mechanical seals and packing types for pumps ( sealing for rotating shafts )

1. • This presentation is made by
• Mohamed El-keik on 17/10/2016
• Email: mohamedelkeik@gmail.com
• Pardon me if there are any wrong information .
• as I am a chemical engineer, and Seals are not my specialty and I had no work
experience at the time it was made :D .
• but I simply made it as a quick reminder for me, from the couple of references (and
other people presentations, credit to them and thank you for sharing your work ) I read
about mechanical seals in hope it will be useful one day.
• And I decided to share it hopping that it may benefit someone else .
• Also it was a part of a presentation on pumps so it will focus on pump sealing .
Sealing systems for rotating shafts

2. INTRODUCTION
• All rotating shafts require some form of a seal allowing motion of the shaft from some external device
(motor) while sealing process fluid so no leaks occur between the shaft and the body .
• The general term for this mechanism is sealing.
But How to allow a moving shaft to pass through what needs to be an impenetrable barrier to some fluid ?
• we simply can make the clearance between the shaft and the containing body (housing) very small which will
reduce leakage but also as the shaft rotates high friction between metals will lead to wearing of the shaft and
body very quickly leading to replacing these expensive parts so that’s will not be a practical solution .
• A more traditional solution ( mechanical packing ) will be to wrap the shaft in a flexible material that
maintains a close fit to the shaft without binding its motion. Thus eliminating the metal to metal contact and
seal the annular space between the shaft and the body .
• the traditional packing material for a ship propeller shafts is
flax. Some form of lubrication is usually provided so this
packing material does not impose excessive friction on the
shaft’s motion .
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3. • In the case of a ship’s stuffing box, a little bit of water leakage is not a problem since all ships are equipped
with pumps to pump out collected water over time. However, leakage is simply unacceptable in many
industrial applications where we must minimize Fugitive emissions ( any unwanted escape of process
substance into the surrounding environment ) usually from leaks around pump and valve shafts.
• So another form of sealing is needed to meet more strict process requirements ( mechanical seal ) .
• But in an overall view we can see that all seals have the same functions :
1. Minimize or prevent* leakage according to application requirements.
2. Minimize power loss results from friction.
3. Protect the expensive parts from wearing like the shaft and the housing.
• The previous functions are translated into benefits to the process
1. Economical : wear reduction / sometimes the sealed fluid can be expensive and thus losing it will
lead to higher operational cost .
2. Environmental : as regulations now put more strict emission limits .
3. And finally safety & health : where the sealed fluid can be toxic , hazardous , flammable or
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4. I. MECHANICAL PACKING (GLAND PACKING)
• Gland packing is the traditional solution to seal against fluids and yet it is very effective and desirable
for many applications where small leakage does not posses problems .
• A series of pieces or “rings” are installed around the shaft into the stuffing box and they are
compressed tightly by the packing gland so that they create a difficult leak path for the liquid to leak
with out binding the shaft motion .
• Some of The packing materials used are Teflon (PTFE) & graphite .
• Mechanical packing components :
1. Stuffing box
2. Packing rings
3. Lantern ring
4. Packing gland
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5. • the stuffing box houses the mechanical packing components ,
where packing rings are placed and a gland (end plate)
provides the compressive force by tightening the gland plate
bolts for squeezing and pressing them down the shaft.
• The narrow passage, between the shaft and the packing
housed in the stuffing box, provides a restrictive path to the
liquid which causes a pressure drop and thus prevents leakage.
• When packing is dry it can damage the shaft thus It is good
practice to tighten the gland just enough to allow for a minimal
leak through the packing. This slight leakage of the liquid acts
as a lubricant as well as a coolant to absorb the heat generated
in the packing due to friction with the shaft .
• Periodic retightening of gland necessary for wear compensation.
• Lantern ring can be provided for cooling /lubrication .
• The minimal leak through the packing ( which is used as a lubricant ) cannot be allowed for hazardous and
toxic liquids, but then gland packings are also not used in such applications.
• When toxic or corrosive liquids are handled, it is necessary to insure complete sealing of the stuffing box.
Leakage of such liquids is a hazard to the plant personnel and can also be detrimental to the outer surface
of the pump and foundation. It can also result in the loss of a valuable product.
