pump & mechanical seals

8/9/2019 Pump & Mechanical Seals

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PUMP & MECHANICAL SEALS

By : Lalit Chhajer


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ContentGeneral Components of Pump

Mechanical Seal


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PUMP


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Pump - Typical

Suction

Discharge

Motor

Seal

Coupling


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Pump - Sectioned

Impeller Shaft

Seal

Bearings

Oil


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Components of Pump Pump Casing - To keep the fluid in the pump. Impeller - The component that dries the fluid

to a higher pressure Shaft - The rod that connects the motor to the

impeller Motor - The part that po!ers the pump Packing Seal , Mechanical Seal - To keep

the fluid from leaking out to the atmosphere.There are some magneticall" driencentrifugal pumps that do not need suchseals or packing.

Bearing - To keep the shaft rotating freel" inplace.

Outboard bearing - Bearing at motor end of

shaft Inboard bearing - Bearing at impeller side of

pump. #eed $ %earing to hold shaft in place Oiler - To proide oil to lu%ricate the %earing

so it !ill not &am.


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PUMP PER!RMANCE CUR"E


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PUMP PER!RMANCE CUR"E


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#ASIC RE$UIREMENT %

Smoot& !pe'ation#o Caitation

Minimum 'lo!

#o (eakage ) *mission


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CA"ITATI!N It can %e referred to as HEA! A!!AC"

to a pump. The steps in Caitation are

'ormation of Bu%%les inside the li+uid

Gro!th of Bu%%les

Collapse of Bu%%les

CA#I!A!IO$


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MINIMUM CIRCULATI!NContinuous operation of a pump at lo!

flo! or reduced capacities leads to a

num%er of unfaora%le conditions, educed Motor *fficienc", *cessie adial Thrust

,*cessie temperature rise in pumping li+uid

, Internal e-circulation


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N! LEA(A)E * EMISSI!NBad Seal is a ma&or contri%utor for

(eakage or *mission

If the product is toic/ p"rophoric/ thenleakage in a pump result in serious

0ealth ha1ard.

If the product is costl" then/ it can resultin significant loss.


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MECHANICAL SEAL


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LEA(A)E R!M PUMP

(eakage


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)land Pac+in, % An olde'

"e'sion to seal

P%MP

SI&E

MO!O

SI&E

P2C3I#G G(2#D

P%MP

SHA'!


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MECHANICAL SEAL % #asic

"e'sion

P%MP

SI&E

MO!O

SI&E

P%MP

SHA'!


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&at is Mec&anical Seal .

2 mechanical seal is a t"pe of seal utili1ed inrotating e+uipment/ such as pumps andcompressors.

4hen a pump operates/ the li+uid could leak out ofthe pump %et!een the rotating shaft and thestationar" pump casing. Since the shaft rotates/preenting this leakage can %e difficult.

*arlier pump models used mechanical packing toseal the shaft. Since 44II/ mechanical seals haereplaced packing in almost all applications.


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Mec&anical Seal undamentals

2 mechanical seal must contain four functional components5

67 Primar" sealing surfaces/

$7 Secondar" sealing surfaces/

87 a means of actuation and

97 a means of drie.

67 The primar" sealing surfaces are the heart of the deice. 2 common com%ination consists of a hard material/ suchas silicon car%ide em%edded in the pump casing and a softer material/ such as car%on in the rotating sealassem%l". Man" other materials can %e used depending on the li+uid:s chemical properties/ pressure/ andtemperature. These t!o rings are in intimate contact/ one ring rotates !ith the shaft/ the other ring is stationar".These t!o rings are machined using a machining process called lapping in order to o%tain the necessar" degree offlatness.

$7 The secondar" sealing surfaces ;there ma" %e a num%er of them7 are those other points in the seal that re+uire afluid %arrier %ut are not rotating relatie to one another.

87 In order to keep the t!o primar" sealing surfaces in intimate contact/ a means of actuation must %e proided. Thisis commonl" proided %" a spring. In con&unction !ith the spring/ it ma" also %e proided %" the pressure of thesealed fluid.

97 The primar" sealing surfaces must %e the onl" parts of the seal that are permitted to rotate relatie to one another/the" must not rotate relatie to the parts of the seal that hold them in place. To maintain this non-rotation a methodof drie must %e proided.


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MECHANICAL SEAL %

undamentals

Secondary SealSecondary SealPrimary SealPrimary Seal

Secondary/Secondary/

Tertiary Seal Tertiary Seal


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Spring or Spring ForceSpring or Spring Force

Mating Ring or SeatMating Ring or Seat

Primary Ring or FacePrimary Ring or Face

MECHANICAL SEAL %

undamentals


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PRIMAR/ SEAL

Fluid is forced between faces to lubricateFluid is forced between faces to lubricate

Springs keep faces closed when no pressureSprings keep faces closed when no pressure

MatingMating

RingRingPrimaryPrimary

RingRing

SpringsSprings


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PRIMAR/ SEAL

MatingMatingRingRing

PrimaryPrimaryRingRing

HumanHuman

HairHair

Fluid FilmFluid Film

0!"#00!"#0

$m$m

%0%0

$m$m

'aces lapped flat to !ithin 6 - 8 light %ands'aces lapped flat to !ithin 6 - 8 light %ands& light band ' 00000&&(& inch or 0000# mm& light band ' 00000&&(& inch or 0000# mm


