1. 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. 2.5 – March 13, 2019

2. Process Instrumentation and Control - Prof. M. Miccio
ACTUATORS
Actuators are the mechanical equipment that supply the force necessary to open or close a valve.
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
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Process Instrumentation and Control - Prof. M. Miccio

3. Process Instrumentation and Control - Prof. M. Miccio
MANUAL ACTUATOR
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.
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Process Instrumentation and Control - Prof. M. Miccio

4. GLOBE VALVE: FORCES ACTING ON THE CLOSURE MEMBER
HYPOTHESES:
P1 > P2
No stem bending
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 P1 F P2
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Process Instrumentation and Control - Prof. M. Miccio

5. single or double seat valvesF F F
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Process Instrumentation and Control - Prof. M. Miccio

6. double seat GLOBE valve
from BELIMO glossary:
Leakage on closure is high since getting the seats to touch the discs simultaneously is difficult.
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Process Instrumentation and Control - Prof. M. Miccio

7. 1st Example of a CONTROL VALVE with PNEUMATIC ACTUATOR
Yoke
Construction drawing Construction drawing
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Process Instrumentation and Control - Prof. M. Miccio

8. MEMBRANE 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 with 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
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 the travel of the closure member by means of a graduated scale placed on the yoke.
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Process Instrumentation and Control - Prof. M. Miccio

9. MEMBRANE PNEUMATIC ACTUATOR
ENEL SpA
Thermal power plant Sulcis – Sardegna
Valve and pneumatic Actuator
Picture
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Process Instrumentation and Control - Prof. M. Miccio

10. MEMBRANE PNEUMATIC ACTUATOR
Construction drawing Animated drawing
actuador-diafragma. swf
(su Safari)
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Process Instrumentation and Control - Prof. M. Miccio

11. MEMBRANE PNEUMATIC ACTUATOR
Bottom valve
Animated drawing
Operating scheme
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Process Instrumentation and Control - Prof. M. Miccio

12. Process Instrumentation and Control - Prof. M. Miccio
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). 
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Process Instrumentation and Control - Prof. M. Miccio

13. Control Valve with Positioner
Schematic drawing
Schema di principio
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Process Instrumentation and Control - Prof. M. Miccio

14. Control Valve with Positioner 2
Schematic drawing
Schema di principio
from US Department of Energy Instrumentation and Control Module 2
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Process Instrumentation and Control - Prof. M. Miccio

15. PNEUMATIC MEMBRANE ACTUATOR
direct action
flow-to-open
reverse action
flow-to-close
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.
Air-to-open valves are normally held closed by the spring and require air pressure to open them - they open progressively as the air pressure increases.
see also:
§ Stephanopoulos, “Chemical process control: an Introduction to theory and practice”, Prentice Hall, 1984
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Process Instrumentation and Control - Prof. M. Miccio