Rotary Seal Design Guide - Ceetak Sealing Solutions · Pages 5-14, 6-12, LDS TB TC 10-1 Pages 12-5, 6-12, VA + TB TBV CL 6-16 Pages 12-9, 6-12, SSW + TB SB + SB LS 8-22 DB DC Page

Rotary Seal Design Guide

Rot

ary

Seal

s

Catalog EPS 5350/USA

Parker Hannifin CorporationEPS Division

Toll Free: (800) 233-3900

!WARNING:

Failure, improper selection or im-proper use of the products and/or systems described herein or related items can cause death, personal injury or property damage.

For safe and trouble-free use of these products, it is important that you read and follow the Parker Seal Group Product Safety Guide. This Safety Guide can be referenced and downloaded free of charge at Parker.com, or ordered, without charge, as Parker Publication No. PSG 5004 by calling 1-800-C-PARKER.

This document, along with other information from Parker Hannifin Corporation, its subsidiaries and authorized distributors, provides product and/or system options for further investigation by users having technical expertise. It is important that you analyze all aspects of your application and review the information concerning the products or systems in the current product catalog. Due to the variety of operating conditions and applications for these products or sys-tems, the user, through his or her own analysis and testing, is solely responsible for making the final selection of the products and systems and assuring that all performance, safety and warning requirements of the application are met. The products described herein, including without limitation, product features, specifications, designs, availability and pricing, are subject to change by Parker Hannifin Corporation and its subsidiaries at any time without notice.

OFFER OF SALEThe items described in this document are hereby offered

for sale by Parker Hannifin Corporation, its subsidiaries and its authorized distributors. This offer and its acceptance are governed by the provisions stated on the separate page of this document entitled “Offer of Sale.”

©2006, 2014, 2017, Parker Hannifin Corporation

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Introduction

Engineering

Materials

Product Offering

Clipper® Oil Seals

Parker Oil Seals

Shaft Sleeves

ProTech ™ Bearing Isolators

FlexiLip ™

FlexiCase™

FlexiSeal® Rotary

V-Seals and Excluders

Rotary SealDesign GuideTable of Contents

See Appendices A through J for:

Design Action Request FormRotary Lip Seal Inch SizeRotary Lip Seal Metric SizesSolid to Split Seal Calculator Inch & MetricSleeve & V-Seal SizesProTech™ Sizes Inch & MetricConversions — Size/Speed/Temp.Chemical CompatibilityInterchangeOther Parker EPS Products

••••••••••

Parker Hannifin Corporation EPS DivisionToll Free: (800) 233-3900

www.parker.com/eps

Design Action Request Form

Rotary Lip Seal Inch Sizes

Rotary Lip Seal Metric Sizes

Solid to Split Seal Calculator Inch & Metric

Sleeve & V-Seal Sizes

ProTech ™ Sizes Inch & Metric

Conversions — Size/Speed/Temp.

Chemical Compatibilit y

Interchange

Other Parker EPS Products

Rotary SealDesign Guide

Appendix

Parker Hannifin Corporation EPS DivisionToll Free: (800) 233-3900

www.parkers.com/eps

A

B

C

D

E

F

G

I

H

J


1-1 Parker Hannifin CorporationEPS Division

Toll Free: (800) 233-3900www.parker.com/eps

IInnttrroodduuccttiioonn

The completeness ofParker’sproductline allows us toprovide theoptimal designfor any rotatingapplication.

Parker’s Rotary Sealing Solutions Program providesthe most complete coverage in the industry of shaft seals forrotating applications, for both OEM and MRO requirements.The completeness of the product line allows Parker to providethe optimal design for any given application. Parker is morethan just product. A complete solutions package has beencreated by supplementing the broadest range of productswith full engineering support, strict quality standards, directfactory field support, R&D and premier customer service. AtParker EPS, seals are not an add-on to our business, seals areour only business.

Clipper® Oil SealThe Clipper Oil Seal is the anchor of the rotary seal

product line. The Clipper design features an integrally moldedrubber fiber outer case and an elastomeric seal lip. Theunique, nonmetallic construction will not rust or corrode andforms a gasket-type seal between the equipment housing andthe seal outside diameter (OD). With a wide range of profilesand material options, Clipper seals are available for shaftdiameters from 0.250" (6.35 mm) to over 65" (1651 mm).

Clipper Split Seals are known worldwide for being theeasiest split seal to install because they do not require acoverplate to keep them in the housing. The robust, compositeOD provides the best retention of any split seal on themarket. Replacing failed seals in the field with Clipper SplitSeals saves on downtime and lost production expenses. Tomake replacement even easier, specify Clipper solid seals asthe OEM solid seal. When cutting a metallic seal is required for in-field replacement, there is the the possibility of metalshavings entering the bearing. The non-metallic design of theClipper seal eliminates this possibility.

Parker Oil SealParker Oil Seals provide additional coverage and include

the common metal OD construction for inch requirements andrubber covered OD construction for metric requirements.Single lip and double lip profiles are available as well as over100 special profiles for applications with unique operatingconditions. The typical size range is for shaft diameters from0.200" (5 mm) to 10" (254 mm).

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IntroductionCatalog EPS 5350/USA

FlexiLip™, FlexiCase™ and FlexiSeal®

FlexiLip, FlexiCase and FlexiSeal PTFE seals extend theParker application range by providing coverage whereoperating conditions exceed the capabilities of elastomeric lipmaterials. Conditions such as high speed and high pressure,and requirements for chemical resistance and low torque areeasily accommodated by one of our 50 standard profiles. The typical size range is for shaft diameters from 0.125"(3 mm) to 16" (406 mm).

ProTech™ Bearing Isolators

ProTech bearing isolators further complement Parker’ssolutions program by offering an answer for applicationswhere improving the mean time between failure (MTBF) iscritical. The ProTech family relies on true non-contactlabyrinth seal technology to provide 100% exclusion of contaminants and 100% retention of bearing lubrication forthe life of the bearing. Fourteen standard profiles are availableto allow for ease of retrofitting most equipment. Typical sizerange is for shaft diameters from 0.492" (12.5 mm) to 38"(965 mm). ProTech has also been independently tested toIEEE IP55, IP56, IP66 and IP69k.

Quick Sleeve™, Wear Sleeve and V-Seals

Quick Sleeves, Wear Sleeves and are V-Sealsauxiliary components that provide additional convenienceto the Parker Sealing Solutions Program. Quick Sleeve shaftrepair sleeves and Wear Sleeves are economical, convenient solutions to create proper shaft surfaces.V-Seals can be added as a slinger type seal to protect theprimary seal or used as a primary seal to exclude dirt ingrease applications.

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Seal Decision TreeOil Retention, Shaft Speed under 3,000 fpm (15 m/s)

Pages 5-14, 5-26,5-26, 9-1LUP MIST LifeLine LDN-S

Pages 8-25, 8-29LW MLE

Over 14" OD?

Pages 5-27, 8-27R Series Split SLE

YesNo

Pages 5-17, 6-18OL OSB

Split?

YesNo

Bore Rotates?

YesNo

Pressure > 5 psi?

YesNo

Pages 9-10, 5-16 LFN LFE-S MP

Pages 10-8, 6-15,10-9

CFE NSC4 CGE

Pages 10-85-16

, 10-9,CEN CDE HP

Page 10-8CHE CHN

Page 11-7, 11-8FCC FFC

< 60 psi

< 125 psi

< 250 psi

< 500 psi

< 3,000 psi

Pages 5-15, 6-17,5-15LUPW SME LDSW

High Runout?

YesNo

Pages 9-1, 10-1,8-22LFE CME LS

Pages 5-14, 6-12,10-1LDS TB TC

Pages 12-5, 6-12,6-16VA + TB TBV CL

Pages 12-9, 6-12,8-22SSW + TB SB + SB LS

Page 6-14DB DC

ExcludingContaminantsIs Critical?

YesNo

Chemical Service

LightContaminants

ModerateContaminants

HeavyContaminants

Separate Fluids

Pages 5-14, 6-12LUP SB SC SDPages 9-1, 10-1,5-25, 6-19LEN CMN TMAL TN

GeneralService

ChemicalService

Note: Intended for use as a general design guide only.

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1 Introduction




Clipper Oil Seal and Parker Oil Seal Profiles

Style A Style E Style L Style S BDC BDV BSC BSV

CAP CB CH CL Clipper Sliptite DA DB DC

DC4 DL DS DM H HP KA KAP

KB KBJ KBP KC KC8 KCJ KG KM

LDS LDSF LDSW LifeLine LPD LPDSpring Retainer

LPDW LUP

LUPW MP MIST NSC1 NSC3 NSC4 NTC1 NTC3

NTC4 OKA OKB OKC OKM OL OSA OSB

OSC OSM OTA OTB OTM OTC OUA OUB

OUC OUM OVA OVB OVC OVM P RPD

RPDT RUP RUPW SA SAE SAP SB SBF

SBJ SBP SC SCE SCF SCJ SD SD2

SEC SEM SDS SG SM SME SS SSW

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1IntroductionCatalog EPS 5350/USA



Clipper Oil Seal and Parker Oil Seal Profiles (Continued)

STLUP STLUPw/Buttons

ST MIST ST MISTw/Buttons

SXA SXB SXC TA

TAP TB TBF TBH2 TBH4 TBJ TBP TBV

TBY2 TBY3 TC TC8 TC12 TCF TCJ TCV

TCK TC9 TD TD6 TDN3 TEA TEC TEM

TG TG13 TM TMAL TMAS TN TSS UA

UB UC VA VAP VB VB1 VB3 VB4

VB6 VBJ VBP VC VCJ VG VM VM1

VM2 W WPC WPK WPR **L **R **W

Shaft Seal Profiles

degnalf-noN—eveelSraeWdegnalF—eveelSraeWeveelSkciuQ

ProTech Bearing Isolator Profiles

LS LN WD FS FN SB LB

LM LD LW/LX SL ML MN SM

01/17/17

**Hydrodynamic lip pattern. L = CCW shaft rotationR = CW shaft rotationW = Bi-directional shaft rotation

1 Introduction




For additional information on all profiles, see the Product Offering in Section 4.

