Mechanical Seal-part One.pdf

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

Presented By:

Syed Iqbal Hashmi Presentation Prepared By:

Ali A. Hashmani

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

PARTS OF A CENTRIFUGAL PUMP Suction

Oil Chamber

Discharge

Slinger Ring / Deflector

Impeller

Oil Seal

Impeller Casing / Volute

Roller Bearing

Eye bolt

Ball Bearing

Mechanical Seal/Packing

Shaft

Stuffing Box / Seal Chamber

“O” Rings

Gland

Foundation

Gland Nose

Foundation Bolts

Studs

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

PUMP SURVEY BY UNION CARBIDE FOR SIX MONTHS OF 1980

They wanted to know why 238 of their pumps had failed during that period and needed to be removed to the fitting shop for repair 5

Mechanical Seal Specialization Course Institute Of Mechanical Seal

PUMP FAILURE ANALYSIS 238 IN TOTAL 26

Bearings & Housings

10.92%

2

Case Wear Ring

0.84%

8

Impeller

3.36%

1

Screwes/Setscrews

0.42%

179

Mechanical Seal

12

Shaft

5.04%

9

Sleeves

3.78%

75.21%

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MAJOR REASONS OF MECHANICAL SEAL FAILURE

 The Seal Faces Opened for Some Reason

 One of the Seal Components Damaged

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

SEAL LIFE

 The only way to tell if you are getting satisfactory seal life is to look at the soft face.  If there is still plenty of Carbon you did not get Good Life.  If most of the Carbon has worn away you got Good Life. 8

Mechanical Seal Specialization Course Institute Of Mechanical Seal

GOOD SEAL LIFE

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

GOOD SEAL LIFE

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

GOOD SEAL LIFE  Approximately 85-90% of all mechanical seals fail they do not wear out.  They fail for a variety of reasons and will continue to fail unless you make a change.  You can only make those changes if you know the reasons for failure and then know how to correct the problem. 11

Mechanical Seal Specialization Course Institute Of Mechanical Seal

A DEFINITION OF INSANITY DOING WHAT YOU ALWAYS DID AND EXPECTING DIFFERENT RESULTS IF IT DIDN’T WORK LAST TIME WHY SHOULD IT WORK THIS TIME?

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

HOW TO GET GOOD SEAL LIFE YOU NEED TO KNOW FOUR THINGS  How to choose the correct type of seal  How to install the seal correctly  Know seal applications and how chemicals change state  Know about the different back-up systems to prevent unexpected seal failure 13

Mechanical Seal Specialization Course Institute Of Mechanical Seal

OUR SCOPE OF DISCUSSION  Centrifugal Pump & Pump Parts  Categorizing the Fluid to be Sealed  Checklist for Mechanical Seal Selection  Recognizing Parts of a Mechanical Seal  Selection of Best Seal Design & Metallurgy of Individual Seal Components

 Equipment Inspection for Seal Worthiness  Decision bout Equipment Modifications  Mechanical Seal Classification 14

Mechanical Seal Specialization Course Institute Of Mechanical Seal

OUR SCOPE OF DISCUSSION Generation of Mechanical Seal Mechanical Seal Selection Data Sheet  Mechanical Seal Installation Guideline  Mechanical Seal Repair  Mechanical Seal Trouble Shooting ________________ Note: Discussion will be with reference to pump but same technique is applicable on all rotating equipment to be sealed (e.g. Mixer, Agitator, Gear Box etc.) 15

Mechanical Seal Specialization Course Institute Of Mechanical Seal

A Typical Mechanical Seal Have The Following Parts, Manufactured From Variety Of Materials:

1. The Metal Parts – Case, Springs, Set Screws, etc. 2. The Elastomer (O-Rings) – Viton, EPR, Teflon, etc. 3. The Rotary Face – usually Carbon Graphite, but many other materials are available

4. The Stationary Face – Ceramic, Tungsten carbide, SS etc.

Cont’d…

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Institute Of Mechanical Seal

Mechanical Seal Specialization Course

A Typical Mechanical Seal Have The Following Parts, Manufactured From Variety Of Materials:

Springs

Allen Screws

Rotary Face

Stationary Face

O-Rings Case/Metal Retainer Gland Plate (Stationary Holder) 17

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Gland

Gasket

(Stationary Holder)

Drive Mechanism Shaft Seal

Rotary Seal Ring

Stationary Seal Ring

Spring Mechanism

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL COMPONENTS 1. 2. 3. 4. 5. 6.

Stationary Seal Ring (Face) Rotary Seal Ring (Face) Spring Mechanism Drive Mechanism Shaft Seal Gland (Stationary Holder)

7. Gasket 19

Mechanical Seal Specialization Course Institute Of Mechanical Seal

SELECTING THE CORRECT SEAL OPERATING PARAMETERS  Media to be Sealed  Liquid used for Flushing  Temperature  Pressure  Speed  Stuffing Box Dimensions  Seal Worthiness of Pump 20

Mechanical Seal Specialization Course Institute Of Mechanical Seal

CATEGORIZING THE FLUID TO BE SEALED 1. Fluids Sensitive to Small Changes in Stuffing Box Temperature and / or Pressure 2. Fluids that Require Two Mechanical Seals with a Barrier Fluid Circulating Between them 3. Non Lubricating Liquids, Gases and Solids 4. Slurries-Classified as Solids in Liquid. The Solids may or may not be Abrasive

5. Liquids Sensitive to Agitation 6. Liquids that React with each other to form a Solid 7. Clean Lubricating Liquids 21

Mechanical Seal Specialization Course Institute Of Mechanical Seal

CRITICAL SEALING SITUATION 1. 2. 3. 4.

Hot Products Cryogenic Fluids High Pressure Application Hard Vacuum

5. High Speed 6. Excessive Radial and Axial Motion 7. Excessive Vibration 22

Mechanical Seal Specialization Course Institute Of Mechanical Seal

1) Fluids that are Sensitive to Changes in Temperature and / or Pressure

a) Corrosive Liquids • Corrosion Rate-Temp Relationship • Rubbing Damage Causing Localized Corrosion • Unutilized Cooling Jacket

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

1) Fluids that are Sensitive to Changes in Temperature and / or Pressure

b) Liquid that Vaporize • Causes • Low Specific Gravity • High Stuffing Box Temp. • Low Stuffing Box Pressure 24

Mechanical Seal Specialization Course Institute Of Mechanical Seal

1) Fluids that are Sensitive to Changes in Temperature and / or Pressure

b) Liquid that Vaporize •

Consequences •

Seal Faces open

•

Seal Faces Damages Due to Residue

•

Cyclic Opening / Closing Damage Seal Face

•

Freezing Effect

•

Fugitive Emission

•

Restriction in Movement of Sliding Parts of Mechanical Seal Example: Hot Water, Propane, Freon

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

1) Fluids that are Sensitive to Changes in Temperature and / or Pressure

c) Liquids that Solidify • Common Problem in Stand by Pumps & Suction Side of Running Pumps Lifting the Liquid.

Example: Paint, Glue, Polymers 26

Mechanical Seal Specialization Course Institute Of Mechanical Seal

1) Fluids that are Sensitive to Changes in Temperature and / or Pressure

d) Viscous Products •

Viscosity- Temperature Relationship

•

High Viscous Liquid:

•

•

Interfere with Free Seal Movement

•

Seal Face Separation Problem

Low Viscous Liquid:

• •

Increase in Seal Face Wear Due to Insufficient Film Thickness Color Problem Due to Excessive Wear of Carbon Face Example: Cold Fuel, Oil, Asphalt, Sugar Syrups

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

1) Fluids that are Sensitive to Changes in Temperature and / or Pressure

e) Film Building Liquids •

Coking Problem Causing •

Seal Face Separation and Leakage

•

Restriction in Sliding and / or Flexing of the Seal Components

•

Destruction of Dynamic “O” Ring Due to Magnetite Pickup in the System. Example: Hot Oil, Hard Water

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

1) Fluids that are Sensitive to Changes in Temperature and / or Pressure

f) Liquid that Crystallize •

Carbon Faces Destroy and Run-Out Quickly due to Crystal Formation

•

Crystal Formation on Sliding or Flexing Components Lead to seal Face Opening.

• Solution •

Control Temp and / or Pressure

•

Avoid Use of Two Hard Faces

•

Use Balanced Mechanical Seal Only Example: Sugar, Caustic, Salt Water

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

2) Liquid that Require Two Mechanical Seals • Costly Liquids • Fugitive Emissions

• Dangerous Products •

Radiation, Toxic, Fire, Explosion, Bacteria etc.

