mechanical seal for pumps

Presented byPrasad roshan1982@gmail.com

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