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CONTROL VALVES


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Catégorie :Category: mViewer GX Creator App HP-Prime
Auteur Author: dodopace
Type : Application
Page(s) : 15
Taille Size: 1.56 Mo MB
Mis en ligne Uploaded: 15/09/2021 - 18:53:06
Uploadeur Uploader: dodopace (Profil)
Téléchargements Downloads: 1
Visibilité Visibility: Archive publique
Shortlink : http://ti-pla.net/a2792446

Description 

UNIVERSITÁ DEGLI STUDI DI SALERNO


Bachelor Degree in Chemical Engineering


Course:
PROCESS INSTRUMENTATION AND CONTROL
(Strumentazione e Controllo dei Processi Chimici)


VALVE TECHNOLOGY

TECHNOLOGY OF CONTROL VALVES


Rev. 3.2 of April 15, 2021
ACTUATORS
Actuators are the mechanical equipment that supply power/force necessary to open or
close a valve.
Mechanical actuators are, essentially, the alternative to manual operation of a valve.

Tasks of an actuator
The actuator provides the forces able to:
• put the closure member in the specified position
• exert the force necessary to maintain hermetic seal on the seat (if the full closing of
the valve is requested)
• win all the resistant forces, e.g.:
 friction forces exerted on the stem
 force due to the pressure drop on the two sides of the closure member


Types of actuators
• pneumatic (with a membrane)
• oleo-dynamic (hydraulics)
• electric
• manual

15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 2
MANUAL ACTUATOR FOR CONTROL VALVES
MANUAL HANDWHEEL

It is set up on the pneumatic actuator of a control valve in order to
allow functioning in the absence of air
or in case of emergency, e.g.
• crack of the diaphragm,
• failure of the controller or during the start-up,
• etc.




UNIDIRECTIONAL HANDWHEEL

It is the most common manual emergency control for the simplicity
of construction and for the little maintenance.
The handwheel always acts opposing to the spring and therefore
moves down the closure member.
It can be set up on a wide range size of valves.



15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 3
PNEUMATIC ACTUATOR FOR CONTROL VALVES




travel indicator




Yoke
travel indicator




Construction drawing Construction drawing
15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 4
MEMBRANE PNEUMATIC ACTUATOR

PNEUMATIC ACTUATOR
THE PNEUMATIC ACTUATOR IS THE MOST COMMON AND TRANSFORMS THE PNEUMATIC
SIGNAL IN A UNIFORM AND LINEAR MOVEMENT OF THE CLOSURE MEMBER.
IT IS MADE OF:

DIAPHRAGM OR MEMBRANE
IT IS MADE OF NEOPRENE WITH INSERTION OF NYLON, WHICH GIVES A GOOD MECHANICAL
RESISTANCE AND A HIGH OPERATING TIME.
DIAPHRAGM DISK
IT IS MADE OF STEEL AND IS A UNIQUE ITEM WITH THE SHAFT OF THE
SERVOCONTROL WITH A THREAD COUPLING.
IT ALLOWS THE INVARIABILITY OF THE CALIBRATION OF SERVOCONTROL IF THE
MEMBRANE IS REPLACED.
YOKE
IT IS A SUPPORTING MONOBLOC IN CAST IRON.
IT IS CONNECTED TO THE DIAPHRAGM CASING BY MEANS OF HEX CAP SCREWS AND
BLOCKED TO THE BODY OF THE VALVE THROUGH A SCREWED RING NUT.

TRAVEL INDICATOR
IT IS MADE OF STAINLESS STEEL, CO-AXIAL AND COUPLED TO THE STEM BY MEANS
OF TWO SCREW NUT.
IT ALLOWS A VISUAL READING OF THE TRAVEL OF THE CLOSURE MEMBER BY
MEANS OF A GRADUATED SCALE PLACED ON THE YOKE.




15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 5
MEMBRANE PNEUMATIC ACTUATOR
Operating scheme



Bottom valve




Animated drawing
15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 6
MEMBRANE PNEUMATIC ACTUATOR




ENEL SpA
Thermal power plant
Sulcis – Sardegna

Valve and
pneumatic Actuator
Picture
15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 7
SERVO-POSITIONERS

They are accessory devices which measure the stem position and
regulate it to a specified reference value


 ADVANTAGES
• They improve the positioning reducing the effects of hysteresis,
frictions, pressure drop of the supplied air, delay time of the response.
• They limit the positioning velocity (upper limit).
• They allow to some extent a linear response with a first-order
dynamic response in a small range of the stem position (the dynamic
response is characterized from the saturation of the velocity for high
variations).




15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 8
CONTROL VALVE with POSITIONER
Schematic drawing




15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 9
CONTROL VALVE with POSITIONER 2




Schematic drawing




from US Department of Energy Instrumentation and Control Module 2


15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 10
GLOBE VALVE:
NET FORCE ACTING ON THE CLOSURE MEMBER

HYPOTHESES:
P1
• P1 > P2 P2

• No stem bending
F

• Sott= area of the closure member on which the fluid pressure acts
supposed equal both upstream and downstream.

F1 = P1 Sott (upstream closure member force)

F2 = P2 Sott (downstream closure member force)


F = F1 - F2 = (P1 - P2)Sott # 0


15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 11
SINGLE OR DOUBLE SEAT VALVES
F




F F




CUTAWAY DRAWING

15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 12
DOUBLE SEAT GLOBE VALVE




from BELIMO glossary:
Leakage on closure is high since getting the seats to touch the discs simultaneously is difficult.
15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 13
OPERATING TERMINOLOGY OF CONTROL VALVES




direct action
flow-to-open valve




reverse action
flow-to-close valve

AD AD


Air-to-close valves are valves which are held open by the valve spring and
require air pressure (a control signal) to move them towards the closed position.
see also:
Air-to-open valves are normally held closed by the spring and require air § 13.5 - Stephanopoulos, “Chemical process control: an
pressure to open them - they open progressively as the air pressure increases. Introduction to theory and practice”, Prentice Hall, 1984
15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 14

Archive contentsContenu de l'archive

Action(s) SizeTaille FileFichier
3.06 Ko KB readme.txt
3.65 Ko KB lisezmoi.txt
1.09 Ko KB CONTROL_.hpprgm
1.56 Mo MB CONTROL_.hpappdir.zip
95 octets bytes appslist.txt

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