Filling Oxygen Cylinder; Air Conditioning System - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
2-77. FIL LING OXYGEN CYLINDER. The filler valve or valves for the oxygen system are accessible
through doors located on the lower left side of the nose section below the access panel for the front
cylinder and on the right side of the fuselage tail section aft of the rear baggage compartment.
a.
To fill the oxygen cylinder or cylinders, open the access door, remove the cap from the filler
valve, and attach the filler hose from the oxygen recharge unit to filler valve. Ascertain that all fittings are
free from oil. grease, dirt, etc.
NOTE
If the airplane's oxygen cylinder pressure is below 50 psi, the
system should be purged as described in Section XIV.
b. To obtain the correct filling pressure for the oxygen system at various ambient temperatures, a table is
included for your convenience. The pressures given are not exact, but sufficiently accurate for practical
purposes of working pressures between 1800 and 2400 psig cylinders. The cylinder should be allowed to cool to
a stabilized temperature after filling before checking against the figures given in Table II-VII.
c. When using a recharge unit consisting of one supply cylinder, slowly open the valve of the supply
unit and allow the oxygen to transfer.
d. When using a recharge unit consisting of two or more supply cylinders (cascade storage system).
it is recommended that the following procedure be used:
1. Before opening any valves, check the pressure remaining in the airplane's oxygen cylinder. If
it is still partly charged, note the pressure indicated on the cylinder gauge. Then open and close each valve
on the cascade storage system and determine which cylinder has the lowest pressure. When found if this
cylinder has a pressure lower than the oxygen cylinder in the aircraft, do not attempt using it for filling; use
the storage cylinder that has a pressure higher than the aircraft's cylinder but lower than the others.
2. Open the valve on only the one storage cylinder with the lowest pressure. When the pressure
indicated on the aircraft's oxygen gauge and charging gauge has become equal, close the valve of the storage
cylinder: then go to the storage cylinder with the next higher pressure and repeat the procedure.
3. If after using the last storage cylinder the aircraft's oxygen system is still not fully charged. a
full storage cylinder should be put in place of a cylinder with the lowest pressure and used in the same
manner.
4.
A good deal of oxygen will remain in the large cylinders used in the cascade system after
filling only one of the cylinders but such remaining oxygen will be at a pressure something less than the
1850 psi which is not sufficient pressure to completely refill another aircraft cylinder, although it will refill
several smaller cylinders.
5. It is not economical even on a three or four cylinder cascade system to begin recharging
with oxygen at less than 300 psi pressure in the 300 cubic foot bank of cylinders. So use 300 cubic foot
cylinders down to approximately 300 psi; then return for refilling. In two cylinder systems use to
approximately 100 psi; then return for filling.
e. When the pressure gauge on the recharge unit or in the aircraft reaches 1800 to 1850 psi, close
the pressure regulator valve on the recharge unit. Disconnect the filler hose from the filler valve; replace the
protective cap on the filler valve and close the access cover. Check the cylinder pressure according to Table
II-VII after the cylinder temperature stabilizes.
2-78. AIR CONDITIONING SYSTEM. Servicing this system consists of periodically checking the Freon
refrigerant level by operating the system and observing the sight gauge window in the upper end of the
receiver-dryer. This is done by gaining access to the receiver-dehydrator sight gauge located in the right
wheel well. The inboard gear door must be opened to get to the unit. Refer to Section VI of this manual for
details on opening the gear doors. Check for signs of foam or bubbles in the sight gauge. If these conditions
are observed, refer to Section XIV for further instructions on the air conditioner. If the system must be
recharged, it is advisable to check the oil in the compressor at this time before recharging the system, and
replace the receiver-dryer and any O-rings in connections which were opened.
Reissued: 9/23/80
HANDLING AND SERVICING
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