(h)
Placelandinggear selectorhandle in full up position.

(i)  
Close bypass valve very slowlyuntil handle tripsback to neutral. Ensuregauge pressure readingscomplywith those in 29-00-00, Chart2 when handleis tripped to neutral. Allowtime for time delayvalveto open.

(j)
Adjust handlerelease, if required.

(k)
Ensurelandinggearselectorhandle is in down neutralpositionandlanding gear is down and locked.

(I)  
Disconnecttest unit and removeairplane from jacks.

9.  CheckingPriorityValve.
(a)
Connecthydraulictest unit and place airplaneon jacks (refer to 7-10-00).

(b)
Runlandinggearthrough two completecycles.

(c)
Withgear down and locked and test unit operational, turn master switchoff and move gear handle to down position causingdoors to open and handle to return to neutral position. Keep switchoff, leaving doors open, facilitatingcompletionof check.

(d)
Openhydraulic test unit bypass valve.

NOTE:  As priority valveopens,nose gear down lock starts releasing. Read pressure gauge at that point.

(e)
Place landinggear selector handle fully up. Close bypass valvevery slowly, observepressure gauge of test unit, and note at which pressurereadingpriorityvalve opens. Priorityvalve must open at 600 -650 psi, as indicatedin 29-00-00, Chart 2.

(f)  
Makerequired priority valveadjustments.

(g)
Ensure landing gear selector handle is in down, neutral position, and landing gear is down and locked.

(h)
Disconnecttest unit and removeairplanefrom jacks.

EFFECTIVITY: 040-999

Jan 10/90 29-1 0-00
PIPER AIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCE MANUAL

A. Main (continued)
10. Checkingmain relief valve.
(a)
Connect test unit.

(b)
Open test unit bypass valve.

(c)
Holdlandinggear selector handlein full down position.

(d)
Closebypass valve slowlyand note pressure build-up and point where pressurestabilizeson testunit gauge. Stabilization indicatesrelief valve settingas listed in 29-00-00, Chart2.

(e)
Adjustment of power pack main relief valve is completed withpower pack installed in airplane. Removetop cover and drain fluid to gain access to adjusting screw.

(f)
Disconnect hydraulic test unit.

11. Checkhandpumpreliefvalve.
(a)
Placelandinggear selector handle, locatedright of pilot seat under floor, in full down position. Withmaster switch off, extend handleandoperateemergency hand pumpto open landinggear doors.

(b)
Disconnectdooropen line (upper fitting) from main gear door cylinder. Connecthydraulictest unit pressure hose to door open line. Cap actuator fitting.

(c)
Close bypass valve on hydraulic test unit.

(d)
Operateemergency hand pump and note at which reading on hydraulic test unit pressure gaugehand pump relief valve open. Pressure must be between 2025 -2100 psi (indicated in 29-00-00,Chart2).

(e)
Adjustment of power pack hand pump relief valve is completed with power pack installed in airplane. Remove cover and drain fluid to gain accessto adjusting screw.

(f)
Open bypass valve on test unit to release pressure. Disconnect test unit pressure hose from dooropen line. Remove cap from actuator fitting and reconnect dooropen line to main door actuator.

(g)
Replenishrequiredhydraulicreservoirfluid.

12. Checkingfor SuctionAir Leakage.
(a)
Remove engine cowling for access.

(b)
Disconnecthydraulic pump suction hose from pump. Connect test unit suction hose to airplane suction hose with suitable fitting.

(c)
Disconnect hydraulic pump pressure hose from pump. Connect test unit pressure hose to airplanepressurehose with suitablefitting.

(d)
Connecttest unit electrical cable to electrical power source.

(e)
Jackairplaneand cycle landing gear through five complete cycles.

(f)
Checktest unit reservoir for air bubbles indicating leakage in suction line, hose, or fittings. Replacedefectiveparts.

NOTE: If replacement parts eliminate visible air in test unit reservoir,but air still enters hydraulic system, engine driven pump may contain suction leak.

(g)
Ensure landing gear selector handle is in down, neutral position, and landing gear is down and locked.

(h)
Remove airplane from jacks. Disconnect test unit.

EFFECTIVITY:

040-999
29-10-00
PAGE7
0 Jan 10/90
PIPER AIRCRAFT

PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL
A. Main (continued)
13. DisconnectingTest Unit.
(a)
Ensure landing gear selector is in the down, neutral position, and the landing gear is down and locked.
　
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