valves, types and operations

Valves,

Types, and

Operations Prepared by

Osama Hasan Intern ‘11 Batch 03 (Enven 1.3)

Engro Fertilizer

Mentor: Aah

1 July 2011

Outline

Valve

Construction

Types

Gate, Globe, Plug, Ball, Diaphragm, Check

Operations

Fouling, Stem Breakage, Packing Leakage,

Gaskets Leakage

Valves,Types and Operations

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Valve

Mechanical devices that are used in

industrial piping for flow control by varying

the pipe opening in three positions:

Fully opening

Fully closed and

Throttling

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See Animation

http://www.tlv.com/global/flash/steam-theory/0704ballvalve_TI.swf

Construction Body; connected to the pipe

Bonnet; mounted on the body to form a tight enclosure

Stem; attached the structure (gate or disk) that resist the flow

The body of the valve is flanged with bolt holes in them to be

held together with pipe; with a gasket in between to provide a

leak-proof connection

4


Construction Gate or Disk; controls the

opening

Stuffing Box; located in bonnet and filled with packing, holds the stem and avoids leaks

Hand Wheel; lifts gate or disk on rotating and vice versa

Seat Rings; perpendicular to flow, make close fit with valve for complete shut down

5


Construction Yoke (For OS & Y);

supports hand wheel and bushing

Flange (for NRS only); resists the stem to move up or down

Valves are characterized by the way they resist the

flow.

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Types

Gate Valve

Globe Valve

Plug Valve

Ball Valve

Diaphragm Valve

Butterfly Valve

Check Valve

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Gate Valve Complete Open / Close

Emergency Shut Down

8 Valves,Types and Operations

Gate Valve

Regulates flow by placing a metal gate or

disc across the opening of pipe.

the gate has to be strong enough to

withstand the pressure of flow.

Gate valves are of two types:

Outside Stem and Yoke (OS & Y) and

Non-Rising Stem (NRS)

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See Animation

http://www.tlv.com/global/flash/steam-theory/0704sikiriben_TI.swf

OS & Y Gate Valve Stem is Threaded at the

hand wheel and screwed through stem bushing

Solidly connected with the hand wheel and turns along with it

Bottom is solidly connected to the gate, neither of which can turn

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OS & Y Gate Valve

The hand wheel and

bushing are also

supported by an

outside yoke.

Stem can be seen

when the valve is

open, therefore needs

stem clearance.

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NRS Gate Valve

Stem threaded on

the bottom, with a

gate threaded on

the inside.

Used in areas,

where not much

overhead

clearance exists.

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NRS Gate Valve

The part of the stem that passes through the bonnet has a flange on it, due to which the stem cannot move up or down; instead engages the gate on turning wheel and pulls it up or down and vice versa.

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Types of Gate

Solid wedge gate

Parallel disc gate and

Solid split gate

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Solid Wedge Gate Made of one part and

bears pressure of the flow on one side only.

Complete shut off is accomplished through a close fit between gate and seat rings.

On lowering or raising of gate there is more friction between gate and seat rings which tends to wear out one seat rings quicker (against the side of flow).

15


Parallel Disc Gate Made out of many parts.

When lower wedge or spreader reaches the stop, it forces the upper spreader to the lower one.

This pushes the discs outward against the seat rings and ensures a very tight closing.

Although one side of disc is more worn but tight closing produced by the wedging action, it still allows complete shutoff.

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Parallel Disc Gate

The discs are attached to the spreader in such a way that they rotate when the gate is raised or lowered, this causes an even wear.

As the upper wedge is raised, it releases the wedging pressure and disc become freer.

17


Parallel Disc Gate

On high temperatures,

pipe expansions can

wrap the body of the

valve, causing extreme

pressure on the gate.

These gates are not used

with material with coarse

particles and in vertical

positions.

18


Solid Split Gate

A solid split gate is made of one piece,

with flexible outer edges. These edges

bear pressure on the gate when a valve

body wraps up.

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Gate Valve Malfunction Gate valves malfunction due to erosion of

gate or seat rings which makes tight closure difficult.

This happens due to the friction between gate and seat rings on rising or dropping the gate very often.

It could be avoided by using gate valves in pipes who are not much disturbed during normal operation i.e. are completely open or completely closed.

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Globe Valve


Globe Valve The line of flow changes

its direction, which creates higher pressure drop and turbulence.

Seat rings are parallel to the line of flow and stem guides the disc into the seating. Opening is controlled by a disc.

Flow starts as soon as the contact of disc and seat is broken.

