Piper COMANCHE PA-24-180 Service Manual page 62

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 airplane, do not attempt using it for filling. Use the
storage cylinder that has a pressure higher than the airplane'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 airplane'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 airplane'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 1800
pounds, 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 600
psi, then return for filling.
e. When the pressure gauge on the recharge unit or in the airplane reaches 1800 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 cylinder pressure against chart after cylinder temperature
stabilizes.
2-59. Inspection and Overhaul Time Limits. It is recommended that inspection and overhaul be conducted
by an FAA Approved Station; or, the manufacturer, Scott Aviation. The following checks and chart gives
recommended inspection and overhaul times for the various parts of the oxygen system.
a. The oxygen cylinder can be identified by the ICC or DOT identification stamped on the cylinder. The
standard weight cylinder (ICC or DOT 3AA 1800) must be hydrostatic tested at the end of each 5 year
Iperiod. The month and year of the last test is stamped on the cylinder beneath the ICC or DOT identification.
b. The outlets should be checked for leakage both in the non-use condition, and for leakage around an
inserted connector.
c. The high pressure gauge may be checked for accuracy by comparing its indicated pressure with that of
a gauge of known accuracy.
d. Inspection of the regulator may be effected by introducing into an outlet a mask connector to which is
attached a 100 psi gauge. With one other outlet flowing through a plugged in mask, the indicated regulator
output pressure shall be not less than 45 psig at sea level with 200 psig supply cylinder pressure. It should be
noted that the permissible leakage through the 1/16 diameter vent hole in the side of the upper regulator
housing is 10 cc/ min. maximum, when the regulator is turned on. There shall be no external leakage
anywhere on the regulator when it is turned off. All fittings shall be leak free.
HANDLING AND SERVICING
Revised: 8/1598
PIPER COMANCHE SERVICE MANUAL
1C14