FlexiLip, FlexiCase and FlexiSeal Rotary Profiles

LFN-N LEN-N LDN-N LMN-N LFE-N LEE-N LDE-N LGN-N

LFN-S LEN-S LDN-S LMN-S LFE-S LEE-S LDE-S LGN-S

CFN CFE CMN CME CEN CEE CDN CDE

CGN CGE CJN CJE CHN CHE FCC-V FCS-V

FCC-C FCS-C FHC-V FHS-V FHC-C FHS-C FFC-V FFS-V

FFC-C FFS-C FFN-H

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1IntroductionCatalog EPS 5350/USA



Engineering ExcellenceEngineering support is another feature of the

Parker Sealing Solutions Program. Every productgroup is fully supported by Parker’s internalengineering staff. As the leader in seal design engineering, Parker designs sealing solutions fornew applications, modifies designs to improveperformance and troubleshoots problem applications in addition to designing like replacements.

Quality CommitmentQuality commitment is a feature of the

Parker Sealing Solutions Program that we takevery seriously. Quality was built around thetough requirements of MIL-I-45208A andMIL-STD-45662 and refined for certification forISO-9001 and AS-9100. All manufacturing plantsare either ISO-9001 or QS-9000 certified to assureconsistent quality.

Customer SupportField Service is provided by over 90 direct

factory representatives to keep customers up todate on the latest technologies and provide a widerange of on-site services.

Research & Development efforts arecontinuous and ensure the latest in sealingtechnology design and materials are available.Testing capabilities allow seal performance to beverified prior to a customer launch of a newproduct.

Premier Customer Service is a key componentof the Parker package. Electronic orderingsystems such as EDI and PHconnect makeplacing and tracking orders easy. For personalcontact, our fully trained staff of customer servicerepresentatives are only a phone call away at1-800-233-3900.

Parker Sealing Solutions is a completeprogram, not just product.

PackagingTraditional non-fluoroelastomer Clipper Oil Seals arepackaged in the bluebox.

FluoroelastomerClipper Oil Seals arepackaged in the brownbox.

Parker Oil Seals arepackaged in the goldbox.

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Worldwide and local support is just a phone call away. Your local Parker sales representative provides a single point of contact for local sealing support. Our established worldwide network of over 300 distributor and service center locations, including global sales and engineering, means you can always get quality products when and where you need them. It also means that sound advice from Parker sealing experts is never far away.

Parker Oil Seals with ParKote™ bore sealant

Introduction




Applications

Rotary Seals for Steel & Paper Industry

Rotary Seals for Industrial Equipment

Bearing Isolators for Industry

Rotary Seals for Heavy Equipment

Rotary Seals for Power Generation

PTFE Seals for High Performance

• Backup Rolls

• Mill Stands

• Felt Rolls

• King & QueenRolls

• Reducers

• Gearboxes

• Pumps

• Motors

• Bearings

• ANSI Pumps

• Electric Motors

• Split Pillow Blocks

• Turbines

• Gearboxes

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• Mining

• Construction

• HD Reducers

• Turbines

• Blowers

• Pumps

• Motors

• Bearings

• Centrifuges

• Pumps

• Gearboxes

• Mixers

• Instrumentation

• Semiconductor

• Medical Equipment

1




Sealing SystemsThe completeness of Parker’s rotary seal

offering allows customers to improve performance

System incorporating lip sealand a shaft repair sleeve

System incorporating two seals back-to-back with grease purge for improved

contaminant exclusion and oil retention

Standard lip seal with internal DS slingerto protect lip from lubricant surge

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System incorporating SSW slinger andProTech bearing isolator for optimalexclusion on vertical up application

System incorporating two lip sealswith grease purge and SSW slinger for

maximum exclusion

Elastomeric lip seal for oil retentionwith PTFE lip seal for exclusion

by utilizing a sealing system. This approach uses multiple sealing products when require-ments exceed the capability of a single seal. Some of the more common systems are pictured below.

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Introduction




V-Seal used to protect primary oilseal from excessive contamination

Multi-lip FlexiCase design for sealinghigh pressure and excluding dust

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Opposed dual spring-loaded lips forseparation of two fluids

FlexiCase in gas turbine engine sump for high speed, 15,000 sfpm

FlexiCase in refrigerant recovery system, 300 psi

FlexiLip in air conditioning compressor260 sfpm, 20 - 300 psi

FlexiSeal used in tank cleanerslow speed, 1000 psi

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2Catalog EPS 5350/USA



EEnnggiinneeeerriinnggContents

Rotary Shaft SealsWhat Is the Purpose of a Seal? . . 2-1

History of Shaft Seals . . . . . . . . . . 2-2

How Do They Work? . . . . . . . . . . . 2-3

Seal Components . . . . . . . . . . . . . 2-4

Lubricant Considerations . . . . . . . 2-6

Shaft Considerations . . . . . . . . . . 2-6

Testing for Machine Lead . . . . . . . 2-7

Shaft Tolerances. . . . . . . . . . . . . . 2-8

Underlip Operating Temperature . . 2-8

Seal Torque . . . . . . . . . . . . . . . . . 2-9

Internal Pressure . . . . . . . . . . . . . 2-10

Shaft Speed . . . . . . . . . . . . . . . . . 2-10

Housing/Bore Considerations . . . . 2-11

Shaft to Bore Misalignment. . . . . . 2-11

Shaft Runout . . . . . . . . . . . . . . . . 2-12

Shaft Seal Summary. . . . . . . . . . . 2-12

Shaft Seal Installation. . . . . . . . . . 2-12

Handling and Storage . . . . . . . . . . 2-14

PTFE Shaft SealsHow Do I Choose the Right Profilefor My Application? . . . . . . . . . . . . 2-15

Spring Designs . . . . . . . . . . . . . . . 2-16

Lip Shapes . . . . . . . . . . . . . . . . . . 2-20

Shaft Considerations . . . . . . . . . . 2-21

Housing/Bore Considerations . . . . 2-22

Pressure and Shaft Velocity . . . . . 2-23

Lubrication . . . . . . . . . . . . . . . . . . 2-24

Rotary PTFE Product Choice . . . . 2-24

Shaft Misalignment and Runout . . 2-25

Rotary PTFE SealConsiderations . . . . . . . . . . . . . . . 2-26

Alternate HousingConfigurations . . . . . . . . . . . . . . . 2-26

Bearing IsolatorsGeneral Theory of Operation . . . . 2-27

Testing and Validation . . . . . . . 2-30

Rotary Shaft Seals

What Is the Purpose of a Seal?

Today there is a wide selection of designs available foruse in rotary applications. They range from the traditionalsingle and double lip elastomeric configurations to PTFE-based designs. Even more complex designs incorporatemultiple lips, differing materials and hybrid labyrinth designs.The purpose of this reference guide is to assist engineersand maintenance professionals in selecting the best designfor a specific application based on service life requirementsand cost objectives.

One of the most common purposes of a lip seal is toprotect the bearing that is used to support a shaft in a rotatingapplication. Retaining the bearing lubricant and keeping itclean ensures maximum bearing life and increases the overallservice life of the equipment. Such applications includeautomotive wheels, electric motors, pumps, gearboxes andlarge rolls used in steel and paper manufacturing.

Radial lip seals are used throughout industries in a varietyof other applications under a wide range of operatingconditions. These conditions can vary from high-speed shaftrotation with light oil mist to low speed reciprocating shaft inmuddy environments. Radial lip seals can be found sealinglube oil in high speed crankshaft applications for gasoline anddiesel engines that operate from the tropics to the arctic, insubmarines, oil tankers, spacecraft, windmills, steel mills,paper mills, refineries, farm tractors, appliances andautomobiles. In fact, they can be found in anything that has arotating shaft.

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Parker rotary shaft seals retain lubricationand exclude contaminants even in the mostextreme environments.

Engineering




In rotating applications, a seal can also impactthe service life of indirect components such asmechanical seals, couplings, pulleys or other in-line coupled equipment. If a seal allows the systemlubricant to run below safe levels or allows foreignmaterial to enter the bearing cavity, the bearing willsoon begin to show signs of failure. As the bearingfails, vibration from excessive shaft runout will betransferred to all other in-line components and willshorten their service life as well.

The advantages of radial lip seals include: lowcost, small space requirements, easy installationand an ability to seal a wide variety of applications.

In review, the primary purpose of the radial lipseal is to retain lubricants within a sump or cavity.The secondary purpose is to excludecontaminants from the system lubricant. Lip sealsare also used to separate two different fluids,retain internal pressure or exclude an externalpressure.

