(b)
Disconnect hydraulic lines at engine driven pumps.

(c)
Drain hydraulic fluid from power pack reservoir using suction, fill, and drain fitting on bracket located at lower aft comer of nose access panel opening behind hydraulics components cover.

(d)
Disconnect hydraulic lines at actuating cylinders and drain fluid from all hydraulic lines.

(e)
Removeand replace filter elements located on engine firewall. Flush out filter bowls.

(f)
Flushhydraulic system with clean hydraulic fluid (MIL-H-5606). Examine several seals and cylinder bores for damage.

(g)
When hydraulic system is completely flushed and no indication of contamination exists, reconnectpreviously disconnected fittings and replenish system with clean hydraulic fluid.

(h)
Bleed hydraulic system (described in Bleeding the Hydraulic System) and check for leaks.

(i)
Replace engine cowlings (refer to 71-10-00).

2.  Hydraulic System Operational Checks Using Piper Test Unit.
The test unit (P/N 753 080) can be used to check hydraulic systems, the hydraulic power pack
landing gear cycling operation, power pack operating pressure checks and adjustments etc, all
performed without operating engines.
The unit consists of an electric, motor driven hydraulic pump,bypass valve, fluid reservoir, filter, pressure gauge, hoses, and adapter fittings housed in a metal cabinet and mounted on casters.
3.  Hydraulic Test Unit (Optional).
Multi-purposehydraulictest units can also be used to provide the same functions as the Piper unit. Thetest unit must be capable of duplicatingand monitoring the operating pressuresand the flow rate given in 29-00-00, Chart 2.
NOTE: The following procedures are written for Piper or optional hydraulic test units. Use proper operatingmanual for specific unit being used.
4.  Connecting Test Unit.
(a)
Removeaccess panel on right side of nose section. Open access in hydraulics components cover.

(b)
If system requires fillingonly, remove protectivecap from suction; fill and drain valve mounted onbracket on lower aft comer of nose access panel opening. Connectpressurehose from test unit. Open valve on suction port, place control lever in up position, and proceed to fill system perinstructionswith test unit. Observe fill lines so not to overfill reservoir.

(c)  
If system is to be operated during various ground checks,overhaul, or inspection of components,remove protective caps from suction and pressure ports, connect test unit pressure hose to pressureport and test unit suction hose to suction port. Open valve on suction port and operate test unit according to supplied instructions.

EFFECTIVITY:

29-10-00PAGE
Jan 10/90

PIPER AIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A Main (continued) Pump-Engine Driven
Filter
Pressure Port Valve SuctionPort
Toggle Valve
Power Pack Assembly
A. MainReliefValve
L

B. Engine Pump Check Valve
C. Priority Valve
D. Door Solenoid Valve
E. Vent Valve
Cylinder
ValveF. Time DelayCheck Valve

G. Time Delay Valve
H. Hand Pump Relief Valve
J. Selector Valve Detent
K. Selector Valve Spring Return Actuator, Nose Gear
Shuttle Valve Shuttle Valve Nose Gear Main Gear

ShuttleValve MainGear

Un-Lock Actuator Un-Lock
Actuator
Actuator Main Gear Cylinder Assembly
Cylinder Assembly

Actuator Main Actuator Main Gear Door Gear Door
Shuttle Valve, Main Gear Bulkhead Tee & Cap (Test Port)
Hydraulic System -Schematic Diagram
Figure 1.

EFFECTIVITY:

040-999 Jan 10GE
2 9-10-00
Jan 10/90
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL

A. Main (continued)
GroundGearWarning Horn
Horn Relay

Bus Limit Switch
Up

MainGear Main Gear Limit Switch (Right) Limit Switch (Left)
Down Down
NOTES
1.
Gearisshowndownand locked,doorsclosed andselectorhandle in downneutral,power on.

2.
Poweron -doors closed Poweroff -doorsopen

Schematic of Power Pack Electronics System
Figure 2.

EFFECTIVITY:
040-999
29-10-00
Jan 10/90

PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A. Main (continued)
2.
5. Gear Actuating

7. Hydraulic
9.

Pump,Right
Hydraulic System Installation Figure3.
5. CyclingLanding Gear.
(a) Connecthydraulictest unit (described in Connecting Test Unit) and jack airplane (referto 7-10-
00).
(b)
Set hydraulic testunit bypass valve open.
　
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