Valves and Piping (1)

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Module 11

PIPINGS and VALVES



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Course Contents

1. Pipe

2. Piping standard

- Nominal pipe diameter- Schedule number

- Piping standards code

- Tubes

- Fittings and other piping auxiliaries

3. Method of joining sections- Threaded

- Bell and spigot

- Flanged

- Welded connection

- Fitting

4. Types of flanged joints

5. Expansion joints

6. Blinds

7. Spaces



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Course Contents

8. Valves

- Types of valves

9. Valves

- Gate valve

- Globe valve

- Diaphragm valve

- Plug valve- Ball valve

- Butterfly valve

- Needle valve

- Check valve- Safety valve

10. Function of valve

11. Basic control function of valves



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Course Contents

10. Application of Valve types

11. Valve ratings

12. Valve operation and maintenance

13. Do’s and don’t for better valve service

14. Pressure relieving devices

- How high pressure develops

- Types of pressure relieving devices15. Definition of pressure relief terms



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Pipes

• Piping systems are the arteries and veins of a petrochemical plant just as they are in the human body. In a petrochemical, piping

systems handle all liquids, solids, gas or vapor.

• Material is frequently stored and handled in the fluid state. Most fluid

cannot be handled in open channels but required closed ducts.

• In ancient these ducts were hollowed logs and later they were madeof section of wood or of pottery.

• Development of iron brought about the manufacture of cast iron andwrought iron pipes.

• Any structural material now available is used for pipe in applicationwhere its peculiar advantages are most valuable.



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Piping Standards

Nominal pipe diameter

Pipe sizes are based on the approximate diameter and are reported as

nominal pipe sizes. Although the wall thickness varies depending on

the schedule number, the outside diameter of any pipe having a given

nominal size is constant and independent of the schedule number. This

permits the use of standard fittings and treading tools on pipes of

different schedule numbers



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Piping Standards

Schedule number

• Pipes were originally classified on the basis of wall thickness

as standard (extra strong, and double extra strong).

• Because of modern industrial demands for more exact spec,

pipes are now specified according to wall thickness by astandard formula for schedule number designated by the

American Standards Association.

• Schedule number is defined by ASS as: = 1000 Ps/Ss

where Ps = safe working pressure

Ss = safe working fiber stress



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Piping Standards

Schedule number

• Ten schedule numbers are in use at present.

• These are 10, 20, 40, 60, 80, 100, 120, 140, 160

• For pipe diameters up to 10 in, schedule 40 corresponds to the

former “standard” pipe and schedule 80 corresponds to the

former “extra strong” pipe.



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Piping Standards

Schedule number

How they came up with the formula?Bursting pressure of a thin walled cylinder may be estimated from

the following equation:

Pb = 2STtm/Dm where: Pb = bursting pressureST = tensile strength

tm = minimum wall thickeness

Dm = mean diameter



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Piping Standards

Schedule number

A safe working pressure Ps can be evaluated from equation if the

tensile strength is replaced by a safe working fiber stress Ss

Ps = 2Sstm/Dm



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Piping Standards

Piping standard codes

• The American National Standards Institute (ANSI) and the American Petroleum Institute (API) have established dimensionalstandards for most widely used piping components

• ANSI B31- List of those standards can be found in the ANSI B31 code

section

- Section also lists specifications for pipe and fitting materials

and testing methods of the American Society for Testing and

Materials (ASTM)- American Welding Society (AWS) specification

- Standard of the manufacturers Standardization Society of the

Valve and Fitting Industry (MSS)



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Piping Standards

Piping standard code (con’t)

The design of piping system applied to this project is listed as

ASME B31.3

• ASME stands for American Society of Mechanical Engineer

• ASME 31.3 is actually a section of ANSI B31

• ASME (ANSI) 31.3 is a Standard Number and designation isChemical Plant and Petroleum Refinery Piping

• ASME (ANSI) 31.1 scope and application:

- For all piping within the property limits of the facilities engaged

in the processing or handling of chemical, petroleum or relatedproduct unless specifically excluded by the code

• Information on latest issue can be obtain for ASME. 345 East

47th st. New York NY 10017



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Piping Standard

Tubing

Copper tubing, brass tubing are used extensively in industrial

operations. Other metals, such as nicklel and stainless steel, are also

available in the form of tubing.

Although pipe specifications are based on standard nominal sizes,

tubing specs are based on the actual outside diameter with a

designated wall thickness.