History of Shaft Seals

The earliest seals were rags and pieces ofleather straps tied at the end of cart wheel axles toretain the animal fat or olive oil used at that timefor lubrication. This slowly evolved to morecomplex sealing systems and lubricants, such asgrease made with olive oil and lime.

The Industrial Revolution accelerated sealinginnovations with bores in the wheel hubs to holdpackings and ropes to seal rotating shafts. Highershaft speeds increased operating temperaturesand the development of thinner lubricantsdemanded constant improvements in seal design.This brought along better braided ropes made byspecialists using different impregnations such aswaxes and pitch.

In the 1930s, seals with beveled leatherwashers crimped in metal cases were produced.These assembled seals did not requireadjustments and were easy to install and fit inmuch less space than the packings and stuffingboxes previously used. Leather inserts with tallerflexible lips were also used because they werebetter able to follow the wobble of the shafts.

Springs were added to the leather lip seal inthe 1940s. Leather was treated to reduce theseepage of lubricants through the sealingelements, but even with different coatings andimpregnations, leather could only work slightlyabove the boiling point of water, so a bettermaterial was needed. The new material becamesynthetic rubber and was introduced as a lipmaterial during World War II. During the war,copper coating and later chemical coats wereused to bond the rubber to metal washers thatwere assembled in metal cases.

In the 1960s, the bonding became reliableenough that rubber lips were molded directly to theouter case. This eliminated possible leakage frombetween the assembled components. This wasdue to the components becoming loose fromcompression set of the rubber or distortion of thecomponents from assembly into the bore. Leatheralso remained a common lip material throughoutthe 1970s.

Today, assembled seals made with leather orrubber are no longer recommended because oftheir high cost, internal leakage, and lack ofdimensional control. Most manufacturers haveconverted small diameter seals to the bondeddesign; however, the need to use advanced materials such as thermoplastics (primarily PTFE)that can be difficult to bond to a metal case may still require an assembled case design. Largediameter seals have been much slower to moveaway from the antiquated assembled design, soextra care should be used when sourcing sealsfor large diameter applications.

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Early seals were made from leathercrimped in metal cases.

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EngineeringCatalog EPS 5350/USA



How Do They Work?

Rotary shaft seals work by squeezing andmaintaining the lubricant in a thin layer betweenthe lip and shaft. Sealing is further aided by thehydrodynamic action caused by the rotating shaft,which creates a slight pumping action.

The second function of the seal is to excludeoutboard material that can contaminate thesystem lubricant or directly damage the bearing.The type of contamination the seal will need toexclude is dependent on the application. The morecommon types are moisture and water, and drymaterials including dust, sand, dirt or particulatessuch as those generated by manufacturingprocesses.

Figure 2-1. Rotary Shaft Seal at Work

The seal’s ability to retain the system lubricantand exclude contaminants plays a key role in theservice life of equipment components such asbearings, gears and any other component thatrelies on the system lubricant. The seal can have adramatic impact on the service life of the systemlubricant by retaining the optimal level, reducingexposure to excessive frictional heat andexcluding foreign matter.

Typical petroleum oil has a useful life of thirtyyears at 86 °F (30 °C) if it is not contaminated withwater or particulate matter, but the same oil has alife of only a month at 212 °F (100 °C). As little as0.002% water in oil lubrication can reduce ballbearing life by 50%, primarily through hydrogenembrittlement. Solid particles cause more rapiddamage to the bearing race through high-localizedstresses and increased frictional heat.

ContaminantsSeal Lip Lubricant

Hydrodynamic Pumping Action

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Rotary shaft seals provide protection by performing two critical functions. In most applications the primary function of the seal is to retain the bearing or system lubricant. There are thousands of different types of lubricants available today, but in general bearings are either oil or grease lubricated.

The sliding contact between the seal lip and the shaft will generate friction, increasing the contact temperature beyond the temperature caused by the bearings and other sources. Heat accelerates the breakdown of the oil and starts forming a varnish on the hot spots. Over time, the varnish changes to carbon and builds in thickness as the surrounding oil loses its lubricity. How quickly this happens is dependent on temperature. The deposit can lift and abrade the lip, causing leakage. The time to reach each stage is cut in half for each 18 °F (10 °C) increase in temperature. The heat also accelerates the cure of the rubber, especially at the contact surface between the seal lip and the rotating shaft. Eventually the lip surface hardens, small cracks form and the surrounding rubber stiffens. The cracks get larger and the lip stiffer,until it can no longer follow the movement of the shaft or seal. In order to maximize seal life, it is critical to minimize the amount of frictional heat of the application.

The amount of frictional heat that is generated is a combination of many operating parameters.Shaft surface, internal pressure, operating speed, lubricant type, lubricant level, lip geometry and lip material are just a few of the conditions that need to be considered. It is important to note that these conditions are very interactive. For example, an increase in shaft speed will increase the sump temperature. If not vented, the temperature rise will increase the pressure inside the housing. The internal pressure will push on the seal lip and create additional force between the seal lip and the shaft. In turn, the operating temperature under the seal lip will see a significant rise in temperature and can cause premature seal failure within hours.

2

Engineering




It is easy to see why an understanding ofrotating shaft seals is critical when trying to reducethe mean time between failure of rotatingequipment. To better understand how rotary lipseals work, knowledge of basic seal componentsis needed.

Seal Components

Typical rotary shaft seal components include arigid outer component and a flexible inner lip (seeFigure 2-2). The seal lip can be springless orspring-loaded.

Figure 2-2. Seal Components

The outer rigid material can range from carbonsteel, aluminum and stainless steel to anonmetallic composite as pictured above. Thepurpose of the outer component is to position andretain the seal in the housing. The seal’s outercomponent must also be able to maintain a leak-free fit between the seal and the housing.

The seal element is attached to the outer rigidmaterial by bonding it as it is cured in a moldingpress or mechanically crimping a cured elementbetween metal components. Designs that use highperformance composite materials for the rigidouter section provide the advantages of a one-piece molded construction. One-piece moldeddesigns and bonded designs should be usedwhenever possible. Assembled designs (small orlarge diameter) are easily damaged duringhandling and installation, causing the assembledcomponents to loosen. This creates leak pathsbetween the various components.

The sealing lip configuration will vary based onthe type of service, speed, pressure and dynamicrunout for which the seal is designed. The sealgeometry may also include hydrodynamic pumpingfeatures which are normally molded into the lipelement on its air side. Common hydrodynamicpatterns are triangular and helical. They functionby pumping oil that has passed by the primary lipback under the lip to reduce leakage, extendingseal life. Refer to Section 4 for lip profile options.

The oil side of the seal lip has an angle in therange of 35 to 55 degrees. The air side has amuch shallower angle and is typically 15 to30 degrees. These angles determine the contactfootprint of the lip on the shaft. Incorrect angleswill form a footprint that cannot maintain a sealwith the shaft and explains why heavy leakageoccurs if a lip seal is installed backwards, or withthe steep lip angle facing away from the oil side.

Seal Outer Diameter

LubricantSide

FlexThickness

GarterSpring

HeelSection

Air SideSurface

ContactPoint

“R” Value

Lip InnerDiameter

HeadThickness

ScraperAngle

BarrelAngle

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The outside diameter of the seal is larger than the seal housing to create a press fit. The actual seal diameter will depend on the size and material of the seal, the size and material of the housing and expected internal pressure and temperature. For general industry standards on OD press fit, see Tables 6-2 and 6-3 on Page 6-3.

2




This also means that the primary function ofsingle spring-loaded designs is dependent on theinstallation direction. While the seal will performboth retention and exclusion functions, they arenot performed equally.

If the primary function is retention, the sealshould be installed with the steep lip angle facingtowards the lubricant. This is normally the open-faced side. If the primary function of the seal is toexclude, the steep angle needs to face toward thecontaminant (see Figure 2-3).

Figure 2-3. Installations Facing Lubricant andContaminant

If both retention and exclusion are critical andthe level of contaminants is heavy, one seal shouldbe used to retain the lubricant, and exclusioncapacity should be added using another lip seal,auxiliary excluders or by upgrading to a bearingisolator (see Page 2-27).

The purpose of the spring is to provide aconstant, uniform load of the lip on the shaft for thelife of the seal. The spring keeps the seal lip incontact with the shaft during higher shaft speedsand also overcomes compression set and wear ofthe lip material. Compression set of the lipmaterial is normal as it is subjected to thermalcycles during operation.

Several spring types are used to energize thelip. The most common is a wound spring, oftenreferred to as a garter spring. Finger springs areanother option, although their loading is typicallyless uniform and they can be subject to severedistortion prior to or during installation, leading toareas of the lip that are not properly loaded. Otherspring types used are cantilever, canted-coil andhelical which are normally used in PTFE designs.In order for the spring to maintain the proper loadover the life of the seal, the spring must becompatible with the fluids and the temperature ofthe application.

The dimensional relationship between thecenter of the spring and the lip contact point iscalled the R value. The leading edge of the lipshould be toward the oil side, with the centerlineof the spring slightly toward the air side. If thecenterline of the spring is too far toward the airside (too positive R value) it will put too much ofthe lip (wide footprint) in contact with the shaft andcause excessive wear. A spring position that is tooclose to the lip contact point (negative R value)can cause the lip to become unstable or roll anddump the spring.

