Rotary Seal Design Guide - Seals Unlimited

Catalog EPS 5350/USAEngineeringOther 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).Shaft Sealin fpm=Increase UnderlipTemperature3000 fpm = 55 °FAs sump temperatures increase, the differencebetween sump and lip temperaturedecreases.Figure 2-8 shows the relationship of shaftdiameter, shaft speed and sump temperature andthe impact they have on the temperature at thecontact point of the seal lip and the shaft(underlip temperature).Underlip Temperature – °F320300280260240220200Sump Temperature – °C80 90 100 110 120 130 1405000 Rpm4000 Rpm3000 Rpm2000 Rpm1000 Rpm0 Rpm15014013012011010090Underlip Temperature – °CSeal TorqueThe 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 approximatevalue for elastomer shaft seals. When thetorque value is critical for the application,testing should be performed.Seal Torquein-ounces= 0.65 Shaft Dia. Rpm 1/3in inchesTorque 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 whenlow torque is required because they add virtuallyno torque to the system.22218080160180 200 220 240 260 280 300Sump Temperature – °FFigure 2-8. Example Shaft ConditionsAn easier but more crude estimate is 20 °F(6.7 °C) higher than the sump for each 1,000RPM of shaft speed for sump temperatures about75 to 210 °F (24 to 99 °C).03/28/062-9 Parker Hannifin CorporationEPS DivisionToll Free: (800) 233-3900www.parkerseals.com