Conventional system, such as the Birmingham wire gauge (BWG) are

used to indicate the wall thickness.



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Piping Standard

Fittings and other piping auxiliaries

• Fittings, flanges, valves, flow meters, steam traps and many other

auxiliaries are often rated on the basis of the safe operating

pressure as

25 psi – low pressure125 psi - standard

250 psi – extra heavy

300 to 10,000 - hydraulic



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Method of Joining Sections

Method of joining sections

The methods of joining sections are generally similar for all

materials. The principal methods involve are

1. Threaded

2. Bell and spigot

3. Flanged

4. Welded connections

5. Fitting



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Threaded Joints

• Threaded pipe is most commonly encountered in industry because

practically all small sizes of pipe are joined by thismethod, whether

fabricated of steel, wrought iron, cast iron, brass, or plastic.

• This system is simple because the outside diameters of the pipe are

kept constant with a tolerance of 1/64 in. oversize and 1/32 in.

undersize, and the inside diameters of fittings are kept within the

same limits, regardless of materials.

• The tolerance for the wall thickness of the different materials varies

but is usually 12.5 per cent.

• Pipe larger than 12in. Is rarely threaded, and the outside diametercorresponds to the nominal pipe size.

• Standard lengths of pipe are from 16 to 22 feet.



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Bell and Spigot Joints

Bell and spigot connected pipe handle more fluid than any other

connection since it is the most practical type of joint in large pipe

sizes when pipes are made of materials other than steel. These

joints are usually calked with oakum and lead but the mechanical

joint is becoming more popular because of the tighter joint, simplicity

of installation, greater latitude of angular displacement andexpansion. These joints may be “locked” with a groove in the spigot

which prevents pulling apart the joint, “roll on” with a rubber gasket

tightened with a bolted ring or “screwed gland”, with a ring gland

drawn up against the gasket when screwed into threads in the bell.

Materials for pipe joined in this manner are usually cast iron, clay,

or concrete, although glass, plastic and cement asbestos are

sometimes employed.



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Welded Connections

• The modern trend for pipe in sizes above 2 in. is toward more

welded connections. No threading, calking, or bolts is needed, and

no gaskets are required when the system is fused into an unknown

line of material.

• Pipe ends needs no treatment other than scarfing (beveling) and

very few fittings are required if the welder shapes the necessary

pieces from pipe sections.

• Fittings and valves are of steel and are of two types, butt weld and

socket weld. The butt weld fittings are of the same dimension as the

pipe, and the socket weld fittings have enlarged ends similar to

threaded fittings, but the pipe slips into place and is fillet welded.



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Fittings

Threaded joint fittings

• Couplings – join successive straight length of pipes with no change

in direction or size.

• Reducing couplings – used when size is to be reduced or enlarged.

• Elbows – used when direction is to changed (90 and 45 deg elbowsare available)

• Reducing elbows – used when both size and direction are changed.

• Nipples – because of the mechanical difficulty of cutting sharp

thread, nipples are made in factory in a series of standard lengths

from about 4 pipe diameter in length to close nipples, whose threadsmerge from each end of the section.

• Tees and crosses – used if more than 2 branches of piping are to be

connected at the same point.



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Fittings

Threaded joint fittings (con’t)

• Unions – since most piping must be broken at interval for

maintenance and since standard pipe threads are right hand, thus

making it impossible to use right hand fittings exclusively in

connecting pipe from one fixed point to another fixed point, a union

serves as a connector. The two halves of the union may be

tightened to the pipe section independently, and the final connection

made by tightening the bonnet of the union.

• Reducing bushing – used if size reduction is desired at a tapped

connection.

• Street elbow – used if a simultaneous change in direction and

connection to a tapped outlet is required. (male thread at one end

female thread on the other).



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Fittings

Threaded joint fittings (con’t)

• Cap – used to close end of a pipe

• Plug/capped nipple – used to close an opening in a piece of

equipment.



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Fittings

Welded connections

Fittings are of steel and are of 2 types, butt weld and socket weld.

The butt weld fittings are of the same dimension as the pipe, and the

socket weld fittings have enlarged ends similar to threaded to

threaded fittings, but the pipe slips into place and is fillet welded.

Fittings are similar to equivalent threaded type.



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Fittings

Bell and spigot connections

Fittings [of the same materials as the pipe] are similar in type and

function to those for threaded pipe.



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Fittings

Compression fittings

• Compression fittings are widely used for small sized tubing at both

low and high pressure. These are convenient and efficient,

particularly if the connection is to be broken.



