en_lo2-ud2 classifications and construction characteristics of valves
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UNIVERSIT DEGLI STUDI DI SALERNOFACOLT DI INGEGNERIA
Bachelor Degree in Chemical Engineering
Course:Instrumentation and Control of Chemical Processes
VALVE TECHNOLOGY
CLASSIFICATIONS AND CONSTRUCTION
CHARACTERISTICS OF VALVES
Rev. 3.51 June 8, 2012
INTRODUCTION
The requirement to regulate and control the flow rate of fluids inhydraulic circuits is very common in industrial process.
It recurs in energy and steam production, control of level and
pressure in tanks containing liquid and gas, control of temperaturein rooms and pipes, control of chemical composition of a specifiedproduct.
The final control elements used to regulate the flow rate of fluidsare valves and pumps.
The selection of the valve type, its characteristics and the properdesign can significantly affect the performance of a control system.
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INTRODUCTION
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VALVE DEFINITION
A mechanical device that is used in a fluid power system, which is
used to provide some change of state of the fluid.from http://www.engnetglobal.com/tips/glossary.aspx?search=valve
GENERIC VALVE SYMBOL
CONTROL VALVE DEFINITION
A valve that modulates the flow of fluid in a conduit in response to asignal from a process measurement control system.
From http://www.answers.com/topic/control-valve
VALVES: COMPONENTS
Body
Closure member
Actuator (device that supplies force and motion to a
valve closure member)
Joints
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VALVES(schematic drawing)
CLOSURE MEMBER
ACTUATOR
JOINTS
taken from:Magnani, Ferretti e Rocco (2007)
BODY
COMPRESSED AIR
SEAT
MEMBRANE
INGOINGFLUID
OUTGOINGFLUID
SPRINGSTEM
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1st CLASSIFICATION OF VALVES(based on FUNCTION)
Valves have the function of:
ON/OFF: valves having two positions:
In the one position the passage of a fluid is stopped (with a leak-tight seal).
In the other position flow is allowed with a low pressure drop
DIVERT SERVICE: valves having two positions, which never block flow:
In the one position flow is allowed from the common port to port A.
In the other position flow is allowed form the common port to port B
THROTTLING: in order to regulate the fluid flow rate by changing the
position of the closure member
PRESSUREREGULATING: in order to regulate pressure of gas and
steam
SAFETY/PRESSURE RELEASE: in order to prevent the overcoming of ahazardous pressure for structural resistance of piping and equipment
CHECK VALVE: to allow the one way flow of a fluid only
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VALVE FUNCTIONS:EXAMPLES
ON/OFF valve Check valve Safety valve
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scheme Divert valve section drawing
2nd CLASSIFICATION OF VALVES(based on SIZE and/or EXTERNAL SHAPE )
BIB COCK (NPS
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2nd CLASSIFICATION OF VALVES(based on size and/or external shape )
BIB COCK (NPS
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SIDE VIEW TOP VIEW
The ball valve is themost common devicefor ON/OFF switch ofa flow in pipes.
It operates by meansof the 90rotation of
a spherical closuremember in acylindrical cavity,coaxial to the flow.
This valve allows thefull closure/openingand, to some extent,the pressure-regulation of theflow.
BALL VALVE/COCK (for ON/OFF)
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SCHEMATIC DRAWING
CUTAWAY DRAWING
MODULATING BALL VALVE
(for THROTTLING)
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SCHEMATIC DRAWING
CUTAWAY PICTURE
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EXAMPLE OF MODULATING BALL VALVE
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CUTAWAY PICTURE
PLUG VALVES/COCKS(conically-tapered, cylindrical)
NPS 1
SIDE VIEW TOP VIEW
SCHEMATIC DRAWING
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TWO-PORT CONICALLY-TAPERED PLUG COCK
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MULTI-PORT COCKS(spherical, cylindrical, conically-tapered)
NPS 1
THREE-PORT
PLUG COCK
FOUR-PORT
PLUG COCK
TOP VIEW
SCHEMATIC DRAWING
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BUTTERFLY COCK
SCHEMATIC DRAWING ANIMATED DRAWING
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SIDE VIEW FRONTAL VIEW TOP VIEW
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BUTTERFLY VALVE
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BUTTERFLY VALVE(DN 32-1200)
Construction details:
1. Body and flanges; stem extension for theinsulation.
2. Stem with position indicator.
3. Disk.
4. Interchangeable hose.
5. Plain bearing.
6. Lap-jointed disk.
7. External gasket.8. Anti-ejection gasket.
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CUTAWAY DRAWINGS
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2nd CLASSIFICATION OF VALVES(based on size and/or external shape )
BIB COCK (NPS
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EXAMPLES OF GATE VALVES(for ON/OFF)
Constructiondraw
ing
Picture
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2nd CLASSIFICATION OF VALVES(based on size and/or external shape )
BIB COCK (NPS
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GLOBE VALVES and COCKS
NOTE:
They operate for THROTTLING.They are known as globe because their body was formerly spherical.
