Inlet & Exhaust ValvesInlet & Exhaust Valves&&

Actuating MechanismActuating Mechanism

OverviewOverview

Inlet and exhaust valves play an important role in the gas Inlet and exhaust valves play an important role in the gas exchange process of 2-stroke and 4-stroke internal combustion exchange process of 2-stroke and 4-stroke internal combustion engine.engine.

Inlet and exhaust valves of medium speed engines are subject Inlet and exhaust valves of medium speed engines are subject to severe operating conditions.to severe operating conditions.

Inlet valves do not generally present any serious problems as Inlet valves do not generally present any serious problems as they are cooled by incoming charge air.they are cooled by incoming charge air.

However, exhaust valves are subjected to higher temp and their However, exhaust valves are subjected to higher temp and their life is limited by deposits and high temp corrosion from sodium & life is limited by deposits and high temp corrosion from sodium & vanadium compounds.vanadium compounds.

It is very important to keep valve seat temp below 450 It is very important to keep valve seat temp below 450 ooC.C.

ObjectivesObjectives

Function of cylinder head valves (inlet & exh)Function of cylinder head valves (inlet & exh)

Working condition of cylinder head valvesWorking condition of cylinder head valves

Design featuresDesign features

Construction featuresConstruction features

Problems of exhaust valveProblems of exhaust valve

Factors influencing exhaust valve lifeFactors influencing exhaust valve life

Valve actuating mechanismValve actuating mechanism

Valve maintenanceValve maintenance

Why 4-stroke Engine has Multiple Valves ?Why 4-stroke Engine has Multiple Valves ?

Multiple valves are employed to give larger valve areas Multiple valves are employed to give larger valve areas

than single valve than single valve

Larger valve areas allow larger gas flow and better Larger valve areas allow larger gas flow and better

flow pattern flow pattern

Improve performance of gas exchange processImprove performance of gas exchange process

Less back pressure on piston during exh stroke reduces Less back pressure on piston during exh stroke reduces

loss of useful work of the crank shaft loss of useful work of the crank shaft

Heat dissipation problem with single valve (exh)Heat dissipation problem with single valve (exh)

Mechanically Operated Exhaust Valve

SULZER RTA

EXHAUST

VALVE

MAN B&W

EXH VALVE

Working Condition of Exh V/VWorking Condition of Exh V/V

Passing large volume of burnt gas in short timePassing large volume of burnt gas in short time

Working under high temp conditionWorking under high temp condition

Due to repeated heating and cooling causing thermal Due to repeated heating and cooling causing thermal

stress and possibility of hardening stress and possibility of hardening

Hot and cold corrosion due to burning HFO of poor qualityHot and cold corrosion due to burning HFO of poor quality

Valve bouncing and vibrationValve bouncing and vibration

Valve tampering and wearValve tampering and wear

Valve StressValve Stress

Mechanical stressMechanical stress

- at flame face centre in radial- at flame face centre in radial direction direction - at blend radius circumferentially- at blend radius circumferentially

Thermal stressThermal stress

- at valve seat area- at valve seat area

Combined stressCombined stress

- at valve neck- at valve neck

Effect of StressesEffect of Stresses

Valve leaking and burningValve leaking and burning

Dishing-in of valve headDishing-in of valve head

Crack at centre of flame faceCrack at centre of flame face

Cracks at the seatCracks at the seat

Valve breakage at neck causing heavy damageValve breakage at neck causing heavy damage

Damaged

Exh Valve

Spindle

Exhaust valvesExhaust valves

High Temp UndesirableHigh Temp Undesirable

Reduces volumetric efficiencyReduces volumetric efficiency

Excessive deposits take placeExcessive deposits take place

Causes valve burning & valve failureCauses valve burning & valve failure

Avoid large valvesAvoid large valves

Difficult to accommodateDifficult to accommodate

Destroy compactness of combustion chamber Destroy compactness of combustion chamber

Small inlet valves can induce turbulenceSmall inlet valves can induce turbulence

Larger the valve, higher will be the temperatureLarger the valve, higher will be the temperature