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Flanged Joints

Flanged joints are the most common method for joining pipe in sizes

2 inches and above. The use of flanges allows for making the piping

up in sections that are easy to handle and also allows access for

cleaning, draining, etc.

1. Socket welding flanges

2. Slip on welding flanges

3. Threaded flanges

4. Welding neck flanges

5. Lap joint flanges



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Flanged Joints

Socket welding flanges

• Socket welding flanges are widely used for moderate service,

particularly in the smaller sizes, because of the ease of fit p and

alignment. Although usually welded at the flange hub only, the pipe

end may also be welded without having to reface the flange. The

pipe end weld can be ground to provide a smooth bore.



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Flanged Joints

Slip-on Welding Flanges

• Slip-on flanges are popular for normal service conditions because of

the ease of fit up and alignment and the greater tolerance

permissible in cutting the pipe to length. Recommended fabricationpractice is to wed at both the flange hub and the pipe end.



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Flanged Joints

Threaded Flanges

• Threaded flanges are widely used because no welding equipment is

required for assembly and both the pipe and flange can be

completely salvaged upon dismantling. Accurately cut, clean,

tapered pipe threads dimensioned to ANSI A2. 1 Pipe Threads,

assure strong, tight joints.



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Flanged Joints

Welding Neck Flanges

• Welding neck flanges are designed to be butt welded to the pipe.

The long tampered hub reinforces the flange, permits stress-

relieving, magnafluxing or x-raying the weld, when required, and

removes the flange face from the heat affected zone. These

advantages make welding neck flanges particularly suitable for

severe service involving high pressure, extreme temperatures, or

hazardous fluids.



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Flanged Joints

Lap Joint Flanges

• Lap joint flanges, while requiring a separate end connector, provide

a joint in which the product does not come in contact with the flange.

In addition, the ability of the flange to rotate simplifies assemble and

alignment of bolting on systems requiring frequent dismantling.

• Screwed flanges must be seal welded after the screwed joint is

made up tight. Threading of pipe above 2” is difficult and this type is

not used too often.

• Slip-on flanges are widely used because of their low cost, ease of fit-

up and alignment, however, they are not too good for service where

the temperature and pressure fluctuate. In some services corrosion

of the internal weld may be a problem.



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Flanged Joints

Lap Joint Flanges (con’t)

• Welding neck flanges are probably the best all around type of

flange. They are the strongest of all those shown. There are no flow

problems associated with the assembly and the butt joint is the best

method to insure a sound weld.

• Lap joint flanges are good for a combination of alloy pipe and carbon

steel flanges. This combination reduces the cost and usually

reduces the delivery time compared to waiting for solid alloy flanges.

• The gaskets used with flange joints must always be softer than the

flange material because one or the other must be deformed in order

to make a tight joint.



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Flanged Joints

Lap Joint Flanges (con’t)

• The elastomers include rubber, nylon, plastic, etc. These materials

have a disadvantage in that they can cold flow when squeezed - -

even at room temperature. Thus, it is difficult to maintain a tight joint.

These materials also have a tendency to flow out ant must be

reinforced with cloth or wire mesh if any significant pressure is

involved. Some elastomers are good for no more than 100oF. At this

temperature that will soften and some will actually begin to melt.

Some elastomers are soluble in oil.

• The spiral wound metal gasket with asbestos filler requires special

flange finishing. Tightening of joints using these gaskets normally

requires special attention and will take more time to properly tighten.



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Expansion Joints

Expansion Joints

• All metals expand with increasing temperature. Steel pipe is no

exception to this rule. Expansion must be considered to

accommodate the change in length in the change from atmospheric

temperature to operating temperature. Expansion joints are used to

absorb the effect of the increased length with temperature. These

can be bends or corrugated expansion joints. The attached piping

must be properly anchored and guided to direct the expansion to

utilize the expansion to utilize the expansion joint most effectively.





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Spacers

Spacers are required when there is a blind of appreciable thickness

to be used. It is ordinarily impossible to spring the flanges far

enough apart to install a blind of thickness beyond ½ in.

• Under the above conditions a spacer is required to take up the

space occupied by the blind when the equipment is returned to

operating condition.

• Sometimes the blind and the spacer are attached to each other

and in this case it is known as figure 8 or spectacle blind.



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Valves

• Valves are used for the control of volume and pressure of fluids

moving through piping or in enclosed vessels. They may be

operated automatically or by hand. Type of construction is as varied

as the operations within the plant; each is designed for the service to

be performed.



