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Valves
Functions


Block flow



Throttle flow



Prevent flow reversal



Safety

Valve Action

Explanation

ON / OFF

Starting Flow / Stopping Flow

Regulating

Varying the rate of Flow

Checking

Permitting Flow in one direction only

Switching

Switching Flow Along different Router

Discharging

Discharging fluid from a system.
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Valves
General procedure for valve selection

1. Identify design information including pressure and temperature, valve function,
material, etc.
2. Identify potentially appropriate valve types and components based on application and
function (i.e., block, throttle, or reverse flow prevention).
3. Determine valve application requirements (i.e., design or service limitations).

4. Finalize valve selection. Check factors to consider if two or more valves are suitable.
5. Provide full technical description specifying type, material, flange rating, etc.

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Valves
End Connections

Function Of Valve

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Valves

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Valves

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Valves
Gate valves: Gate valves are the most common type of valve sials
 Gate valve consists of a body that contains a gate that interrupts flow
 Normally used in a fully open or fully closed position

 Gate valves may be used in systems where flow direction varies and can be reversed as
this valve type is “bi-directional
 Gate valves larger than 2 in. (51 mm) usually have port openings that are approximately
the same size as the valve end openings which is called a full-ported valve
 Reduced port gate valves have port openings that are smaller than the end openings.

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Valves
Gate valves

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Valves
Gate valves

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Valves
Gate valves: (disadvantages)


The full stem travel requires many turns of a handwheel and many more turns when fitted with gearing.



Due to the long stroke and the outside appurtenances necessary to accommodate this stroke, a longer
space envelope (over-all length) is required.



Body seat surfaces for gate valves are more difficult to machine or refinish.



Solid wedge gate valves in systems where severe temperature changes occur are also subject to
excessive seat leakage due to changes in angular relationship between the wedge and the seat faces
due to pipe loads exerted on the valve ends.



Metal-seated gate valves should not be used for air or gas service because they do not have the
bubble-tight closure necessary for these services.

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Valves
Globe Valves


Most economic for throttling flow



Can be hand-controlled



Provides “tight” shutoff



Not suitable for scraping or rodding



Too costly for on/off block operations

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Valves
Globe Valves
 Process fluid enters the globe valve and is directed through a 90° turn to the

bottom of the seat and disc
 Globe valves must be installed properly to work efficiently.

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Valves
Globe Valves
Applying
 Globe valves are commonly used as throttling valves as well as stop valves.
 The throttling capability of the valve is very dependent on the design of the disc.
 Globe valves can be used in gas applications and provide “bubble-tight” closure
if the discs are furnished with resilient inserts.

 Some typical globe valves disc designs are shown in the following figure.

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Valves
Globe Valves

Note that the V-Port type Plug Disc is usually intended for fine
throttling applications, and the other discs fall into the quick- opening or
semi-throttle category.

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Valves
Globe Valves
Four Common Disc Designs

Plug

Composition

Needle

Ball

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Valves
Globe Valves

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Valves
Plug Valves

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Valves
Plug Valves

 Plug valves usually used to close off flow
 A plug valve consists of a tapered or cylindrical plug fitted snugly into a
correspondingly shaped seat in the valve body
 When the valve is open, an opening in the plug is in line with the flow
openings in the valve body
 A plug valve is closed by turning the plug one-quarter turn so that its
opening is at right angles to the openings in the valve body
 Plug valves are either lubricated or non-lubricated

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Valves
Plug Valves

 Lubricated plug valves use a grease- like lubricant that is pumped into the
valve

 Non-lubricated plug valves use as sealing elements metal seats or nonmetallic
sleeves, seats, or complete or partial linings or coatings.

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Valves
Ball Valves
 A ball valve is one-quarter turn valve similar
to a plug valve with a ball inside
 Ball valves usually function as block valves
to close off flow
 Ball valves are used as bubble-tight stop
valves for relatively clean fluid systems,
such as air, water, and gas.
 The multiport ball valve is used frequently
for diverting flows to several directions using
a single valve.

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Valves
Ball Valves

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Valves
Ball Valves

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Valves
Ball Valves

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Valves
Diaphragm Valves

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Valves
Diaphragm Valves

 A diaphragm valve is a packless valve that contains a diaphragm made of a flexible
material that functions as both a closure and a seal
 Diaphragm valves not used extensively in the petrochemical industry but they do have
application in corrosive services below 121 °C where a leak tight valve

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