Brush sealsWorld class sealing technology

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One-stop sourceMeanwhile, MTU has expanded its brush sealactivities far beyond the engine domain, find-ing customers in diverse industries. Brush sealsare increasingly being used also in industrialgas and steam turbines, as well as in com-pressors and for mechanical engineering ap-plications. To fulfil the needs of all the variousapplications and meet the high demands ontechnology, the company has pulled the nec-essary know-how and specialty expertise to-gether in a brush seal team, so that designand development, production, sales and mar-keting and support are all under one roof. Itsexperts are closely cooperating with cus-tomers at the various sites to introduce thistechnology in the most diverse industries.They also directly benefit from MTU’s enginemanufacturing background, having access tothe company’s advanced test rigs and partici-pating in significant research and developmentprograms. In the process, they have achieveda number of innovations in this field, such asKevlar brush seals and seal housings producedusing additive techniques. And brush seals arenow finding their way into a host of new appli-cations, such as sub-sea compressors.

MTU brush seals enhance the efficiency of:

• aircraft engines• industrial gas turbines• steam turbines• industrial compressors• many mechanical engineering

applications

MTU brush seal team High-tech from a technology leaderThe MTU brush seal team is a highly special-ized center of expertise of MTU Aero Engines,Germany’s leading aero engine manufacturer.Its specialists have been developing innovativeturbomachine seals for over thirty years. Theirspecialized dedication has its origins in mili-tary engine construction. Until recently, dy-namic components were sealed off from theengine gas flow with the aid of labyrinth-typeseals, which were embarrassed by relativelyhigh leakage rates. That is why in 1983, MTUAero Engines began experimenting with brushseals and soon, in 1985, filed a patent for itsnew technology. Today, the company is aglobal leader in this area.

More efficiency at less volumeThe technology behind MTU brush seals is assimple as it is brilliant. Thousands of wires orbristles are safely fixed via a clamping tube,using a core wire, to form a flexible seal.Incoming gases press the wire pack against asupporting ring, compressing it still furtherand so minimizing the seal’s permeability togas. Compared with conventional labyrinthseals, then, losses are reduced to almostnothing. If you take a medium-haul aircraftconsuming 20,000 tons of fuel a year, youeasily save one percent fuel, which equates toan amount carried by a fleet of ten 20-ton fueltrucks.* Another advantage is that for giventightness requirements MTU brush seals needless space. This permits much more compactdesigns and substantially reduces the weightand size of turbomachines.

* Source: NASA TM-1998-206961

1983 MTU begins experimenting with brush seal manufacturing processes1985 First patent application for MTU brush seal1986 Test stand trials1992 First flight tests1996 Testing in industrial turbomachines1998 Production release for aero engine applications1999 Production launch for industrial compressors and turbines2000 First use as semi-static brush seal2002 Testing of Kevlar brush seals2003 Testing of semi-static brush seals in industrial gas turbines2005 Production launch of semi-static brush seals2006 Production launch of Kevlar brush seals2007 Development and market launch of new brush seal variants2008 Testing of new sealing positions in the Geared Turbofan™ demonstrator engine 2012 Application of brush seals in organic Rankine cycle (ORC) steam turbines2013 Certification of the PW1500G (engine for the Bombardier CSeries), equipped with MTU brush seals2013 Expansion into new business areas: Sub-sea compressors and coal pulverizers2014 Testing of additive techniques for brush seal housing production

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The new Airbus A320neo powered by PW1100G-JM engines.

Brush seal technology milestones

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Design of the MTU brush seal

HousingThe outer housing contour may be designedfreely, allowing MTU brush seals to be optimally adapted to suit given installationenvironments.

MaterialsApart from metallic wires like Haynes 25,use can be made also of bristles like Aramidor Polymer. Their sealing effect is evenbetter than that of metallic wires.

Sealing elementThe sealing element is designed to reliablyseal off circular as well as any other two- orthree-dimensional geometries.

Pressure relief chamberThe pressure inside the pressure reliefchamber is nearly the same as that up-stream of the seal. This relieves the pressure acting on the upper portion ofthe bristle pack and in turn enhances thefunction and service life of the seal.