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Valves

Types of valves

1. Gate valves

2. Globe valves

3. Diaphragm valves

4. Plug valves5. Ball valves

6. Butterfly valves

7. Needle valves

8. Check valves

9. Safety valves



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Valves

Gate valves

• The gate valve is probably the most widely used valve in plantoperations, particularly in the larger sizes of piping installations andthose of the most severe service.

• It consists of a main body and a stem which raises or lowers a “gate”

across the fluid flow. In high pressure installations the gates must beof heavy construction and are sometimes difficult to open. Some aremotor operated and some have a small by-pass line for equalizingthe pressure on both sides of the gate before opening.

• The rising stem gate valve is used in both water and process piping.It requires more overall space for installation, but is used to anadvantage in handling corrosive streams that tend to damage stemthreads in other type valves.



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Valves

Gate valves (cont)

• The non-rising stem gate valve is used extensively in water piping.

Its chief disadvantage is the fact that the degree of opening cannot

be readily determined.

• A gate valve should be used only in service where it can be kept in afully opened position. In partially opened positions the gate will

vibrate and mar the seating surfaces, preventing complete closure.

• Wrenches and levers should not be used to exert extra pressure on

valve stems when the gate has become completely seated in

closing. This practice will result in galling and marring of the seat

and disc, making complete closure impossible.



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Valves

Gate valves

– used to minimize pressure drop in the open position and tostop flow rather than to regulate it.



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Valves

Globe valves

• The essential feature of this type valve is a globular body with aninternal, horizontal partition having a circular opening in which isinserted a ring or seat. The globe or disc seats on this ring to effectshut-off.

• The valve opening is so arranged that flow through it must make two

90-degree changes of direction. This results in a relatively highpressure drop, or resistance to flow.

• The globe valve is generally used in small sized piping for throttlingor control. They are used principally in steam or air service wherethrottling and a positive shut-off is desirable.

• Installation should be such that flow is up through the seat ring andagainst the bottom of the disc or glove. This will prevent openingdifficulties caused by the accumulation of debris above the disc.This should be avoided.



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Valves

Globe valves (cont)

• With this type of valve it is important that the valve is installed with

flow passing through it in the correct or required manner. Normally

the flow enters the “S” shaped passage underneath the valve plug.

When the plug lifts, the liquid flows up past the plug and through the

outlet. This method of installation keeps the pressure from the

packing gland when the valve is in the closed position.

• Occasionally the flow is reversed and the inlet pressure flow enters

on top of the seat. This is normally done when it is wished to have

the pressure assist or ensure the closing of the valve. With oils of a

certain type, this is bad practice as, if the oil has a tendency tocongeal, gum will form on the valve stem and prevent the valve plug

and stem from rising.



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Valves

Globe valves - offer ease in throttling



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Valves

Diaphragm valves



45

Valve

Diaphragm valves

– limited to 50psi, excellent for fluid containing suspended solids

Diaphragm valves



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Valves

Plug valves

• The plug valve, or cock, is a conical plug within a body. Its chiefadvantage is in its tight shut off. A one quarter (90 degree) turn ofthe plug changes it from a fully closed to a wide open position

• Since the plug tends to stick when used in high temperature andhigh pressure service, some types of these valves have been

provided with a means of lubrication through the stem of the cock.• A rotary life plug valve is non lubricated. In operation, as the stem is

turned, the plug lifts slightly from its seat, rotates to the oppositeposition then lowers back into place. This operation can beperformed in about one-fourth to one-half a turn in the smaller sizes.Large valves require more rotation of the stem.

• The quick opening principle of plug valves makes them impracticalas a means of controlling rate of flow.



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Valves

Plug valve – for throttling service, little likelihood of leakage when

closed.



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Valves

Ball valves

• Ball valves are adaptations of plug valves using ball-shaped discsinstead of conical plugs located within the body. A hole through thecenter of this disc provides the straight-through flow which ischaracteristic of ball valves. Ball valves are used to shut off or permitfull flow of fluid through the valve.

• Ball valves have all the advantages of plug valves in terms ofexcellent flow characteristics - quick opening, straight-through flow,minimum turbulence, tight closure and compactness - plus theadditional advantage of not requiring any lubrication or sealant.They achieve tight closure by establishing a controlled squeeze ofthe ball against the sear rings which are made of plastic material

such as teflon.



