Rotary Seal Design Guide - Seals Unlimited

Catalog EPS 5350/USAEngineering22Pressure in psi10,000500Unlubricated PV LimitFlexiSeal PV LimitPressure — Velocity CurvesAssumptions• Optimal seal profile choice• Ambient temperature• Low shaft runout• Generally non-extreme conditionsRapid Wear ZoneLubricated PV LimitFlexiLip & FlexiCase PV Limit1000Velocity in surface feet per minute500Figure 2-21. Pressure — Velocity ChartThe 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.LubricationWhile 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 lubricantbetween 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 ChoiceWhile 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.03/28/062-24 Parker Hannifin CorporationEPS DivisionToll Free: (800) 233-3900www.parkerseals.com