AssemblyofTimeDelayCheckValve 26
InstallationandAdjustmentof InboardGearDoorsSwitch
26

PowerPackBenchTestAdjustment 26
BleedingtheHydraulicSystem 27
RemovalandInstallationof Hydraulic Lines 27
RemovalandInstallationofHydraulicFilters 27
Replacementof FilterElements
27

HydraulicPumpOperationalCheck 28
ProcedureafterHydraulicPump Failure 28
Removalof Hydraulic Pump 29
Disassemblyof Hydraulic Pump 29
Assemblyof Hydraulic Pump 31
Cleaning,Inspection,Repairof Hydraulic Pump 31
Installationof Hydraulic Pump
33

PrimingHydraulicPump 33
Hand Pump (Emergency) 33
Disassemblyof Hand Pump 33
Assemblyof HandPump 35
Cleaning,Inspection,andRepairof HandPump 35
Installationof Hand Pump 35
BleedingHandPump 35
HandPumpTest 36
EFFECTIVITY:
040-999

Jan 10/9
0 CONTENTS
PIPERAIRCRAFT
PA-42-720 (Advanced Trainer)

MAINTENANCEMANUAL

HydraulicPower
A. General
The hydraulic power pack provides the hydraulic power required to operate the landing gear. The power pack is located in the right side of the fuselage nose section at Bulkhead Station 57.00 in front of the forward pressure bulkhead. The power pack is operated by a flexible shaft with a selector lever fashionedlike a wheel mounted on the instrument panel left of the engine control quadrant. The power pack contains the system reservoir and assorted valves which control the system operation. The power pack works in conjunction with the engine driven pumps, solenoid valves, and hydraulic cylindersto perform the desired operation sequenceselectedwith the control lever in the cockpit.
WARNING: TO ENSURE LANDING GEAR DOES NOT MOVE TO THE UP (RETRACTED) POSITION WHILE AIRCRAFT IS ON GROUND, THE FOLLOWING CHECK MUST BE PERFORMED PRIOR TO APPLYING HYDRAULIC PRESSURE TO SYSTEM. ATTEMPT TO MOVE SELECTOR LEVER TO UP POSITION. IF LEVER CAN BE MOVED TO UP POSITION, AN IMPROPERLY ADJUSTED SELECTOR MECHANISM EXISTS OR ANTI-RETRACTION SYSTEM IS INOPERATIVE. BE SURE TO SELECT GEAR DOWN PRIOR TO APPLYING SYSTEM PRESSURE OR STARTING ENGINE.
Duringan electrical failure, the door solenoid valve in the power pack moves (spring pressure) to OPEN door position and remains in that position. Doors will not open until selector lever is moved to gear down position and gear extension cycleis started.
WARNING: PRIOR TO ANY CHECK OF HYDRAULIC SYSTEM, PLACE AIRPLANE ON JACKS (REFER TO 7-10-00).
B. HydraulicSystem Failure
Emergencyuse of hand pump to extend gears indicates enginedriven pumps are operating without sufficientfluid. This condition causesadditionalwear on engine driven pumps. Remove and check filter elements evenif pump failure is not apparent.
1.
Removefilter elements. Check for metal particles.

2.
If no metal particles exist, replace filter element and replenish fluid.

3.
If metal particles are evident in either filter, proceed as follows:

(a) Inspect, replace, or repair both hydraulic pumps.
(b)Prime pumps and do not connect pumpsto rest of hydraulic system until system is flushed.
(c) Proceedtoflush system.
For Hydraulic System Failure fault isolations, place airplane on jacks (refer to 7-10-00) and perform a
system operational check.
NOTE: If hydraulic system is serviced properly, hydraulic components used in this airplane manufacturedby the Wieble Tool Company do not require overhaul until 10,000 hours of service or 10 years, whichever comes first. If any problems arise during inspection, corrective action must be taken regardless of time in service
EFFECTIVITY:

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

B. HydraulicSystem Failure (continued)
CHART 1
FAULTISOLATION(HYDRAULICSYSTEM)

Fault  Cause  Remedy 
Landing Gear system  Selector lever disconnected.  Connect lever. 
fails to operate. 
Select lever out of  Adjust lever. 
adjustment. 

CAUTION: PULL CIRCUIT BREAKERSOF THE ICE PROTECTION CIRCUITAND THE STALL WARNHEAT CIRCUIT BEFORE DEPRESSINGTHE "q" SENSOR OVERRIDESWITCH TO AVOID DAMAGING THE HEATINGELEMENTS.
NOTE: A solenoidoperated lock, located behind the instrumentpanelas part of the selector assembly, preventsleverfrom being inadvertently movedto the up position while the airplane is on the ground or in flight below 100 ± 4 KIAS. To cycle the gear with the airplane on jacks, depress the q sensor override switch unlocking thegear selector handle. The gear can now be operated as required.
Hydraulicfluid reservoir Fillthe power pack with belowoperating level. hydraulicfluid.
Leak or obstruction in Checkthe system with hydraulic lines. hydraulic test unit or hand pump.
　
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