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Valve

Ball valves



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Valves

Butterfly valves• The butterfly valve derives its name from the wing-like action of the

disc which operates at right angles to the flow. Ordinarily, they are

not intended for tight shut off, but resilient seats have broadened

their possibilities and they are now frequently advertised as having

“bubble tight” closure.



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Valves

Butterfly valve



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Valves

Needle valves• Needle valves are designed to give very fine control of flow in small

diameter piping systems. They get their name from their sharp-

pointed conical disc and matching seat. The stem threads are fine

so that more turns of the hand wheel are required to increase or

decrease the opening through the seat.



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Valves

Needle Valves – offer flow adjustment on small lines



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Valves

Check valves• Check valves are automatic in operation. They prevent flow in one

direction, but allow it in the other. These valves should be carefully

checked for direction of flow in lines.

• Swing check valves are unsuitable for use in vertical lines. Note

importance of correct installation of a check valve in relation to thestream flow. Usually the valve body has features that indicate

correct direction.

• Sometimes an arrow indicates the direction of flow permitted

through the valve. Do not rely upon a check valve to give full shut-off

against a back flow. Only on special occasions, [authorized] will thecheck valve be depended upon to prevent back flow of liquid or

other hazardous material when opening lines into other systems or

to the atmosphere. Always use a block valve when possible.



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Valves

Safety valves• Safety valves are installed in strategic locations to provide pressure

relief for process equipment subjected to excessive pressure.

• A safety valve consists of six basic parts; spring, spindle or stem,

adjusting screw, disc, nozzle or seat, and body. Safety, or relief,

valves are intended for emergency protection only and should not beused as an operating valve.

• Frequent “popping” of a relief valve contributes to their failure,

therefore, they should set at 25% above working pressure. For

example, relief valves on the discharge of reciprocating pumps will

relieve with each pump stroke if the set pressure is too low.Continuous pounding of the disc upon the seat causes damage and

resultant leakage of the valve.



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Valves

Safety valves (cont)• Other causes of valve leakage are spring failure and debris on

seating surfaces. Extreme caution should be exercised in tampering

with relief valves while a unit is in operation. The proper place for

reseating a leaking valve is in the shop. Pressure should be reset on

the test rack.

• When pressure builds up in a vessel or line, pressure is also exerted

on the plug. The plug is lifted from its seat and the excess pressure

in immediately released. At the same time, the spring tends to push

back the plug on to its seat. When the spring tension is once again

greater than the vessel pressure then the plug will again reseat.



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Pressure Relieving Devices

Conventional Relief Valve





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Functions Of Valves

(cont)

• When valves are large size, difficult to operate due to flow

conditions, located in inaccessible positions, require rapid opening

and closing, or need to be operated remotely from a central control

area, mechanical or power actuated operators are frequently

installed on these valves. Gear operators, chain wheels, or electric

motor operators are some of the mechanical or power actuated

operators most often used.

• Each type of valve is designated for a specific purpose to meet

and/or satisfy the following basic control functions desired in a

piping system.



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Basic Control Functions Of Valves

• Starting and stopping Flow

To start or stop the fluid flow is the function for which valves are

most generally used. Gate, plug, ball, butterfly and diaphragm

valves effectively perform this function with very little pressure drop

through the valve.• Regulating and throttling Flow

Regulating or throttling flow is most efficiently performed with globe,

angle, or needle valves. These valves are seldom used in size

above 8 inches because of the difficulty opening and closing the

larger valves against pressure.Butterfly and diaphragm valves are also effective as regulating or

throttling valves at limited fluid flow characteristics.



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Basic Control Function Of Valves

(cont)

• Preventing backflow

Check valves perform the function of checking or preventing

reversal of flow in piping systems. Flow keeps these valves open if

the flow is in the right direction, while gravity and reversal of flow

closes them automatically. Check valves are available in two basictypes - swing and lift checks.

• Relieving Pressure

Relief and safety valves are installed on equipment such as boilers,

vessels, drums, piping systems, etc. which can be seriously

damaged if subject to pressures in excess of the equipment design.They are usually spring loaded and automatically open to release

pressure which exceeds the limit for which the valve was set.





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Application Of Valve Types

Globe valves

• Globe valves are named after the globular shape of their body.

They are most suitable for throttling fluid flows because of their type

of seating arrangements, however, they can also be used in fully

shut off and fully open service

• Globe valves seating is parallel to the line of flow with all contactbetween seat and disc ending when flow begins.

• The fluid flow through a globe valve follows a changing course

which causes resistance to flow and considerable pressure drop.

