Valves and Controls Final
Transcript of Valves and Controls Final
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Are devices that regulates the flow of
fluids by opening, closing, and or partially
obstructing passageways (usually pipes).
Valves have a wide variety of uses in the
distribution of water, oil, gas, and even
hazardous substances in power and industrial
sector, sewerage systems, and even in our very own houses.
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Valves are classified according to their
usage and are the following:
1. Isolation/ Stop Valves
2. Flow Regulation
3. Back Flow Prevention
4. Pressure Regulation
5. Pressure Relief Valves/ Safety Valves
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1. ISOLATION/ STOP VALVE:
The isolation of the downstream system from the
upstream system by the use of an isolation /stopvalve is a critically important function..The prime
requirements of this valve are “TIGHT SHUT
OFF” when closed and “MINIMUM
RESTRICTION” to flow when opened.
Valves used for this function include gate valves,
globe valves, ball valves, plug valves, butterfly
valves, diaphragm valves,angle valves, andpinch valves.
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TYPES OF
ISOLATION/ STOP
VALVES:
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GATE VALVES:Are valves
that are used
intermittentlyrequiringstraight flow
and minimumflow restriction.
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As the name implies, its main workingmechanism (sealing mechanism) resembles
that of a “gate which is wedge-shaped”.
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Such types of valves are not used for throttling as the wedge-shaped gate is prone to
stress which could hamper its operation.
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Are probably the most
common type of valve
and although called a
“GLOBE”, its positive
identification is done
internally as there are
other valve types thatare also globular in
appearance.
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A double ported
globe type of
valve….INTAKE DISCHARGE
SEALING
MECHANISM
SEALING
MECHANISM
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Such valves areused for “FREQUENT
OPERATION
(throttling) ” as there
is less stress imparted
on the closing
mechanism.
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With its flowpattern in the form of aletter “S”, it resultsinto “PRESSUREDROP” between thetwo (or three) sectionsof the pipe.
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Such valves
provide a “FASTER
SHUT-OFF or FASTEROPENING” unlike in
the case of gate
valves…..
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Is a form of GLOBE
VALVE since most of its
internal mechanismcould be found in a
typical globe valve.
ANGLE VALVES:
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It is used in
instances with “SPACE
CONSTRAINTS”…
This is made
possible as flow is
diverted at a right
angle.
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Since the divertion of fluid is at
right angles, a “LARGER PRESSURE
DROP TRANSLATES (fluid friction ishigh)”.
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As a type
of GLOBE VALVE, it
too could also be
used for throttling
since its internalmechanism is not
that much prone to
stress.
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BUTTERFLY VALVES:
A quick-acting
throttle type of valve
that has a circular
disc in a resilient
seat used in a wide
variety of chemicals.
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Quick acting inthat a quarter of a turn
permits a fully open or
fully closed disc.
FULLY OPEN – plate/ disc is parallel with the
pipe axis.
FULLY CLOSED – plate/ disc is perpendicular
with the pipe axis.
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They can be used
effectively in areas where
space is limited and light
in weight.
Large butterfly valves
operate through a gearing
arrangement to operate
the valve itself.
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Since there is not
much obstruction in the
passageway, there isminimal pressure drop
(fluid friction is at a
low).
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BALL VALVES:
Another type of
throttling valve and asthe name implies, its
internal working
mechanism is in theform of a “BALL”
punctured at the
middle.
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Can be used for throttling purposes
according to the design of its internal
mechanism.
There is minimal pressure drop between
the intake and discharge sides of the pipe.
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Like butterflyvalves, ball valves
are also quick
acting…
A 900 turn fully
opens or fully
closes the “ball”.
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PLUG VALVES:
Have cylindrical tapered “plugs” that has one
or more passageways where fluid is to pass
through when the valve is opened. By
design, they are simple and economical.
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A Three (3) way plug
valve.
Two(2) discharge
points with a
particular source.
Discharge A
Discharge B
Source
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PINCH VALVES:Are types of valves that
are ideal in conveying
“COLLOIDAL
SOLUTIONS” and
“SLURRIES” as there are
no internal mechanism/
obstructions that canblock or slow down the
flow.
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A pinch valve has an
elastomeric sleeve
that is eventually
sandwiched by two
rectractable portions
as the handle is
actuated to close thevalve.
As the valve is opened,
the pressure is
released where againthe retractable parts
move in the opposite
direction.
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DIAPHRAGM VALVES:
Uses a diaphragm as the
closing device and
usually is used to isolate
or block flow.
Since the membranematerial chemically
degrades,
diaphragm valves are
used under theconditions of low
pressure and a limited
temperature operating
range.
