Piper Navajo PA-31 Service Manual page 306

PIPER NAVAJO SERVICE MANUAL
6-3. TROUBLESHOOTING. Malfunctions of the hydraulic system will result in failure of the landing gear
to operate properly. When trouble arises, jack up the airplane (refer to Jacking, Section II) and then
proceed to determine the extent of the trouble. Generally, hydraulic system troubles fall into two types;
troubles involving the hydraulic supplying system and troubles in the landing gear hydraulic system. The
extent of trouble can be found by operating the selector valve on the Power Pack. Table VI-IV, at the back
of this section, lists the troubles which may be encountered and their probable cause, and suggests a remedy
for the trouble involved. A hydraulic system operational check may be conducted beginning with Paragraph
6-5. When the trouble has been recognized, the first step in troubleshooting is isolating the cause. Hydraulic
system troubles are not always traceable to one cause. It is possible that a malfunction may be the result of
more than one difficulty within the system. Starting first with the most obvious and most probable reasons
for the trouble, check each possibility in turn and, by process of elimination, isolate the troubles.
NOTE
If it is found that the Power Pack is at fault and requires
disassembly, it is recommended that it be replaced on an exchange
basis or overhauled by a recommended overhaul shop. If, however,
this cannot be achieved, the Power Pack may be repaired in
accordance with the instructions in this manual.
6-4. FLUSHING HYDRAULIC SYSTEM. When contamination of the hydraulic system is suspected, the
complete system including brakes if incorporated should be drained and flushed to remove the
contaminated fluid. The cause and type of contamination should be determined and corrected. Use the
following steps to perform this operation:
a. Remove the engine cowlings as explained in Section VIII.
b. Disconnect the hydraulic lines at the engine driven pumps.
c. Drain the hydraulic fluid from the Power Pack reservoir.
d. Disconnect the hydraulic lines at the actuating cylinders and drain the fluid from all the
hydraulic lines.
e.
Remove the filter elements and flush out the filter bowls, and install new filter elements. (Refer
to Paragraphs 6-150 to 6-152.)
f.
Flush the hydraulic system with clean hydraulic fluid (MIL-H-5606). Examine several seals and
cylinder bores for damage.
g. When the hydraulic system is completely flushed and there is no more indication of
contamination, reconnect the previously disconnected fittings and replenish the system with clean
hydraulic fluid.
h. Bleed the hydraulic system and check for leaks. (Refer to Paragraph 6-107.)
i. Replace the engine cowlings as explained in Section VIII.
6-5. HYDRAULIC SYSTEM OPERATIONAL CHECKS.
6-6. HYDRAULIC TEST UNIT (PIPER NO. 753 080).
6-7. INTRODUCTION (PIPER TEST UNIT). This test unit would offer invaluable assistance in checking
hydraulic systems, hydraulic Power Pack and related components in the PA-31. Examples are: gear cycling
operation, Power Pack operating pressure, main relief valve cracking pressure, thermal relief vent valve
cracking pressure, landing gear detent release pressure, etc.
This 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 mounted on casters.
Reissued: 10/12/79
HYDRAULIC SYSTEM
2A24