However, in order to control the fluid flow we must sacrifice some

pressure drop.



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Angle valves

• Angle valves are similar to the design of globe valve but have less

resistance which results in less pressure drop.

• The angle valve effectively utilizes globe valve seating principle

while providing for a 90 degree turn in piping. It is less resisting to

flow than the globe valve it displaces. Requires fewer joints; savesmake-up time and labor.



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Needle valves

• Needle valves are designed to give very fine control of flow in small

diameter piping systems.

• Generally used in chemical injections to process and delivery lines





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Plug valves (cont’)

Teflon, however, has its own problems in terms of cold flow and

temperature limitations.

• The lubricated plug valve with lubricant or sealant injected into the

valve under pressure to maintain a leak-tight seal and to permit ease

of movement of the plug inside the valve utilizes the lubricant as ahydraulic jack to raise the plug slightly to reduce the friction during

operation of the plug valve.



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Ball valves

• Ball valves are adaptations of plug valves using ball-shaped discsinstead of conical plugs located within the body. A hole through thecenter of this disc provides the straight-through flow which ischaracteristic of ball valves. Ball valves are used to shut off or permitfull flow of fluid through the valve.

• Ball valves have all the advantages of plug valves in terms ofexcellent flow characteristics - quick opening, straight-through flow,minimum turbulence, tight closure and compactness - plus theadditional advantage of not requiring any lubrication or sealant.They achieve tight closure by establishing a controlled squeeze ofthe ball against the sear rings which are made of plastic material

such as teflon.



69


Ball valves (cont’)

• Because of the sealing of ball valves is accomplished with a ball

shaped disc seating against plastic materials, the temperatures for

which these valves can be used are limited.





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Check valves

• The principal function of a check valve is to automatically prevent

reversal of the direction of the fluid flow. Pressure of the fluid flowing

through the check valve keeps it open – reversal of the flow closes

it. Most manufacturers plainly mark check valves for direction of

flow. The design of check valves are relatively simple and are

available in three basically different types - swing check, lift check,

and ball check.




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Check Valves

• Used to prevent reversal of flow

1. Swing check valve

- Normal design is for use only in horizontal lines

2. Lift check valves

- Vertical lift check valve – for installation in vertical line, where

the flow is normally upward- Globe check valve – for use in horizontal lines

- Angle check valve – used for installation where a vertical line

with upward flow turn horizontal

3. Tilting disk check valve

- May be installed both horizontally and vertically. Less pressuredrop at low velocity but greater at high velocity. Arrests

slamming.



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Swing check valve

• Swing check valves have a disc, hinged at the top, which seats

against a machined seat in the tilted bridge wall opening. The disc

swings freely in an arc from the fully closed position to one providing

unobstructed flow. The fluid flows through the body in a straight line.

The straight line flow results in low pressure drop because of the

minimum resistance to flow.




74


Check Valves

Swing check valve




75


Tilting disk check valve

Check valves





77


Lift check valve (vertical)

Check valves




78

pp yp

Lift check valve (angle)

Check valves



79


Ball Check Valve

• Ball check valves are similar to lift check valves except that a ball is

used in place of the lift disc for closure purposes. The ball is pushed

away from the seat during fluid flow and closes rapidly when flow

stops or is reversed. This valve has extensive use in piping systems

moving hot oils and can only be used in vertical lines.



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Stop-Check or Non-Return Valve

• A special and more complicated check valve called the stop-check

or non-return valve is essential to the safe operation of a boiler.

Their design must conform to the ASME Boiler Construction Code

for Non-Return Stop valves. The valves are intended to perform four

important functions in boiler steam piping:

1. Act as an automatic non-return valve preventing backflow of

steam from the connected main steam header into the boiler in the

event of failure of that boiler.



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• Stop-Check or Non-Return Valve (cont’)

2. Assist in cutting out a boiler, when ceasing to fire that boiler. In

this case, the disc automatically closes and prevents steam header

pressure from entering the boiler. The valves are equipped with a

hand wheel which permits closing the valves under pressure or, if

already closed automatically, permits holding the disc in the closed

position.

3. Assist in bringing a boiler into service after shutdown. This

operation requires considerable care when performed manually but

is accomplished automatically by a stop-check valve without

pressure fluctuations or disturbance of the water level.





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• Water drain valves

Compressed air system, constantly accumulate water and oil. Such

liquids in air lines are a hazard and a hindrance to effective use of

the air system for process uses, tools, machinery, air cylinders, etc.