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Better at handling
at handling viscous
fluids, thick slurries, and
fluids containing solids.
Its design flaw is
that since it has longdiaphragm movements, it
has a short life span and
necessitates need for
maintenance.
Elastomers are normally used for such
diaphragm material.
Straight Through Type
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Such diaphragm
type valve providestight shut-off with
low operating force.
Has a short
diaphragm movement
thus has a longer span
of life with minimal
maintenance.Much better at throttling flow but has
very low flowrates involved.
Weir Flow Type
2 FLOW REGULATION VALVE:
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2. FLOW REGULATION VALVE:
Many applications require the flow of the fluid be
regulated (throttled). This is achieved byintroducing resistance to flow, or by bypassing
flow or by changing the direction of the flow.
Manually operated valves of this kind indicates
the direct proportionality of the flow with respectto the handwheel position.
Valve types for this function include globe,
needle, ball, butterfly with the globe and needlevalves giving optimum performance.
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TYPES OF
FLOW REGULATION
VALVES:
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NEEDLE VALVES:
Another GLOBE VALVE TYPE and
as the name implies has its principal
mechanism in the form of a needle.
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They are usually
located at the end of every
process cycle combinedwith delicate gauges where
small delicate pressure are
required.
They protect
delicate equipments from
sudden surges of fluid
under high pressure.
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3. BACK FLOW PREVENTION VALVE:
In some circumstances it is important to preventreversed fluid flow as it could cause damage to
the prime mover of fluid which are the “PUMPS/
FANS”.
Such valves are automatic in operation and thatit does not necessitate any external mechanical
means for its operation. They operate due to
fluid flow and by gravity.
Two main valve types are available for this
function lift check valves or swing check valves.
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CHECK VALVE:
Also called“ONE-WAY VALVE” in
that it allows fluid to
flow through it in onlyone direction.
Such type of
valves is automatic inoperation and is
actuated by fluid flow.
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SPRING LOADED
LIFT CHECKVALVES:
Uses a spring to
move the disc/ seat
upon the flow of fluids.
The spring is
calibrated to thepressure of incoming
fluid.
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FOOT VALVES:
Normally used in water pipe applications, such type of
valves are used to help non-
priming pumps to lessens their
work in pumping out water.
They are normally located
in the suction side of the pipe(vertical) and eventually traps
water from going back into the
water table.
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4. PRESSURE REGULATING VALVE:
Certain processes require a constantpressure supply of gas and these may come
from a wide range of gas supply…
Such valve uses a adjustable spring to eventually
reduce the pressure from high to low..Pressure regulating valves which finds of great
use in the industrial and power plant sector could
also be found in our homes as in attachments to
our LPG tanks and in shops/ hospitals that usesoxygen and gaseous fuel tanks.
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5. PRESSURE RELIEF VALVES/
SAFETY VALVES
A very important valve for safety is the pressurerelief valve.
This valve is used in applications where excessive
pressure in the system can cause damage or failure
or can introduce a safety risk. Uncontrolledexcessive pressures can result in disastrous
accidents e.g. when potentially explosive gases are
being controlled.
Relief valves are mainly spring loaded but they can
also be gravity operated and other more specialised
designs are available.
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WHAT ARE VALVE ACTUATORS?
Valves employed in the industrialfield employ such means to actually
operate the valve itself.
1. Manual Actuators2. Diaphragm Actuators
3. Electrical Actuators
4. Piston Actuators
5. Rack and Pinion Actuators
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Manual actuators are operated manually
and usually are in the form of a rotating
wheel/ handle which can be located in
various positions.
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Diaphragmactuators are
pneumatically
driven andmainly employs
the use of
springs in its
mechanical
system.
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Piston actuators uses
a mechanical
system employingthe use of pistons
that are
pneumatically
driven
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Has its mechanicalsystem featuring a
rack and pinion that
is driven by anelectric motor.
Such actuators are
compact in size.
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A typical schematic diagram of a control
valve (not manually controlled).
TYPE OF SERVICE/ CONDITION:
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GLOBE VALVE
GATE VALVE
BUTTERFLY VALVE
BALL VALVE
NEEDLE VALVE
ANGLE VALVE
PINCH VALVE
DIAPHRAGM VALVE
PLUG VALVE
CHECK VALVE
TYPE OF SERVICE/ CONDITION:
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
Yes
Yes
No
No
Yes
Yes
Yes
No
Yes
Yes
No
No
Yes
No
Yes
Yes
No
No
No
No
No
No
No
No
No
Yes