• Pollutants 30

Mechanical Seal Specialization Course Institute Of Mechanical Seal

3) Sealing Non-Lubricants •

Problems: • •

•

Rapid Face Wear Due to Thin Film Excessive Carbon Wear Causing Color Contamination & Lesser Life of Mechanical Seal

Categories of Non-Lubricants: Dry Gases

Dry Solids

Excessive Heat Generation Problem

Clogging of Sliding Components

Don’t Forget to Vent the Stuffing Box

No Lubrication to Seal Faces Destruction of Lapped Faces Shaft Speed & Seal Size are Important 31

Mechanical Seal Specialization Course Institute Of Mechanical Seal

4) Slurries – Especially Abrasive Slurries • Problems: •

Clogging

•

Seal Face Damage

•

Deposits on Sliding Components

•

Impeller Wear out Causing Dynamic Balancing Problem

•

Severe Wear of Spring or Bellows

Example: River, Water, Sewage, Raw Products 32

Mechanical Seal Specialization Course Institute Of Mechanical Seal

5) Liquids Sensitive to Agitation • Types: •

Newtonian Fluids Viscosity does not change with agitation

•

Dilatant Fluids (Formation of Butter From Cream) Viscosity increases with agitation

•

Thixothropic Fluids (Non-Drip Paints and Automobile Wax) Viscosity lowers with agitation

•

Plastic Fluids 33

Mechanical Seal Specialization Course Institute Of Mechanical Seal

5) Liquids Sensitive to Agitation • Problems: • Excessive Face Wear • Color Contamination • Seal Face Opening • Continuous Rotation of Fluid is Required in Stuffing Box Area, in Case of Dilatants 34

Mechanical Seal Specialization Course Institute Of Mechanical Seal

6) Liquids that Combine Together to Form a Solid • Problems: - Thorough Flushing Mandatory Between the Batches • Examples: Epoxy, Styrofoam, Anaerobic Fluids (e.g. Super Glue) 35

Mechanical Seal Specialization Course Institute Of Mechanical Seal

7) Clean Lubricating Liquids

 Ideal for Mechanical Seal Application

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

Categorizing the Fluid to be Sealed 1. Is it Continuous or Intermittent Service?  Thermal Stress  Start-up Torque  Start-up Axial Thrust 2. Changing State of the Product 3. Relevant Specifications and Standards  OSHA  Nuclear  FDA  API etc. 37

Mechanical Seal Specialization Course Institute Of Mechanical Seal

CRITICAL SEALING SITUATIONS 1. Hot Products:  

Too Hot for One of the Seal Components. Cause the Fluid to Change State

2. Cryogenic Fluids:  

Problem for Elastomer and Carbon Faces Example: Liquid Nitrogen and Oxygen

3. High Pressure: 

Stuffing Box Pressure > 400 Psi (28 bar)

Examples: 1) Boiler Circulating Pump 2) Multi Stage Pumps 3) Elbow Pumps

•

Problems:  Seal Face Deformation  High Face Loading

 Elastomer Extrusion  Push – off the Set Screws

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

CRITICAL SEALING SITUATIONS 4. Hard Vacuum 5. High Speed 

Shaft Speed > 5000 FPM Examples: Sundyne Pumps

6. Excessive Motion: 

Axial or Radial Movement > 0.005 Inches (0.15 mm) Examples: Mixers, Agitators, Long Shaft Pumps, Pumps with Sleeve or Babbitt Bearings 39

Mechanical Seal Specialization Course Institute Of Mechanical Seal

CRITICAL SEALING SITUATIONS 7. Excessive Vibration: - Problems:  Open the Lapped Seal Faces  Chip the Outside Diameter of the Carbon Face  Fatigue or Break the Metal Bellows Used in Some Seal Designs  Wear the Driving Pins Used to Transmit Torque from the set Screws to the Seal Faces  Loosen Drive Screws  Shorten Bearing Life 40

Mechanical Seal Specialization Course Institute Of Mechanical Seal

CRITICAL SEALING SITUATIONS 7. Excessive Vibration: - Problems:  Damage (frett) Expensive Sleeves and Shafts as the Shaft Moves through the Dynamic Elastomer. You will Eventually Experience Leakage at the Fretting Location  Frett the Shaft Under the Bearing Grease Seals - Solution:  Use Vibration Damper Seal of Correct Type & Design 41

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Operating Parameter Study For Seal Selection

Speed  <5000 FPM use Rotating Seals (Not recommended in case of fugitive emission)  >5000 FPM use Stationary Seals to Avoid “Cocking” Problem  Lower the Spring Pressure  60/40 Balance Ratio 42

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Operating Parameter Study For Seal Selection

Pressure  Use Hydraulically Balanced Seal for Stuffing Box Pressure of one Torr Vacuum to 400 Psi  Use Heavy Duty Seal Designs for Greater Pressure Incorporating:  Back up rings to Prevent Elastomer  Thicker Cross Section Components to Prevent Face Distortion  Laminated Metal Bellows for all Metal Version  Specify Two Way Balance for Dual Seal Applications 43

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Operating Parameter Study For Seal Selection

Temperature  Check “O” Ring Compatibility  Use Non-Elastomers (metal bellows) for Higher Temperatures 44

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Operating Parameter Study For Seal Selection

Motion Capability:  Use Wider Hard Faces  More Internal Clearance with in the Seal Components  Axial Movement Capability without Changing Spring Load  Use Dynamic “O” Rings to Compensate for Shaft Run Out. 45

Mechanical Seal Specialization Course Institute Of Mechanical Seal

EQUIPMENT INSPECTION FOR SEAL WORTHINESS  Check the Stuffing Box Face: 

Flat and Smooth



If Uneven Machine it



Stuffing Box must be Clean and Clear along its Length



Check Misalignment of the Stuffing Box Relative to the Shaft using Dial Indicator Max. 0.003” TIR/in OR 0.003 mm TIR/mm of Shaft  (For Cartridge Seal 0.005)



Check Pipe Storm as it may Misalign a Stuffing Box



Rotary Portion of the Seal shouldn’t Touch Stuffing Box. Rotary Shaft shouldn’t Touch Stationary Seal Face. 46

Mechanical Seal Specialization Course Institute Of Mechanical Seal

EQUIPMENT INSPECTION FOR SEAL WORTHINESS  Check the Shaft or Sleeve:  Remove all Burrs & Sharp Corners-Especially in the Area where “O” Ring has to Slide  Cover Threads & Key ways Slots with a Thin Tape

 Shaft Finish no Rougher than 32µ in (0.8 microns)  Shaft  Tolerance <= + 0.002”  Shaft Run out <= 0.001”  End Play <= 0.005 47

Mechanical Seal Specialization Course Institute Of Mechanical Seal

EQUIPMENT INSPECTION FOR SEAL WORTHINESS  Check the Shaft or Sleeve:  For Cartridge Seal, Protect the Sleeve “O” Ring by Lubricating the shaft with a Clean Silicon Based Lubricant

 Check if the sleeve Gasket / “O” Ring is in Place and Sealing  In Case of Hardened Shaft Set Screws will not Hold it. Use a Seal that Clamps Around the Shaft OR Use Hardened or Carbon Steel Set Screws 48

Mechanical Seal Specialization Course Institute Of Mechanical Seal

DECISION ABOUT EQUIPMENT MODIFICATION Best Location for Mechanical Seal is near bearings to avoid shaft displacement.

Causes of Displacement : 

Pump / driver misalignment



A high ratio of shaft length to shaft diameter (L3/D4)



Operating the pump off its best efficiency point (B.E.P.)



Starting a pump with a throttled or closed discharged valve



An elbow located too close to the pump suction. There should be ten diameter pipe between the pump suction and the first elbow



A dynamically unbalanced rotating assembly 49

Mechanical Seal Specialization Course Institute Of Mechanical Seal

DECISION ABOUT EQUIPMENT MODIFICATION Causes of Displacement :  A Bent Shaft  Pipe Strain  Thermal Growth

 Impeller Adjustments  Vibration  Caviation 50

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Controlling Environment to Prevent Premature Seal Failure  Either control the stuffing box environment to operate Mechanical Seal in a clean, cool, lubricating liquid.

OR  Select a Mechanical Seal with built in features to handle the adverse conditions 51

Mechanical Seal Specialization Course Institute Of Mechanical Seal

GOOD SEAL SPECIFICATIONS  Able to fit most pumps without modification

 Seal repair should be easy, on site and low cost.

 Widest range of chemical capability

 Should not damage the shaft or sleeve.

 Should be able to convert packed pumps to seals

 Must operate over a wide range of speed, temperature and pressures

 Low inventory of spare parts 52

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Desirable Features in Mechanical Seals  Flat, Parallel Seal Faces

 Concentric, Cartridge Mounting

 Hydraulically Balanced

 Non clogging / Springs Out of the Fluid

 High Performance Face Materials

 Simple Design – Easy to install and Repair

 Flexibly Mounted Stationary - Rotary Seal (how?) - Stationary Seal (by design)

 Competitive Price 53

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Desirable Features in Mechanical Seals Cont’d…

1) Centering Ability: – Piloting the Inside of the Stuffing Box if the Stuffing Box is Concentric with the Shaft – Piloting the Outside Diameter of the Stuffing Box Face if the Stuffing Box is Concentric with the Shaft – Cartridge Centering Clips

2) Anti Clogging Features: – – – –

Spring Out of the Fluid The Dynamic Elastomer Moves to a clean location Seal is Positioned in such a way that Solid Particles are Thrown Out of the Seal Faces Teflon Coated Components for Non-Sticking Properties

3) Non-Fretting Design: – No Dynamic Elastomers Touching the Shaft or Sleeve – Use Solid Shaft to Avoid Deflection at Start up & Beyond BEP 54

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Desirable Features in Mechanical Seals Cont’d…

4) Built In Environment Controls: – – – –

Flush / Recirculation / Vent Connection A Vent and Drain / Quench Connection Disaster Bushing for Bearing Failure A Gland Cooling Jacket

5) The Smallest Cross Section Possible: – To Cater for Radial Shaft Movement – Centrifuge Heavier Solids