A spring-energized lip is required for positiveoil retention, but not typically for grease retention (see Figure 2-4).

Figure 2-4. Oil and Grease Seals

the sealing system. There are several key The rotary shaft seal is only one component in

operating parameters that can work in unison tooptimize seal life, or conversely, if misapplied,can reduce seal life to a few operational hours.

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laeSesaerGlaeSliO

2

Engineering




Lubricant Considerations

Figure 2-5. Sealing System

The contact lip is designed to run on a thin filmof oil. Without the oil film, the seal lip will rundirectly on the rotating shaft and generateexcessive friction and fail within hours. Thelubricant selected needs to remain viable over theexpected service life. If the underlip temperatureexceeds the lubricant rating, carbonization of theoil will occur.

Abrasive carbonized oil particles will build upat the seal lip and accelerate lip and shaft wear. Asthe oil film becomes less than optimal, the lipfriction increases, as does lip wear.

When selecting a lubricant keep the followingin mind:

1. Do temperature limits of the lubricant matchthe underlip operating temperature of the seal?

2. Are the base oil and additives compatiblewith the lip material?

3. Does the oil level provide adequatelubrication and cooling at the seal lip?

Shaft Considerations

Housing

LubricantShaft Speed

Pressure

18 Ra

18 Ra

18 Ra

Surface Finishes

A proper shaft finish provides small pockets to hold the needed oil film between the lip and shaft, preventing direct contact that would otherwise cause friction and wear as the shaft rotates. The shaft surface must also be smooth enough to avoid peaks that are large enough to break through the lubrication film.

The optimal surface for elastomeric shaft seals is a plunge ground finish of 8 to 17 μin Ra (0.20 to 0.43 μm Ra) (0.010" [0.25 mm] cutoff) with a lead angle below 0.05 degrees. (See Table 2-5 on Page 2-21 for shaft finish requirements for PTFE seals.)

Recent studies show that the Ra measurement alone is insufficient to quantify a proper surface. The surfaces below have the same Ra finish, but the impact on seal performance will vary.

Two additional requirements are needed: Rz (the average peak to valley height) of 65 to 115 μin (1.65 to 2.90 μm), and RPM of 20 to 50 μin (0.5 to 1.25 μm), the average peak to mean height. For additional information, refer to Rubber Manufacturers Association Technical Bulletin OS-1-1.

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When a shaft is turned to size, a continuousspiral groove is imparted on the shaft as thecutting bit traverses the shaft. This is called shaftlead.

If not removed by plunge grinding or othermethods, the groove will act as an auger when theshaft rotates. The underlying groove will eitherpump oil past the seal lip or contaminants into thebearing housing, depending on the direction of theshaft rotation.

If a shaft is going to be plated, the machinelead must still be removed prior to the platingprocess.

Testing for Machine Lead

When lead is suspect and there is a need forverification in the field, the following field test canbe performed:

1. Mount the shaft in a chuck and verify theshaft is level.

2. Lightly coat the shaft with silicone oil with aviscosity of 5 to 10 cps.

3. Drape a thread (unwaxed quilting thread0.009 inches or 0.23 mm dia.) weighted with aone-ounce (30 g) weight around the shaft and tiethe ends together so it is long enough to contactabout 2/3 of the circumference of the shaft with theweight hanging. Position the thread so that theknot is not touching the shaft.

4. Rotate the shaft at slow speed, 60 RPM.

5. Place thread at both ends as well as centerof shaft and observe for axial movement of thethread under BOTH CW and CCW rotation.

· Movement of the thread in oppositedirections, CW versus CCW rotation,indicates lead is present.

· If the thread moves in the same directionunder both CW and CCW rotation, verifythat the shaft is level.

· If the thread remains stationary whenchecking the ends and center of shaftunder both CW and CCW rotation, significantlead is not present.

Figure 2-6. Shaft Lead Testing

Please note that this method does notguarantee the absence of lead as some patternsmay go undetected using the string test. However,this simple test has been very successful indetecting if a significant lead is present.

The preferred material for the shaft-sealingsurface is carbon steel (SAE 1035 or 1045) with aminimum hardness of Rockwell C30 (30 Rc). Whenheavy amounts of abrasive contamination arepresent, abrasive additives are used in the lipcompound or high-pressure seal designs are goingto be used, a minimum shaft hardness of 45 Rc isrecommended to resist excessive shaft grooving.Softer materials such as bronze, aluminum orplastic will experience heavy wear (grooving), and should be avoided.

Shaft Lead

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Engineering




Shaft Tolerances

Shaft diameters should be held to thetolerances specified below:

The leading edge of the shaft should have aburr-free chamfer to ease installation bypreventing lip roll-back, spring dumping anddamage (nicks or cuts) to the seal lip. Both ends ofthe chamfer should be free of sharp edges.

Figure 2-7. Shaft Profile

Special precautions should be taken whenreplacing a seal over a used shaft because it iscommon for shafts to become grooved duringservice. Grooving is normally caused by eithercarbonized oil or an abrasive foreign mattergetting trapped between the lip and the shaft.Over time, deep grooves can form.

Replacement seals should never be installedover a grooved shaft. Dressing the shaft withemery cloth is not recommended because it isextremely difficult to obtain an optimal finish andlead will normally be imparted. If the shaft is worn,it should either be re-ground or fitted with a shaftrepair sleeve. See Section 7 for shaft repair options.

Underlip Operating Temperature

When selecting a seal design, lip material andsystem lubricant, the operating temperature underthe seal lip should be used as the upper limitrather than using the sump temperature.

Underlip temperature can exceed sumptemperature by 60 °F (33 °C) or more, dependenton shaft diameter, shaft speed, fluid type and

Table 2-1. Shaft Tolerance for Inch/Fractional

Shaft Diameter ToleranceUp to 4.000" ± .003"4.001 – 6.000" ± .004"6.001 – 10.000" ± .005"Over 10.000" ± .006"

Table 2-2. Shaft Tolerance for Metric*

Shaft Diameter ToleranceUp to 10 mm +0 to -.09 mmOver 10 – 18 +0 to -.11 mmOver 18 – 30 +0 to -.13 mmOver 30 – 50 +0 to -.16 mmOver 50 – 80 +0 to -.19 mmOver 80 – 120 +0 to -.22 mmOver 120 – 180 +0 to -.25 mmOver 180 – 250 +0 to -.29 mmOver 250 – 315 +0 to -.32 mmOver 315 – 400 +0 to -.36 mmOver 400 – 500 +0 to -.40 mm*ISO Standard 286-2, h11

Shaft Grooving

Spring dumping can occur during seal installation when the lip rolls back on itself, causing it to fall out of the spring pocket. Heavy shock loads that can occur when installing a metal cased seal using a direct blow from a metallic driving tool can also force the spring out of the spring pocket and is also referred to as spring dumping.

level. The increased temperature can exceed the limits of both the lip material and lubricant that is selected based on the sump temperature alone.

Table 2-2a Min. Chamfer LengthEnglish Metric

Shaft Dia Length Shaft Dia LengthUp To And "w" Up To And "w"Including (inch) Including (mm)

0.375 0.051 10 1.30.750 0.068 20 2.01.250 0.085 30 2.21.500 0.102 40 2.62.000 0.119 50 3.02.750 0.136 70 3.53.750 0.153 95 3.95.000 0.188 130 4.89.000 0.239 240 6.1

+18.000 0.375 480 10.0

30°

At 30°

w See Table 2-2a for chamfer length

2




Other operating parameters such as a roughshaft finish or internal pressure will drive theunderlip temperature even higher. As a generalrule, the °F increase in underlip temperatureabove the sump temperature can be estimated asthe square root of the shaft speed in feet perminute. (Replace the feet per minute units with °F.)This would be 55 °F (30 °C) for a shaft running at3000 fpm (15 m/s).

Figure 2-8. Example Shaft Conditions

Seal Torque

The underlip temperature increase is due tothe friction between the shaft and seal lip. Torqueis the frictional force the shaft must overcome torotate in the seal. The energy consumption of theseal can be determined when the torque and shaftspeed are known. Different seal designs, rubbercompounds, fluids, fluid levels, temperatures, shafttextures, pressures and time in service each affectfriction, so there is no exact calculation to predicttorque. However, the following can give an approx-imate value for elastomer shaft seals. When thetorque value is critical for the application,testing should be performed.

Torque from a dry running seal is 2 to 3 timesthe above.

For example: Torque is about 90 in-ounces fora three-inch shaft rotating at 3600 revolutions perminute in 250 °F SAE 30 weight oil to the shaftcenter. The energy in kilowatts the seal uses is7.395 x 10 -7 x torque x revolutions per minute. Inthis case, 0.24 kW.

Bearing isolators are an excellent choice when low torque is required because they add virtually no torque to the system.

Shaft Sealin fpm

Increase UnderlipTemperature=

3000 fpm 55 °F=

80 90 100 110 120 130 140

150

140

130

120

110

100

90

80

300

280

260

240

220

200

180

160 180 200 220 240 260 280 300

320

Sump Temperature – °C

Sump Temperature – °F

Und

erlip

Tem

pera

ture

–°F

Und

erlip

Tem

pera

ture

–°C

5000 Rpm

4000 Rpm

3000 Rpm

2000 Rpm

1000 Rpm

0 Rpm

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Seal Torquein-ounces 0.65

Shaft Dia.in inches

2Rpm

1/3=

As sump temperatures increase, the differ-ence between sump and lip temperature decreases.

