and a 90-degree elbow.

4- The angle valve is available with the same seating variations as the globevalve: plug type disk, conventional disk, and composition disk.

However, many refineries do not encourage the use of angle valves because

of standardization programs. An angle valve can be used only at a 90-degree

change of direction, whereas a straight-though globe valve has a more flexible

usage, both in location and open ability, due to its more advantageous

orientation.

5- Needle Valve

A needle valve is similar in principle to a globe valve except valve

closure is achieved by lowering a slender point fitting into a conical or needle

seat. These valves have been widely used to accurately regulate the flow of

liquids and gases at low flow rates. The needle point of the stem and the

conical seat are both normally metallic, though elastomeric seats have been

used for fine adjustments, See Fig. (1).

Fig. (1) Needle Valve

6- Plug Valves

Like gate valves, plug valves are essentially intended for on-off service.

The disadvantages of using these valves for throttling device are:

1- The internal parts wear rapidly

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2- The flow is not a linear function of the degree of closer.

The only primary moving part in typical plug valve is the tapered or

cylindrical plug. This is transversely pierced to allow liquid to flow when the

pierced section is exposed to the valve port. In simple, single-port plug valves,flow is controlled by turning the plug 90 degree.

Plug valves can be classified as:

1- Lubricated

2- Non-lubricated.

Both types are identical in operation, but differ in plug and seat design,

see figure (1). Common lubricated plug are equipped with peripherallubrication channels is forced, under pressure, through these channels to

provide a thin film between the plug surface and the seat wall.

The lubricant is kept within the valve by a ball check valve in the stem.

The lubricant reduces wear between the two surfaces and reduces friction and,

hence, the tendency to jam. Non-lubricated plug valves must process liquid.

Either of two methods is employed to prevent leakage and provide

smooth operation: an elastomeric or polymeric sleeve surrounding the plug or

an elastomeric or polymeric coating on the plug itself. Materials having self-

lubricating properties, such as "Teflon", "Penton", " Nylon", etc., are used.

Plug valves have the following advantages:

1- Simple of construction.

2- Compactness.

Their simple seals are suitable for multi-port service. These can handle

three to four separate streams. The most common valves are three and four-portunits handling two and three and four streams, respectively. A single four-way

plug valve can take the place of four straight flow valves. This also reduces the

piping and the number of fittings needed.

Multi-port plugs, however, are more complex than single-port units.

Although in single-port plugs, the valve can be opened or closed by a 90 turn,

the multi-port units require intermediate positions for each stream. Suitable

stop-tabs are normally supplied but inexperienced operators can be easily make

mistakes.

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Lubricated plug valves are available in sizes ranging from 1/4 to 30

inches NPS. These normally operate at pressures up to 5500 psi (37.92 Mpa)

and temperatures up 600 F (315 C).

Non-lubricated plugs, particularly those using "Teflon" sleeves, arecommonly found in sizes ranging from 1/4 to 16 inches NPS. Since "Teflon"

deforms under extreme temperature and pressure conditions, these valves are

limits to 425 F (218 C) and 750 psi (5.17 Mpa), respectively, Fig. (2) .

Fig. (1) Plug Valves

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Plug Valves


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Plug or stop cock valves are one of the oldest types of valves and are still

widely used for on-off service. Plug valves are made with both cylindrical and

tapered plugs, see the next figure.

Early models of the cock valve used metal-to-metal seals that were non-lubricated. This design is still used, but problems with galling and sticking limit

their usefulness. The use of lubricant between the plug face and the seat

eliminates most of these problems. The lubricant helps to control leakage

around the plug, reduces wear between the valve contact surfaces, and slightly

lifts the plug to reduce the operating torque required to operate the valve. Plug

cock valves tend to be used for smaller flow rates, while the related ball valve

is used for a much wider flow rate range, Fig. (3).


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7- Ball Valves

Ball valves use a spherical element for sealing, which minimizes

misalignment problems. These valves are limited to moderate temperature

service (below 250 C) by the plastic seats that create a seal around the ball.

The type of seat can vary with the valve pressure rating and materials of

construction. Some valve seats are a single molded form, while other valve

seats with higher pressure ratings often incorporate a trunnion design where

each face of the ball is sealed separately. This type of design is similar to a plug

cock valve, except the spherical sealing element in these valves is less likely to

freeze in position. They have found applications in flow control, as well as

on/off use in isolating a pipe stream. The pressure drop across the valve in a

fully open position is minimal for a full-port design. However, with restricted-

port designs the pressure drop can be significant.

Ball Valves

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Ball Valves.

Ball Valves with Actuators.

Ball Valve with Gear Operated.

Multi port Ball Valve.

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Ball Valve with Actuator Operated.

Ball valves, as the name implies, are stop valves that use a ball to stop or

start the flow of fluid. The ball, shown in the next figure, performs the same

function as the disk in the globe valve. When the valve handle is operated to

open the valve, the ball rotates to a point where the hole through the ball is inline with the valve body inlet and outlet. When the valve is shut, which requires

only a 90-degree rotation of the handwheel for most valves, the ball is rotated

so the hole is perpendicular to the flow openings of the valve body, and flow is

stopped.

Typical seawater ball valve.

Most ball valves are of the quick-acting type (requiring only a

90-degree turn to operate the valve either completely open or closed),but many are planetary gear operated. This type of gearing allows the

use of a relatively small handwheel and operating force to operate a

fairly large valve. The gearing does, however, increase the operating

time for the valve.

Some ball valves contain a swing check located within the ball

to give the valve a check valve feature. Ball valves are normally

found in the following systems aboard ship: seawater, sanitary, trimand drain, air, hydraulic, and oil transfer.