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Safety valves

• Applications of safety valves will be discussed separately later in

this module under pressure relieving devices.






86




87




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Valve Ratings

Most valve manufacturers comply with MSS Standard MarkingSystem SP-25 in the identification of their valves. The followingsymbols are generally used:

S - Steam

O - OilG - Gas

W - Water

L - Liquid

General purpose valves may show two service ratings. One is asteam rating, based on a specific pressure/temperature condition.The second rating is for cold service.

V l R ti



89

Valves Ratings

• Steam Ratings

Steam ratings are used as a basis for determining the suitability of a

material for a given application. For lower temperatures the safe

working pressure of a material is usually greater that the steam

rating.

• Cold Ratings

Most valves have two service ratings. In addition to the steam

rating, explained above, cold service ratings are usually designated

by the mark WOG, which stands for cold water, oil, or gas, non-shock.

V l R ti



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Valve Ratings

• Steel Ratings are Different

Temperature and pressure are not always the only factors to be

considered, however. Frequently, steel materials are used for their

structural ability to meet unusually severe conditions beyond the

range for which brass or iron are recommended, such as shock,

vibration, line stresses, fire hazard etc.



V l O ti A d M i t



92

Valve Operation And Maintenance

Variations in Stem Operation of Gate, Globe and Angle Valves

1. Rising stem with outside screw and yoke. In this construction the

stem screw remains outside the valve body whether valve is opened

or closed. Stem threads are not subjected to the effects of fluids in

the line - such as caused by corrosion, erosion, sediment, etc. This

construction also permits convenient lubrication of stem threads.

The rising stem shows at a glance the position of the disc.

Adequate headroom must be provided for the rising stem when the

valve is opened, and the stem should be protected against damagewhen raised.

V l O ti A d M i t



93

Valve Operation And Maintenance

(con’t)

2. Rising stem with inside screw. This is the simplest and most

common stem construction for gate, globe, and angle valves in the

smaller sizes. The position of the stem indicates the position of

the disc. The stem should be protected against damage when the

valve is open.

3. Non-rising stem with inside screw. Stem does not rise when

disc is raised, but merely turns with handwheel. Ideal where

headroom is limited. Since stem merely turns when operated,

wear on packing is minimized.

Do’s And Don’t For Better Valve Service



94

Do s And Don t For Better Valve Service

1. Don’t expose valves to damaging blows. Valves can’t be abusedand still operate efficiently. A bent stem not only cripples valves, butmay cause a shutdown that results in costly delay and repair.

2. Don’t overlook leaks – big and small. A leak in a valve often can

be remedied simply and in a hurry, if caught in time. Stem leaksnormally can be fixed by slightly tightening the packing nut or gland.

Stuffing box leaks usually can be stopped by merely “pulling” up thepacking nut. On bolted glands, care must be taken to tighten bolts

evenly… as severely coking the gland will bind the stem. If thestuffing box must be repacked, this repair should be scheduled forqualified maintenance mechanics.

Do’s And Don’t For Better Val e Ser ice



95


(con’t)

2. Bonnet and flange leaks can be caused by bolts loosening under

service strain, If tightening the joints doesn’t stop the leak, the

gasket may be damaged and this repair should also be scheduled

for qualified maintenance mechanics.

3. Don’t spare the oil can. Wear on stem packing is due mainly to

the rising and turning motion of the valve stem, combined with

deteriorating effects of service conditions. A few drops of oil on the

stem, now and then, help to reduce friction - - and wear, Don’t

forget to lubricate exposed stem threads.




96


(con’t)

4. Don’t operate gate valves continuously in a “cracked open”

position because the valve seats will be severely damaged.

Damage to valve seats will cause valve to leak when closed.

5. Do not use large pipe wrenches to close valves.

6. Rising stem valves should be backed off slightly to relieve

tension on the stem.

Pressure-Relieving Devices

H hi h d l



97

How high pressure develops

The possibilities for development of excess pressure exist in nearly

every process plant.Excess pressure can develop from:

1. explosion

2. chemical reaction

3. reciprocating pumps or compressors

4. process upsets5. external fire around equipment

• In addition to the possible injury to personnel, the loss of equipmentcan be serious and an economic setback

• Most countries have laws specifying the minimum attention

required in the applications of pressure-relieving equipment inprocess and steam power plants.




