As previously stated, naval aircraft equipped with high-pressure oxygen systems are designed for approximately 1,800 psi, and working pressures reduce to 60 to 70 psi by a reducer or regulator. Systems equipped with pressure reducers are referred to as reduced high-pressure systems. The reduced high-pressure gaseous oxygen system shown in figure 4-5 is typical of such systems. Oxygen is stored in three high-- pressure cylinders and supplies three regulators- one each for the pilot, copilot, and flight engineer.

SYSTEM OPERATION

The pressure manifold, which is equipped with internal check valves, receives oxygen flow from the cylinders, directs the flow into a common line, and routes it to the pressure reducer. The manifold assembly also connects to a filler line, allowing the three cylinders to be recharged simultaneously from an external supply. The pressure reducer decreases the pressure to 65 psi. Incorporated on the low-pressure side of the pressure reducer is a relief valve, which connects

Figure 4-5.- Reduced high-pressure oxygen system schematic,

through tubing to an overboard discharge indicator. In the event of excessive pressure developing within the low-pressure section of the pressure reducer, the excess pressure will flow through the relief valve and out the overboard discharge line. This flow will rupture the green disc in the discharge indicator, giving a visual indication of a malfunctioning pressure reducer. A line from the high-pressure side of the pressure reducer connects to a gauge in the cockpit. This gauge gives the pilot an indication of pressure in the three storage cylinders. The oxygen flows from the low-pressure side of the reducer to the three regulators. A flexible hose attached to each regulator is for attachment of the oxygen mask.

Portable Oxygen Systems

Portable oxygen systems include walkaround cylinders, survival kits, and bailout units. These systems are used primarily to maintain crew functions in the event of failure of the fixed oxygen systems. The survival kit oxygen system also performs the same function during descent after bailout. All of these are small, lightweight, high-pressure, self-contained gaseous systems, which are readily removed from the aircraft.

Walkaround Cylinders

Walkaround cylinders are standard equipment on many transport, patrol, and early warning aircraft, and are used separately or in addition to a permanently installed oxygen system. Each system consists of a reducer and regulator assembly mounted directly on a small oxygen cylinder. Figure 4-6 illustrates a high-pressure walk-around oxygen system. A 295 or 514 cubic inch-capacity, 1,800 psi cylinder is equipped with a regulator, which is connected to the cylinder with a short coiled length of copper tubing. A short flexible breathing tube, clamped to the outlet of the regulator at one end and fitted with a connector at the other end, provides the necessary assembly for the attachment of the demand mask tube. Straps fastened to the cylinder bracket provide the means for securing the unit to the user's seat or part of the aircraft's structure. The cylinder bracket may be placed horizontally or stood on end while in use. The straps can be used as a handle to carry it from place to place. Because of its weight, the walkaround unit should not be carried by its breathing tube, regulator, or copper tubing.