Exhaust valvesExhaust valves

Valves – design featureValves – design feature

Valve DiameterValve Diameter

Usually exh v/v diameter is smaller than inlet v/vUsually exh v/v diameter is smaller than inlet v/v

as it opens against higher pressureas it opens against higher pressure

assists in keeping coolassists in keeping cool

better performancebetter performance

Exhaust Valve – design featureExhaust Valve – design feature

MaterialMaterial

Inserted v/v seatInserted v/v seat

CoolingCooling

– v/v spindlev/v spindle

– v/v guidev/v guide

– v/v seatv/v seat

– v/v housingv/v housing

MaterialMaterial

Strength at high tempStrength at high temp

Good corrosion & erosion resistanceGood corrosion & erosion resistance

High thermal conductivityHigh thermal conductivity

MachineableMachineable

Nimonic ( 80% nickel, 20% chrome) valves are used in Nimonic ( 80% nickel, 20% chrome) valves are used in highly rated engines with … highly rated engines with …

stellite seats (50% cobalt, 30% chrome,20% tungsten)stellite seats (50% cobalt, 30% chrome,20% tungsten)

Exhaust Valve ProblemsExhaust Valve Problems

V/V bouncingV/V bouncing

Seat tampering & wearSeat tampering & wear

Hot CorrosionHot Corrosion

Cold corrosionCold corrosion

Valve BurningValve Burning

Exhaust Valve ProblemsExhaust Valve Problems Due to …Due to …

Fuel quality (ignition)Fuel quality (ignition)

Impurities in fuel oilImpurities in fuel oil

- catalytic fines - catalytic fines

- S, V, Na compound - S, V, Na compound

CombustionCombustion

Leaky valve due to seat distortionLeaky valve due to seat distortion

Cylinder power in excess of design ratingCylinder power in excess of design rating

Factors Accelerate Valve FailureFactors Accelerate Valve Failure

Mechanical dentsMechanical dents

Spallation of salt layerSpallation of salt layer

Sealing face corrosionSealing face corrosion

High Temperature Corrosion Damage of Exhaust Valve

Low Temp CorrosionLow Temp Corrosion

Due to the presence of Due to the presence of SulphurSulphur in Fuel oil in Fuel oil

Counter MeasuresCounter Measures

Correct CW outlet tempCorrect CW outlet temp

Coating in gas ductCoating in gas duct

Thicker gas duct wallThicker gas duct wall

Cooling water by-passCooling water by-pass

High Temp CorrosionHigh Temp Corrosion

Due to presence of ….Due to presence of ….

Sodium Sodium

VanadiumVanadium

Which produces corrosive flux at high temp. Which produces corrosive flux at high temp.

Exhaust Valve

High Temp Corrosion

High Temp CorrosionHigh Temp Corrosion

CountermeasuresCountermeasures

limit fuel oil vanadium concentrationlimit fuel oil vanadium concentration

minimise fuel oil and charge air sodium concentrationminimise fuel oil and charge air sodium concentration

avoid excessive exhaust gas temp.avoid excessive exhaust gas temp.

use of Nimonic v/v spindleuse of Nimonic v/v spindle

v/v stem coated with Cermet using HVOF processv/v stem coated with Cermet using HVOF process

v/v lid facing combustion chamber is coated with Inconel 625 v/v lid facing combustion chamber is coated with Inconel 625

Counter MeasuresCounter Measures

DesignDesign

MaintenanceMaintenance

OperationOperation

DesignDesign

Heat shieldHeat shield

Cooling Cooling

Use of seat ringUse of seat ring

Surface treatment of seat and spindleSurface treatment of seat and spindle

Limiting v/v temp by efficient bore cooling arrangementLimiting v/v temp by efficient bore cooling arrangement

Valve rotating deviceValve rotating device

Minimising v/v bouncing by hydraulic operationMinimising v/v bouncing by hydraulic operation