Figure 2-8 shows the relationship of shaft diameter, shaft speed and sump temperature and the impact they have on the temperature at the contact point of the seal lip and the shaft (underlip temperature).

An easier but more crude estimate is 20 °F (6.7 °C) higher than the sump for each 1,000 RPM of shaft speed for sump temperatures about 75 to 210 °F (24 to 99 °C).

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Engineering




Internal Pressure

Most elastomeric lip seals are designed to workin vented applications with zero internal pressurebut will provide satisfactory service with pressuresup to 3 psi (0.20 bar). Higher pressure will forcethe lip against the shaft and cause excessivefriction. Severe pressure will distort and force theairside of the lip to contact the shaft and cancause massive failure within hours of operation.See Figure 2-9 below. Excessive pressure canalso push the seal out of the housing.

Figure 2-9. Internal Pressure

Parker offers several designs for applicationswhere high internal pressure cannot be avoided.Elastomeric designs include MP, HP, NTC, TDN,and depending on design, can handle service upto 300 psi (20 bar). Refer to Pages 5-13 and 6-11.

Most PTFE designs can handle pressure, some up to 10,000 psi (690 bar). See Tables 9-4,10-4 and 11-4.

Shaft Speed

Most seal manufacturers rate the speed limitusing surface feet per minute (or meters persecond). This is a measurement of how manysurface feet (meters) pass a given point at the seallip per minute (second) in time. Since this methodconsiders the shaft diameter in addition to speed, itis a better service indicator than RPM alone.

The formulas below can be used to determinethe fpm (feet per minute) or m/s (meters persecond) for metric applications.

Inch

Metric

A typical seal design in NBR material canoperate up to 3,000 fpm (15 m/s) assuming allother operating parameters are reasonable. If anyof the other operating conditions are excessive,seal designs and material upgrades are availableto improve performance. Parker FKM and PTFEseals can be used for applications approaching6,000 fpm (30 m/s) and ProTech bearing isolatorsfor even higher speeds.

10/13/16

Shaft Diameter RPM 0.262 fpm=

Shaft Diameter (mm) RPM 0.0000523 = m/s

Shaft seals operate in a wide range of speeds. When shaft speeds increase, so does underlip temperature, wear and internal pressure, if oil sumps are not vented. To assure optimal performance, select the proper seal design and material to accommodate for these factors.

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Housing / Bore Considerations

Typical radial shaft seals are pressed into thebore to assure proper OD sealing and sealretention in the housing. The most commonly usedmaterials for seal housings are steel and cast iron.Care must be taken when softer materials such asaluminum, bronze or plastics are used for thehousing material. Aluminum has a thermalexpansion rate almost double that of steel. Steelcase designs can lose the required press fit in analuminum housing when they go through thermalcycles.

A seal with an aluminum, composite or rubbercovered OD should be used for aluminum housings.These materials help maintain the press fit in the housing during thermal cycles and reduce the possibility of galvanic corrosion. Plastic housings can also expand at rates that can create problemsif a metal OD seal is used.

The following chart shows typical values ofthermal expansion for common metals in inch/inch/°F.

Fiber reinforced and rubber OD seals are moreforgiving so their bore tolerance can be greaterthan for metal OD seals. Aluminum bores aretypically smaller than steel bores for metal ODseals to compensate for some of the difference inthermal expansion. A finish range of 40 to 100 μinRa (1.0 to 2.5 μm Ra) is recommended for servicepressures up to 3 psi (0.20 bar). If the fluid is thick,such as a grease, a 125 μin Ra (3.17 μm Ra) finishwould be acceptable with no system pressure.

The finish on aluminum bores is more sensitiveand must be maintained to keep seals fromspinning in the bore and should not be smootherthan 60 μin Ra (1.5 μm Ra).

A lead-in chamfer is highly recommended forall seal housings. The chamfer aligns the sealduring installation and helps prevent the seal fromcocking. Both corners of the chamfer should befree of burrs and sharp edges.

Figure 2-10. Housing Profile

Shaft to Bore Misalignment (STBM)

When the center of the shaft rotation is not thesame as the center of the bore, the shaft pushesagainst the lip on one side of the seal greater thanthe other. This can cause the lip to wear rapidly inone place and have inadequate contact on theopposite side.

Figure 2-11. STBM

Table 2-3. Typical Values of Thermal Expansion

Item Value

Aluminum 0.000013

Brass 0.000011

Carbon Steel 0.0000058

Cast Iron 0.0000059

Stainless Steel 0.000010

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Bore Chamfer

15 to 30°

0.060 to 0.090"(1.5 to 2.2 mm)

Bore Centerline Shaft Centerline

Seal HousingCavity Diameter(Bore)

MisalignmentEccentricity

With eccentricity, onlystatic radial deflection is

imposed on the seal.

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Engineering




Shaft Runout

When the shaft does not rotate around itscenter, it wobbles. This condition is called runout.The seal lip has to move back and forth tomaintain contact. The life of a seal is shortened asthe runout is increased, and when the runoutexceeds the capability of the lip, it will leak.

Parker offers seals for misalignment conditions.See Pages 5-15 and 6-17.

Figure 2-12. Shaft Runout

Shaft Seal Summary

In conclusion, because the seal is only onecomponent of the sealing system, all the followingoperating factors need to be considered foroptimal seal life:

Lubrication: A seal is designed to run on a filmof oil. Without the film of oil, the sealing lip willharden and crack due to the heat generated byexcessive friction. The lubricant must also becompatible with underlip temperatures to avoid thebuildup of abrasive, carbonized particles at the seallip.

Shaft Finish: A shaft finish that is too smoothwill cause a stick slip flutter that will let the fluidescape under the lip and cause excessive heatthat will harden the lip. Excessive roughness willpenetrate the lubricant film, cause leakage andaccelerate lip wear. Maintaining the desiredsurface finish is critical for maximizing the servicelife of any contact rotary lip seal.

Shaft to Bore Eccentricity: When the center ofthe shaft rotation is not the same as the center ofthe bore, the shaft pushes against the lip on oneside of the seal greater than the other. This cancause the lip to wear rapidly in one place and haveinadequate contact on the opposite side.

Dynamic Shaft Runout: When the shaft doesnot rotate around its own center, the lip has tomove back and forth to follow it. In excess, the lipwill be unable to maintain contact as the shaftrotates, causing leakage.

Pressure: Excessive pressure will force the lipagainst the shaft and cause excessive frictionalheat and wear.

Bore: A bore finish that is too coarse cancause a leak path by itself. If it has burrs or othersharp edges, they can scar the metal diameterduring assembly, causing a leak path on the sealOD.

Speed: Shaft speed causes the underliptemperature to increase in addition to elevating theoverall sump temperature. Over time, the heat willharden the elastomeric lip and reduce the seal’sability to maintain positive contact with the entirecircumference of the shaft.

Operating Temperature: Controlling thetemperature of the sealing system is key tomaximizing seal life. The relationship betweenspeed, sump temperature, underlip temperature,pressure and shaft finish need to be consideredsince these operating parameters are interactiveand will determine the service life of both the lipmaterial and system lubricant.

Shaft Seal Installation

1. Prior to installation the seal should beexamined to ensure that it is clean, undamagedand the correct seal for the application.

2. Verify spring is present for spring-loadedseal designs.

3. Prelubricate the seal lip with a system-compatible lubricant. It is preferable to use thesystem lubricant.

4. For seals with a rubber outside diameter,lightly lubricate seal OD with a system compatiblelubricant. DO NOT LUBRICATE THE OD OF ACLIPPER OIL SEAL THAT HAS A COMPOSITE OD.

Bore Centerline

Shaft RunoutEnvelope

Shaft CenterlineOrbits around theaxis of rotation

Shaft Axis ofRotation

Shaft RunoutEccentricity

Shaft GeometricCenterline

In this case, cyclical radial deflection due to runout issuperimposed on static radial deflection due to eccentricity.

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5. Verify the desired lip direction for theapplication (lip toward oil for best retention).

6. Examine the leading edge of the shaft.Shaft should be properly chamfered and free ofnicks and burrs that could cut or nick the seal lip.

7. Examine the leading edge of the housing.The seal bore should be chamfered and free ofnicks and burrs that could gouge the seal outsidediameter or make the seal difficult to install into theseal housing.

8. Examine the shaft where the lip will makecontact. This surface must be free of grooves fromprior service. If shaft is damaged or worn in thisarea, dress shaft for proper finish or install a QuickSleeve or wear sleeve. If using a Quick Sleeve, anoversized seal is not required. If using a standardwear sleeve, the replacement seal must have aninside diameter that is designed to be used withthe wear sleeve’s outside diameter.

9. If the seal lip must pass over keyways orsplines on the shaft, use an installation sleeve toprotect the seal lips as they pass over these areas.If an installation sleeve is not available, wrapmasking tape around the shaft to form a protectivebarrier.

10. Slide the seal over the shaft to the sealhousing. With finger pressure, start seal intohousing with a slight rotating motion until seal hasa light press fit in the housing. Be sure seal issquare or perpendicular to the shaft. If the seal iscrooked or cocked, continuing with installation willdamage the seal.

11. Position the installation tool and drive theseal into the housing until it is flush with thehousing or recessed into the bore the properdistance. Please note that a screwdriver, punch orhammer should not be used to install the seal.Refer to the diagrams at right for recommendedinstallation tools.

12. When using a metal driver to install metalclad seals, extra care is needed to be sure theshock load does not dislodge the spring.

13. If the seal is cocked in the housing, removeseal and start over using a new seal. Attempts tosquare the seal in the housing using direct blowswill damage the seal.

14. Inspect the seal to be sure it is straight andflush. Examine the face of the seal for damage. Ifit is dented from installation, the lip will bedeflected and will normally cause prematurefailure.

Counter Bore Installation — Flush Mount

Tool bottoms out against machined face ofhousing to position seal.

Counter Bore Installation

Seal is positioned square by seating againstcounter bore.

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Engineering




Recessed Installation

Tool bottoms out against end of shaft toposition seal in the housing.

Installation Sleeve

Use to install seal over keyways and splines.

Handling and Storage

1. Care should be taken when storing rotaryshaft lip seals to ensure optimal performance.

2. Seals should be stored in a cool, dry areabelow 86 °F (30 °C) with an average relativehumidity of 40 to 70%.

3. Rotating stock is important. If inventory isold, seals should be used on a “first in, first out”basis. Based on the relative low cost of a lip sealcompared to the expense associated with a failedpiece of equipment, a good practice is to discardaged inventory since old seals may havedeteriorated lip materials.

4. Seals should be stored away from direct orreflected sunlight and electrical equipment toavoid UV and ozone aging of the lip material.

5. Avoid storing seals in damp areas or wherehigh humidity is present. Excessive humidity willdeteriorate some seal element materials. Metalcases and springs will also rust and corrode ifexposed to high levels of moisture or humidity.

6. Seals should not be exposed to radiation.

7. Keep seals stored in proper packaging. Donot store unpackaged seals on the shelf.

8. Do not use wire or string to tag a seal. Wirecan easily cut the seal lip. Wire or string can alsodeform the lip beyond the point of recovery andcan lead to leakage at start-up.

9. Do not store seals on hooks, nails orpegboard. Over time the weight of the seal restingon the hook will deform the lip beyond recovery.

10. Avoid storing seals where high levels offumes are present. Depending on the chemicaland concentration, it can chemically interact withthe lip material.

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2




PTFE Shaft Seals

How Do I Choose the Right Profile for MyApplication?

Parker’s PTFE product line includes bothstandard designs for the most commonapplications and custom designs that ourengineers can help you develop.

For the long term, we suggest that youfamiliarize yourself with the design elements in thisEngineering section that are critical whenchoosing a FlexiLip™, FlexiCase™ or FlexiSeal®.

For quick reference and ease of sortingthrough the many standard designs, we haveprovided simple decision trees and placed themthroughout this design guide. If it becomesapparent that you need a custom design to meetyour unique needs, or if you just want us to confirmthe standard seal choice you’ve made, pleasecontact Parker’s PTFE Engineering team at801-972-3000.

Parker designs and manufactures a completeline of PTFE seals for both reciprocating androtary applications. This guide focuses on sealsfor rotary applications. For reciprocatingapplications please refer to publication EPS 5340PTFE Lip Seal Design Guide.

PTFE lip seals are commonly used as anupgrade over elastomeric lip seals whenconditions are severe. Common reasons forupgrading to a PTFE material include chemicalcompatibility, poor lubrication at the lip, highpressure, high speed or high temperature.

For rotary applications, Parker offers threeprimary design groups: FlexiLip, FlexiCase andFlexiSeal.

FlexiLip seals are available in the above basicprofiles. Excluder lips and internal metal stabilizerbands can be added to each profile depending onapplication requirements. The main difference isthe shape of the primary lip. Additional optionsare available for the lip and O-ring material foradded design flexibility.

LF = Mandrel Formed LipLE = Elf Toe LipLG = Lip With Garter SpringLM = Machined LipLD = Dual Lip

FlexiLip seals are intended for continuousrunning rotary shafts under various operatingconditions. An O-ring is used on the OD forpositive static sealing and proper bore retention. Typical operating limits are up to 6,000 sfpm,150 psi and 450 °F (30 m/s, 10 bar and 232 °C).See Table 9-4 on Page 9-10 for specific limits.

CF = Mandrel Formed LipCM = Machined Lip FormCE = Elf Toe LipCD = Dual LipsCH = High Pressure Dual LipCG = Lip With Garter Spring

FlexiSeal rotary seals are spring-energizeddesigns and are available in the basic profilesabove. Three spring options are available for eachprofile: cantilever, canted-coil and helical. Shaftspeeds are very limited (below 1,000 sfpm or5 m/s) but they can provide positive sealing to10,000 psi (690 bar). This is the preferred designfor rotating unions as well as oscillating and slowrotating shafts under high pressure conditions.

LF LE LG LM LD

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CF CM CE CD CH CG

FC FH FF

FlexiCase designs feature PTFE lip elements encased in a metal jacket and are available in the above basic profiles. FlexiCase designs can be used in the same applications as FlexiLip profiles where more bore retention is required. Excluder lips can be added for additional exclusion capac-ity. Additional options are available for the lip and case material for added design flexibility. Typical operating limits are 6,000 sfpm, 500 psi and 450 °F (30 m/s, 34 bar and 232 °C).

2




Spring Designs

FlexiSeal profiles utilize threedifferent spring designs.

The two elements to consider whenselecting a spring design are its loadvalue and its deflection range. Thespring’s load affects the sealing ability,friction and wear rate. As the springload is increased, the lips seal tighter,with friction and wear increasing

V Series — Cantilever

C Series — Canted-Coil

H Series — Helical

proportionately. The spring’s deflection range affects theseal’s ability to compensate for variations in gland tolerancesand for normal seal wear. Each spring size has a specificdeflection range. The available deflection increases as theseal and spring cross-section increase; this could be adeciding factor in selecting one cross-section over another.Springs with a wide deflection range should be used whensealing surfaces are nonconcentric (see Page 2-25).

Figure 2-13. Spring Loading

Figure 2-14. FlexiSeal Spring Energizers

Figure 2-14 shows a relative comparison of load vs.deflection curves for the three spring types. The signifiesthe typical deflection when the seal is installed. The hatchmarks indicate the deflection range through which the sealwill function properly. Notice that H Series has a muchsmaller deflection range than both the V and the C Series.

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Spring Loading ProvidesPositive Sealing Contact

Spring-Loaded,Positive Contact

Not Loaded,Poor Contact

V Series

C SeriesH Series

Spring Compression

Spr

ing

Load

2




Cantilever Springs — V Series

The FlexiSeal Cantilever spring ismade from flat metal strip stock of300 Series stainless steel or Elgiloy®

as an option. The strip stock is punchedor chemically etched into a serpentinepattern and formed into a rounded“V” shape. It is available in either a lightor medium load spring. The mediumspring is suitable in most applications,but the light load spring can be used ifhaving low friction is more importantthan sealability. The medium springload deflection curve is depicted inFigure 2-14 on Page 2-16.

The cantilever spring is intended fordynamic applications involving rotary orreciprocating motion. It can also beused in static conditions when there isneed for a higher deflection spring dueto wide gland tolerance, excessiveexpansion and contraction, or lift-offdue to high pressure.

The long beam leg design puts thespring load out at the leading edge ofthe seal, creating the best load locationfor the FlexiSeal to act as a scraperwhen the optional scraper lip is selected.

The geometry of the V Seriescantilever spring provides flexibility byutilizing individual tabs, separated bysmall gaps. This shape allows thespring to flex into radial and axial sealdesigns. The spring tabs can overlapon the ID and spread apart on the ODwhen the cross-section is too large forthe diameter.

Table 2-4 provides the minimumdiameters for V Series springs for rodand piston seals, as well as internaland external pressure face seals. Fordiameters smaller than those listed,C or H Series spring designs arerecommended.

Features

• V-shaped spring with moderate load vs. deflection

• Standard inch/fractional and MIL-G-5514 sizes

• Standard 300 series stainless steel springs

• NACE compliant Elgiloy springs available in medium springload, -450 to 600 °F

• Scraper lip designs for abrasive medias

• Available as external & internal pressure face seals

Recommended Applications

• Reciprocating rods & pistons

• Rotary shafts



Canted-Coil Springs — C Series

The FlexiSeal C Series spring is made from round wire that is coiled and formed into a canted or slanted shape. The result is a radial compression spring with a very flat load versus deflection curve as illustrated in Figure 2-14 on Page 2-16. Both 302 stainlesssteel and Hastelloy®* C-276 alloy are available as standards in three different spring loads.

The canted-coil spring is intended for dynamic reciprocating and rotary applications. It is also used in static applications when wide gland tolerance or misalignment is present. The flat load curve of this design makes it an ideal choice for friction sensitive applications.

The C Series spring can be fit into small seal diameters without overlapping the individual spring coils. Because the ID coils tend to butt up to each other, the spring has very small gaps providing maximum spring contact. This geometry is well suited for dynamic rod seal applications less than 1/2" diameter.

The C Series spring is available in Light, Medium and Heavy load ranges.

• Light: Applications that requireextremely low break-out and runningfriction when sealing ability is lessimportant than friction.

• Medium: General application.Medium friction but reliable sealingcapability. Normally the starting pointfor new applications. Balancefunctions of friction, sealing abilityand dynamic wear.