98


Types of pressure relieving devices1. Relief valves

2. Safety valves

3. Safety-relief valve

4. Conventional and balance valves5. Frangible disk (rupture disk)




99


Relief Valve

• A relief valve is an automatic pressure-relieving device actuated by

the static pressure upstream of the valve, and which opens further

with increase in pressure over the set pressure

• Opening of valve is proportional to the increase in pressure over the

opening pressure

• Used primarily for liquid services

• Rated capacity is usually attained at 25 percent over pressure






101


Bellows Relief Valve




102


Emergency Relief Vent




103


Safety Valves

• An automatic pressure relieving device actuated by the static

pressure upstream of the valve, and characterized by rapid full

opening or pop action upon opening.

• It is used for steam, gas or vapor service.

• Rated capacity is reached at 3, 10 or 20 percent overpressure,depending upon applicable code.




104

Safety-relief valve

• Safety relief valve is an automatic pressure relieving device

actuated by the static pressure upstream of the valve andcharacterized by an adjustment to allow either a “pop” or a “nonpop” action and a nozzle type entrance

• Suitable for use as either a safety or relief valve, depending onapplication.

• Safety, relief and safety relief valves are installed in strategiclocations to provide pressure relief for process equipment subjectedto excessive pressures. These valves consist of six basic parts:spring, stem, adjusting screw, disc, nozzle or seat, and body.

• Rated capacity is reached at 3 or 10 percent overpressure,depending upon code and/or process conditions. Pressure relievingvalves are intended for emergency protection only and should notbe used as an operation valve. Frequent “popping” of a relief or

safety valve contributes to their failure and are therefore set at 25%- 50% above the working pressure.




105

Safety-relief valve (con’t)

• For example, relief valves on the discharge of reciprocating pumpswill relieve with each pump stroke if the set pressure is too low.

Continuous pounding of the disc upon the seat causes damage and

resultant leakage of the valve.

• Other causes of valve leakage are spring failure and debris on

seating surfaces.• Used on steam, gas, vapor and liquid (with adjustments) and is

probably the most general type of valve in petrochemical and

chemical plants

Do not tamper with relief valves while a unit is in operation. Theproper place for reseating a leaking valve is in the shop with pressure

reset on the test rack.




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Safety relieve valve




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Conventional and balance safety valve• Conventional safety valves operate satisfactorily only when there is

relatively constant back pressure. Changes in back pressure can

seriously affect its operational pressure and flow capacity

• Balance valves operate satisfactorily under varying back pressure

as this has little influence on performance




108


Frangible disk (rupture disk)• A rupture disk is a thin diaphragm (metal, plastic, non metallic) held

between flanges and designed to burst at a predetermined pressure.

• Each bursting requires the installation of a new disk

• Used in corrosive service, and for required bursting pressure not

easily accommodated by the conventional valve.

• Applicable to steam, gas vapor and liquid system

Definition of Pressure Relief Terms



109


1. Set pressure• Is the inlet pressure at which the safety or relief valve is adjusted

to open

• This pressure is set regardless of any back pressure on the

discharge of the valve




110


2. Overpressure• Pressure increase over the set pressure of the primary relieving

device is over pressure

• It is the same as accumulation when the relieving device is set at

the maximum allowable working pressure of the vessel




111


3. Accumulation• Pressure increase over the maximum allowable working pressure

of the vessel during discharge through the safety or relief valve,

expressed as a percent of that pressure.




112


4. Maximum allowable working pressure• The maximum allowable working pressure of an unfired pressure

vessel is that pressure determined by code requirements, the

metal material of construction and its operating temperature,

above which the vessel may not be operated

• For a given metal temperature, this pressure is the highestpressure at which the safety device may be set to open.




113


5. Operating pressure• Pressure (gage), to which the vessel is subjected in service

• A processing vessel is usually designed for a maximum allowable

working pressure, which will provide a suitable margin above the

operating pressure to prevent undesirable operation of the relief

device• Margin is approximately 10 % higher, or 25 psi – which ever is

higher.




114

e o o essu e e e e s

6. Blowdown• The reduction in flowing pressure below the set point required for

a device to close

• Is the difference between the set pressure and the reseating

pressure of a safety or relief valve

• Expressed as percent of the set pressure or psi




115

7. Back pressure• Pressure developed on the discharge side of safety valves is back

pressure

• This pressure may be generated by the flowing fluid as it passes

through the relief discharge piping, or it may be an established

pressure as a part of a discharge vent system into which the valveis discharging

• It may be combination of these two.

Vacuum Breaker



116

Electric Solenoid



117

Thermal Valve



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