Rotary Seal Design Guide - Seals Unlimited

Catalog EPS 5350/USAEngineeringProTech Bearing Isolators88The O-ring press fit allows for easy sealinstallation while also providing excellent boreretention. The press fit will withstand a torque ofup to 500 in-ounces (36,000 g-cm) to eliminatespinning in the housing. The press fit has beentested in the vertical down position to ensure thestator will not walk out of the seal bore.The stator has a sophisticated series ofgrooves to retain oil splash. Before ProTech,bearing isolators relied on a single inboard groovefor oil retention. Results from independent testingby a major pump OEM showed Parker’s design tobe the most effective for oil retention whencompared to various competitor designs.RotorThe secondcomponent, the rotor,uses an external O-ringto maintain a static pressfit on the shaft. Sincethe rotor spins with theshaft, it will not wear,groove or damage theshaft, so the costsassociated with havingto recondition thesealing surface of theshaft are eliminated.The wrap-around profileof the ProTech rotorprovides optimal waterexclusion.The rotor and stator are assembled at theParker factory where they are permanentlyunitized by means of a patented process. Theunitized design allows for one-piece installationand maintains a minimal clearance between therotor and stator interface for the life of the seal.This interface is the first line of defense againstcontamination. A unitized design maintains theseal’s integrity by keeping high-pressure waterspray, vibration or axial movement from separatingor increasing the gap between the rotor and stator.Controlling Laminar FlowProTech RotorProTech relies on true non-contact labyrinthseal technology. When the rotor and stator areassembled at our factory, a true non-contactlabyrinth is created. For successful waterexclusion, the labyrinth must control the laminarflow properties of the liquid entering the seal.Laminar is the flow of a liquid in an organizedlayered manner, or as the name suggestslaminates. A liquid flowing through a pipe hasvarious flow levels ranging from zero at the outerwall to a maximum along the centerline.RrIntroduction of TurbulenceAn effective seal design must introduceturbulence into the flow. Turbulence slowsdown the rate of flow of the liquid so that gravityalone is enough to expel the liquid through theseal drain port. The left side of Figure 8-1 depictsthe faster moving laminar flow. The arrows showhow the individual water molecules line up ineven planes. The right side shows that whilelaminar flow is still present close to the seal wall,most of the fluid is a slower moving turbulent flow.The direction change, pressure differential, plus thefriction of the molecules themselves, aid in slowingthe rate of flow.StatorRotorV mTypical Laminar Flow PatternLaminarPressure DifferentialShaftTurbulentGravityFigure 8-1. Effects of TurbulenceV mTurbulentBuffer LayerLaminar Sublayer03/28/068-8 Parker Hannifin CorporationEPS DivisionToll Free: (800) 233-3900www.parkerseals.com