Valves, Types, and Operations Prepared by Osama Hasan Intern ‘11 Batch 03 (Enven 1.3) Engro Fertilizer Mentor: Aah 1
July 2011
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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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See Animation
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
Valves,Types and Operations
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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 Valves,Types and Operations
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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 Valves,Types and Operations
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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. Valves,Types and Operations
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Types Gate
Valve Globe Valve Plug Valve Ball Valve Diaphragm Valve Butterfly Valve Check Valve Valves,Types and Operations
Gate Valve Complete Open / Close Emergency Shut Down
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Valves,Types and Operations
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See Animation
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)
Valves,Types and Operations
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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 Valves,Types and Operations
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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. Valves,Types and Operations
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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. Valves,Types and Operations
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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. Valves,Types and Operations
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Types of Gate Solid
wedge gate Parallel disc gate and Solid split gate
Valves,Types and Operations
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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). Valves,Types and Operations
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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. Valves,Types and Operations
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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. Valves,Types and Operations
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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. Valves,Types and Operations
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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.
Valves,Types and Operations
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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. Valves,Types and Operations
Globe Valve
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Valves,Types and Operations
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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. Valves,Types and Operations
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See Animation
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. Valves,Types and Operations
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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. Valves,Types and Operations
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Types of Disc Three
types of disc are used in globe valves:
Plug disc Composition disc and Conventional disc
Valves,Types and Operations
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Plug Disc Cone
shaped Used for heavy throttling service Continues to give positive shut off even after some wear
Valves,Types and Operations
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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. Valves,Types and Operations
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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.
Valves,Types and Operations
Plug Valve
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Valves,Types and Operations
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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 Valves,Types and Operations
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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. Valves,Types and Operations
Ball Valve
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Valves,Types and Operations
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See Animation
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. Valves,Types and Operations
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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.
Valves,Types and Operations
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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. Valves,Types and Operations
Diaphragm Valve
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Valves,Types and Operations
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See Animation
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 weirtype because the straight-way type requires additional stretching, which can shorten the diaphragm's life-span. Valves,Types and Operations
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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. Valves,Types and Operations
Check Valve
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Valves,Types and Operations
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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. Valves,Types and Operations
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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. Valves,Types and Operations
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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.
Valves,Types and Operations
Operations
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Valves,Types and Operations
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Operations Accumulation
of Sludge/ Fouling
Incomplete shut off / opening Remedy: Addition
of Anti fouling sludge Dismantling of Valve
Valves,Types and Operations
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Operations Stem
Breakage
Replacement of Valve Else Raising the Stem By
using a Jack Screw By using over had hoist
Valves,Types and Operations
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Operations Raising the Broken Stem by using a Jack Screw
Valves,Types and Operations
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Operations Raising the Broken Stem by using an Overhead Hoist
Valves,Types and Operations
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Operations Packing
Leakage
Opening the valve to max. limit Achieving Back-Seating Dangerous and only opted in emergency
Valves,Types and Operations
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Operations Gaskets
Leakage
Valves,Types and Operations
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Thank You Prepared by Osama Hasan School of Chemical and Materials Engineering (SCME) National University of Sciences and Technology (NUST)
[email protected]
Valves,Types and Operations
