mechanical seal for pumps
TRANSCRIPT
Presented byPrasad [email protected]
Cross section view of pump with mechanical seal
Pumping liquid
NEED FOR SEALS
Seal is a device for closing a gap or making a joint fluid tight ( liquid or gas ) NEED * To minimize leakage * To prevent toxic fluids escaping to atmosphere * To reduce power loss .
TYPES OF SEALS
Static Seals
Dynamic Seals
STATIC SEALS Sealing takes place between two parts that don’t move in relation with each other.
Application - Pipe flanges ,vessel /Tower nozzles, pump casing joint. - Fan /Blower casing joint , Compressor casing joint. - Turbine casing joint, Heat exchanger joints Types - Gaskets - O-rings - Liquid gaskets
GASKET
Packing designed to go between two rigid parts in stationary conditions May be in form of sheet , strip , bulk.
PropertiesImpermeabilityAbility to flow into joints AgeingCorrosion resistance
Classification of Gaskets
Non-metallic gasketsMetallic gaskets
Non-metallic gaskets Asbestos Cork and rubber PTFE
METALLIC GASKET Corrugated Plain
Asbestos filler Metal clad Soft material like asbestos CAF enclosed
in metal covering . Provides additional mechanical strength Spiral wound
Alternate layers of v- sections , metallic strip and
non- metallic filler compressed to a predetermined
amount Metal – SS , Monel , Inconel , Titanium. Fillers – Asbestos fibres , PTFE lead,
ceramic paper, graphite foils
DYNAMIC SEALS Used for sealing fluid between parts that move in relation with each otherApplication * Centrifugal pump gland, valve gland , bearing housing
* Turbine/compressor inter stage and end sealing
* Reciprocating compressors cylinder sealing
TYPES Gland packings Mechanical contact seals Labyrinth seal Oil seal Oil film seals
GLAND PACKING
Enclosed in a stuffing box Compressive force by tightening the gland plate produces radial pressure Slight leakage is allowed for lubrication Periodic retightening of gland necessary for wear compensation. Lantern ring for cooling /lubrication
Stuffing box pressure No of rings (bar) up to 35 4 35-70 6 70-140 8 140 10
Gland packing
Braided by PTFE fibre yarns and used in acids, alkalis, gas, ammonia, chemicals, etc. The packing with PTFE impregnated (YP006)are also available. Spec:6mm - 50mm
GLAND PACKING WITH PERMISSIBLE LEAKAGE
GLAND PACKING
GLAND PACKING
• packing material vegetable based fibre yarns for oil and water service –cotton hemp flax textile asbestos yarns graphite packings
• lubricants graphite mica with Mo di sulphide and PTFE dry lubricant tallow silicone greases
WHY MECHANICAL SEALS
CONVENTIONAL SEALING CONVENTIONAL SEALING IS BY MEANS
OF GLAND PACKING .THE PROBLEMS WITH GLAND PACKINGS ARE:
1] PRODUCT LOSS 2] EXCESSIVE WEAR ON SHAFT & SLEEVE 3] FREQUENT ADJUSTMENTS 4] ENERGY LOSS
PRODUCT LOSS
GLAND PACKINGS WORK ON PRINCIPLE OF CONTROLLED LEAKAGE FOR PROPER LIFE .GLAND PACKING 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
MECHANICAL SEALS
CLASSIFICATION By arrangement 1. Single seal - Inside mounted / Outside
mounted 2. Multiple design - Double seal/ Tandem seal By design 1. Unbalanced seal 2. Balanced seal 3. single spring 4. Multiple spring 5. Pusher seal 6. Non – pusher seal
MECHANICAL SEALS
Components
1. rotary seal face 2. stationary seal face 3. springs 4. retainer 5. sealing /flushing media 6. o-rings
MECHANICAL SEALSTHE BASIC DESIGN OF A MECHANICAL SEAL
COSISTS OF FOLLOWING ELEMENTS.
1] FLEXIBLY MOUNTED SEAL FACE2] RIGIDLY MOUNTED SEAL FACE3] COMPRESSION DEVICE4] DRIVING MECHANISM5] SECONDARY SEALS
MECHANICAL SEALS
Shaft
Vessel
Shaft
Mechanical seal for arresting leakage
Liquid
Agitator blade
Shaft
Seal follower
Stuffing box
Retainer
Spring Static seal
Dynamic seal
Liquid
Bolt for locking
Gasket
Secondary seal
Discharge
Seal flushing line , liquid took from discharge line
Static & dynamic seal
PRICIPLES OF MECHANICAL SEALS
IN MECHANICAL SEALS, THE SEALING SURFACES OF EVERY KIND ARE LOCATED IN A PLANE
PERPENDICULAR TO THE SHAFT AND USUALLY CONSIST OF TWO HIGHLY POLISHED SURFACES RUNNING ADJACENTLY.
