TM 1-411, Airplane Hydraulic Systems and Miscellaneous Equipment: 8 - Oxygen Equipment

SECTION VIII: OXYGEN EQUIPMENT

47. General.-Oxygen equipment in aircraft is used to supply flight personnel with the necessary oxygen to make up the deficiency in the atmosphere at high altitudes. In all but exceptional cases, individual instruments for the regulation of supply are provided for each person participating in the flight and the systems have a flexibility in that two users may be supplied from a common source or, in the case of extended flights at high altitudes, two cylinders may be used to supply one person.

FIGURE 51.-Oxygen regulator.

48. Description.-Although the quantity of equipment varies with the particular airplane, the basic units in aircraft installations include regulator, supply cylinder, high pressure tubing and manifold connections, low pressure tubing, and mouthpiece or mask.

a. Regulator.-The current type oxygen regulator is used to reduce the high cylinder pressure to a pressure slightly above atmospheric and to regulate accurately the flow of oxygen needed by personnel engaged in high altitude flights. The instrument incorporates a sensitive flow-metering device combined with an accurate indicator. The needle valve which regulates the flow of oxygen to the user is manually controlled. The standard model is adjusted to supply the amount of oxygen normally required at high altitudes. Figure 51 shows a view of the assembled instrument. Figure 52 shows a schematic diagram of the internal mechanism. A relief valve is provided in the back cover to protect the mechanism against overpressure in case of failure of the regulating valve.

This valve is set and locked by the manufacturer. - The dial is marked directly in altitude for simplification, the proper flow for any altitude being obtained when the pointer is set at the corresponding graduation by opening or closing the needle valve. The cylinder pressure indicator is connected directly to the line from the oxygen tank. This indicator shows the condition of the supply at a glance.

b. Cylinders.-There are four standard lightweight types of oxygen supply cylinders for aircraft use as shown in the following table:

The storage of oxygen and the details of the cylinder are discussed in section V.

c. Connections.-(1) The high pressure tubing is of seamless copper, silver soldered to the connector fittings, and is used to connect the regulator with the oxygen cylinder. Manifold connections made of the same material are employed to provide connection of two regulators to one cylinder or one regulator to two cylinders.

(2) The low pressure tube (type B-1) is constructed of flexible tubing and is used to connect the outlet of the regulator with the mouthpiece or mask. This assembly is available in two standard lengths, 3 and 6 feet.

49. Operation.-If the oxygen valve cannot be reached during flight, it is turned on before the take-off when flights over 10,000 feet are contemplated. In order to relieve the pressure on the regulator, the cylinder valve is closed again on landing. The operation of the needle valve to regulate the rate of flow during flight is discussed in paragraph 48a.

50. Maintenance.-At the completion of flight, mouthpieces or nipples on the ends of the supply tubing assemblies are sterilized by immersing in a cresol solution for 5 minutes and thoroughly rinsing, both inside and outside, in pure water. In checking the operation of oxygen equipment, it should be noted that a properly working regulator will give a flow indication of at least 35 as the needle valve is fully opened for any cylinder pressure from 500 to 2,100 pounds per square inch. At regular periods the regulator is removed and calibrated. Oxygen cylinders are stored in a cool, dry place and away from any oil or grease. A mixture of litharge (red lead oxide) and glycerin is used for sealing the threads at connections. Oil and grease under no circumstances are to be applied on any connections, packings, valves, gages, or other oxygen equipment. Failure to observe this precaution may result in an explosion. Castile soap may be used on the threads of the needle valve in case lubrication is required.