6) Design that Mount Close to the Bearings: – This Avoids High Cost of Over size Stuffing Box

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

Desirable Features in Mechanical Seals 7) Cartridge Designs: – Easy Impeller Adjustment

8) Vibration Damping: – Especially with Metal Bellows Design

9) Slotted or Other Forms of Non-dedicated Glands 10) Design that Rotate the Fluid in the Stuffing Box 11) Designs that Pass Environmental Standards 12) Repair Kits Availability: – – – – – –

Carbon / Graphite Face Springs Elastomers Set Screws Gaskets Hard Face

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

First Generation Mechanical Seal Design  Unbalanced - High Wear & Energy Cost, Short Seal Life  Shaft Fretting Corrosion - Rapid Equipment Shaft/Sleeve Damage

 Clogging - Premature Leakage  Low Pressure and Speed Capabilities 57

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Second Generation Mechanical Seal Design  Balanced - Low Wear & Energy Cost, Longer Seal Life  Non fretting - No Equipment Shaft/Sleeve Damage

 Non clogging - Longer Life

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

Third Generation Mechanical Seal Design  Greatest Reliability - Long Seal Life & Emissions Control  Totally Non-fretting - No Equipment or Seal Damage  Easy to Install or Repair  Highest Performance Design & Materials  Monolithic Flat Seal Faces – Thermal Cycling - Stress Relaxation – Pressure Distortion and Frictional Heat

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

O.E.M. MECHANICAL SEAL PROBLEMS  Unbalanced  Manufactured From Unnamed Grade of Mystery Materials

 Seal Fails Long Before the Sacrificial Seal Faces are Worn out

 Improper Stuffing Box Design 60

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Problems With Individual Components 1. Carbon Face: 

Unidentified Grade of Carbon – Graphite with Low Density (Filled with Binders & Fillers)

 

Attacked by Product Not Suitable for High Temperature Application

2. Elastomer:      

Unidentified Grade Material Temperature Limits Chemical Compatibility Problems Limited Shelf Life Sensitivity to Steam Cleaning / Lubricants Not Free to Flex or roll on the shaft leading to Fretting Problems (Sacrificial Sleeve Weakens Shaft)

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

Problems With Individual Components 3. Springs:   

Chloride Stress Corrosion Failure Clogging Due to location in Sealing Medium Single Spring Sensitive to Direction of Rotation of Shaft

4. Glands:  Non-Standard Leading to a Larger Inventory 5. Discharge Re-circulation:  Stuffing Box Soon Fills With Dust  Filter in the Line will Clog and Cause Heating Problems

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

Problems With Individual Components 6. Rubber Bellows:  Sensitive to Installation Lubricant and Heat  Limited Shelf Life  Frequent Failure due to the Bellow Rupture

7. Design Limitations:  Impeller Adjustment not Possible  Failure Due to Axial Movement  Sensitive to Diameter, Tolerance and Surface Finish of the Shaft or Sleeve

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

Check List For Mechanical Seal Selection Cont’d…

1. Design Consideration:         

Failure Controllable or uncontrollable Can the Seal Handle Pump / Driver Misalignment Location of Elastomer – If it is Near Seal Face then it will be subject to heat generation Can Seal Handle Shaft Dynamic Unbalance Is the Hard Face Wide Enough to Prevent the Narrow Face Running off Due to Shaft Run Out? What will Happen if Bearing Fails? Is Impeller Adjustment Possible? Gland is Standard or Not? Seal Face Centering Feature Available? 64

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Check List For Mechanical Seal Selection

 

Are Elastomers Sensitive? How much Axial or Radial Movement Seal can Take?

    

Has Vibration Damping been Provided? Anti Clogging Feature Available? Is the Seal Hydraulically Balanced? In Case of Dual Seal can it Take Reverse Pressure? Seal Designed on Finite Element Program?

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

Check List For Mechanical Seal Selection

2. Metallurgy:  Standard or Mystery Materials?  Proper Grade Material has been Used or Not?  Operating Limits are Known to You? 66

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Check List For Mechanical Seal Selection

3. Spare Kit:    

Repair or Not? Spare Kit Readily Available or Not? Repair is Expensive or Inexpensive? How to Dispose of Contaminated Parts? 67

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Check List For Mechanical Seal Selection

4. Manufacturing:  Mass Produced or Tailor-Made?  Ex-Stock Availability  Shelf-Life of Seals and Spares 68

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Check List For Mechanical Seal Selection

5. Environment Controls:  Does it Meet Fugitive Emission Standards?  Can you Vent the Seal Faces in a Vertical Installation?  Flush or Re-circulation Connection 69

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Check List For Mechanical Seal Selection Cont’d…

6. Installation:         

Is Installation Easy? New Gland will be Required? Can a Packed Pump be Converted into Mechanical Seal without Major Modification? Shaft / Sleeve Change Required? Is the Static Elastomer in the Correct Location? Is Special Lubricant Needed for the Elastomer? Is there a Method of Centering the Wearable Face in the Hard Face? Is Stuffing Box Face Square? Accurate Measurement Required to set the Proper Spring Load? 70

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Check List For Mechanical Seal Selection



Can Impeller be Adjusted Afterwards?



Do You Need a Print to Tell the Correct Installation Length?



Can Machine Tell that Mechanical Seal has been Installed Correctly after Assembling?



Are the Faces Protected before Installation?



Self-Alignment Feature?

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 1.

By Design Configuration:

a.

Inside Seal: An inside seal, seals fluid on the outside diameter of the seal faces. Typically the seal is in the fluid.

Fluid is sealed on the outside diameter of the seal faces.

Stationary Face Rotary Face

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 1.

By Design Configuration:

b.

Outside Seal: An outside seal, seals fluid on the inside diameter of the seal faces. Typically the seal is “out” of the fluid.

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 2.

By Rotary Design:

a.

Rotary Mechanical Seal: A rotary mechanical seal will have the spring located in the rotating part of the seal.

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 2.

By Stationary Design:

b.

Stationary Mechanical Seal: A stationary mechanical seal will have the springs located in the stationary part of the seal.

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 4.

By Assembly:

a.

Component Design: A component mechanical seal requires assembly of Rotary and Stationary parts on the equipment shaft/sleeve.

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 4.

By Assembly:

b.

Cartridge Design: A cartridge mechanical seal is fully pre-assembled on a sleeve and enclosed in a Gland. Seal faces remain in contact during handling and installation.

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 5.

By Metallurgy:

a.

Metallic Seal: A metallic seal has metallic parts in contact with the product.

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 5.

By Metallurgy:

b.

Non-metallic Seal: A non-metallic seal does not have metal parts in contact with the product.

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 6.

By Balancing:

a.

Balanced Design: A balanced mechanical seal arrangement balance the axial fluid force acting on the seal faces.

Seal Balance Line

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 6.

By Balancing:

b.

Unbalanced Design: An unbalanced mechanical seal does not reduce the axial fluid forces on the seal faces. Unbalanced Seal No Balance Line

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 7.

By Configuration:

a.

Non-Split Mechanical Seal: One or all parts of the seal are solid pieces requiring equipment to dismantle for installation.

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 7.

By Configuration:

b.

Split Mechanical Seal: All parts are split for installation without equipment disassembly.

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 8.

By Seal Faces:

a.

Single Seal: A single mechanical seal uses one set of seal faces.

One set of seal faces

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Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL CLASSIFICATION 8.

By Seal Faces:

b.

Dual Seal: A Double (or Dual) Mechanical Seal uses two sets of seal faces.

Two sets of seal faces.

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Institute Of Mechanical Seal

Mechanical Seal Specialization Course

High Performance Face Materials Carbon – Pure P-658RC:

 80% Carbon, 20% Graphite, <1% Binder  High Strength, Hardness & Modulus of Elasticity  High Lubricity  Low Permeability Sintered Silicon Carbide:

 Less than .5% free silica  Highest Hardness  Highest Thermal Conductivity  Chemically Inert 86

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

High Performance Face Materials Duplex Carbide – Pure PG-9723:

 70% Reaction-Bonded Silicon Carbide (6% free silica.)  30% Graphite  Balanced Lubricity and Hardness Solid Tungsten Carbide:

 6% Nickel Binder  High Strength and Toughness  Good Thermal Conductivity 87

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Seal Face Combination Characteristics Face Comb.

Heat Gen.

Chemical Comp.

Abrasion Resist.