GENERAL EXAMPLE of GLOBE VALVE
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Construction drawing Animated drawing
GLOBE VALVES (NPS>1)
Automatic globe valve with float
Guided-flow valveor
Z-body globe valve
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Free-flow valveor
Y-body globe valve
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3rd CLASSIFICATION OF VALVES(based on the position/coupling with the piping
in the process)
ANGLE VALVE
BOTTOM VALVE
STRAIGTH-FLOW VALVE
NOTE:The bodies of valves have an
arrow indicating the directionof the flow.For bidirectional valves, suchas butterfly, globe and gatevalves, no indication isreported.
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ANGLE GLOBE VALVE
1. Body
2. Bonnet
3. Closure member
4. Seat
5. Stem
6. Handwheel
7. Gland nut
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BOTTOM GLOBE VALVE
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DIAPHRAGM VALVE(OR MEMBRANE OR PINCH VALVE)
Schematic drawing Animated drawing Section drawing
WEIRVALVE
HOSE
VALVE
Guided-flow Free-flow
NOTE:The throttling and the
hermetic are directlyperformed by thecompression of an elasticor plastic membrane onthe body of the valve
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Picture
DIAPHRAGM VALVE(OR MEMBRANE OR PINCH VALVE)
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4th CLASSIFICATION OF VALVES(based on the shape of the CLOSURE MEMBER)
DISK VALVE
CAP VALVE
PISTON VALVE
NEEDLE VALVE
CAGE VALVE
V-PORT
GATE VALVE
BUTTERFLY VALVE
PLUG VALVE (spherical, cylindrical, conically-tapered)
G
lobevalve
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CLOSURE MEMBERS
DISK CLOSURE MEMBERThe increase of the flowrate occurs almost exclusively in the first part of the opening , afterwhich further increase of flowrate are almost negligible.
For this reason, the disk closure member is also formerly known as quick opening.It is commonly used for on/off function.
LINEAR CLOSURE MEMBERIn this case a linear relation between the opening of the valve and the flowrate.The shape of the closure member is usually parabolic.Closure members with a linear characteristic are used when the operating pressure drop orflowrate do not change significantly with the time during the process.
EQUAL PERCENTAGE CLOSURE MEMBERIn this case for a constant increase of the trim travel we have an equal percentage increaseof the flowrate, for the same pressure drop. Considering and increase of 10% of the opening,the flowrate increases about 50% of the initial flowrate. It follows that the most increase offlowrate of the valve occurs in the last part of the travel of the closure member.
The equal percentage closure members are used when most of the pressure drop islocalized in the plant and only the lower part occurs crossing the valve. They are alsosuggested when the flowrate and the operating pressure drop are subjected to significantchanges during the process.
see also: 13.5 - Stephanopoulos, Chemical process control: an
Introduction to theory and practice, Prentice Hall, 1984
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CLOSURE MEMBERSIN THROTTLING GLOBE VALVES
taken from Magnani, Ferretti e Rocco (2007)
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NEEDLE VALVE
Picture
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CAGE VALVE
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Picture
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V-PORT GLOBE VALVE
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5th CLASSIFICATION OF VALVES(based on the MOVEMENT of the closure member)
LINEAR VALVES
ROTARY VALVES
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2nd CLASSIFICATION OF VALVES(based on size and/or external shape )
BIB COCK (NPS
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RUPTURE DISK
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CHECK VALVES
Fig. 32.67 - Valvola diritegno a "clapet".
Fig. 32.69 - Valvola di ritegno a flusso libero.
Fig. 32.68 - Valvola diritegno orizzontale aflusso avviato
Fig. 32.70 - Valvola diritegno verticale
Clapet checkvalve
Guided-flowcheck valve
Vertical check valve
Free-flowcheck valve
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ROTARY VALVES for bulk solids
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Exploded view drawing
ROTARY VALVES for bulk solids
Animated drawing