Support ringThe support ring prevents bending of thebristle pack in axial direction.

Cover ringThe cover ring serves to largely eliminatethe adverse effects of the gas flow on thefront bristle rows.

Compact designBrush seals are compact and need appreciablyless space than labyrinth seals. That providesadditional options for the design of rotors andcasings.

Angular orientationThe wires or bristles are normally arrangedat an angle of 45° or 20° with the rotor’sdirection of rotation. With their elasticity,they compensate for all rotor excursions,invariably returning to their original position.

ClampingThe wires are mechanically clamped inposition, eliminating the need to weldthem. This produces a perfectly safe andlong-lived positive connection.

Rotor to be sealed

Operating conditions

• Operating media: gas/gas or gas/liquid• Differential pressure per sealing

element: up to 2,000 kPa• Temperature: up to 700°C• Sliding speed: up to 500 m/s

The advantages at a glance Simple concept—big effectMTU brush seals comprise a sealing elementand a housing. The sealing element includes acore wire, a wire or bristle pack and a clamp-ing tube. This design ensures safe positiveretention and permits the use of non-metallicbristles.

The housing comprises a cover ring to protectthe wires or bristles and a support ring to propthem up when under gas pressure.

Reduced height

Conventional design MTU design

Compared with conventional labyrinth seals, MTU brush seals reduce leakage rates inengines, gas turbines, steam turbines and compressors by up to 80%.

Leakage reduction by MTU brush seals

Three-fin straight labyrinth seal

Three-fin stepped labyrinth seal

MTU brush seal

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Patented design advantages of the MTU brush sealThe design of the MTU brush seal ensuressecure retention of wires or bristles since eachindividual bristle is bent around the core wireand positively fixed in place by means of theclamping tube. This prevents bristle loss dur-ing operation. The compact design providesadditional options for the design of rotors andcasings.

MTU brush seals are characterized by enhancedradial flexibility. Due to its high elasticity thesealing element is extremely resistant to wearover a long time.

The cover ring, which is integrated in thehousing, protects the bristle pack from turbu-lences and makes it tolerant to swirls in thegas flow which are typical in turbomachines.

Another important advantage afforded by theMTU brush seal is that it allows the use ofvarious metallic wires and also of non-metallicbristles. These are all produced by the samemethod which ensures high process stability.

Since the housing design is not dictated bythe sealing element design both constituentscan be separately optimized to suit any givensealing environment.

Brush seals stand out for:

• leakage rate reduction by up to 80%• optimum preservation of clearance• compensation of axial and radial

movements • ease of replacement at overhaul• compact design• stable operating behavior• long service life

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

30%

80%

up to 80% lessleakage

Individual solutions to suit every requirementMTU’s approach to design the sealing elementand the seal housing separately permits theseals to be optimally adapted to the specificconditions at a particular seal location. Thesealing elements can be combined with anyform of housing or be integrated in a housingprovided by the customer which is a particu-larly cost-effective solution.

Portfolio of MTU brush seals This approach results in a variety of designoptions for each type of seal. A selection ofseals from MTU’s product portfolio is shownin the table below.

Brush seals–product portfolio of MTU brush seals

DesignSizeIllustration

Housing

sheet-metal part<Ø 300mm

turned part<Ø 650mm

injection molded part<Ø 250mm

sheet-metal part>Ø 300mm

without housingoptional

Sealing element type:Haynes 25Wire diameter 0.07 mm:100 Bpmm/200 BpmmWire diameter 0.10 mm:140 BpmmWire diameter 0.15 mm:50 Bpmm

Customers can choose from a variety of brush seal designs or have the brush seal tailored to their individual needs.

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Sealing element type:Aramid (Kevlar)Bristle diameter 0.012 mm:4,000 Fpmm/6,350 Fpmm

Brush seals–sealing elements

Design features:• angular orientation

optional (radial/axial)• sealing element form

optional (also three-dimensional)

• no limitation as to size

In the next step, these two sealing element types are fitted in housingsto produce the various MTU brush seal types.

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MTU brush seals are successfully being used on:

Potential applications

Purpose

MTU brush seals are used in new installations and in retrofits.