Common Use

CB/CER

1

7

2

General

CB/TC

2

7

2

API

CB/RSC

1

7

2

CB/SSC

1

8

2

Good First Choice

SSC/DC

4

7

6

Hard Face/Lubricity

SSC/TC

6

8

9

Oils

SSC/RSC

7

8

10

Abrasives

CER/CER

10

9

N/A

Oxidizers

TC/TC

9

8

9

Mechanical Shock

SSC/SSC

8

10

10

Strong Acids

Based on a rating of 1 to 10. Values are relative for comparison with 10 being highest and 1 being lowest. They do not reflect magnitudes of difference. 88

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Mechanical Seal Specialization Course

Seal Face Combination Characteristics Carbon vs. Ceramic: Unfilled Carbon Graphite vs. 99.5 Ceramic is best choice for most applications. But Carbon, in any form, is not acceptable in the presence of a strong oxidizing agent. Following are the most common chemicals that will affect Pure Grade Carbon 658RC: Aqua Regia HNO3 & HCL

Oleum (Fuming Sulfuric)

Perchloric Acid, Fluorine

Sulfur Trioxide

Nitrite Acid > 20% & 250°F

Sulfuric Acid > 75% & 250°F

Iodine > 5% & 200°F

Chloric Acid > 10% & 200°F

Ferric Chloride > 50% & 200°F

Hydrofluoric Acid > 40% & 200°F

Calcium & Sodium Chlorate > 5%

Sodium Hypochlorite > 5%

89

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Mechanical Seal Specialization Course

Seal Face Combination Characteristics Carbon vs. Ceramic:

The Following Chemicals will not attack Carbon 658RC but severe abrasive wear can occur. Chromic Acid Chrome Plating Solutions Sodium Chromate

Chromic Oxide (Aqueous) Potassium Dichromate (Aqueous) Sodium Dichromate 90

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Mechanical Seal Specialization Course

Seal Face Combination Characteristics 99.5 Ceramic vs. 99.5 Ceramic: 99.5 Ceramic vs. 99.5 Ceramic is the face material for strong oxidizing chemicals. Sometimes Carbon is not acceptable because of color contamination. (This happens in Pharmaceuticals & Papers Industries). If Carbon is not acceptable then 99.5 Ceramic vs. 99.5 Ceramic may be used.

Carbon vs. Tungsten Carbide: Carbon vs. Tungsten Carbide is used when Ceramic is not desired or it is evident that it is breaking in the application. If Plated Tungsten Carbide is to be used then it must be the nickel binder type. 91

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Seal Face Combination Characteristics Tungsten Carbide vs. Tungsten Carbide: Tungsten Carbide vs. Tungsten Carbide (both faces must be solid) is used when a product has a tendency to stick the faces together or it abrasives are penetrating through the lapped faces.

Silicon Carbide: Silicon Carbide, because of its lower cost, is an acceptable substitute for Tungsten Carbide.

92

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

RELAPPING OF FACES The Following faces can be relapped if there are no chips or cracks that penetrate 10% across the face:

 Tungsten Carbide  Ceramic  Silicon Carbide Carbon / Graphite Face Relapping: Carbon should not be relapped. It is not a good idea to relap carbon graphite faces. Imbedded solids are pushed even further in, causing scoring and wearing of the hard face. Remember carbon can not wear a hard face, only foreign material stuck in the carbon can do that, and relapping can not remove it. 93

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

O-Ring Materials Mechanical Seals have many O-Rings. The correct O-Ring usage is crucial in maintaining the integrity of the Mechanical Seal chosen. The various types of O-Rings typically used are:

 Viton  Buna-N  Aflas  Chemraz

 EPR  Neoprene  Kalrez  Vanway 94

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

O-Ring Materials Viton – Trade name for Fluorocarbon made by DuPont Corporation

 Excellent Chemical Resistance  Good Chemical Memory  Rated to 400 °F (205 °C)  Typically used with acids EPR – Ethylene Propylene Rubber

 Good Chemical Resistance  Excellent Memory  Not used with petroleum based products  Rated to 300° F (160 °C)  Typically used in bases (Caustic)

95

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

O-Ring Materials BUNA-N (Nitrite)

 Rated to 210 °F (105 °C)  Good Chemical Resistance  Susceptible to Ozone attack Neoprene

 Rated to 300 °F (160 °C)  Specifically designed to seal ammonia and refrigeration oils  Designed for low temperature services 96

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

O-Ring Materials

Aflas – Trade name for Fluorocarbon made by 3M Corporation.

 Excellent Chemical Resistance  Good Chemical Memory  Rated to 400 °F (205 °C)  Typically used with acids and low concentration bases

97

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

O-Ring Materials Kalrez (Two compounds 1050 & 4079) 1050LF or 1050

 Rated to 550 °F (250 °C)  Excellent Chemical Resistance to Strong Acids and Solvents  Compression sets during temperature cycling

4079

 Rated to 550 °F (250 °C)  Excellent Chemical Resistance except in: Hot Water Steam Amines

98

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

O-Ring Materials Kalrez (Two compounds 1050 & 4079) 4079

 Better than 1050 in: Aldehydes Organic Acids Inorganic Acids

 Does not compression set as readily

99

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

O-Ring Materials Chemraz 513

 Perfluoroelastomer  Rated to 450 F (232 C)  Excellent Chemical Resistance except in: Sulfuric Acid Black Liquor White Liquor

Acetic Acid Green Liquor

Vanway (AKA Style 76)

 Teflon encapsulated Viton  Rated to 350 F (176 C)  Excellent Chemical Resistance  Good Static Seal If product permeates Teflon and attacks Viton core, O-ring will fail 100

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

O-Ring Materials ChemLast 550 Temperature Range: Compound Description:

15°C to 260°C (-5°F to 500°F) Black, High Temperature, 75 Shore A, Perfluorinated Elastomer

Properties Shore A Hardness

Typical Results 80

Tensile Strength, MPa

14.1

Elongation, %

135

Compression Set, 22 hours at 230°C, ASTM D395 Method B, 2-214 Size O-rings % Permanent Set…………………….

23

Compression Set, 70 hours at 200°C, ASTM D395 Method B, 2-214 Size O-rings % Permanent Set…………………….

19 101

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

O-Ring Materials ChemLast 250 Temperature Range: Compound Description:

15°C to 300°C (5°F to 575°F) Black, Ultra High Temperature, 75 Shore A, Perfluorinated Elastomer

Properties Shore A Hardness

Typical Results 75

Tensile Strength, MPa

12.0

Elongation, %

124

Compression Set, 70 hours at 200°C, ASTM D395 Method B, 2-214 Size O-rings % Permanent Set…………………….

12

Compression Set, 70 hours at 316°C, ASTM D395 Method B, 2-214 Size O-rings % Permanent Set…………………….

45 102

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

O-Ring Materials

O-Ring Test Test an O-Ring by immersing it in the product for 7 to 10 days. Look for a change in weight, shape, dimensions or appearance. If nothing is changed then O-Ring is chemically compatible with the product.

103

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Listed below is the data required to properly size a Mechanical Seal.

(A) Stuffing Box Diameter (B) Shaft Size (C) Stud Length (D) Stuffing Box Depth (E) Stud Diameter (F) Bolt Circle Diameter (G) Distance to First Obstruction 104

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

WHAT IS MECHANICAL SEAL A mechanical seal consists of two extremely smooth flat surfaces, called faces, held together to prevent fluid from escaping. In a mechanical seal, one face must rotate with the shaft and is commonly called the “Rotary” and the other mechanical seal face is fixed and is called the “Stationary” Application: Pumps, mixers, agitators, reactors and rotating equipment. 105

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Equipment Inspection for Seal Worthiness: A seal will run properly if installed correctly in a proper piece of equipment on a shaft that runs true, and with any control necessary to correct adverse sealing requirements.

Determine if the pump is in good condition. Prior to seal installation, a thorough inspection of the equipment should be made. The condition of the equipment should fall within manufacturer’s guidelines. Other parameters listed below and the checking process should be made as described. Equipment design variances may change the requirements of inspection. 106

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Equipment Inspection for Seal Worthiness: A. Check the Shaft or Sleeve. 1. Remove all burrs and sharp corners, especially in area where the O-rings has to slide. Covers threads and key-way slots with a thin tape to prevent cutting the O-Ring. 2. The shaft finish should be no rougher than 32 micro inches (0.8 microns) AA. It should feel smooth if you run your fingernail along the shaft in the axial direction. 3. Make sure the shaft or sleeve diameter is within tolerance (no more than +/- 0.002” [0.05mm] from nominal). Example: 1.750” (50 mm) shaft should not be larger than 1.752” (50.05 mm) or smaller than 1.748” (49.95 mm). 107

Cont’d…

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Equipment Inspection for Seal Worthiness: 4.

Use a dial indicator to measure the shaft run out in the area where the seal is to be installed. Reading should not exceed 0.001” TIR per inch (0.001 mm TIR per millimeter) of shaft diameter.

5.

Place the dial indicator on the end of the shaft in the axial direction to measure end play. If the bearings are in a good condition, end play should not exceed 0.005” (0.13 mm) TIR.

6.

In case of Cartridge Seal, Protect the sleeve O-Ring by lubricating the shaft with a clean silicon based lubricant.

7.

If the shaft is fitted with a sleeve, is the sleeve gasket & O-rings in place and sealing? A leaking sleeve gasket looks like a leaking seal face.

8.

If the shaft or sleeve has been hardened, the set screws will not hold. In this case, use a seal that clamps around the shaft such as Chesterton Style 440, provided it is used within its operating parameters. Harden or Carbon Steel set screws may be used. 108

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Equipment Inspection for Seal Worthiness: Cont’d…

B. Check the Stuffing Box Face: 1.

The stuffing box face must be flat and smooth enough to seal the stationary gland. Typically, 125 micro inches (3.2 microns) AA maximum for gasket 32 micro inches (0.8 micron) AA for O-Rings.

2.

Split case pumps often have an uneven stuffing box face. This must be machined flat.

3.

Make sure the stuffing box is clean and clear along its entire length.

4.

