mechanical seal for pumps

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prasadroshan1982@gmail.com

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By: patkidk (35 month(s) ago)

Very nice prsentataion . Very very useful for the electrical engineers / mech engineers. kindly send a soft copy . Regards Patki. muku1068@gmail.com

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Presented by A.Prasad roshan MECHANICAL SEAL

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Cross section view of pump with mechanical seal

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Pumping liquid

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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 .

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TYPES OF SEALS Static Seals Dynamic Seals

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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

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GASKET Packing designed to go between two rigid parts in stationary conditions May be in form of sheet , strip , bulk. Properties Impermeability Ability to flow into joints Ageing Corrosion resistance

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Classification of Gaskets Non-metallic gaskets Metallic gaskets Non-metallic gaskets Asbestos Cork and rubber PTFE

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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

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DYNAMIC SEALS Used for sealing fluid between parts that move in relation with each other Application * Centrifugal pump gland, valve gland , bearing housing * Turbine/compressor inter stage and end sealing * Reciprocating compressors cylinder sealing TYPES q Gland packings q Mechanical contact seals q Labyrinth seal q Oil seal q Oil film seals

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GLAND PACKING q Enclosed in a stuffing box q Compressive force by tightening the gland plate produces radial pressure q Slight leakage is allowed for lubrication q Periodic retightening of gland necessary for wear compensation. q Lantern ring for cooling /lubrication Stuffing box pressure No of rings (bar) up to 35 4 35-70 6 70-140 8 140 10

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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

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GLAND PACKING WITH PERMISSIBLE LEAKAGE

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GLAND PACKING

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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

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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

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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

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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

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MECHANICAL SEALS Components 1.      rotary seal face 2.      stationary seal face 3.      springs 4.      retainer 5.      sealing /flushing media 6.      o-rings

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MECHANICAL SEALS THE BASIC DESIGN OF A MECHANICAL SEAL COSISTS OF FOLLOWING ELEMENTS. 1] FLEXIBLY MOUNTED SEAL FACE 2] RIGIDLY MOUNTED SEAL FACE 3] COMPRESSION DEVICE 4] DRIVING MECHANISM 5] SECONDARY SEALS

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MECHANICAL SEALS Shaft

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Vessel Shaft Mechanical seal for arresting leakage Liquid Agitator blade

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Shaft Seal follower Stuffing box Retainer Spring Static seal Dynamic seal Liquid Bolt for locking Gasket Secondary seal

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Discharge Seal flushing line , liquid took from discharge line Static & dynamic seal

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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 .

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LEAKAGE - PATH

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CLASSIFICATION OF MECHANICAL SEALS 1] 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

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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

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SINGLE SPRING SEALS

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Gap in between seal faces, resulting leakage

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Shaft Seal follower Stuffing box Retainer Spring Static seal Dynamic seal Liquid Gasket Secondary seal

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Shaft Seal follower Stuffing box Retainer Spring Static seal Dynamic seal Liquid Gasket Secondary seal Outside mounted mechanical seal Liquid

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Static seal Dynamic seal Liquid Gasket Secondary seal Barrier fluid 1 bar more than process Process liquid

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Cooling system and API planes Process liquid is taken heat which is developed by friction of seal face

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SINGLE SPRING SEALS

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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.

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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.

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MULTI SPRING SEAL

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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.

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NON PUSHER TYPE SEALS

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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.

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METAL BELLOWS Metal 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.

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DOUBLE SEALS

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Optically Flat Faces 0 psi Rotary Face Stationary Face 100 psi

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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 oil Spring SS 304, SS 316, Hastalloy , Monel , Alloy-20

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MECHANICAL SEAL

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MECHANICAL SEAL

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Thank you