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Globe Valve Very little wear due to

friction and even wear; however partial opening of valve exposes all parts of disc to flow.

Even wear permits complete closure even after long use.

Flow from under the disc creates less turbulence than flow from the disc.

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See Animation

http://www.tlv.com/global/flash/steam-theory/0704tamagataben_TI.swf

Globe Valve

Globe valves are also

installed on turnings,

called Angle Globe

Valves.

Flow through angle

valve has fewer

changes of direction

and therefore is less

turbulent.

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Types of Disc

Three types of disc are used in globe

valves:

Plug disc

Composition disc and

Conventional disc

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Plug Disc

Cone shaped

Used for heavy

throttling service

Continues to give

positive shut off even

after some wear

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Composition Disc Made of softer materials.

When completely closed, seat ring can make a contact with the soft part of disc.

Fine particles in flow often accumulated on seats or discs can be embedded on the soft part of the disc ensuring a tight closure.

27


Conventional Disc

Smaller disc-to-seat

area than plug discs.

Can crush small

particles more easily

but if nicked or worn,

tight closure is not

possible with them.

28


Plug Valve


Plug Valve Controls the opening

through a hollow plug, which is turned/rotated and aligned with the pipe to permit a straight line of flow.

Plug is turned a quarter turn, to stop the flow.

The valve can be opened or closed more quickly than previous examples and produce little turbulence and pressure drop

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Plug Valve Friction develops between

the body and the plug, which wears the plug giving it a loose fit.

The shank of the plug has a lubricant fitting that makes it possible to apply special lubricant to the plug itself. Lubrication is done often to reduce friction and also prevent leakage.

31


Ball Valve


Ball Valve Good shut-off

capabilities.

Quarter-turn (90°) completely opens or closes the valve.

Minimal valve operation time and decreases the likelihood of leakage due to wear from the gland seal.

33


See Animation

http://www.tlv.com/global/flash/steam-theory/0704ballvalve2_TI.swf

Ball Valve

Ball valves can be divided into two

categories:

Reduced bore: valve opening is smaller

than the diameter of the piping

Full bore: valve opening is the same size as

the diameter of the piping.

valued because they minimize the pressure

drop across the valve.

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Ball Valve Recommended for use in the fully open or

fully closed position.

Not suited to regulate flow by being kept partially open because ball valves make use of a ring-shaped soft valve seat.

When used in the partially open position, pressure is applied to only a portion of the valve seat, which can cause it to deform.

If deforms, its sealing properties are impaired and will leak as a result.

35


Diaphragm

Valve


Diaphragm Valve ‘Pinching' method to stop the

valve flow using a flexible diaphragm.

Available in two types:

Weir and

Straight-way

The most common is the weir-type because the straight-way type requires additional stretching, which can shorten the diaphragm's life-span.

37


See Animation

http://www.tlv.com/global/flash/steam-theory/0704ballvalve2_TI.swf

Diaphragm Valve Advantages:

Valve components can be isolated from the process fluid.

Construction helps prevent leakage of the fluid without the use of a gland seal (packing)

Disadvantages:

Diaphragm becomes worn more easily

Regular maintenance is necessary

Not suited for very high temperature fluids

Mainly used on liquid systems.

38


Check Valve


Check Valve Ensure that flow goes in

desired direction and does not reverses.

Valve is automatically opened by the flow pressure and is closed when the pressure falls.

It allows flow from one side only, and on reverse flow, disc gets closed restricting flow.

40


Lift Check Valve Similar to globe valve

structure, with flow raising the disc and gravity pulling it down.

Direction of flow is always kept from under the disc to minimize turbulence.

It works in both horizontal and vertical positions, but with slight structural modifications.

41


Ball Check Valve

A check valve with

flow not in a straight

line.

Similar to lift check

valve with the disk

replaced with a ball.

42


Operations


Operations

Accumulation of Sludge/ Fouling

Incomplete shut off / opening

Remedy:

Addition of Anti fouling sludge

Dismantling of Valve

44


Operations

Stem Breakage

Replacement of Valve

Else Raising the Stem

By using a Jack Screw

By using over had hoist

45


Operations

Raising the Broken Stem by

using a Jack Screw

46


Operations

Raising the Broken Stem by

using an Overhead Hoist

47


Operations

Packing Leakage

Opening the valve to max. limit

Achieving Back-Seating

Dangerous and only opted in emergency

48


Operations

Gaskets Leakage

49


Thank You

Prepared by Osama Hasan School of Chemical and Materials Engineering (SCME)

National University of Sciences and Technology (NUST)

[email protected]


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