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6. Packing rings
Lantern ring
Packing
gland
Gland
bolts
Shaft
Stuffing box
Leakage pathRetainer
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7. Retighten gland bolts to reduce leakage that
results from wear of packing rings with time
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9. Stuffing box assembly
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10. The stuffing box
is a chamber or a
housing that
serves to seal
the shaft where
it passes through
the pump casing
lantern rings are
rings with holes
drilled along its
circumference.
Used in high
pressure
services
The gland is used
to keep packing
rings squeezed and
pressing them
down the shaft.
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11. Packing with lantern ring Normal Packing
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12. The lantern ring
• When pumps are handling dirty or
high-pressure liquid, lantern rings
are used. These are rings with
holes drilled along its
circumference and has torturous
path making it difficult for the
pumped fluid to escape .
• Function : cooling , lubrication
and provides extra sealing .
• Extra sealing :By supplying ‘back
pressure’, which aids in impeding
the entrance of abrasive and
corrosive material into the
stuffing box. Abrasives and
corrosives will damage the shaft
or sleeve, and disintegrate the
packing.
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13. Lubrication & cooling
• Water which is directed from
the discharge side of the pump
and ported to the center of
the lantern ring where it
enters into the shaft through
the lantern ring holes and
provides cooling and
lubrication .
• In dirty services water can be
pumped into the ring from
other sources .
• Oil, water, grease, or any liquid
or substance compatible with
the fluid are forced under
pressure into the packing
through the lantern ring .
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14. Mechanical packing
• Advantages • Disadvantages
• Inexpensive
• Adjustable in operation
• Maintainable
• Wide range of materials for multiple applications
• Requires lubrication
• Constant monitoring & adjustment
• In-precise adjustment leads to wear on shaft .
• Higher power consumption due to friction
• Product loss .
• Gland packings work on principle of controlled leakage for proper life ( has to leak to perform ) .
• The product loss resulting from this leakage can be quantified as follows,
Leakage rate quantum
One drop every five seconds 550 ltrs/year
Two drops per seconds 5500 ltrs/year
Steady stream leakage 40000 ltrs/year
• Product loss = above quantities * cost/lt of liquor
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15. II. MECHANICAL SEALS
• Mechanical seals are simply another mean of controlling leakage where other means (packing) are deemed
to be less capable of performing the task adequately .
• Advantages of mechanical seals over mechanical packing :
1. Lower mechanical losses
• One of the largest of these mechanical losses comes from the frictional drag of the shaft running
against packing. A mechanical seal, on the other hand, has considerably less mechanical loss, thus
improving efficiency.
2. Less Sleeve Wear
• the sleeve under the packing is subject to wear, especially if the pumped liquid has any abrasives in it
or if the packing is tightened too much. With a mechanical seal, this wear of the shaft sleeve is
eliminated.
3. Reduced Maintenance .
4. Zero or limited leakage of product meeting process requirements .
5. Ability to seal higher pressures and more corrosive environments.
6. The wide variety of designs allows use of mechanical seals in almost all applications.
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16. HOW IT WORKS ?
• Mechanical seals are simply a sealing device depends on the idea of transforming the leakage path from
being parallel to the shaft to perpendicular to it and hence shaft will not be subjected to wear and small
running clearance between two sealing faces can be achieved .
Leakage path parallel to the shaft Leakage path perpendicular to the
shaft
• To do so mechanical seals forms a running seal in a plane perpendicular to the shaft consist of two highly
polished surfaces running adjacently.
• One surface being connected to the shaft and the other to the stationary portion of the housing. The
polished surfaces which are of dissimilar materials are held in continual contact by a spring, forming a fluid
tight seal between the rotating and stationary members with very small frictional losses .
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17. • The fluid try to exist from the high pressure red region ( inside the process ) to the low pressure light blue
region ( atmosphere ) to do so the fluid losses energy in form of pressure loss to overcome the restriction (
tiny fluid path ) imposed by the seal and escape . So it’s pressure decreases as it moves down the sealing
faces , and it also gains energy ( heat ) results from friction between seal faces until it reaches a point where
it is vaporized (the vaporization point in a perfectly designed seal is at the outer tip of the seal faces ) and the
leakage is so minute that actual droplets of liquid are not detected. Instead, the leakage is a gas or vapor.
