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CHAPTER73 -ENGINE FUEL ANDCONTROL

TABLE OF CONTENTS

SUBJECT CHAPTER PAGE
73-00-00
Engine Fuel and Control 1
Description and Operation 1

73-10-00

Distribution 1 Fuel Control Pneumatic (P3) Filter Maintenance 1 Fuel Manifold Adapter Removal and Installation 1 Functional Check of Fuel Manifold Assemblies 1 Engine Driven Fuel Pumps 1 Main Fuel Supply Pump 1 FCU Engine Driven Fuel Pump 1 FuelScavenge System 5 73-20-00 Controlling 1 Preparation of Fuel Control Unit for Service -Off Engine 1 Preparation of Fuel Control Unit for Service -On Engine 1 Preparation for Shipping 1 Removal of Fuel Control Unit 1 Installation of Fuel Control Unit 1 Fuel Control Unit Checks and Adjustments 1 73-30-00 Indicating 1 Description and Operation 1 Fuel Flow Indicating System 1 Removalof Fuel Flow Transmitter 1 Installation of Fuel Flow Transmitter 1 Removal of Signal Conditioner 1 Installation of Signal Conditioner 1 Removal of Fuel Pressure Transmitter 1 Installationof Fuel Pressure Transmitter 2 Removal of Fuel Pressure Indicator 2 Installation of Fuel Pressure Indicator 2 Test and Adjustment of Fuel Pressure Transmitter and Gauge 2
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PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)

MAINTENANCEMANUAL

EngineFuelandControl
A. DescriptionandOperation
Theflowdivideranddumpvalveassembly,mountedonbottomofenginegasgeneratorcase, performsseveraloperationsdependingonengineoperatingcondition.Duringenginestartup,the valveallowsmeteredfuelto enterprimaryfuelmanifold.At apresetpressure,thevalveallows meteredfueltoenterprimaryandsecondarynozzles.Whenfuelcontrolunitshutsofffuelsupply duringengineshutdown,fuelinletpressuredecreases,andaninternalspringinvalvemovesa piston withinvalvebodyto blockfuelinletportandallowsfuelwithinprimaryandsecondarymanifoldsto drainoutdumpport. Afuelscavengesystemcollectsthisresidualfuelafterengineshutdownand duringstartup. Theexcessfuelistheninjectedintoaircraftfueltankafterenginestart.
Thedualfuelmanifoldassemblydeliversmeteredfuelfromflowdividerto primaryandsecondaryfuel nozzles.Themanifoldassemblyconsistsoffourteenfuelmanifoldadapters(sevenprimary,six secondaryanda secondaryinletadapter).Allmanifold areinterconnected
adapters bypairsoffuel transfertubes.
For detailedinformationregardingremoval,installation,and checksto variousenginefuel system componentsnot coveredin this manual,referto Pratt& WhitneyEngineMaintenanceManual,No. 3034342.
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PIPERAIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCEMANUAL

A. Distribution
1. Fuel Control Pneumatic(P3)Filter Maintenance
The P3 filter is an in-linetypefilter located in the P3 line just aft of the rear fire seal. Thefilter must
be removed and inspectedfor contamination at 100-hourintervalsand replaced if necessary. A
new filter must be installedevery 1000 hours. Do not attemptto clean filter with solvent.
2. FuelManifoldAdapter Removal and Installation
Beforeremovinganyadaptersfrom engine, markeachadapterusingsuitablemarkerto ensure
returningthe adaptersto their originalpostion on the engine. Numberpositionsclockwise1 to 14,
lookingfromrear of engine,with number 1 position at 12 o'clock location. (For complete removal,
leakagetest andinstallation of manifoldadapters,refer to Pratt & Whitney EngineMaintenance
Manualp/n 3034342.)
3. Functional Check of Fuel Manifold Assemblies
NOTE: Referto Pratt and Whitney Maintenance Manualp/n 3034342,Chapter 73, for Functional Checkof Fuel ManifoldAssemblies.
4. EngineDriven Fuel Pumps
(a) MainFuel Supply Pump (Figure301)
Themainfuel supply pump is mounted to a dualdrive pad which also drives a hydraulic pump.
(1.) With engine at idle rpm, fuel pressure mustbe 32 + 1 psi.
(2.) If adjustment is required,backoffjamnut on pump adjustmentscrew. Rotatescrew clockwiseto increase pressure,or counterclockwise to decrease pressure.Tightenjam nut.
(b) FCUEngineDrivenFuelPump(Figure 302)
Thefuelcontrolunit fuel pump suppliestheFCUwith fuel, and isthe main fuelpressuresource for fuel deliveredintoengine. This pumpis a positivedisplacementgear-typepump, interconnectedwith the FCUandmountedto right side of accessory gearbox.Thepump uses a 74 microninletscreenand a 10 micron outletscreen.The inlet screen is cleanable whilethe outletscreenmustbe replaced. Referto Pratt & WhitneyEngine Maintenance Manual,p/n 3034342,Chapter73 for detailedserviceof fuel pumpandfilters.
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PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL