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TRAINING PROGRAMON
MECHANICAL SEAL
Andrew Maxwell
Mechanical Engineer Madina Group WLL
Doha, Qatar June 2010
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What is a Seal?A Seal is a device which prevents the passage,
leakage or flow of fluid
Why seal is Required? To isolate a high pressure system from surrounding
Transmission of Power requires an opening in thepressure body, necessitating a seal
Environmental factors extending from aesthetics of aclean shop to water pollution
Survivability of fluid handling equipment
Reduce Energy & Production loss
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Seal
Static Seal Dynamic Seal
Clearance Seal Contact Seal
Face Seal/Mechanical SealLabyrinthSeal Bushings CompressionSeal
Packed Gland
Lip Seal
Seal Classification
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Typical Centrifugal Pump
1. Suction 2. Impeller 3. Discharge 4. Stationary casing 5. Shaft
6. Mechanical Seal 7. Gland Plate 8. Bearings
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Gland packing
Lea
Flush port
Gland follower / plate
Gland packing
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Typical Stuffing Box with Gland
Packing
Compression
Packing
Fastener
Packing Pusher Impeller
Stuffing Box
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LEAKED FLUID
GLAND PACKING ARRANGEMENT
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Limitations of Packed Glands
Power consumption is High. The ratio ofpower consumption of Mechanical Seal to
compression packing is 1:8
Leakage is very high and unpredictable. Varies with
compression on the packing. The ratio of Leakage ofmechanical seal to compression packing is 1:600
No automatic wear compensation
Fretting on sleeve or shaft
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MECHANICAL SEAL IS A DEVICE THAT
PREVENTS / RESTRICTS UNDESIRABLE
LEAKAGE OF FLUID IN ROTATING
EQUIPMENT FROM HIGH CHAMBERPRESSURE TO LOWER ONE SIDE .
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PUMP WITH MECHANICAL SEAL.
MECHANICAL SEAL
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A Simple Mechanical Seal
Seal Holder
Collar
Grub ScrewSprings Drive Pin Seal Plate
O Ring
Seal Seat
Seal Face
O Ring
Hardwares:Seal Holder, Seal Plate
Seal Faces :Seat and FaceSecondary Seals :O Rings
Tertiary Seals :Gaskets
Gasket
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A Simple Mechanical Seal
P th f L k
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Paths of LeakageTertiary Seal
Secondary
Seal
Secondary
Seal
Primary Seal
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PRINCIPLE OF SEALING
BASIC SEAL WORKS ON THE PRINCIPLE OF :
THIN LIQUID FILM BETWEEN THE TWO SURFACES.
ONE SOFT FACE (ROTATING) AND ONE HARD FACE (STATIONARY)AGAINST EACH OTHER.
NO INTERRUPTION IN LIQUID FILM.
NO GAS PHASE TO PREVENT FACE CONTACT.
NO SOLID PARTICLES TO DAMAGE SEAL FACE.
Cl ifi ti f M h i l S l
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Classification of Mechanical Seal
1. By Mounting Inside Mounted Outside Mounted
2. By Hydraulic
Balance
Unbalance Seal Balance Seal
3. By Loading
Mechanism
a. Pusher Type Single Spring Seal Multiple Spring Sealb. Non Pusher Type Metal Bellow Seal Teflon Bellow Seal Rubber Bellow Seal
4. By Arrangement a. Single Sealb. Double Seal Tandem Seal Back to Back Seal Face to Facec. Catridge Seal
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1. Seal By Mounting
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Unbalance seal
Hydraulic Load plus Spring load Close Faces
Area A always Greater Than Area BFace stress is therefore high
High Temperature
High face wear
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A Single Unbalanced Seal
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Single Balanced Seal
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REVERSE BALANCE SEAL
A Si l C il S i P h S l
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A Single Coil Spring Pusher Seal
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PUSHER SEAL
Multiple Spring Seal
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Pusher versus Bellows seal
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Cartridge Seals
Most seals used on modern plants are cartridgeseals.
These come pre-set as a complete package.
All you have to do is fit them to the shaft, and
fasten the plate to the pump and REMOVE thegrub screws holding the rotating section to the
stationary section.
Any maintenance on these is normally done by
the manufacturer.
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Failure Modes For most seals if any of the conditions required for
operation are absent, even for a short time, failure willresult.
Common causes are dry running, this is when theliquid film between the faces is interrupted.
The faces will become very hot, thermal crazing willoccur, which will lead to fracture of the faces.
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Test your knowledge
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Any Questions?