2. Control Valves
A Control Valve is a power-operated device
used to modify the fluid flow rate in a process
system.
There are two basic types of control valves
Control Valve
a) Rotary motion valves having ball, butterfly or plug
type closures.
b) Linear motion valves having globe , diaphragm or
pinch type closures.
3. Control Valve Classification
Control
Valve
Linear Rotary
Motion Motion
Globe Diaphragm Pinch Ball Butterfly Plug
Control Valve
Globe Angle 3 way
Single Double
Seated Seated
4. Linear Motion
Types Of Closure
1.Globe
1.1. Single Seated
1.2. Double Seated
1.3 Three way
2. Diaphragm
3. Pinch
Linear Valve Features
Control Valve
i. TORTUOUS FLOW PATH
ii. LOW RECOVERY
iii. CAN THROTTLE SMALL FLOW RATES
iv. OFFERS VARIETY OF SPECIAL TRIM DESIGNS
v. SUITED TO HIGH-PRESSURE APPLICATIONS
vi. USUALLY FLANGED OR THREADED
vii. SEPARABLE BONNET
5. Single Seated Globe Valve
Features
o Large amount of force
required to drive the stem
o Tight shut off
o Used in small diameter
applications
Applications
Control Valve
o Used for controlling large
range of process
parameters hence used in
oil and gas
production, power
generation
6. Double Seated Globe Valve
Features
o Stem can be driven with small
amount of force
o Can not achieve perfect
closure resulting in leakage
o Used in larger diameter
applications
o Body parts wear out due to
Control Valve
erosion and cavitations which
results in annoying noises
Applications
o Used for high flow and high
pressure services
7. Three Way Valves
Features
o High flow capacity
o Valve used for mixing and
diverting liquids.
o High rangeability
o Leakage capability
consistent with normal
Control Valve
single seated globe valve
Applications
o Used in textile industries
8. Diaphragm Valves
• Features
o Consists of a saddle
or seat upon which
the diaphragm
closes the valves.
o Can handle
corrosive fluids.
Applications
o Used as shut off
Control Valve
valves in food and
beverage
, pharmaceutical and
biotech industries
9. Pinch Valve
• Features
o Tight shut off
o The flexible sleeve
allows the valve to
close drop tight around
solids , solids that
would typically be
trapped by the seat or
Control Valve
stuck in crevices in
globe, diaphragm, butte
rfly, gate or ball valves.
• Applications
•Best used in
controlling corrosive
10. Rotary Motion
Types Of Closure
1. Ball
2. Butterfly
3. Plug
Rotary Valve Features
i. STREAMLINED FLOW PATH
ii. HIGH RECOVERY
Control Valve
iii. MORE CAPACITY
iv. LESS PACKING WEAR
v. CAN HANDLE SLURRY AND ABRASIVES
vi. FLANGELESS
vii. INTEGRAL BONNET
viii. HIGH RANGEABILITY
11. Ball Valve
Features
o Tight Shut Off
o Minimum obstruction for the
flowing media.
o High flow capacity
o Can withstand high pressure and
temperatures
Control Valve
Applications
o Used for hazardous and corrosive
fluids
12. Butterfly Valve
Features
o High flow capacity
o Unlike ball valve the
disc is present in the
flow of the liquid and
hence a pressure
drop is always
induced in the flow.
Control Valve
o Tight shut off
Applications
o Used in Steel
, Sugar and textile
industries
13. Actuators
In control valve we have seen that , the operation of a
control valve involves positioning its movable part (the
plug, ball or vane) relative to the stationary seat of the
valve. The purpose of the valve actuator is to accurately
locate the valve plug in a position dictated by the control
signal.
The actuator accepts a signal from the control system
and, in response, moves the valve to a fully-open or
fully-closed position, or a more open or a more closed
position
The major types of actuators are :
1. Pneumatic type
2. Electric type
14. Pneumatic Actuators
They are basically of two types
1. Piston actuator
2. Diaphragm actuator
These actuators are designed so that
with a specific change of air
pressure, the spindle will move
sufficiently to move the valve through
its complete stroke from fully-closed to
fully-open.
15. Piston Actuator
They can withstand
higher input
pressures.
Can offer small
cylinder volumes.
They are generally
used where the
stroke of a
diaphragm actuator
would be too short
or the thrust is too
small.
16. Diaphragm Actuators
• They have compressed
air applied to a flexible
membrane called the
diaphragm
• They are single acting
i.e. air is supplied from
single side of the
diaphragm
18. Electric Actuators
Electric actuators use an electric
motor with voltage requirements in the
following range: 230 Vac, 110 Vac, 24
Vac and 24 Vdc.
There are two types of electrical
actuator 1. VMD (Valve Motor Drive)
2. Modulating.
19. VMD ( Valve Motor Drive )
This basic version of the
electric actuator has
three states:
I. Driving the valve open.
II. Driving the valve closed.
III. No movement
• The controller
positions the valve by
driving the valve open
or closed for a certain
time, to ensure that it
reaches the desired
position. Valve position
feedback may be used
with some controllers.
20. Modulating
In order to position the control valve in
response to the system requirements a
modulating actuator can be used.
These units may have higher rated
motors (typically 1 200 starts/hour) and
may have built-in electronics.
A positioning circuit may be included in
the modulating actuator which accepts
an analogue control signal (typically 0-
10 V or 4-20 mA). The actuator then
interprets this control signal, as the
valve position between the limit
switches.
To achieve this, the actuator has a
position sensor (usually a
potentiometer), which feeds the actual
valve position back to the positioning
circuit. In this way the actuator can be
positioned along its stroke in
proportion to the control signal.