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Forging brass ball valve

Technical standard

Nominal Pressure: 1.6Mpa Working Medium: Water, Oil, Gas

Working Temperature: under 100C

Parallel Pipe Thread to GB8464

Advantage Ball Valves

Trunnion mounted designs permit much larger sized and higher pressures

Non-resilient and metal seats extend temperature range to 1000

Environmental protection and emission control techniques widely

available

Infinite choice of materials of construction in combination with design

options and choice of seating

Manual, pneumatic, hydraulic and electric operators

Top entry designs facilitate field inspection and maintenance

Taper seating permits wide temperature cycling and reduces wear

Erosive and viscous media easily handled

Ball control valves deal with simple throttling and complicated process

control systems

Welded body ball valve

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Bolted body ball valve - stainless steel 10"

Bolted body ball valve - 6"

Top entry ball valve - 24" Rising stem ball valve

8- Butterfly Valve

The sealing action of a butterfly valve is achieved by rotating a disk of

approximately the same diameter as the pipe from a position in line with fluid

flow to a position perpendicular to flow. The axial length of these valves is less

than any other valve, which in cases where flange faces are used with large

pipe sizes (greater than 10 inches) these valves have the lowest initial cost.

If resilient seats or piston rings on the disk are used, these valves can be

sealed by relatively low operating torque on the valve stem. This sealing action

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is assisted by the fluid-pressure distribution that tends to close the valve. This

same hydraulic unbalance requires that a latching device or worm gear be

installed to prevent unwanted closure of manually operated valves. Though

butterfly valves are used for low-pressure drop applications, the pressure drop

across the valve is quite high with large flow rates as compared to a gate valve.

Butterfly Valves

There are three types of butterfly valves:

1- The lug body.

2- The wafer body.

3- The two-flange body.

The lug body has lugs to match the companion flanges bolting pattern, see the

next figure (a). The wafer body does not have lugs for bolting, it simply

sandwiches between the companion flanges, see the next figure (b). The two-

flange body has built in flanges, see the next figure (c). Gaskets are notrequired for a butterfly valve since the valve linear itself forms a gasket on both

flange faces. Gaskets may be used, however, for protection of the liner where

frequent disassembly of the associated piping may be required. Thick, soft

gaskets should be avoided. The word disk is marked on the stem below the

flats to indicate the position of the disk.

A butterfly valve can be used as a control valves or as a block valve if

mounted with a diaphragm. Butterfly valves are used in water service, oil

service, etc. They are also used a lot in commercial tanker ships. When a

butterfly valve is in the open position, the flow runs parallel to the pipeline

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around the disk. To shut off the flow, all that is required is a 90 degree turn,

which places the disk against the valve liner and body.

(a)Lug body.

(b) Wafer body. (c) Two-flange body

Butterfly valves have the following advantages:

1- Compactness and simplicity.

2- Low pressure drop.

3- Good for slurries since they are self-cleaning.

4- Satisfactory throttling characteristics over most of

the range.

Butterfly valves have the following disadvantages:

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1- The unbalanced torque on the disk (expect when the valve is fully open or

closed) tends to close the valve.

2- Large valves require a large amount of force to operate the disk.

3- Throttling characteristics are poor when the disk is less than 15 from the

fully closed positing. A number of different methods are used to seal the disk inbutterfly valves. In light duty valves, the disk seats directly on the body wall,

making a metal-to-metal contact. This does not normally give a bubble tight

seal.

For high-pressure service or where really right seals are required, the disk

can be equipped with a resilient lip on its periphery. Alternative, seal rings can

be incorporated into the valve wall. Butterfly valves are available in diameters

from 1 inch to specially made units as large as 10 feet. The disk- to-wall seal is

the limiting factor for temperature and pressure.

Valves with metal-to-metal seals are generally able to withstand higher

temperatures than those with resilient seating materials such as "Teflon",

rubber or "Hypaln". Valves with seal ring insert have been used successfully at

pressures up to 3000 psi (20.685 MPa). As explained before the butterfly valve

are available in wafer and lug type. The Wafer valve can be installed between

two flanges using bolts or nuts and studs. While the lug style valve have metal

inserts installed in the valve's bolt holes and the valve is installed between two

flanges using a separate set of bolts for each flange as seen clearly in the next

figure.

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Butterfly valve with Lug type.

Butterfly valve with Wafer type.

Butterfly Valves can be utilized Universally. Its application range includes,

Process in the Chemical, Pharmaceutical, Power, Plant, Paper, Sugar, Drilling

Rigs, Heating & Air Conditioning, Cooling, Water, Water Treatment Plants, &

even in the construction industries for compress Air, Water, Fuel, Oils, Gases,

Slurries with suitable seat (lining) & Disc material for a wide range of pressure

& temperature. These Valves are wafer type and have been design to fit

Without gasket between flanges.

Specifications of some Butterfly valves : -

TYPE Wafer type, Slim - Seal

MOC C.I. / C.S. / SS 304 / 316

SEATNeoprene / Nitrile / Viton / Silicon /

PTFE

RATING ASA 150#, 300#

END CONNECTION Wafer type, Lags type, Flanged End

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SIZES AVAILABLE 40MM TO 600MM

In the next figures there is some Butterfly valves with motorized operated,

with Gear operated and with pneumatic actuator.

Butterfly Valve with Motorized operated.

Butterfly Valve with Gear operated.

Butterfly Valve with Pneumatic Actuator.

1 Gate Globe Ball Butterfly1[1]

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