Heat and corrosion resistance materialHeat and corrosion resistance material

Efficient scavengingEfficient scavenging

Optimising v/v timingOptimising v/v timing

Exhaust Valve With W-seat

W-seat

W-seat enables

to achieve

lower temp

in the v/v seat

and increase

v/v life & TBO

MaintenanceMaintenance

Areas requires special attention:Areas requires special attention:

Valve stemValve stem

Valve seatValve seat

Guide bushGuide bush

Valve cageValve cage

Coil spring / air springCoil spring / air spring

Rotocap / vanesRotocap / vanes

Actuating mechanismActuating mechanism

MaintenanceMaintenanceTappet ClearanceTappet Clearance

Necessary to allow for thermal expansion of valve spindle at Necessary to allow for thermal expansion of valve spindle at

working temperature and ensures positive closing of valve.working temperature and ensures positive closing of valve.

Clearance should be set at cold condition of engine.Clearance should be set at cold condition of engine.

Excessive clearanceExcessive clearance will cause the valve to open late and will cause the valve to open late and close early with reduction of max lift, causing hammering and close early with reduction of max lift, causing hammering and damage.damage.

Insufficient clearanceInsufficient clearance will cause the valve to open early and will cause the valve to open early and close late with increased max lift. close late with increased max lift.

It may prevent valve from closing, causing loss of power and It may prevent valve from closing, causing loss of power and v/v burning.v/v burning.

Shrouding of valve

• Shrouding occurs due to excessive manual grinding

• If v/v is harder than seat, shroud builds up in the seat

• If seat is harder than the v/v, shrouding occurs in v/v

• Normally shroud builds up in both valve & seat

• Even small amount of shrouding can seriously affect the air

and gas flow across a valve

Different angle of

Valve seat and

Valve head

Improves

Valve Life

OperationOperation

Fuel QualityFuel Quality

Engine LoadEngine Load

Scavenging Scavenging

TurbochargingTurbocharging

Engine Power BalancingEngine Power Balancing

Engine Cooling Engine Cooling

Valve Actuating MechanismValve Actuating Mechanism

MechanicalMechanical

– rocker arms & push rodrocker arms & push rod

– double valves may be actuated from a single pushdouble valves may be actuated from a single push rod in several ways… rod in several ways…

forked rockers (master & slave)forked rockers (master & slave)

twin rockers and a yoke actuating two valvestwin rockers and a yoke actuating two valves

– disadvantage of increased wear on spindle & guide disadvantage of increased wear on spindle & guide

Valve Actuating MechanismValve Actuating Mechanism

HydraulicHydraulic

– Common in X-head engines but used in 4-stroke engines alsoCommon in X-head engines but used in 4-stroke engines also

– Replaces push rod and mechanical coiled springReplaces push rod and mechanical coiled spring

– No transverse thrust results in less guide wearNo transverse thrust results in less guide wear

– Controlled closing of valve reduces tampering and valve-seat wearControlled closing of valve reduces tampering and valve-seat wear

– Valve rotation by vanes ensures well balanced thermal & mechanical Valve rotation by vanes ensures well balanced thermal & mechanical

stress and uniform valve seating stress and uniform valve seating

– Reliable operationReliable operation

– Reduces maintenance cost with increased TBOReduces maintenance cost with increased TBO

SULZER RTA

EXHAUST

VALVE

Valve RotationValve Rotation

Prolongs valve lifeProlongs valve life

Minimises risk of local overheating and valve distortionMinimises risk of local overheating and valve distortion

Prevents deposits and built up of vanadium on the valve seatPrevents deposits and built up of vanadium on the valve seat

Prevents hammering on the same spotPrevents hammering on the same spot

Valve rotation is achieved by:Valve rotation is achieved by:

Rotocap UnitRotocap Unit

Valve Stem SpinnerValve Stem Spinner

Rotocap Valve Rotator

High Exhaust temperatureHigh Exhaust temperature

High CW temperatureHigh CW temperature

Hissing NoiseHissing Noise

Low Pcom and PmaxLow Pcom and Pmax

Smoky exhaustSmoky exhaust

T/C surging in extreme caseT/C surging in extreme case

Indication of Leaky ValveIndication of Leaky Valve