• Heavy: Applications where optimumresilience is required due to hardwareseparation. Accelerated seal materialwear in dynamic applications. Usedwhen primary objective is sealing andfriction and/or wear is secondary.

The C Series spring produces compression load near thecenter of the seal. The standard beveled lip seal geometryputs the point of contact slightly in front, forcing the springback into the spring cavity. The lip design providesconcentrated unit load at the sealing interface, and allowslubrication to the dynamic lip, increasing the wear life.Because of this geometry, the C Series is not the best choicefor abrasive medias. For abrasive conditions the FlexiSeal VSeries is recommended. See Page 2-17 for details.

Features

• Canted coil spring with flat load vs. deflections

• Light, medium and heavy load springs standard


• Standard 302 series stainless steel springs

• Hastelloy C-276 alloy springs available• Available as external & internal pressure face

seals


• Friction sensitiveapplications

• Reciprocating rods &pistons

• Rotary shafts



Helical Springs — H Series

The H Series spring is made fromflat ribbon metal strip stock that isformed into a helix shape. The standardmaterial is 17/7 PH stainless steel, andElgiloy® is offered as an option. Thefinished spring produces a very highload versus deflection curve as shownin Figure 2-14 on Page 2-16.

The helical spring design isintended for static applications due tothe high unit load. It can be used in veryslow or infrequent dynamic conditionswhen friction and wear are secondaryconcerns to positive sealing.

The H series spring producesevenly distributed load across eachindividual band, with very small gapsbetween the coils. This tight spacingprovides near continuous load,reducing potential leak paths. This,combined with the high unit load,makes the H series well-suited forvacuum and cryogenic applications orwhen pressure is too low to energizethe seal.

The load provided by the H Seriesspring is directly through its centerline.The lip design of the FBN-H profile is afull radius at the sealing interface,providing maximum load to the contactpoints to effect a tight seal. The springis welded at the ends. When the seal iscompressed into the hardware, thespring cavity is designed to allow axialspring growth.

The relatively small deflectionrange of the H Series spring prevents itfrom being used in applications havingwide gland tolerances, eccentricity ormisalignment. The V or C SeriesFlexiSeal should be considered forthese conditions.

Features

• Helical wound ribbon spring with high load vs. deflection


• Standard 17/7 PH stainless steel springs

• NACE compliant Elgiloy springs available

• Available as external & internal pressure face seals


• Static rods & pistons

• Static internal & external pressure face seal applications

• Slow dynamic applications




Formed Lip

Machined Lip

Elf Toe Lip without Spring

Chamfered Lip

Lip Shapes

Formed Lips — The formed lip is the most commonprofile for general rotary service. After the lip is machined tosize, a mandrel is used to form the lip to the desired inter-ference to achieve the optimal lip load. Both FlexiLip andFlexiCase designs are available with single or multiple formed lips. Formed lips are used to retain lubricant, can handlepressure up to 150 psi (10 bar) and are rated for shaft speeds up to 5,000fpm (25 m/s). Because the lip is not spring-loaded, its ability to handle misalignment and runout conditions is limited.

Machined Lips — The machined lip allows for tightercontrol of the lip interference and is used for specialapplications where the lip load is critical. Both FlexiLipand FlexiCase designs are available with a single machinedlip for lubricant retention. Machined lips are also commonlyused as an excluder lip in conjunction with a primaryformed lip. The machined lip normally has a narrowercontact footprint on the shaft so it is more sensitive toeccentricity and runout than the formed lip.

Elf Toe Lips — The elf toe lip profile has a sharp angle onthe leading edge of the lip to help keep abrasive media fromgetting trapped under the lip. The pocket that is formed bythis profile also allows a garter spring to be added. Theaddition of a garter spring allows the lip to maintain contactwith the shaft under high misalignment conditions up to0.020" (0.5 mm) Total Indicator Runout (TIR).

Chamfered Lips — The most common spring-energizd lip shape is the chamfered or back-beveled design and isavailable with the V and C Series spring types. This designallows for ease of installation and permits lubrication to nestunder the lip and feed through in reciprocating dynamicapplications. The result is a microscopic film of lubricationthat increases seal andhardware service life. Since thefootprint of a chamfered lip is a single point, all of the sealingforce is concentrated, yielding the highest sealabilityand lowest friction. The high lip contact force limits the use in rotary service to 1000 sfpm (5 m/s).

Scraper Lips — Applications often involve medias withabrasive particles that can get caught between the seal lipand the mating hardware. This increases wear to both theseal and the mating surface. The scraper lip contact pointis positioned directly over the load point of the spring ineach design for maximum scraping action. The scraper lipcan be positioned on the ID, OD or both. The high spring-loaded contact point limits the use in rotary service tolow speed applications.

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Abrasive MediaScraped by Lip

Flanged Scraper Lip at ID

Scraper Lip at ID

Abrasive MediaScraped by Lip

2

2




Shaft Considerations

The shaft finish required for PTFE seals is justas critical as that for elastomeric lip seals (seePage 2-6).

Proper surface finish is critical to ensure positivesealing, and achieve the longest seal life possiblein rotating applications. Rotating surfaces that aretoo rough can create leak paths and can be veryabrasive to the seal. Unlike elastomer contactseals, PTFE-based Flexi designs can run on verysmooth surfaces with or without lubrication. Due tothe toughness and low coefficient of friction ofPTFE, Flexi designs, unlike seals made of othermaterials, slip over the high points of the matingsurface and resist abrasion. To maximize sealperformance, the recommendations for surfaceroughness in Table 2-5 should be followed.

Dynamic surfaces with relatively rough finisheswill result in higher wear rates, which decrease theseal life and may compromise performance.Additionally, dynamic surfaces which have a finishsmoother than recommended may also decreasethe seal’s effectiveness. The optimum surfaceroughness allows a film of the fluid being sealed toflow between the seal and the mating surface, whicheffectively lubricates and extends the life of the seal.

PTFE rotary seal applications require a hardrunning surface on the dynamic portion of thehardware. The harder surface allows the use ofhigher reinforced seal materials that will increasethe seal and hardware life. Softer running surfacesmust use lower wear resistant materials that willnot damage the hardware and normally yieldshorter seal life. A balance between seal materialand dynamic surface hardness must be met toensure that the seal remains the sacrificialcomponent. Table 9-3 includes minimumrecommended surface hardness for Parkermaterials in dynamic applications, based ontemperature, motion and speed.

When the dynamic surface hardness is below45 Rc, most seal materials will polish the runningsurface of the hardware and the seal. This initialbreak-in period will cause seal wear to taper offover a period of time, depending on the sealmaterial, surface finish and PV of the application.When hardness exceeds 45 Rc, the initial surfacefinish is very important since the surface is muchharder to polish and the time to achieve break-in ismuch longer. Surface hardness above 65 Rc willgenerally not polish and therefore the initialsurface finish is even more critical to seal life. Thehardness of the dynamic hardware surface affectsthe wear rate of the seal. Additionally, some seallip materials are abrasive and will wear softermetal shafts or dynamic components. In general,higher surface finish results in better overall sealand hardware performance. The ideal hardness ofthe dynamic surfaces of the hardware is 50 to 60Rockwell C. The actual hardness used is normallya balance between the additional cost associatedwith finishing harder materials versus themaximum seal life that will be achievable.

Figure 2-18. Shaft Profile

Table 2-5. Surface Roughness, Ra

Media BeingSealed

DynamicSurfaces

StaticSurfaces

μ inch μ m μ inch μ mCryogenics 06 max. 0.15 max.008 max. 0.2 max.Helium GasHydrogen GasFreon

08 max. 0.2 max. 12 max. 0.3 max.

AirNitrogen GasArgonNatural GasFuel (Aircraft andAutomotive)

012 max. 0.3 max. 16 max. 0.4 max.

WaterHydraulic OilCrude OilSealants

12 max. 0.3 max. 32 max. 0.8 max.

01/01/17

30°

At 30°See Table 2-2a on Page 2-8for chamfer lengthw

For additional information on understanding and applying the benefits of appropriate hardware surface finish specifi-cations, please consult the Engineering Section (Pages 2-9 through 2-13) of Parker's Fluid Power Seal Design Guide(Catalog EPS 5370).

2

Engineering




The leading edge of the shaft should have aburr-free chamfer to ease installation bypreventing lip roll-back. Because PTFE lip sealsare not as flexible as rubber lip seals they tend tobe more difficult to install over the shaft. First timeinstallers of PTFE lip seals normally destroy a fewseals before realizing they are more difficult tostart over the shaft than a rubber lip seal. Whenpossible, use an installation sleeve to get thePTFE seal started over the shaft. The sleeve willalso protect the lips from sharp edges commonwith keyways or splines.

Housing/Bore Considerations

Typical FlexiLip and FlexiCase shaft seals arepressed into the bore to assure proper OD sealingand seal retention in the housing. The mostcommonly used materials for seal housings aresteel and cast iron. Care must be taken whensofter materials such as aluminum, bronze orplastics are used for the housing material.Aluminum has a thermal expansion rate almostdouble that of steel. Metal case designs can losethe required press fit in an aluminum housingwhen they go through thermal cycles due to thehigher rate of thermal expansion of aluminum.