• The fluid ( leakage ) running between sealing faces acts as a lubricant
But What happens to the fluid in that perpendicular leakage path between those rotating
sealing faces ?
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18. Components of a mechanical seal .
• All mechanical seals are constructed of three basic sets of parts.
2. A set of secondary seals known as shaft pickings and insert
mountings such as 0-rings, and V-rings.
1. A set of primary seal
faces: one rotary
and one stationary.
3. Mechanical seal
hardware for
attaching, positioning
and maintaining face
to face contact
including : gland
rings, collars,
compression rings,
pins, springs and
bellows.
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19. Shaft
Seal
follower
Stuffing box
Retainer Spring Static sealDynamic seal
Liquid
Bolt for locking
Gasket
Secondary
seal
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20. C. Between the rotating
element and the shaft
Sealing on the shaft
(secondary seal ) B. Between the stationary
element & the seal chamber
(secondary seal )
D. The seal gland to the
stuffing box
A. Between the seal faces ( primary seal )
• The previous components serve the function to seal leakage across four points :
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21. A. Between the faces (rotary and stationary) of the seal ( primary seal ).
• The primary seal is achieved by two extremely flat, lapped (lapping is a polishing process) faces which create
a difficult leakage path perpendicular to the shaft. Rubbing contact between these two flat mating surfaces
minimizes leakage.
• one face is held stationary in housing and the other face is fixed to, and rotates with, the shaft. and held in
contact using a combination of hydraulic force from the sealed fluid and spring force from the seal design.
the spring pressure holds the primary and mating rings together during shutdown or when there is a lack of
liquid pressure .
• The mating surfaces of the seal faces are made of dissimilar
materials One of the faces is usually a non-galling material
such as carbon-graphite. The other is usually a relatively hard
material like silicon-carbide. Dissimilar materials are usually
used for the stationary insert and the rotating seal ring face in
order to prevent adhesion of the two faces. The softer face
usually has the smaller mating surface and is commonly called
the wear nose.
• The faces in a typical mechanical seal are lubricated with a
boundary layer of gas or liquid between the faces.
• Flatness of the faces determines the quality of the seal & is measured in “Light
Bands” (refers to the variations in the surface of the face & equivalent to
0.000011 inch ).
Wear nose
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22. B. Between the stationary element and the seal chamber housing ( secondary seal ).
C. Between the rotary element and the shaft ( secondary seal ) .
D. Between the seal gland and stuffing box .
• The secondary seal in this locations achieves sealing by 0-ring, V-ring or gaskets
V ringO ring
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23. Mechanical seal lubrication .
• IF the seal faces were rotated against each other without some form of lubrication they would wear and quickly
fail due to face friction and heat generation. For this reason some form of lubrication ( fluid film ) is required
between the rotary and stationary seal face.
• In most mechanical seals the faces are kept lubricated by maintaining a thin film of fluid between the seal faces.
This film can either come from the process fluid being pumped or from an external source.
• The need for a fluid film between the faces presents a design challenge in allowing sufficient lubricant to flow
between the seal faces without the seal leaking an unacceptable amount of process fluid, or allowing
contaminants in between the faces that could damage the seal itself.
• This is achieved by maintaining a precise gap (≈1micron ) between the faces, that is large enough to allow
in a small amounts of clean lubricating liquid, but small enough to prevent contaminants from entering the
gap between the seal faces and reduce leakage through it ( is so small that it appears as vapor – around ½ a
teaspoon a day on a typical application ).
• This micro-gap is maintained using springs and hydraulic force to push the seal faces together, while the
pressure of the liquid between the faces (the fluid film) acts to push them apart.
• Without the pressure pushing them apart the two seal faces would be in full contact, this is known as dry
running and would lead to rapid seal failure.
• Without the process pressure (and the force of the springs) pushing the faces together the seal faces would
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24. • Mechanical seal engineering focuses on increasing the longevity of the primary seal faces by ensuring a high
quality of lubricating fluid, and by selecting appropriate seal face materials for the process being pumped .