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SEC!N0AR/ SEAL

O-ing


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API PLANSLUSHIN) & C!!LIN)


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API PLANS

Since the rotating seal !ill create heat/ this heat !ill needto %e carried a!a" from the seal cham%er or else the seal!ill oerheat and fail. T"picall"/ a small tu%e connected toeither the suction or the discharge !ill help circulate the

li+uid. Other features such as filters or coolers !ill %eadded to this tu%ing arrangement depending on theproperties of the fluid/ and its pressure and temperature.*ach arrangement has a num%er associated !ith it/ asdefined %" 2PI.2PI Plans are there to

, 3eep the Seal faces clean of an" dirt

, 3eep the Seal cool, (u%ricate the Seal 'aces There are 6< 2PI plans aaila%le for Mechanical Seal

applications.


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E1ample % API Plan 22 3SEAL

C!!LIN)4

Product recirculation lineProduct recirculation line


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RecirculationRecirculation

for coolingfor cooling

E1ample % API Plan 22 3SEAL

C!!LIN)4


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Multiple Seals

Tandem

=npressurised


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Multiple Seals

Since almost all seals are designed toleak slightl"/ dangerous chemicals or

flamma%le petroleum must not %eallo!ed to leak into the atmosphere oronto the ground. In these applications asecond seal is placed after the primar"

seal along the pump shaft. The space in%et!een these t!o seals is filled !ith aneutral li+uid or gas.


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Sin,le seal is not enou,&

Single seals utiliseSingle seals utilise

process gas or )uid toprocess gas or )uid topro*ide thepro*ide the

lubricating interfacelubricating interface

+lm+lm

=se multiple seals if5

, product is toic

, product is flamma%le

, enironmental

, isolation re+uired, product changes state

, product is not a goodlu%ricant or is a%rasie

, suction pressure is lo!

, epensie product

, critical machine


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MULTIPLE SEALS T!o common arrangements

, !andem, lo! pressure %uffer fluid

, high integrit" secondar" containment, in%oard seal lu%ricated %" product

, Pressurised &ouble )e*g*, Back+to+Back

,pressurised %arrier fluid

, in%oard seal lu%ricated %" %arrier fluid There are man" other arrangements

, 'ace-to-'ace> Dual> Concentric> etc.


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TAN0EM SEAL Buffer'luid


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TAN0EM - IN#!AR0 SEAL

ProductProduct

lubricateslubricates

this sealthis seal

This seal is This seal isunder fullunder full

productproduct

pressurepressure

,nboard Seal,nboard Seal

-ote possible-ote possible

contaminatiocontaminatio

n of bu.ern of bu.er

)uid)uid


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lean bu.erlean bu.er

)uid)uid

lubricateslubricatesthis sealthis seal

utboard Sealutboard Seal

1u.er )uid1u.er )uid

is at lowis at low

2atmospheri2atmospheri

c3 pressurec3 pressure

TAN0EM - !UT#!AR0 SEAL


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4 ,nboard seal most likely,nboard seal most likely

to fail +rstto fail +rst4 1u.er )uid le*el/pressure1u.er )uid le*el/pressure

will risewill rise

4 utboard seal acts asutboard seal acts assecondary containmentsecondary containment

4 Process can continueProcess can continueuntil completeduntil completed

TAN0EM SEAL


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PressurisedPressurised

barrier )uidbarrier )uid

is circulatedis circulated

round theround the

sealsseals

This This

lubricateslubricates

both sets ofboth sets of

seal facesseal faces

0ou5le Seals6 #ac+-to-#ac+


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,f outboard,f outboard

seal fails5seal fails5

barrierbarrier

pressure willpressure willfail andfail and

pump mustpump must

be switchedbe switched

o. aso. as

product willproduct will

leak outleak out

0ou5le Seals6 #ac+-to-#ac+


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StationarStationar

y sealsy seals

RotatingRotating

MatingMating

RingRing

Similar in operation to back"to"back double sealSimilar in operation to back"to"back double seal

Much shorter " only one mating ringMuch shorter " only one mating ring

Simple rotating componentsSimple rotating components

0ou5le Seals6 ace-to-ace


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Multiple Seals

In a tandem seal/ the seal !illleak to the unpressuri1edcait". If the cait" registers adramatic increase in pressure/

operator !ill kno! that theprimar" seal has failed. If thecait" is drained of li+uid/ thenthe secondar" seal failed. In%oth instances/ maintenance!ill need to %e performed. This

arrangement is commonl"used !hen sealing fluids that!ould create a ha1ard orchange state !hen contactingopen air.


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Multiple Seals

In a dou%le seal/ the li+uidin the cait" %et!een thet!o seals is pressuri1ed.

Thus if the primar" sealfails/ the neutral li+uid !illleak into the pump streaminstead of the dangerouspumped fluid escaping intothe atmosphere. This

application is usuall" usedin gas/ unsta%le/ highl"toic/ a%rasie/ corrosie/and iscous fluids.

pump & mechanical seals

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