MTU offers a suitable brush seal for any application.

Steam turbines/ORC

• balance piston seals• shaft end seals• interstage seals

• efficiency improvement• improvement of rotor

dynamics• reduction of cost by

shorter length

Compressors

• shaft seals• interstage seals• impeller seals

• reduction of leakage• improvement of rotor

dynamics• efficiency improvement

Mechanical engineeringapplications• machine tools • pumps• ship building• special machinery• coal pulverizers• efficiency improvement• ensuring machine

serviceability• omission of sealing air

system• improvement of rotor

dynamics

Aircraft engines andstationary gas turbines• bearing chamber seals• shaft seals • interstage seals• static seals

• reduction of fuelconsumption

• reduction of size and weight

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Secondary air system seal

Bearing chamber seal

MTU brush seals in the EJ200 engine powering theEurofighter.

Fit for the future: MTU’s brush seals are now being used also on the new PurePower® PW1100G-JM Geared Turbofan™, which will power the Airbus A320neo.

Standard in next-generation aircraftenginesMTU brush seals have widely proved theirworth, being superior to labyrinth seals fromvarious aspects. This is why the technology isfinding a home on practically every engine inthe pipeline worldwide. MTU’s brush seals areindeed proving their worth in operation, havingaccumulated well over 7.5 million runningcycles in advanced aircraft engines. MTU’sinnovative seals have likewise found a homein next-generation Geared Turbofan™ enginesof Pratt & Whitney: All PurePower® PW1000Gfamily engines will come equipped with brushseals made by MTU. The PW1100G-JM engineto power the Airbus A320neo alone will in-corporate MTU’s seals at four locations. Com-pared with labyrinth seals, MTU’s brush sealshave halved the cooling air losses at all in-stallation positions in the engine. As a result,efficiency is improved while fuel burn and car-bon dioxide emissions are reduced. The seal’striumph is bound to continue, considering theenormous application potential of MTU brushseals.

MTU brush seals as semi-static sealsOne innovation developed by the MTU expertsis the semi-static brush seal. In this field ofapplication, MTU brush seals are used to sealoff non-rotating or stationary parts of amachine in operation by compensating move-ments of several millimeters in a mostly hotenvironment of up to 700 degrees Celcius.This innovation has already proved its worthon several occasions.

MTU brush seals replace labyrinth sealsMTU brush seals are highly efficient and par-ticularly easy to install. This warrants retro-fitting them on entire engine production runs.A prime retrofit example are the RB199 jetengines that have been powering the Tornadomulti-role combat aircraft since 1969. To fur-ther improve the operational safety and per-formance of the engine, MTU in 1995 begandeveloping brush seals tailored to the specificneeds of the Tornado. The new system wentinto production as early as in 1999. MTU brushseals are successfully employed also in theEurofighter’s EJ200 engine. On each engine,six MTU brush seals make sure the high-techfighter achieves its rated performance.

Aviation—well proven in practice

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CompressorsThe use of MTU brush seals in industrial com-pressors drastically reduces leakage losses.That in turn reduces the compressor’s energydemand while increasing its product through-put. On a 590-kW geared air separationcompressor, for instance, about 500 kg/h inproduct loss can be prevented. The compres-sor’s energy consumption is reduced by 60 kW.Additionally, the overall length of the shaftcan be reduced to improve rotor dynamics.

While owing to natural wear by rubbing or ero-sion, labyrinth seals need replacing regularly,the use of brush seals appreciably boosts thelife of the sealing system.

General mechanical engineeringIn mechanical engineering, the use of MTUbrush seals is recommended at all sealingpositions requiring high sealing efficiency andreliability. The function and design of MTUbrush seals permit their use at high tempera-tures, high pressure differentials and highperipheral speeds.

The use of MTU brush seals also often permitsthe seal environment to be simplified; in part,the need for sealing positions may even beobviated, allowing for instance drive shafts tobe shortened.

MTU brush seals permit solutions to be imple-mented that for practical sealing purposes hadso far been impossible to realize.

MTU’s brush seals lend themselves to use ina wide variety of industrial applications andprovide excellent sealing solutions at variousinstallation positions. These benefits are win-ning over more and more machine operators,with MTU’s technology already having chalkedup well over 10.5 million running hours in sta-tionary turbomachinery.

