Rotary Seal Design Guide - Seals Unlimited

Catalog EPS 5350/USAEngineering22The 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.15 to 30°Bore Chamfer0.060 to 0.090" (1.5 to 2.2 mm)Installation with SleeveHousing/Bore ConsiderationsTypical 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 ProfileFor 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 devicesshould be used with FlexiLip designs in applicationsover 2 psi (0.15 bar) and FlexiCase designs over30 psi (2 bar).FlexiLip in GlandFlexiCase in Gland03/28/062-22 Parker Hannifin CorporationEPS DivisionToll Free: (800) 233-3900www.parkerseals.com