If possible, attach the base of dial indicator to shaft and rotate shaft and indicator slowly while reading the run out of the stuffing box face. Misalignment of the stuffing box relative to the shaft should not exceed that specified by the stationary manufacturer. Typically, a maximum of 0.003” TIR per inch (0.003 mm TIR per millimeter) of shaft diameter is recommended. For Cartridge Seals 0.005” TIR per inch (0.005 mm TIR per millimeter) of shaft diameter. 109

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Equipment Inspection for Seal Worthiness: 5.

Pipe strain can misalign a stuffing box and cause excessive seal movement.

6.

If the rotary portion of the seal (in case of component seal) hits or rubs anything stationary in the stuffing box, the faces will open. Also remember that if the rotating shaft touches the stationary seal face, seal failure will occur

L3/d4 Ratio for Shaft Deflection d

L

7.

L3/d4 Ratio of shaft is very critical to avoid shaft deflection. Shaft with less length and more thickness is ideal for Mechanical seal. A properly designed pump with shaft stiffness ration (L3/d4) of under 2.4 mm or 60 inch is suitable. Mounting the seal as close as possible to the radial bearings is a positive step towards reduced emission and seal failure chances. 110

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Mechanical Seal Selection Guide*

SEAL TYPE TEMPERATURES

INSIDE

OUTSIDE

UNBALANACED

BALANCED

UNBALANCED

BALANCED

To 250°F To 120°C









250°F – 400°F 120°C – 205°C





Over 400°F Over 205°C





111

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Mechanical Seal Selection Guide*

SEAL TYPE PRESSURES

To 50 psi 3,5 kg/cm² 50-300 psi 3,5-21,1 kg/cm² Over 300 psi Over 21,1 kg/cm²

INSIDE

OUTSIDE

UNBALANACED

BALANCED

UNBALANCED

BALANCED















112

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Mechanical Seal Selection Guide*

SEAL TYPE SPEEDS

INSIDE

OUTSIDE

UNBALANACED

BALANCED

UNBALANCED

BALANCED

To 1500 fpm To 7.6 m/s









1500-3000 fpm 7.6-15.2 m/s





Over 3000 fpm Over 15.2 m/s





113

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Dual Seals Use  Any time you pump:  Dangerous products  Pollutants  Costly products  Fluids that give off fugitive emissions

 If down time is very expensive.  If you need back up seal protection 114

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Dual Seals Use  Dual Seal Configuration:  Rotating face to face.  Rotating tandem  Rotating concentric  Stationary concentric  Stationary tandem

115

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Dual Seals Configuration NOT Recommended

Cont’d…

 Avoid using dual seals in the following configurations:  Rotating back to back  Rotating tandem if the seals are facing into the stuffing box.  Stationary face to face

 Stationary tandem if the first stationary face is positioned in 116 the bottom of the stuffing box.

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Split Mechanical Seals are another Choice The split seal is the one seal that every consumer wanted. The main reason that people continue to use packing in pumps is that no one wants to take the pump apart just to fix a leak. Taking a pump apart involves several problems:

 The mechanic must have enough skill to reassemble the pump, insuring that skill is rapidly disappearing. In some facilities the person that took the pump apart is not necessarily the same person that is going to put it back together again.

 You must go through a complete realignment between the pump and the driver. That can take hours.

 In some instances insulation has to be removed to move the pump. This can involve serious hazardous materials disposal problems.

 In many facilities seal replacement involves many crafts. An electrician to blank out the motor, a pipe fitter to un bolt the piping, a rigger to bring the pump back to the shop, a mechanic to fix it and several work orders to reserve the process when the pump goes back. 117

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Split Mechanical Seals are another Choice

Cont’d…

 When the pump is disassembled to replace the seal, the bearings are often replaced at the same time. More often than not seal replacement often means a complete pump overhaul.

 In some cases the system has to be sterilized if the pump is disassembled. This can involve many hours of heating, flushing, etc.

118

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

There are three accepted methods of joining the split elastomer components:  Vulcanize the components together around the shaft. This is the method that was used on the atomic submarine Nautilus. Its only limitation is that you are not able to manufacture small diameter rings because the stock must go around the shaft and then through the vulcanizing tool. Present technology limits this technique to shaft diameters larger than six inches (150 mm).

 Install extra elastomers over the shaft and into the seal assembly. You can then move out and use them as needed. This is a good technique, but presents major difficulties is seal design.

 Use the “ball and socket” design. CAUTION: Gluing O-Rings is never acceptable for a dynamic elastomer. The glue creates a hard spot that will prevent proper sealing.

119

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

SPLIT SEAL APPLICATIONS  The pump is leaking. You can break off, or cut off the present gland and install a split seal while the leaking seal remains in the stuffing box. The pump can be back on stream in about an hour.

 You can install the split seal in a fire pump and leave the packing in place. This way you will probably not violate any fire codes.

 In most designs you are installing the seal closer to the bearings. If you install a carbon bushing in the stuffing box of the pump you negate most of the bad affects of shaft bending and deflection. Even if you do not use the carbon bushing you are still better off being located closer to the pump anti-friction bearing.

 Mixers and awkward locations. The savings are huge! In some instances you have to take the roof off the building to remove the motor before you can pull the 120 pump.

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

SPLIT SEAL APPLICATIONS

Cont’d…

 Vertical and horizontal split pumps. You do not have to rig a special lifting device and you only have to change the seal that is leaking instead of both of them.

 Shallow stuffing boxes. The seal installs outside the conventional stuffing box but unlike other seals it does not seal backwards. The seal gland is actually an extension of the present stuffing box. CAUTION some split seal designs are actually outside type seals that move the seal faces into the entrained solids as the seal face wears. Check to see what type you have.

 Any time down time is expensive split seals must be considered as the only sensible solution outside of installing two seals in all of your pumps.

 The pump is located in a dangerous area (radiation is a good example) and it is important that the personnel spend as little time in the area as possible. 121

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

SPLIT SEAL APPLICATIONS

Cont’d…

 If you want to measure the savings in electricity between packing and a mechanical seal the split seal is your only choice. Obtain an amperage reading with the packing in the pump and when you are satisfied you know the power being consumed by the pump, pull the packing and install the split seal. The difference in electricity consumption should pay for the seal in less than eighteen months.

 You can install a split seal in a pump that has had the shaft/sleeve damaged by packing or a mechanical seal and save the shaft/sleeve replacement cost, the seal static elastomer sits on a non damaged portion of the pump shaft/sleeve.

 Large diameter shafts are a natural for split seals. Shaft damage is expensive and pump disassembly is a big problem. Many times the packing is left in the pump and the leakage tolerated because of the problems of installing solid seals on shafts larger than four inches (100 mm). Split seals changed all of this and shaft damage can be eliminated entirely.

 If you mount a split seal on a split sleeve you can often change side entering mixer seals without first emptying the mixer.

122

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Mechanical Seal Hydraulic Balance Seal hydraulic balance is one of the most effective tools we have to counter the detrimental effects of heat being generated in the stuffing box area. The original patent for hydraulic

balance was granted in 1938, but the concept has never been adopted by the “original equipment manufacturer: (O.E.M.) and so to this day it remains only as an after market product.

123

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Mechanical Seal Hydraulic Balance

A = The spring loaded rotating face with an area of 2 in² (6 cm²) B = The stationary face held to the front of the stuffing box by gland “G” P = The hydraulic pressure in the stuffing box is given as 100 psi (10 Kg / cm²) 124

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Mechanical Seal Hydraulic Balance There are at least two forces closing the seal faces:

 The mechanical spring force.  The hydraulic force caused by the stuffing box pressure acting on the seal face area. There are at least three forces trying to open the seal faces:

 A hydraulic force is created any time there is fluid between the seal faces. It is pushing in all directions but cannot move the stationary face that is being retained by the seal gland. It can how ever, move the rotating face that is spring loaded.  A centrifugal force that is trying to make the rotating seal face become perpendicular to the rotating shaft. Since the stationary face is by definition not perpendicular to the shaft, the affect is the faces are coming apart.  A hydrodynamic force created because liquid trapped between the seal faces is, for all practical purposes, non compressible. 125

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

. 50 lbs/in² X 2 in² = 100 pounds of force trying to open the seal face, 100 psi.

50 psi. average

0 psi.

. or 5 Kg/cm² X 6 cm² = 30 Kilograms of force trying to open the seal faces. 10 Kg/cm²

5 Kg/cm² average

0 Kg/cm²

126

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

50% seeing closing force

50% not seeing closing force

70% seeing closing force

30% not seeing closing force

127

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Heat in Stuffing Box is undesirable  Heat means a loss of expensive energy.  Heat will affect the elastomer (rubber part) in the seal reducing its life.  Heat can injure some carbon faces by melting the fillers and expanding the air pockets trapped below the surface – causing pits in the carbon that will prevent it from passing a fugitive emission test.  Some hard faces can be damaged by a rapid temperature change.  Plated surfaces can “heat check” and crack due to the differential expansion between the coating and the base metal.  Many products can vaporize at elevated temperature, blowing the faces open and leaving solids between the lapped faces.  Heat will change the viscosity of many liquids. In many cases it will diminish, but in some cases the viscosity can increase.  Corrosion always increases with additional heat.  Petroleum base products can coke between the faces.  Lapped faces can go “out of flat” and critical tolerances change at elevated temperature. 128

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Advantages of Balanced Seal  They will allow you to standardize on one seal style for almost all applications.

 The O-ring version will seal either vacuum or pressure  Balanced seals can compensate for “water hammer” and pressure surges.