Steam turbinesIn our times of relentlessly rising energy costs,efficient sealing systems are needed morethan ever, considering that they significantlyboost the efficiency of quite a few systems. Forexample, one third of the performance lossesof steam turbines is attributable to leakage.*MTU brush seals considerably reduce theselosses, enhancing efficiency by as much astwo percent. For a 20-MW steam turbine, forinstance, they boost power generation byabout 400 kW, enough to cover the powerrequirement of over 900 private households.

* Source: GE Power Systems

In use far and wide—also inindustrial applications

Industrial gas turbinesFor industrial gas turbines, too, enhancingefficiency has taken on additional significanceas primary energy sources are drying up andthe need to relieve the impact of NOX andCO2 emissions on the environment is becom-ing ever more evident. In this context, improve-ment of sealing systems holds the greatestshort-term potential. MTU here provides tailor-made sealing solutions to reduce operatingcosts and improve efficiency as well as sys-tem reliability—to benefit customers and theenvironment alike.

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Assembly of a 375-MW industrial gas turbine.

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Further development of proven technologyMTU is working relentlessly to further improveits brush seals, the aim being for them to re-place as many conventional seals in aircraftengines and industrial gas turbines as possibleto yet further improve their efficiency. Undernational and international research projects,and in cooperation with prestigious universi-ties, MTU is currently investigating alternativedesigns, as well as potential new bristle mate-rials and fibers. MTU is exploring ways to usebrush seals in more sealing positions andmore applications. The potential is there, con-sidering the vast range of possible applications.MTU’s brush seal team is comprised of spe-cialists with a wealth of experience in techno-

The highest of quality standardsAs Germany’s leading engine manufacturer andan established global player in the industry,MTU sets high standards when it comes to itsproducts, procedures and processes. Thesequality and safety standards also apply to brushseals, which are manufactured using a uniquewire looping and clamping method. Once theproduction process is complete, every individ-ual brush seal undergoes careful testing andinspection using sophisticated methods todetect any non-conformances. The stiffness ofthe brush seals, for example, is measured usingtwo different methods: either on a compres-sion-tension testing machine or on a rotable.MTU has developed an optical measurementtechnique for the inspection of the inner dia-meter of the seal (bristle pack), for which acamera is used to take measurements withutmost precision. This ensures the highestcomponent quality, right down to the smallestdetail.

Always one step ahead—MTU’s brush seal expertise

logical research and development. They bene-fit from having direct access to MTU’s expert-ise in aircraft engine development and pro-duction and to the company’s advanced testcells, and use rig set-ups at MTU for brush sealvalidation. Work is now underway for the plan-ning, design, production, and commissioningof a dedicated test cell for brush seals, whichis slated to be up and running sometime in2015 or 2016 and will be the only one of itskind worldwide.

New materials capable of withstanding evenhigher temperatures are already under devel-opment. These materials will make it possiblefor MTU’s brush seals to be used at high tem-peratures well over 650 degrees Celsius, in thehot gas duct of an aircraft engine, for example.In addition, seals with an even more flexibledesign are being tested that better accommo-dates axial and radial rotor expansion. Theseals’ resistance to wear and tear is thus im-proved.

MTU has achieved a milestone in alternativeproduction concepts for brush seals. Newadditive processes, in which components aremade directly from 3D CAD model data bydepositing molten metal powder layer by layerusing a laser, are particularly cost effectiveand are currently being tested by the brushseal experts for production of the seal housing.The first prototypes have already been manu-factured successfully using these additivetechniques.

Utmost precision: Instead of a tactile inspection method, an optical technique with a camera is used to measurethe inner diameter of the brush seal.

MTU has developed a unique manufacturing methodfor brush seals.

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Measuring of the stiffness of a brush seal.

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MTU Aero Engines AGDachauer Straße 66580995 Munich • GermanyTel. +49 89 1489-0Fax +49 89 1489-5500www.mtu.de

Brush seal teamTel. +49 89 1489-5597Fax +49 89 1489-4540www.mtu.de/brushseals