SXL Segmented Shaft Seal Brochure - Thordon Bearings

T H O R D O N B E A R I N G S I N C.SXL Axial and RadialSegmented Shaft Sealsfor Hydro-Turbines

SXL SEGMENTED SHAFT SEALS FOR HYDRO-TURBINESWith over 25 years experience supplying main shaftguide, wicket gate and operating mechanismbearings to the hydro power industry, Thordon is theproven choice for performance and value in bothrehabilitation and new turbine projects. In addition tosupplying bearings, Thordon has also beensupplying segmented shaft seals to the hydro powerindustry for more than 25 years. Thordon SXL has aproven track record as a segmented shaft sealmaterial replacing carbon graphite seals.In addition to proven product performance, Thordonis also an industry leader in polymer research anddevelopment, and in application engineering. Aspart of its ongoing research and developmentprogram, Thordon has built its own test facility forsegmented shaft seals. This facility duplicates theoperating environment of turbine shaft seals andenables Thordon to test various design andconfiguration options. The results of this programhave enabled Thordon to investigate the design ofThordon SXL segmented shaft seals, to determinethe performance parameters of the material and towork on the development of new design options toimprove the performance of Thordon SXL seals.Thordon SXL Segmented Shaft Seal SystemsOperating parameters for Thordon SXL segmentedshaft seals are generally similar to those for carbongraphite seals in terms of maximum interfacepressure and minimum leakage rate. Thordonsegmented shaft seals have been designed forshafts up to 2000mm (80") diameter. They can bedesigned for use in either radial or axial sealingsystems.The main shaft seal of a turbine usually operatesunder high PV-value conditions and may also befrequently exposed to abrasives in the water.Thordon segmented shaft seals are a provensolution working in both clean and abrasive ladenwater. The seal may be located below (see Figure 1)or above the main shaft guide bearing depending onthe system arrangement.Based on Thordon's R&D testing and fieldexperience, Thordon segmented shaft seals areable to operate in a wide range of PV-values withthe maximum water pressure tested up to 0.7 MPa(100 psi).Figure 1. SXL Segmented Shaft SealsDepending on the shaft size, number of segments,machining precision of segments, sealed waterpressure and shaft speed, the amount of leakagecan vary widely. It is difficult to predict the leakagerate accurately at the design stage. However, R&Dtesting has confirmed that for a radial segmentedseal consisting of 6 segments running on a 400 mm(15.75") diameter shaft, the leakage rate would befrom 10 to 40 l/min (2.6 to 10.6 US gal./min).Additional advantages of the segmented sealdesign include easy installation and replacementwithout removing the shaft. Disassembly of othermachine parts may not be required.Thordon SXL vs. Carbon GraphiteSegmented shaft seals for turbines havetraditionally been made from carbon graphite.These seals have low friction and can accept asignificant amount of heat. Carbon graphite is,however, very fragile. It is not unusual to damageseveral segments during installation. Carbongraphite also does not resist the abrasion which canoften be present in the water flowing through aturbine. The elastomeric nature of Thordon SXLgives it superb impact or shock resistance. SXLoffers the advantages of being almost unbreakableand also of being much more abrasion resistant.Optimal sealing performance for SXL can beachieved with an injection of clean water betweenthe first and second rings of the seal. Thordon SXLseals can normally replace existing carbon sealswithout any significant changes to the systemdesign.

Radial SealsTypical radial segmented seals comprise threestages (rings) of interlocking segments (Figure 2).Each ring has both dynamic (against the shaft) andstatic (against the housing) sealing actions.Figure 2. SXL Radial Shaft Seal SegmentsSXL radial shaft seal segmentsAxial SealsAn axial segmented shaft seal works in a similarfashion to conventional mechanical seals. TheThordon axial seal design provides the injectionwater into the central groove of the seal ring (Figure4). The seal segments are normally attached to thestationary tubine casing.Figure 4. Axial Segmented Shaft Seal DesignSXL axial shaft sealFirst stage seals are normally reversed comparedwith the two upper rings, to allow introduction of ahigher-pressure injection flow between the first andsecond rings. (see Figure 3) This higher pressureflow (1.10 to 1.15 times turbine pressure) functionsas a seal lubricant, coolant and a barrier preventingabrasives in the turbine water from entering the sealfaces. A garter spring functions to hold the segmentswith a nominal light force against the shaft duringperiods of shutdown and low pressure and also tomaintain the integrity of the seal ring within thehousing cavity. In normal operation, the seal ring ispressed against the shaft by the force of the water inthe turbine.Figure 3. Radial Segmented Shaft Seal Designclean water injectionThordon axial segmented shaft seals are particularlysuitable for extremely large diameter shafts. It is notunusual for Thordon to install an axial seal with ringdiameter 4000mm (160") or larger. Figure 5 showsone section from a whole sealing ring of an SXL axialsegmented shaft seal.Figure 5. SXL Axial Shaft Seal SegmentShown inverted from Figure 4SXL segmented shaft seal rings

Application Information and Design ParametersAlthough Thordon SXL segmented shaft seals cannormally be used as a direct replacement for carbongraphite, it is recommended to review theprospective application with Thordon Bearings.When evaluating an installation, as much aspossible of the information and design parameterslisted below should be supplied to Thordon forreview.• Water pressure being sealed (water pressureinside turbine)• Shaft diameter• Shaft rotating speed (rpm)• Water quality (clean or abrasive) over the year(i.e. is there spring run-off with abrasives?)• Environmental (water) temperature• Maximum leakage flow allowed• Turbine arrangement (Vertical or Horizontal)• Existing seal design, if application is retrofit• Is a clean, pressurized flush available?Customer Focused To Support Your ImmediateAnd Future NeedsSupply and Service: Geared to provide responseto customer needs, Thordon Bearings understandsthe importance of fast delivery and reduced downtime. Thordon marine and industrial bearings can bedesigned to accommodate the requirements of thecustomer and shipped quickly.Application Engineering: Thordon Bearing’sengineers work closely with customers to provideinnovative bearing and seal system designs thatmeet or exceed the technical requirements of theapplication.Quality: Thordon Bearings Inc. is a Canadiancompany manufacturing to ISO 9001:2000 QualitySystem requirements. With over 35 yearsexperience in polymer bearing design, applicationengineering and manufacturing, Thordon marineand industrial bearings are recognized worldwide forboth quality and performance.Your Local Thordon DistributorT H O R D O N B E A R I N G S I N C.ZERO POLLUTION | HIGH PERFORMANCE | BEARING SYSTEMSSXLSegShaft.12.20093225 Mainway Drive, Burlington, Ontario L7M 1A6 CanadaTel: +1.905.335.1440 Fax: +1.905.335.4033www.ThordonBearings.comISO 9001:2008CGSBRegistration #93649