• Seal flush port
• The gland or seal housing in many seals contains a port for injecting liquid, either from the pump discharge or
from an external source .
Why flushing plan is required?
1. To lubricate and cool mechanical seal.
2. To remove foreign particles.
3. To remove carbon deposition and engrossed
materials on mating surfaces.
4. Prevent seal from dry running.
5. To maintain the operational parameters of
mechanical seal.
Flush arrangements
• It refers to the various methods used to lubricate,
cool and remove deposits and heat in mechanical
seal. And they referred to as API seal plan
• Single seal (01, 02, 11, 13, 14, 21, 23, 31, 32 and
41)
• Double seal (52, 53A, 53B, 53C and 54)
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26. • Mechanical seal types and classification
• Mechanical seals can be classified by arrangement and configuration
By
arrangement
Single
Inside
mounted
Outside
mounted
Dual
Duel
pressurized
Duel
unpressurized
( tandem )
Face to face &
back to back
By design
Pusher
(single & multi
spring)
Balanced
Non-balanced
Non pusher
(metal bellows)
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27. Inside vs outside
Single inside Single outside
Description
• They called inside seals because the seal parts are
located inside the seal housing.
• They are called single seals because there is one
dynamic seal face .
• They called outside seals because the metallic rotary unit parts
are exposed to the atmosphere, only the insert seal ring and
secondary seals are exposed to the product ( non-metallic
components )
• thus can be used in corrosive service .
Advantage
• The seal is submerged in the liquid making it easier to
flush and carry away heat .
• Can be balanced to withstand high seal environment
pressures.
• Hardware items of the seal don’t come in contact with liquid.
• Easier to access for adjustment and trouble shooting.
Disadvanta
ge
• Hardware items of the seal come in contact with liquid
which may be corrosive.
• cannot be adjusted without dismantling the
equipment unless they are cartridge
• lower pressure limit as the pressure of the sealed liquid pushes
the two seal faces apart, rather than forcing them together.
• they are subject to exposure to dust and other environmental
contaminants.
Photo/drawing

28. Dual seals
• Dual mechanical seals are used for extremely tough services, where it is desirable to completely eliminate the possibility of leakage of
sealed fluid . they include two dynamic seals, either mounted in face to face, back-to-back arrangement or other, In either cases, they
have a fluid zone between the two seals & according to this fluid zone configuration they are sub-classified into :
Dual pressurized Dual pressurized gas
(Non-contacting)
Dual unpressurized
(Tandem)
Description
• The fluid zone between the
two seals is at a pressure
higher than the sealed liquid
thus the sealed liquid can not
enter this region .
• The fluid between the two
zones is called a barrier fluid
• If the outside dynamic seal
were to leak, the barrier liquid,
rather than the pumped liquid,
would leak out to the
environment.
• If the inside dynamic seal were
to leak, the barrier fluid would
leak into the pumped liquid .
• The two dynamic seal faces are
always kept completely free of
the pumped liquid .
• In a Gas Lift-Off seal, the faces
theoretically never contact.
• Dual pressurized gas mechanical
seal is a combination of two
seals with a barrier gas (N2 ,
clean air . Co2 etc. ) injected
between the two seals at
pressure 25 to 30 psi higher
than pumped liquid pressure.
• The gas flows through holes in
faces which separates the seal
faces results in non-contacting
faces at both dynamic seal
faces.
• As the seal operates, an
envelope of gas surrounds the
seal faces keeping process liquid
out.
• The fluid zone between the two seals is at a
pressure lower than the sealed liquid.
• The fluid between the two zones is called a buffer
fluid
• The idea of the unpressurized dual seal is that if the
primary seal fails, the operator of the pump can
plan an orderly shutdown to repair the primary
seal, with sealed fluid escaping to buffer fluid and
then sealed by secondary seal rather than escaping
to environment.
• Ordinarily, no pumped liquid reaches the secondary
seal because the primary seal keeps the liquid, so
the secondary seal runs in a non-pressurized clean
lubricating liquid (buffer fluid), so it will generally
last for an extended period of time.
• Usually, the buffer fluid is monitored for pressure,
level, ph, conductivity, or some other convenient
variable, to signify a failure of the primary seal.
