Fuelis delivered to each engine from that wing's main fuel tank through a submerged fuel pump, main feed line, fuelshutoff valve, fuelfilter, the main engine drivenfuelsupplypump, and fuel control unit containinganotherenginedrivenpump. The submerged fuel pump, locatedin the main inboard fuel cellof each wing, functions as a primer pump,an emergency backupto the engine drivenpump,and transfersand crossfeeds fuel.A fuel filter, mountedon the left hand side (facingforward) of each firewall,consistsofa filter assemblyand a pressureswitchwhichdetermineswhenthefilteris partially cloggedand will soonbypass.Thisis a required impendingbypasswarning.The main engine driven fuel supply pumpis an engine driven pump mounted on the accessorysection of the engine on a dual drivepad which also drives a hydraulic pump.
A jet type scavenge pump, incorporated ineach fuel system,controls venting of fuel into the atmosphereduringan engine shutdown.A jet pumpis activated wheneverfuel pressure existsand the condition leveris positioned in idle shutoff. During start,fuel is returnedto the tank by the jet pump topurge any vapor fromthe fuel controlunit fuel pump.
Fueltankdrains are provided at fuel cell or tank lowpoints. Fuel filters,mountedon the forwardside of each firewall, also contain drain valves. Quickdefueldrains,locatedat W.S. 112.90on each wing, areprovidedto rapidly drain the left and right fuel system withsiphon pumps. The siphon pumps attach to the drain with an adapterhose.
EFFECTIVITY:
28-00-00
Jan 10/90

PIPER AIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A. Description and Operation (continued)
Fuel Manifold

Fuel
Crossfeed Valve
SenderUnit
Inbd Fuel Cell
NOTE: 1. Engine driven boost pump operates any time engine gas generator (N1) is turning and suppliesfuel to the fuel control unit.
2. Submergedfuelpumpis used to operate the jet transfer pump, an emergency backup and for crossfeed operation.
FuelSystem Installation
Figure 1

EFFECTIVITY: 040-999

Jan 10/90 28-00-00
PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A. Storage
1.  DescriptionandOperation
(a) FuelVentSystem(referto 28-10-00,Figure1)
Themainfuelventlineextendsfromtheupperportionofthenacellefueltank,downthrough
thewing,outtothetiptank. Afloatvalveisinstalledontheendoftheventlineinthenacelle
tanktopreventfuelfromescapingthroughtheventsystem.ThetwoNACAnon-icingtypevent
assemblies,installedalongtheventline,arenon-siphoningandincorporateflamearrestors.
Thetiptankhasa ventwellassemblycontainingafloatvalve,tiprelieftube,andthemainvent
lineconnectedtoit. Thisventwellissealedfromthefuelstorageareainthetiptank,except
forthefloatvalveandrelieftube,whichextendsto theforwardtopportionofthetank.Thefloat
valveinstalledinthetiptankventwellpreventsfuelfromescapingthroughtheventline.The
relieftubeallowsthefuelsystemtoventduringclimbto altitudewithfullfuelaboardandalso
allowsfueltoescapewhentanksarefullandfuelexpansionoccursdueto heat(suchas
aircraftbeingparkedon rampandexposedto highramptemperatures).
Fuel VentSystem Figure1

EFFECTIVITY: 040-999
PAGE
28-10-00
Jan 10/901

PIPER AIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCEMANUAL

A. Storage (continued)
2. Fault Isolation-Fuel System
CHART 1
FAULTISOLATION(FUELSYSTEM)

Fault  Cause  Remedy 
Unidentifiedleak.  Fuel lines damagedor improperlyinstalled.  Locateand repair. 
O-ringsimproperlyinstalled.  Locateand repair or tighten. 
Tank leak.  Repair leak. 
Fuel leaking from NACA vents.  Full fuel tanksand fuel expansiondue to exposure  Defuelaircraft or park in a shaded or cooler location. 
to heat. 
Float valve in nacelle tank,  Defuel aircraft and 
aft inboard tank or float  inspect valves for 
valvein tip tank sticking  condition. 
open or leaking. 
Fuel leaking from filler caps.  Fillercaps improperly adjustedand not  Adjust filler caps to obtain tight seal. 
sealing properly. 

EFFECTIVITY: 
PAGE  2 
Jan 10/9028-10-00 

PIPERAIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL

A. Storage (continued)
3. Handling and Storage of Fuel Cells
(a)To prevent needless damageto fuel cells, exercisethe following precautionswhenhandling cells:
(1.) Fold or collapse cells for storage, transport,or installation intoairframecavities. (2.) Use protective coversover fitting seal to protect seal surface from contact with cavities
duringremovalorinstallation. (3.) Protect cells from tools, hot lights, etc. (4.) Avoid stepping on folds or creases. (5.) Do not carry cells by fittings. (6.) Maintain original cell contours or folds when refolding. (7.) When repairing, maintainnaturalcontoursof cells, place on well-lit and well-ventilated
　
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