ONE SURFACE BEING CONNECTED TO THE SHAFT AND THE OTHER TO THE STATIONARY PORTION OF THE PUMP.THE POLISHED SURFACES WHICH ARE OF DISSIMILAR
MATERIALS ARE HELD IN COTINUAL CONTACT BY A SPRING,FORMING A FLUID TIGHT SEAL BETWEEN THE ROTATING AND STATIONARY MEMBERS WITH VERY SMALL FRICTIONAL LOSSES .
LEAKAGE - PATH
CLASSIFICATION OF MECHANICAL SEALS1] CLASSIFICATOIN BY DESIGN A] PUSHER TYPE SEALS a] Unbalanced seals 1) Single spring type 2) Multi spring type b] Balanced seals 1) Single spring type 2) Multi spring type B] NON PUSHER TYPE( BELLOWS TYPE) SEALS a] Metal bellows seals b] Teflon bellows seals
CLASSIFICATION OF MECHANICAL SEALS
2] CLASSIFICATION BY ARRANGEMENT: SINGLE SEALS: A] SINGLE INTERNALLY MOUNTED SEALS. B] SINGLE EXTERNALLY MOUNTED SEALS
DOUBLE SEALS: A] BACK TO BACK SEALS B] FACE TO FACE SEALS C] TANDEM SEALS
SINGLE SPRING SEALS
Gap in between seal faces, resulting leakage
Shaft
Seal follower
Stuffing box
Retainer
Spring
Static seal
Dynamic seal
Liquid
Gasket
Secondary seal
Shaft
Seal follower
Stuffing box
Retainer Spring
Static seal
Dynamic seal
Liquid
Gasket
Secondary seal
Outside mounted mechanical seal
Liquid
Static seal
Dynamic seal
Liquid
Gasket
Secondary seal
Barrier fluid 1 bar morethan process
Process liquid
Cooling system and API planes
Process liquid is taken heat which is developed by friction of seal face
SINGLE SPRING SEALS
SINGLE SPRING SEALS
ADVANTAGES: 1] LOW STARTING TORQUE 2] NON-CLOGGING 3] LOW SPRING CONSTANT
LIMITATION: 1] DUE TO SINGLE SPRING THE FACE LOADING IS NOT ALONG THE PERIPHERY OF THE SEAL FACES,
[HENCE THESE TYPE OF SEALS ARE NOT RECOMMENDED FOR VERY HIGH ROTATION SPEEDS] 2]NORMALLY UNIDIRECTIONAL 3] REQUIRE LONG AXIAL SPACE.
MULTI SPRING SEAL
NUMBER OF SMALL SPRINGS ARE USED ON THE PERIPHERY OF THE SEAL FACE TO GIVE A UNIFORM FACE LOADING.
THESE SEALS ARE COMPACT IN NATURE AND ARE UNIVERSALLY USED ON MOST OF THE CLEAR FLUIDS.
DUE TO UNIFORMLY LOADED SEAL FACES THE MULTI SPRING SEALS ARE A MUST FOR HIGH RPM APLICATION.
MULTI SPRING SEAL
MULTI SPRING SEAL
ADVANTAGES: 1] COMPACT IN COMPARISON WITH SINGLE SPRING SEAL. 2] SPRING LOAD UNIFORM,i.e. UNIFORM FACE LOADING. 3] CAN BE GIVEN FOR HIGHER SPPED THAN SINGLE SPRING. 4] FOR EACH SEAL SIZE DIFFERENT SPRING NOT REQUIRED.
LIMITATION: 1] MORE EXPENSIVE. 2] SPRING CLOGGING POSSIBLE FOR DIRTY LIQUIDS.
NON PUSHER TYPE SEALS
NON PUSHER TYPE SEALS
ADVANTAGES:
1] SEAL HANG UP DUE TO SPRING CLOGGING OR CLOGGING OF DYNAMIC ELASTOMERS ON THE SHAFT.
NON PUSHER TYPE SEALS DO NOT HAVE DYNAMIC ELASTOMERS AND HENCE THIS PROBLEM IS AVOIDED.
2] NO SHAFT OR SLEEVE FRETTING AS THERE IS NO DYNAMIC ELASTOMERS.
METAL BELLOWSMETAL BELLOWSMetal bellows are constructed
by welding “leaflets” into a series of “convolutions”. This series of convolutions is referred to as the “Bellows Core”.
The photo shown here is a shaft mounted “Utex-MB”.
Now take a look at how a bellows seal compensates for face wear.
DOUBLE SEALS
Optically Flat Faces
0 psi
RotaryFace
Stationary
Face
100 psi
MOC – MECHANICAL SEALS
Primary seal 1. Ceramic 2. Carbon - Resin impregnated – corrosive
applications - Antimony impregnated – non-
corrosive 3. Tungsten carbide - Ni binder - Co binder 4. Silicon carbide Secondary seal Elastomers - Nitrile , Neoprene ,
Butyl, Hypalon Non –Elastomers - PTFE, Graf oilSpring SS 304, SS 316, Hastalloy, Monel, Alloy-
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MECHANICAL SEAL
MECHANICAL SEAL