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29. •Feature • When pumping volatile liquids, hazardous, corrosive,
abrasive, etc. It is sometimes necessary to insure that
the process liquid does not enter the fluid zone
between 2 seals . Thus Pressurizing this zone higher
than the sealed liquid will prevent process liquid
from crossing the primary seal faces.
• Pumped liquid can’t leak into the environment.
• Less mechanical losses due to
lesser friction .
• without liquid contamination
of the process liquid like in
case of pressurized dual seal .
• If primary seal fails, end
user can plan to
repair/replace seal in
advance without any
product escaping to the
environment.
• The difference between un/pressurized seals , Is In a pressurized dual seal, the outboard or secondary has the tougher job
of the two. It operates sealing high barrier pressure while the inboard or primary seal has clean lubricating liquid applied at
differential pressure of only 20 to 30 psi. and it is vice versa in unpressurized .
Barrier Fluid Characteristics of Barrier/Buffer Fluid Buffer Fluid
• Safe to use, handle inexpensive &
Compatible with seal materials &
process fluid .
• Good flow qualities at operational
temperatures (including very low
temperature service).
• Nonflammable.
• Good lubricity.
• Non-foaming when pressurized.
• Good heat transfer properties.
• Low gas solubility.
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30. Dual seal, with dynamic seals mounted in back to face.
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31. Inside or Primary seal
Outside or Secondary Seal
Immersed in process liquid
in the stuffing box
Buffer fluid warmed
by seal generated
heat returns to the
buffer supply tank
Cool buffer fluid
from the buffer
supply tank enters
via the inlet port
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32. The equipment
can then be started
and process suction
opened allowing
liquid into the
stuffing box.
Gas is supplied
to the inlet port.
UTEX DUAL CO-AXIAL pressurized GAS SEAL
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33. Pusher vs. Non-pusher
• Both pusher and non-pusher types can be either shaft mounted or cartridge assemblies.
• The basic difference have to do with the dynamics of the shaft packing or O-ring and whether or not it moves as the seal wears.
• As the seal faces wear down over time, they must be closed to compensate for lost face material.
Pusher type Non pusher type
Description
• If the shaft O-ring must move when this compensation takes place, it
is pushed forward by the components of the seal and by stuffing box
pressure. Then it is called a dynamic 0-ring and the seal type is a
pusher .
• Can be a single spring or multi-spring design
• Non-Pusher type or Bellow seals have no
dynamic secondary seal under the
movable seal ring instead it is located in
the retainer. & the seal components
compensate for face wear without
“pushing” any sealing points. Then it is
called a static 0-ring and the seal type is
a Non-pusher .
• The bellows can be made of rubber,
Teflon and metal. Rubber bellows are
used for less critical applications , Teflon
bellows are used for low pressure,
moderate temperature acid services.
Metal bellow seal is its ability to run at a
very high
• Eliminates the problem of Seal hang up
due to spring clogging or clogging of
dynamic elastomers on the shaft.
• Single spring • Multi-spring design
 Advantages:
• less –CLOGGING
• low spring constant
 Limitation:
• Not recommended for very
high RPM applications Due
to single spring design
causes non uniform seal
loading
• Require long axial space.
 Advantages
• Number of small springs are used on
the to give a uniform face loading.
• compact in comparison with single
spring seal.
• Due to uniformly loaded seal faces
the multi spring seals are a must for
high rpm application.
 Limitation:
• more expensive.
• spring clogging is more easily .
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34. Pusher type
Single spring design
Multi spring design
Stationary
face
Rotating
face
Retainer
Spring
Antirotation
pin

35. 1. As the softer carbon face wears down, the
rotating face must move to maintain face
closure.
2. Minute particles of carbon and solids from the
process liquid that migrate across the seal faces
build up on the shaft.
3. This build up will ultimately cause
the seal to “hang up” and in most
cases, failure will occur well before
the seal is actually “worn out”.
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36. • Non pusher type
Metal
bellows
Rotatory face
Stationary face
Static O-ring

37. • The bellows core expands to compensate for face wear.
• Debris can build up without causing hang up.
• This feature is probably the most notable selling point when comparing a bellows seal to a pusher type seal.