129

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Two Way Hydraulic Balance There are several reasons why you might want to invest in the higher cost of installing two seal in your pump, or some other piece of rotating equipment:

 The product is dangerous.  A seal leak could cause a pollution problem.

 The product is very costly.  Unscheduled down time is too expensive.  You need fugitive emission protection.  It is a sensible way to institute a predictive maintenance program for mechanical seals. 130

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Two Way Hydraulic Balance

A = The barrier fluid at a higher pressure than the stuffing box. B = The stuffing box pressure. C = Atmospheric pressure. 131

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Two Way Hydraulic Balance In a typical dual seal application. Fluid “A” is circulated between the seals at a pressure at least one atmosphere (14.7 psi or 1 bar) higher than stuffing box pressure “B”. This presents some operating problems.

 Since “B” can vary, the barrier fluid pressure must be kept at one atmosphere higher than the maximum stuffing box pressure and that pressure is very hard to predict because of pressure surges, cavitations, and water hammer in the system.

 Barrier fluid pressure can vary depending upon its source. Shop water is notorious for pressure variations.

 If the system pressure “B” exceeds the barrier pressure “A” the inner seal can blow open. 132

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Two Way Hydraulic Balance  If the barrier fluid piping or fittings are damaged or leaking, the inner seal will blow open allowing the product to escape to atmosphere. Remember that you purchased the second seal to prevent that possibility.

 Some mixer applications alternate between pressure and vacuum.

 If the outside seal wears out, or fails prematurely the barrier fluid pressure “A” will drop, and the inner seal will blow open. In other words, if the seal works properly, both seals will fail at the same time.

133

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Two Way Hydraulic Balance

134

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Are there any disadvantages to this design? Yes, a couple:  A wide seal face is required, restricting the use of the seal to mostly mixer applications because of the additional radial room needed. There seldom is enough room in the typical centrifugal pump stuffing box to accommodate the cartridge version of this design. The wider seal face also generates a little more heat.

 Because one half of the dynamic O-ring groove is mounted in the gland and the other in the seal face, the O-ring must slide when the pressure reverses and in some slurry applications it will “hang up” unless flushing water is available.

 Extra cost is usually involved if it is not a standard seal with your supplier. 135

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

TROUBLE SHOOTING PROCESS 1. Identify or Select the Problem 2. Collect the Data 3. Analyze the Problem 4. Generate the Solution 5. Implement the Solution 6. Evaluate 7. Standardize

136

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

ROTARY & STATIONARY FACES

Rotary Face

Stationary Face

Pure Grade P-658RC Carbon

Alumina Ceramic as standard for component stationary units.

Sintered Silicon Carbide (SSC)

Duplex Carbide

Reaction Bonded Silicon Carbide (RSC)

Tungsten Carbide

Solid Tungsten Carbide (TC)

Sintered Silicon Carbide 137

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Double Seal Face Configuration BACK-TO-BACK BARRIER FLUID

ATMOSPHERE

PROCESS FLUID

ROTATING FACES 138

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

Double Seal Face Configuration TANDEM

BARRIER FLUID

PROCESS FLUID

ATMOSPHERE

ROTATING FACES

139

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Double Seal Face Configuration FACE-TO-FACE

BARRIER FLUID

PROCESS

ATMOSPHERE

FLUID

ROTATING FACES

140

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

Stationary or Rotary Ring (Face) Sym.

Material

Sym.

Material

A

Carbon * (CARB)

K

Cast Stoody (STOODY)

B

Glass filled Teflon* (GFT)

L

Alloy 20/Stellite (#20/STEL)

C

Ceramic* (CER)

M

Colmonoy (COLM)

D

Solid Silicon Carbide* (SIL CARB)

N

Tungsten Carbide-Nick.* (TC-N)

E

Bronze (BRONZE)

O

Titanium Carbide (TITAN CARB)

F

Tungsten Carbide-Cobalt (TC-C)

P

Cast Iron (C.I.)

G

Ni-Resist* (NI-RES)

R

431 or 440 Stainless (431/440SS)

H

316 Stainless/Stellite (316SS/STEL)

S

316 Stainless/Chrome Oxide (316SS/CHR)

J

316 Stainless/Sapphire (316SS/SAP)

T

316 Stainless/Tungsten Carbide* (316SS/TC)

*Designates standard face material

##Registered trademark of Cabot Stellite Division

***Registered trademark Greene, Tweed & Co.

Consult Manufacturer – various grades available

**Registered trademark E.I. DuPont

141

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

HARD FACE MATERIAL CHART Hard Face Material

Hardness

Elastic Modulus E

Tensile Strength

Expansion

Conductivity

Density

Tempt Limit

Mohs

GN/m²

MN/m²

m/mK

Watts/m°K

Mg/mm³

°C(a)

Coeff. of friction Vs. Carbon

Gray cast iron

5

100

200

10

45

7.2

200

-

Hastelloy “B”

6

230

1300

18

45

8.9

800

-

M-2 Tool steel

7

200

2000

11

25

8.2

500

-

Niresist

4

100

400

18

15

7.4

500

-

316 Stainless

4

200

600

16

16

8

600

-

440C Stainless

5

200

800

10

25

7.8

600

-

Stellite

7

220

1000

14

15

8.4

1000

-

T/C – Cobalt

8

600

1400

4

100

15

400

0.07

142

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

HARD FACE MATERIAL CHART

Hard Face Material

Hardness

Elastic Modulus E

Tensile Strength

Expansion

Conductivity

Density

Tempt Limit

Coeff. of friction

Mohs

GN/m²

MN/m²

m/mK

Watts/m°K

Mg/mm³

°C(a)

Vs. Carbon

T/C – Nickel

8

600

600

5

90

15

250

0.07

Ceramic 85%

8

200

150

5

12

3.4

1400

0.07

Ceramic 99.5%

8

350

250

7

25

3.9

1700

0.07

SiC Alpha Sintered

9.7

400

250

4

130

3.1

1000

0.02

SiC Reaction Bonded

9.7

400

250

4

150

3.1

1000

0.02

143

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

891 Rotary Seals Installation Preparation: • Shafts & Sleeve: – – – –

Remove all sharp corner burrs and scratches on the shaft. Make sure that shaft or sleeve diameter is within 0.05 mm of the nominal. Measure shaft run out (0.001mm TIR per mm). Measure end play (should not exceed 0.13 mm of TIR).

• Stuffing Box or Seal Chamber: – Stuffing face must be flat and smooth (0.8 micron max.) – Measure the run out of the stuffing box face.(max. of 0.003 mm TIR / mm). – Disassemble the pump.

• “O” Ring Compatibility: – Check the “O” ring compatibility if required change the “O” ring. 144

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Mechanical Seal Specialization Course

891 Rotary Seals Installation •

•

•

•

Determine the seal installation length using the rotary operating length given on the other side and the stationary installation instructions for the particular CHESTERTON stationary being used with this rotary. The installation length will vary depending on the type of stationary and equipment being sealed. Scribe a mark equal to the installation dimension (determined from the operating length and distance from stationary face to stuffing box face) away from the appropriate reference point (e.g. the stuffing box face). Cover threads and keyways slots with a thin tape to prevent cutting the O-ring. Lubricate the seal sleeve O-ring and shaft with a clean, silicone based grease. A sufficient quantity of lubricant is provided with the seal. Slid the rotary onto the shaft and bring the back of the rotary to the scribe mark. Set screw the seal to the shaft. 145

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

891 Rotary Seals Installation •Reassemble the equipment (with the stationary and gland as required for the particular equipment). Proper installation of the rotary and stationary will set the 891 at its correct operating length without over or under compressing the seal. •Rotate the shaft by hand. The seal should turn freely without binding or using excessive force. •You are now ready to start the equipment. Follow all normal safety procedures when starting the equipment.

146

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Mechanical Seal Specialization Course

440 Seals Installation • Slide on rotary, gland, and stationary when assembling from the impeller end of pump. Reserve procedure when installing from motor coupling end. • Nose of stationary will pilot in stuffing box bore of most pumps. Tighten gland bolts evenly. Do not over-tighten or distortion of stationary may occur. CAUTION: Be sure stationary is not in contact with shaft. Center with centering gauge provided. • Slide rotary up against stationary face and tighten cap screw to clamp drive ring to shaft. On seal 2.750’’ (70 mm) and larger tighten set screw to provide additional clamping. • Remove clips and seal is properly positioned with a 1/16’’ (1,5 mm) spring gap. Be sure to use shroud if required. 147

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

155 / 155A Seals Installation

Cont’d……

•

Check the chemical listing to determine if the Viton* O-ring installed in this seal are compatible with the fluid being sealed.

•

DO NOT LOOSEN THE FLAT HEAD SOCKET SCREWS WHEN POSITIONING THE SEAL. Their loading configuration assists in centering the sleeve on the shaft.

•

If the 155 seal is operating at a stuffing box pressure of over 300 psig (20 Bar) or replace the three 316 stainless steel set screws that go through the larger holes on sleeve with the hardened steel set screws supplied with the seal.

