Valves and Controls Final

8/8/2019 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.

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

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.

TYPES OF

ISOLATION/ STOP

VALVES:

GATE VALVES:Are valves

that are used

intermittentlyrequiringstraight flow

and minimumflow restriction.

As the name implies, its main workingmechanism (sealing mechanism) resembles

that of a “gate which is wedge-shaped”.

Such types of valves are not used for throttling as the wedge-shaped gate is prone to

stress which could hamper its operation.

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.

A double ported

globe type of

valve….INTAKE DISCHARGE

SEALING

MECHANISM

SEALING

MECHANISM

Such valves areused for “FREQUENT

OPERATION

(throttling) ” as there

is less stress imparted

on the closing

mechanism.

With its flowpattern in the form of aletter “S”, it resultsinto “PRESSUREDROP” between thetwo (or three) sectionsof the pipe.

Such valves

provide a “FASTER

SHUT-OFF or FASTEROPENING” unlike in

the case of gate

valves…..

Is a form of GLOBE

VALVE since most of its

internal mechanismcould be found in a

typical globe valve.

ANGLE VALVES:

It is used in

instances with “SPACE

CONSTRAINTS”…

This is made

possible as flow is

diverted at a right

angle.

Since the divertion of fluid is at

right angles, a “LARGER PRESSURE

DROP TRANSLATES (fluid friction ishigh)”.

As a type

of GLOBE VALVE, it

too could also be

used for throttling

since its internalmechanism is not

that much prone to

stress.

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.

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.

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.

Since there is not

much obstruction in the

passageway, there isminimal pressure drop

(fluid friction is at a

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.

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.

Like butterflyvalves, ball valves

are also quick

acting…

A 900 turn fully

opens or fully

closes the “ball”.

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.

A Three (3) way plug

valve.

Two(2) discharge

points with a

particular source.

Discharge A

Discharge B

Source

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

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.

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.

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

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:

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.

TYPES OF

FLOW REGULATION

VALVES:

NEEDLE VALVES:

Another GLOBE VALVE TYPE and

as the name implies has its principal

mechanism in the form of a needle.

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.

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.

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.

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.

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.

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.

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.

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

Manual actuators are operated manually

and usually are in the form of a rotating

wheel/ handle which can be located in

various positions.

Diaphragmactuators are

pneumatically

driven andmainly employs

the use of

springs in its

mechanical

system.

Piston actuators uses

a mechanical

system employingthe use of pistons

that are

pneumatically

driven

Has its mechanicalsystem featuring a

rack and pinion that

is driven by anelectric motor.

Such actuators are

compact in size.

A typical schematic diagram of a control

valve (not manually controlled).

TYPE OF SERVICE/ CONDITION:

GLOBE VALVE

GATE VALVE

BUTTERFLY VALVE

BALL VALVE

NEEDLE VALVE

ANGLE VALVE

PINCH VALVE

DIAPHRAGM VALVE

PLUG VALVE

CHECK VALVE

TYPE OF SERVICE/ CONDITION:

Valves and Controls Final

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