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38. Balanced and unbalanced mechanical seals
• When speaking of “balance” in reference to mechanical seals, we are not talking about mechanical or rotational balance.
Instead, we are referring to hydraulic balance.
• The purpose of a balanced seal is to seal against higher pressures and speeds than possible in an unbalanced
configuration by balancing out the forces try to close the seal with those try to open it .
There are at least 2 forces closing
the seal faces:
There are at least 3 forces trying to open the seal
faces:
• A = The spring loaded face
with an area of 2 𝑖𝑛2
• B = The stationary face held to
the front of the stuffing box
by gland "G"
• P = The hydraulic pressure in
the stuffing box (i.e. 100 psi ).
• The mechanical spring force.
• The hydraulic force caused by the
stuffing box pressure acting on
the seal face area (pressure ×
spring loaded face area).
• A hydraulic force is created any time there is
fluid between the seal faces.
• A centrifugal force created by the action of the
fluid being thrown outward by the rotation of
the pump shaft.
• A hydrodynamic force created because
trapped liquid is non compressible. ( Seal faces
are lapped to within three light bands because
slight waviness is enough to generate
hydrodynamic lifting forces as we try to
compress non-compressible liquid trapped
between the lapped faces.
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39. B a l a n c e d U n b a l a n c e d
Balance
ratio
The balance ratio of a mechanical seal is an area ratio and is related to the seal face load. Balance ratio is defined as
the ratio of the closing area to the opening area.
Balance ratio < 1 Balance ratio > 1
Advantages
• Less hydraulic force acting on seal faces.
• Generate less heat.
• Higher pressure limit.
• Can handle liquids with poor lubricity and high vapor
pressure.
• Inexpensive.
• Less leak.
• Stable when subjected to vibration, misalignment and
cavitation.
Disadvant
ages
• Relatively higher cost.
• Very minor leak is expected.
• Higher hydraulic force acting on seal faces.
• Low pressure limit.
• How is that accomplished? Since the hydraulic closing forces were twice the opening forces (100 psi. Vs. 50 psi.) We
have installed a stepped or shortened primary ring and sleeve inside the seal to reduce the closing area and reduce
the closing force.
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40. Unbalanced Balanced
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41. • The faces of a balanced seal are located so that a portion of the face contact occurs inside the balance
diameter resulting in reduced closing force due to stuffing box pressure.
• Most metal bellows seals are balanced
BalanceLine
FaceIDLine
FaceODLine
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42. Cartridge Mechanical Seal
Description
Mechanical seal Pre-mounted on a sleeve and fit directly to shaft or shaft sleeve ( available single,
double and tandem) .
Advantages
• No requirement for seal setting measurement for installation.
• Eliminate seal setting errors.
• Low maintenance cost.
Photo/Drawing
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43. Mechanical Seal Selection
The proper selection of a mechanical seal can be made only if the full operating conditions are known:
1. Liquid
• Identification of the exact liquid to be handled is the first step in seal selection. The metal parts must be
corrosion resistant, usually steel, bronze, stainless steel, or Hastelloy. The mating faces must also resist corrosion
and wear. Carbon, ceramic, silicon carbide or tungsten carbide may be considered. Stationary sealing members
of Buna, EPR, Viton and Teflon are common.
2. Pressure
• The proper type of seal, balanced or unbalanced, is based on the pressure on the seal and on the seal size.
3. Temperature
4. Characteristics of Liquid
• Abrasive liquids create excessive wear and short seal life. Double seals or clear liquid flushing from an external
source allow the use of mechanical seals on these difficult liquids. On light hydrocarbons balanced seals are
often used for longer seal life even though pressures are low.
5. Reliability and Emission Concerns
• The seal type and arrangement selected must meet the desired reliability and emission standards for the pump
application. Double seals and double gas barrier seals are becoming the seals of choice.
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44. Operational error
1. Dry running.
2. Suction chocking.
3. Foreign material.
4. Material incompatibility.
5. Abnormal process parameters.
6. Flushing plan off.
Maintenance error
1. Improper installation.
2. Shaft misalignment.
3. Shaft run out.
4. Failed bearing.
5. Unavailability of required flushing plan.
How Mechanical Seal Can Fail ?
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