•

Attaching the 478 or any other gland or re-attaching the tabs. – When using the 478 or any other gland instead of the tabs, remove the tabs by removing the tab retaining snap ring and prossing the tabs towards the center of the hub gland and then sliding them out. 148

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

155 / 155A Seals Installation

Cont’d……

– If the tabs need to be re-attached: • Place the seal, lock ring side up, on a flat surface. • To install a tab, compress the tab spring by pressing the tab against the hub gland surface and slide the tab till it bottoms out on the hub gland. As a minimum two pairs of tabs must be used. When the 155 seal is operating at a stuffing box pressure of over 300 psig (20 Bar), four pairs of tabs must be used. • Insert the snap ring in the hub gland groove. The snap ring will prevent the tabs from falling off, but can be removed at any time without affecting the performance of the seal.

• Slide the seal onto the shaft, by pushing on the lock ring. • Reassemble the pump and make necessary shaft alignments and impeller adjustments. • Orientate the flush connection to the location required. • Piping connections should not be made prior to tightening the gland bolts. 149 • Tighten the gland nuts evenly.

Institute Of Mechanical Seal

Mechanical Seal Specialization Course

155 / 155A Seals Installation •

The seal has been designed to promote self-centering of the sleeve on the shaft. – Tighten the three cup point set screws, that are closer to the flat head screws, evenly. If necessary, tighten the three flat head socket screws with the hex keys provided. Then tighten the three cup point set screws, that are further away from the flat head screws, evenly.

•

It is important to make sure that the gland is properly centered over the sleeve. To do this, turn the shaft by hand to make sure the seal turns freely. If you hear metal to metal contact within the seal, it was improperly centered. – Start the centering strap through the slot in the hub gland. – Loosen the gland bolts. – Loosen the set screws.(DO NOT LOOSEN THE FLAT HEAD SOCKET SCREWS AS THIS WILL ALLOW THE LOCK RING TO COME OFF). – Push the strap in until it completely surrounds the seal sleeve. It will pilot between the hub gland, seal sleeve and lock ring. – Re-tighten the gland bolts. – Re-tighten the set screws. 150 – Remove the centering strap.

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

442 Seals Installation A.

Cont’d……

Prepare the Seal for Installation – Disengage the socket head cap screws (item 10) from one half of the gland. With the gland in a horizontal position, springs up, separate the halves and place them on the clean work surface. – You now have access to the rotary holder (item 1). Disengage the two socket head cap screws (item 2) from one half of the rotary holder and place the holder halves on the clean work surface. – Place the rotary and stationary seal faces on the clean work surface. – Make sure that the gland gaskets (item 9), holder gaskets (item 3), stuffing box gasket (item 11, no grease) and static O-ring (item 4) are properly greased and seated in their grooves. DO NOT GLUE THE GLAND OR HOLDER GASKETS IN PLACE. – Snap open the ball and socket joint of the O-rings by pulling at the seam. (NOTE: The rotary O-ring is slightly longer and is marked with a purple dot.) 151

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Mechanical Seal Specialization Course

442 Seals Installation B.

Installation: The gland, holder, and face halves are matched pairs; mixing with components from different seals will result in seal failure. – Assemble the holder halves around the shaft and tighten the two socket head cap screws until snug, but not tight, on the shaft. – Slid the holder against the stuffing box using the “Y” spacer provided against the holder step for the correct installation dimension. – Assemble both O-rings around the shaft; the longer rotary O-ring inboard. – Carefully nest the two stationary halves around the shaft between two O-rings and wrap the outboard O-ring around them. – Carefully nest the two rotary face halves around the shaft and wrap the remaining O-ring over the halves. Again, check that the O-ring joint does not line up with the face splits. 152

Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL DESIGN & TYPES

153

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Design of Mechanical Seals If you were to design a mechanical seal, the simplest form would be a shoulder on a shaft pressed against a machined housing (see fig.). This will work if shoulder and housing rubbing surfaces are properly finished, if horizontal shaft movement (end play) can be totally eliminated, and the proper load can be maintained between the rubbing surfaces (faces) with no axial motion or run-out.

HOUSING MACHINED FACE MACHINED SHOULDER

SHAFT

154

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Design of Mechanical Seals The next progression in design would be to press a rotary sealing ring onto the shaft and a stationary sealing ring into the housing (see fig.) . The sealing surfaces can now be easily machined and lapped. Keeping the sealing faces together would still be a problem. The sealing rings are so rigid that absolute parallelism would have to be maintained to affect a liquid seal.

155

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Design of Mechanical Seals The mounting of resilient gaskets in back of each sealing ring allows more movement (see fig.). This solves several problems; end play is not as critical; repairs are made easier and the leakage paths between shaft and sealing ring, and the housing and stationary ring are eliminated. RESILIENT GASKETS SEAL FACES RESILIENT GASKETS

156

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Design of Mechanical Seals Now by giving either sealing ring axial motion to absorb end play and shaft run-out, the sealing rings can be held together. A coil spring is one method of compensating for greater axial movement while maintaining a load between the two rings. (see fig.)

SPRING

GASKET

157

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Design of Mechanical Seals The addition of a few simple refinements to (last fig.) 4 yields a usable design (below fig.). The entire concept is packaged into a unit. The addition of a positive drive secondary sealing element (boot) to turn the seal’s rotary member and prevent shaft leakage, and a multidirectional spring to a main face load, yields a functional mechanical seal. GLAND PLATE STATIONARY FACE GASKET

BOOT

ROTARY FACE

158

Mechanical Seal Specialization Course Institute Of Mechanical Seal

MECHANICAL SEAL DESIGN & TYPES

There are definite advantages with each type of seal. The selection is usually based on experience and history for a particular application. 159

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Types of Mechanical Seals Inside SealsWhen a seal is mounted inside the stuffing box of the pump, it is called an inside seal. Inside seals are generally more difficult to install, and routine maintenance is more difficult without complete pump disassembly; however, the advantages of an inside seal are: (1) Cooling of the seal is accommodated by product flow by the seal through inlets in the stuffing box or gland. (2) The rotary action of the seal helps to keep it clean. Centrifugal force makes it difficult for suspended solids to migrate across the face of the seal. (3) When these seals leak, they are usually not prone to catastrophic leakage, because of the large mass of material blocking the exit of product from the stuffing box. The hydraulic balancing forces help keep the faces closed. (4) A large variety of base materials and seal faces is usually available. (5) Environmental stuffing box controls can be easily applied and attached. 160

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Types of Mechanical Seals Inside Seals GLAND STUFFING BOX

ROTARY UNIT STATIONARY UNIT

161

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Types of Mechanical Seals Outside SealsAn outside seal is located outboard of the pump stuffing box. An outside seal has the following advantages: (1) easy installation; (2) can be inexpensively made from corrosion resistant materials; (3) suitable for services where it is necessary to quickly remove the seal for cleaning; where stuffing boxes are shallow and inside seals cannot be used due to lack of axial or radial space; where wear of the faces must be monitored; and where access to tightening the seal is difficult or practically impossible. Limitations on the design of outside seals; due to lack of heat dissipation from below the seal faces; outside seals must be used in lower temperature , lower speed and lower pressure applications. (Pressures must be lower than inside seals as the pressures are being exerted outward on seal parts rather than inward.) 162

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Types of Mechanical Seals Outside Seals

ROTARY UNIT

163

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Types of Mechanical Seals Single SealsSingle seals can be mounted either inside or outside the stuffing box and consist of a rotary unit affixed to the shaft in some manner such as set screws or a drive boot. The rotary unit runs against a stationary unit that is generally affixed to the stuffing box with a gland. (below Fig.) is a typical seal arrangement with the seal located inside the stuffing box. (Inside Seal). STUFFING BOX

GLAND

SET SCREW

ROTARY UNIT

STATIONARY UNIT

164

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Types of Mechanical Seals Double SealsDouble seals are arranged either facing towards each other or away from each other. The most common, (below fig.), is used in conjunction with a separate barrier fluid injected at a higher pressure between the two seals than the fluid being pumped. The advantages of double seals are: (1) Increased protection against product reaching the atmosphere. (2) The barrier fluid can be monitored to determine if either seal has failed. (3) The double seal also works well when there is danger of gas pockets being formed in the seal chamber, as is the case with vertical pumps. They have always been used when faced with products that crystallize, burn or cause ice when they contact the atmosphere. Heating or cooling can also be maintained via the barrier fluid. Often called a “back-to-back” double seal. 165

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Types of Mechanical Seals Double Seals BARRIER FLUID INLET

166

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Types of Mechanical Seals Double Seals(Below fig.) illustrates a double seal arrangement with the seals facing each other. When mounted this way, the outside seal receives its lubrication through the hole in the stationary seal ring. In this configuration, the barrier fluid should be pressurized below normal product stuffing box pressure or near atmospheric pressure. Often called a “face-to-face” double seal.

167

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Types of Mechanical Seals Tandem SealThe tandem seal arrangement is the safest of all double seal combinations. In effect it is made up to two inside seals, both with the advantage of inside seals and double seals. In this arrangement a separate clean barrier fluid is sealed by the outside seal and process liquid is sealed by the inner seal. This eliminates one of the major drawbacks of conventional double seal arrangements, that of having process liquid on the underside of the primary seal. The barrier fluid may be held at a slightly higher pressure than the process liquid to help prevent leakage of the pumped fluid into the higher pressure barrier fluid. In this case, the inner seal stationary would require retention in both axial directions. 168

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Types of Mechanical Seals Tandem Seal

169

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Mechanical Seal Classification

Cont’d….

