CHAPTER35 -OXYGEN
TABLE OF CONTENTS
SUBJECT CHAPTER PAGE
35-00-00
Descriptionand Operation 1
Fault Isolation (Oxygen System) 1
35-10-00
Maintenence Practices 1 Oxygen System Servicing 1 Overboard Discharge Indicator 1 Purging 2 Testingfor Leaks 3 OxygenCylinder and Regulator Removal 3 Oxygen Cylinder and Regulator Installation 4 Charging Valve Removal 4 Charging Valve Installation 4 PressureGaugeRemoval 4 PressureGauge Installation 4 Surge Valve Removal 4 Surge Valve Installation 5 Outlet Removal 5 Outlet Installation 5 Oxygen Plumbing Replacement 6 Cleaning 7 Face Mask Cleaning 7
EFFECTIVITY: 040-999
CONTENTSan 10/90
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
Oxygen
A. Description and Operation (refer to Figure 1)
The oxygen system on the PA-42-720 provides diluter/demandoxygen for flight crew and can automatically present constant flow for the passengers. Total oxygen system capacity is 60 cu ft, composed of both a 49 and 11 cu ft storage cylinder. An oxygen pressure gauge mounted on the lower left instrument panel displays to the pilot the storage cylinder pressure (1850 psig-full; 200 psig-empty). Also featured are a regulator valve, external charge valve, outlets, masks, and an ON/OFF control.
Flight crew oxygen masks are diluter/demand type with a quick-donning harness. The masks are stowed in the crew seat headrest and can be donned with one hand. The flight crew need take no further action other than placing the masks on their faces to start the flow of oxygen as the mask supply hose is always charged with oxygen.
Passenger oxygen masks are constant flow type built to TSO-C64. The masks are stowed in four dual mask dropout boxes in the cabin overhead and automatically deployed when the cabin altitude becomes excessive. The passenger need only to grasp a mask when presented, pull it to release a lanyard pin, and place the mask on his face to obtain oxygen.
The mask deployment boxes are pneumatically operated by oxygen supply pressure. When oxygen pressure is applied to the mask box, a piston is actuated which pushes the box lid off its latch and allows the masks to fall into position for passenger use.
Pressure from the oxygen regulator, which is always open, is prevented from reaching the passenger mask deployment boxes by a normally closed solenoid shutoff valve. This shutoff valve is opened on increasing cabin altitude by an absolute pressure switch inside the pressure cabin at an altitude of 12,500 feet. The shutoff valve can also be manually actuated by the flight crew through a lever in the pilot side window moulding to ensure passenger mask deployment in the event of a pressure switch malfunction. In line between the passenger mask deployment boxes and the oxygen shutoff solenoid valve are an altitude compensating regulator and a pressure surge valve. The altitude compensating regulator reduces the oxygen supply pressure to the mask deployment boxes at lower altitudes to reduce the oxygen mask flow. This feature allows a smaller oxygen cylinder to be used and still obtain the required10 minute duration.
A visual oxygen overboard discharge indicator is located on the belly of the nose section, under the baggage compartment area (35-00-00 Figure 1 and 35-10-00 Figure 1). This visual indicator is connected to the oxygen system through a high pressure capillary line. Any system leakage will pressurize this line, and when a line pressure of 60 +20/-20 psig is reached, the green snap-in indicator disc ruptures. The absence of the green disc indicates a system leak despite a normal pressure reading on the oxygen cylinder gauge.
WARNING: EXERCISE UTMOST CARE IN SERVICING, HANDLING, AND INSPECTING THE OXYGEN SYSTEM. A FULLY CHARGED OXYGEN CYLINDER CONTAINS ENOUGH PRESSURE TO CAUSE SERIOUS INJURY TO PERSONNEL AND DAMAGE TO EQUIPMENT. KEEP HANDS, TOOLS, AND WORKING AREA CLEAN. POST NO SMOKING SIGNS. KEEP ALL COMPONENTS OF THE SYSTEM FREE FROM HYDROCARBON-BASED MATERIALS, (OIL, GREASE, FUEL) AND ALL COMBUSTIBLE MATERIALS. KEEP ELECTRICAL EQUIPMENT FROM COMING IN CONTACT WITH CARELESSLY HANDLED TOOLS. AFTER SERVICING OR FUNCTIONALLY TESTING THE OXYGEN SYSTEM, DO NOT SMOKE FOR AT LEAST 10 TO 13 MINUTES. OXYGEN IS LIKELY TO PERMEATE THE CLOTHING AND IS A POSSIBLE COMBUSTION THREAT FOR THIS PERIOD OF TIME. WHEN SERVICING THE OXYGEN SYSTEM OR WHEN PERFORMING ANY FUNCTIONAL TESTS ON THE GROUND, ENSURE THAT THE AIRCRAFT IS ELECTRICALLY GROUNDED USE OXYGEN SPECIFICATION MIL-O- 27210 TYPE I ONLY.
EFFECTIVITY:
040-999
35-00-00 Jan 10/90
PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL
A. DescriptionandOperation(continued)
10.OxygenStorageCylinders
9. Green OverpressureDischargeD
8. External CylinderChargingValve
OxygenSystemInstallation
Figure 1
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