A finish range of 32 to 63 μin Ra (1.0 to 2.5 μmRa) is recommended for service pressures up to3 psi (0.20 bar). If the fluid is thick, such as agrease, a 125 μin Ra (3.17 μm Ra) finish would beacceptable with no system pressure.

A lead-in chamfer is highly recommended forall seal housings. The chamfer aligns the sealduring installation and helps prevent the seal fromcocking. Both corners of the chamfer should befree of burrs and sharp edges.

Figure 2-19. Housing Profile

For pressurized rotary applications, additionalprecautions are needed to ensure the seal is notpushed out of the housing. If the seal is installed inan open bore, a snap ring or cover plate should beadded to retain the seal. The specific pressure thatrequires additional retention is a function of theseal surface area, seal design, internal pressureand bore finish. As a general rule, retention devices should be used with FlexiLip designs in applicationsover 2 psi (0.15 bar) and FlexiCase designs over30 psi (2 bar).

Installation with Sleeve

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15 to 30°

Bore Chamfer

0.060 to 0.090" (1.5 to 2.2 mm)

FlexiCase in GlandFlexiLip in Gland

2




FlexiSeal flanged designs can be used ineither static, rotary or reciprocating applicationsand are designed to be dynamic only on the ID.They excel in rotary applications because theflange can be clamped axially to prevent the sealfrom rotating with the shaft. This extra stabilityallows the flanged design to hold more pressure athigher surface speeds. The housing must be madein two pieces for installation purposes and the sealcan be installed either lips-first or heel-first.

Figure 2-20. Two-Piece Flanged Gland

Since FlexiSeal types FC and FH are primarilyused in pressure applications, they too should beused with a retainer plate.

Pressure and Shaft Velocity

Unlike reciprocating applications, seals thatride on a rotating shaft have a contact point that islocalized in only one small area where dynamicforces and energy are concentrated. In fact, muchof the energy from the shaft is dissipated at theseal in the form of frictional heat and wear, both ofwhich are detrimental to seal life. This effect isaccentuated by increasing the shaft speed or byincreasing the perpendicular force holding the lipagainst the shaft. Shaft speed can be measured insurface feet per minute and the lip force can beapproximated by measuring the differentialpressure across the seal in psi. Shaft velocity insurface feet per minute is calculated as follows:

One way to estimate the exposure to theserisks is to calculate the PV-value by multiplying thepressure held by the seal (P in psi) by the surfacevelocity of the shaft (V in surface feet per minute).The product of this multiplication provides thedesigner with a guide to aid in the choice of sealprofile and material. Let us run through anexample:

Given:Pressure = 45 psiShaft diameter = 1.25"Shaft rotational speed = 350 RPM

C1

R 0.015 Max.

20°

40°

FCC-V in Two-Piece Gland

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SurfaceVelocity(in sfpm)

=Shaft

Diameter(inches)

x xShaftRPM

0.262

SurfaceVelocity

= ShaftDiameter

x xShaftRotational Speed

0.262

= 1.25" x 350 RPM x 0.262= 115 sfpm

PV-value = Pressure x Surface Velocity= 45 psi x 115 sfpm= 5175 ft. lb./in2 min.

Engineering




Figure 2-21. Pressure — Velocity Chart

The PV graph in Figure 2-21 applies tounlubricated rotary applications using a stablerotary seal in a jacket material with a 4 or 5 wearresistance rating. As a rule of thumb, a PTFErotary seal can be used in unlubricatedapplications with a PV of up to 150,000.

This information is intended to be used only asa guide since there are many other factors, suchas sealing media, hardware material and surfacefinish, which affect the amount of heat generatedand the wear life of the seal. In cases where themedia being sealed is a lubricant, these seals canoperate continuously at PV levels 10 to 20 timeshigher than those shown in Figure 2-21.

Lubrication

While Parker PTFE seals have a naturallubricity and can be used in unlubricatedapplications, it is always better to have lubricationpresent in rotary applications. A film of lubricant

between the seal lip and the shaft reduces sealwear and frictional heat generation, makes highersurface speeds possible, and helps prevent theseal from wearing a groove in the shaft. When thelubricant splashes or flows past the seal area, itacts as a coolant, prolonging seal life.

Rotary PTFE Product Choice

While the black and white curves aboveattempt to draw the line between what can andcannot be done, they do not show which profileswork best within the limits of feasibility. The blueand brown curves above show which product lineswork better with regard to pressure and surfacespeed assuming there is no lubrication. RotaryFlexiSeals can be used when pressures are highand speeds are low, while FlexiLip and FlexiCaseprofiles lend themselves more to applications withhigh surface speeds and low pressure.

Assumptions

• Optimal seal profile choice

• Ambient temperature

• Low shaft runout

• Generally non-extreme conditions

Rapid Wear Zone

FlexiLip & FlexiCase PV Limit

500

Unlubricated

PV

Limit

10,000

Pre

ssu

rein

psi

0050001

Velocity in surface feet per minute

FlexiS

eal PV

Limit

Pressure — Velocity Curves

Lubricated PV Limit

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2




Shaft Misalignment and Runout

Applications with rotating shafts come withtheir own set of common problems. Among theseare those associated with the shaft not beingaligned properly with the surrounding hardware.Misalignment most commonly manifests itself asEccentricity and Runout. Every shaft has somedegree of both as described in Figure 2-22.

Eccentricity of a rotating shaft creates twoproblems. One is that it forces the seal lip to followa shaft that is not centered in the bore, wearing thelip more on one side. Because they are lesselastic, PTFE seals are more susceptible to failure,misalignment and runout conditions thanelastomeric lip seals. The second potentialproblem is that it enlarges the extrusion gap onone side, which could be detrimental if highpressure is involved. Extended heel designs willreduce seal extrusion.

Figure 2-22. Eccentricity and Shaft Runout

Shaft Runout is when the shaft is spinning onan axis of rotation that is offset from the geometriccenter of the shaft at the point of seal lip contact.Runout can be caused by a bent shaft or bywhirling deflection while spinning. The seal mustbe sufficiently compliant to maintain contact withthe shaft despite being compressed and extendedeach revolution. It follows that shaft runoutbecomes more of a problem at high speeds.

Figure 2-23. FlexiSeal Eccentricity and RunoutLimits

All rotating shafts have eccentricity and runoutto some degree. The risk of failure increasessignificantly if a system has a considerableamount of both. Figure 2-23 shows the acceptablemaximum for these parameters for all rotaryFlexiSeal profiles except the FFN-H. Figure 2-24shows the limits for FlexiLip and FlexiCase profiles.

Figure 2-24. FlexiLip and FlexiCase Eccentricityand Runout Limits

Shaft Centerline

Seal HousingCavity Diameter(Bore)

MISALIGNMENTWith eccentricity, onlystatic radial deflection isimposed on the seal.

ECCENTRICITY

Bore Centerline

SHAFT RUNOUTECCENTRICITY

Shaft Axisof Rotation

Shaft Centerline(Orbits aroundaxis of rotation)

Shaft RunoutEnvelope

Bore Centerline

Shaft GeometricCenterline

In this case, cyclical radial deflection dueto runout is superimposed on static radialdeflection due to eccentricity.

AXIS OF ROTATION

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1/16 3/32 1/8 3/16 1/4inch

0.010

0.0090.008

0.0070.006

0.005

0.004

0.003

0.002

0.001

inch

1 Maximum Eccentricity with No Runout2 Maximum Shaft Runout (less than 500 RPM) with No Eccentricity

0.011

1

FlexiSeal Cross-Section

0.001 0.002 0.003 0.004 0.005

Eccentricity (inches)

0.004

0.003

0.002

0.001

0.006

Run

out(

inch

es)

Assuming Shaft Speedof 1750 RPM

Acceptable Range

High Leakage andWear Range

2

2

Engineering




Rotary PTFE Seal Considerations

For all rotary seals — FlexiSeal Rotary, FlexiLipand FlexiCase — the designer must consider:

• pressure and shaft velocity• lubrication• shaft misalignment and runout• shaft hardness and surface finish• advantages of different lip shapes• shaft lead• temperature

For additional information on reciprocatingapplications, please refer to publication EPS 5340,PTFE Lip Seal Design Guide.

Alternate Housing Configurations

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FlexiCase with Snap RingBanded FlexiLip withRetainer

Rotary Housing Flanged Rotary Housing

FlexiLip with Retainerfor Higher Pressure

2




Bearing IsolatorsGeneral Theory of Operation

Engineered labyrinth type seals, also called“Bearing Isolators,” should be considered whenincreasing the Mean Time Between Failures (MTBF)is a primary objective for seal selection. Common equipment that uses labyrinth-type seals includesANSI pumps, IEEE 841 rated electric motors, splitpillow block bearings, turbines and gearboxes.

All bearing isolator designs consist of at leasta rotor and a stator. An external O-ring at the statorOD maintains a press fit in the seal housing andprovides a static seal for oil retention. The O-ringpress fit allows for easy seal installation while alsoproviding excellent bore retention. The press fit willwithstand external forces to eliminate movementor spinning in the housing and has even been tested in the vertical down position to ensurethe stator will

Documents

Rotary Seal Design Guide - Ceetak Sealing Solutions · Pages 5-14, 6-12, LDS TB TC 10-1 Pages 12-5, 6-12, VA + TB TBV CL 6-16 Pages 12-9, 6-12, SSW + TB SB + SB LS 8-22 DB DC Page