All seals are available in either unbalanced or balanced versions. A seal is unbalanced when the area exposed to the pumped fluid, acting to close the seal faces, is greater than the area of contact (pressure gradient) between the faces. In simpler terms, it has a unit closing force in excess of the actual pressure to be sealed. For example, if the stuffing box pressure is 50 psig, then the loading or closing force on the faces would be slightly higher at 60 psig. This limits the pressure sealing capacity of the seal. The balanced seal has the same opening area as the unbalanced seal, but the closing area has been reduced in relation to the face area. Because force = pressure x area, reducing the closing area reduces the closing force: less heat is generated, and the seal generally has a longer life. For example, if the stuffing box pressure were 150 psig, then the net closing force would be substantially reduced to 50 psig. 170

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Mechanical Seal Classification Seals can be further classified in a number of ways. There are four further classifications of mechanical seals which can be described by distinct characteristics. Rotary In this type, the spring or springs or bellows rotate with the shaft.

Stationary The spring or springs or bellows do not rotate with the shaft but remain stationary. Non-metallic No metal parts come in contact with the fluid being pumped. All metal Metal parts are used exclusively where application temperatures require it.

171

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Various Seal Designs The basic seal designs have variations that develop seals that meet specific applications. Each seal design has its own strengths and weaknesses.

1 Cartridge Seals The cartridge design changes none of the functional components of the basic seal classifications. In a cartridge seal, all items are containerized and only require the tightening of gland bolts, flush connections, and drive screws. The need to scribe lines and make critical measurements is usually eliminated. Cartridge seal are available in each of the basic types and classifications. The limiting factor in the designing of a cartridge seal is the space available in a pump’s stuffing box area as they may require greater axial depth and radial cross section.

172

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Various Seal Designs Cartridge Seals

173

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Various Seal Designs 2 “U” Cup Seals The secondary seal or “U” cup can be made of PTFE, elastomers or a composite. The large single spring does not drive the rotary but does spread the secondary seal and maintain face loading during pump operations and shutdown. This seal is a heavy-duty balanced design that normally requires greater axial and radial space than does a conventional multi-spring balanced seal.

174

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Various Seal Designs 3 “V” Ring Seals The “V” ring is a sealing device that requires constant loading of the “V” ring in order to seal. If the seal is of the type that will work either inside or outside, then the “V” ring must be turned so that it seals the fluid. To reduce the clogging of multiple spring types, this design is fairly open and allows fluid circulation to clean the springs as the seal rotates.

"V"RING

175

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Various Seal Designs 4 “O” Ring Seals This particular seal has a dynamic “O” ring secondary seal and a static “O” ring shaft seal. The springs in this design are isolated from the pumped fluid by the “O” ring seals and cannot become clogged unless leakage occurs across the seal face. This type of seal is normally balanced within its own component parts.

“O"RING

176

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Various Seal Designs 5 Wedge Seals This seal is shown using a PTFE sliding wedge that mates with a carbon seal face. The wedge makes contact with the shaft and has an interference fit with the carbon. It contains no close tolerance fits. This seal is designed for inside use, but may be used outside at low pressures.

WEDGE

177

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Various Seal Designs 6 Boot Type Seals This seal is shown using a large single spring that maintains face contact but the drive (the turning of the unit with the shaft) is furnished by the rubber elastomer boot. Care should be used when installing the seal, because the elastomer must grip the shaft if the seal is to drive.

BOOT 178

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Various Seal Designs 7 Bellows Seals The welded metal bellows design offers a series of thin washers that are welded together on their outside and inside diameters. Each welded set of plates has a fixed amount of axial (along the shaft) movement. The more welded plates that are added to the seal, the greater the ability of the seal to move to adjust for face wear. The welded plates are usually made of corrosion-resistant material, such as Hastetelloy* or 300 series stainless. Welded metal bellows designs, which have n sliding elastomers can be used at elevated temperatures when outfitted with graphite or metal secondary seals. Bellows seals are balanced by design. * Cabot Stellite Div. Registered Trademark. 179

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Various Seal Designs Bellows Seals

BELLOWS

180

Mechanical Seal Specialization Course Institute Of Mechanical Seal

PUMP DISCHARGE

Pump Jacket HEAT TRANSFER FLUID OUT

• Use with single seal or dual seals

OPTIONAL FLOWMETER

PUMP SUCTION

• Maintains or elevates box temperature to prevent product solidification with polymers, resins, tars • Use to cool seal • Common heat transfer fluids:

EXTERNAL HEAT TRANSFER FLUID IN

- Water - thermal oils - steam

181

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Discharge Recirculation PUMP DISCHARGE

• Use with a single seal • Cools seal • Increases pressure in seal chamber • Clean fluids only – solids can erode seal

PUMP SUCTION

• An orifice can be used to reduce flow 182

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Suction Recirculation PUMP DISCHARGE

• Use with a single seal • Prevents solids hang-up • Lowers seal chamber pressure • Cools seal

PUMP SUCTION

• Reduces seal generated heat • Use caution with low vapor liquids • Stuffing box lantern ring connection can also be used 183

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Cooled Discharge Recirculation HEAT EXCHANGER

COOLANT OUT

• Use with a single seal COOLANT IN

PUMP DISCHARGE PRODUCT OUT

PRODUCT IN

• Cools seal with hot pumps and/or volatile fluids

• Increases pressure in seal chamber • Solids in product can erode deal

PUMP SUCTION

• An orifice can be used to reduce flow 184

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Cooled Seal Recirculation HEAT EXCHANGER COOLANT OUT

COOLANT IN

PUMP DISCHARGE

PRODUCT OUT

PRODUCT IN

• Use with a single seal and with pumping mechanism • Cools seal with hot pumps and/or volatile fluids • Minimizes heat exchanger size and coolant water usage

PUMP SUCTION

185

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Discharge Recirculation With Cyclone Separator CLEAN FLUID PRODUCT WITH ABRASIVES

PUMP DISCHARGE

CYCLONE SEPARATOR

• Use with a single seal where fluid contains some abrasives • Cools seal • Increases pressure in seal chamber

CONCENTRATED ABRASIVES TO PUMP SUCTION

• Density of solids must be significantly greater than fluid • Use caution with high viscosity fluids

PUMP SUCTION

• Chesterton normally does 186 not recommend

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Flush CLEAN FLUSH IS 5-15 PSI GREATER THAN THE MAXIMUM SEAL CHAMBER PRESSURE

FLOWMETER

CLEAN EXTERNAL FLUSH

• Use with a single seal • Prevents solids hang-up

• Acceptable flush fluids - Clean compatible fluid - Water, if compatible - Clean product - Downstream additive

PUMP SUCTION

RESTRICTION (THROAT) BUSHING

187

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Cooled Discharge Recirculation With Cyclone Separator HEAT EXCHANGER COOLANT OUT

PUMP DISCHARGE

PRODUCT WITH ABRASIVES

CLEAN FLUID

COOLANT IN

• Use with a single seal where fluid contains some abrasives • Cools seal with hot pumps and/or volatile fluids • Increases pressure in seal chamber

CYCLONE SEPARATOR PRODUCT IN

• Density of solids must be significantly greater than fluid • Use caution with high viscosity fluids

PUMP SUCTION

• Chesterton normally does not recommend 188

Mechanical Seal Specialization Course Institute Of Mechanical Seal

Circulation With External Buffer Fluid Tank FILL

BUFFER FLUID TANK WITH OPTIONAL HEAT EXCHANGER

• Use with a dual seal VENT

• Low pressure buffer fluid, 10 psi minimum

PUMP DISCHARGE

• Buffer fluid should be clean, compatible and lubricating COOLANT INLET & OUTLET

• Gland inlet and outlet connections dependent

on shaft rotation PUMP SUCTION

189

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Circulation With Pressurized External Barrier Fluid Tank FILL EXTERNAL GAS PRESSURE

BUFFER FLUID TANK WITH OPTIONAL HEAT EXCHANGER

• Use with a dual seal VENT

• Pressurize barrier fluid 15-30 psi over max. seal chamber pressure

PUMP DISCHARGE

COOLANT INLET & OUTLET

• Barrier fluid should be clean, compatible, and lubricating • Gland inlet and outlet connections dependent

PUMP SUCTION

on shaft rotation 190

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Circulation With Pressurized External Barrier Fluid Source FLOWMETER

• Use with a dual seal PUMP DISCHARGE

CLEAN EXTERNAL BARRIER FLUID

• Pressurize barrier fluid 15-30 psi over max. seal chamber pressure

BARRIER FLUID OUT

• Barrier fluid should be clean, compatible, and lubricating • Gland inlet and outlet connections dependent

PUMP SUCTION

on shaft rotation 191

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Circulation With Pressurized External Barrier Fluid Source and DualFlow TM

• Use with a dual seal

OPTIONAL LOW FLOW ALARM

PUMP DISCHARGE

CLEAN BARRIER FLUID IN

BARRIER FLUID OUT

• Pressurize barrier fluid 15-30 psi over max. seal chamber pressure • Barrier fluid should be clean, compatible, and lubricating • Gland inlet and outlet connections dependent

PUMP SUCTION

on shaft rotation 192

Mechanical Seal Specialization Course

Institute Of Mechanical Seal

QUENCH PUMP DISCHARGE

CLEAN EXTERNAL QUENCH IN

• Use with a single

seal • Prevents coking, crystallization PUMP SUCTION

• Common quench fluids: steam, water, nitrogen • Low pressure only DRAIN OUT

193