Aircraft Systems Chapter 4.1 Oxygen PDF

ME3531 Aircraft Systems Chapter 4: Oxygen For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Composition of the Atmosphere The earth’s atmosphere is make up a mixture of gases which is commonly call Air....

ME3531 Aircraft Systems Chapter 4: Oxygen For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Composition of the Atmosphere The earth’s atmosphere is make up a mixture of gases which is commonly call Air. 78% Nitrogen 21% Oxygen 1% Other gases (such as carbon dioxide, water vapour, and ozone) Nitrogen is an inert gas that is not used directly by man for life. Carbon dioxide is utilized by plants during photosynthesis thus food supply for all animals and man depends on it. The percentage of the various gases that comprise the atmosphere Water vapour plays an important role in the formation of weather. Ozone is a form oxygen which contains three oxygen atoms per molecules. They are formed by the interaction of oxygen and the sun’s rays near the top of the stratosphere in an area called ozone layer. Page ▪ 2 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Human Respiration and Circulation Oxygen and Hypoxia The oxygen in the atmosphere is essential to the survival for humans and animals. When aircraft is flying at high altitudes, there is a decrease in the pressure of oxygen in the lungs. A reduction in the normal oxygen supply will affect the human condition: Body function Degree of consciousness Oxygen pressure in the atmosphere at various altitudes The resultant sluggish condition of mind and body produced by insufficient oxygen called hypoxia. Page ▪ 3 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Aircraft Oxygen Systems With the reduction of pressure at high flight altitudes, less oxygen will be forced through the lungs and this can be overcome by: Increase the quantity of oxygen in the air supply. Increase the pressure of the oxygen. Oxygen systems that increase the quantity of oxygen in breathing air are most commonly used as primary in small and medium sized aircraft designed without cabin pressurisation. Increasing the quantity of oxygen available in the lungs, less pressure is required to saturate the blood. This means that the level of oxygen is above the 21 percent found in the atmosphere. For large transport-category and high performance passenger aircraft pressurise the air in the cabin. This is to push more of the normal 21 percent oxygen found in the air onto the blood for saturation. Page ▪ 4 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Forms of oxygen and Characteristics Gaseous Oxygen Oxygen is colourless, odourless, and tasteless gas at normal atmosphere temperature and pressures. Aviator’s breathing oxygen are stored and transported in high-pressure cylinders that are typically painted in green. The water level should be maximum of 0.02ml per liters of oxygen. The presence of water will result in the possibility of it freezing in the small passage ways in valves and regulators. Ice prevent delivery of oxygen to the user. “Aviator’s breathing oxygen” is marked on all oxygen cylinders designed for this purpose Page ▪ 5 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Forms of oxygen and Characteristics Liquid Oxygen (LOX) Liquid Oxygen is a pale blue, transparent liquid by lowering the temperature to below -183°C or placing gaseous oxygen under pressure. This special container is used to store and transport liquid oxygen. It uses an evacuated, double–walled insulation design to keep the liquid oxygen under pressure at a very low temperature. A controlled amount of oxygen is allowed vaporised and is flowed into a gaseous oxygen delivery system downstream of a converter A spherical liquid oxygen on-board that is part of the container assembly. container used by the military A small quantity of LOX can be converted to a large amount of gaseous oxygen, resulting in the use of less storage space compared to that needed for high-pressure gaseous oxygen cylinders. Page ▪ 6 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Forms of oxygen and Characteristics Chemical or Solid Oxygen Generators The chemical oxygen supply is ignited by a spring-loaded firing pin that when pulled, releases a hammer that smashes a cap creating a spark to light the sodium chlorate. Once activated, the generator can provide oxygen supply of 10 to 20 minutes and it cannot be extinguished. The generators are primarily used as backup oxygen devices on pressurised aircraft. A sodium chlorate oxygen candle is at the core of a chemical oxygen generator Page ▪ 7 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Forms of oxygen and Characteristics Onboard Oxygen Generating Systems (OBOGS) OBOGS on military aircraft pass bleed air from the turbine engines through sieve that separates the oxygen for breathing use. The sieves are relatively light in weight and relieve the aviator of a need for ground support for oxygen supply. Onboard Oxygen Generating System uses molecular sieve technology Page ▪ 8 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems and Components Oxygen Systems and Regulators The type of oxygen system used on the aircraft depends on the type of regulator used to dispense the oxygen. Continuous flow oxygen system Installed for both passengers and crew Demand flow oxygen system Widely used as a crew system on large transport aircraft Page ▪ 9 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems and Components Continuous Flow Systems Continuous-flow oxygen system allows oxygen to leave the storage tank through a valve and passes it through a regulator/reducer attached to the top of the tank. The flow of high-pressure oxygen passes through a section of the regulator that reduces the pressure of the oxygen, which is then fed into a hose attached to a mask worn by the user. Once the valve is opened, the flow of oxygen is continuous. Even when the user is exhaling, or A typical portable gaseous oxygen cylinder completes with valve, pressure when the mask is not in use, a preset flow of gauge, regulator/reducer, hose, oxygen continues until the tank valve is closed. adjustable flow indicator, and rebreather cannula. Page ▪ 10 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems and Components Continuous Flow Systems Many continuous-flow systems include a fixed location for the oxygen cylinders with permanent delivery plumbing installed to all passenger and crew stations in the cabin. A pressure relief valve is also typically installed in the system, as is some sort of filter and a gauge to indicate the amount of oxygen pressure remaining in the storage Continuous flow oxygen system found on small to medium size aircraft. cylinder Page ▪ 11 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems and Components Continuous Flow Systems Oxygen cylinder valves and high-pressure systems are often provided with a relief valve should the desired pressure be exceeded. Often, the valve is ported to an indicating or blowout disk. This is located in a conspicuous place, such as the fuselage skin, where it can be seen during walk-around inspection. An oxygen blowout plug on the side of the fuselage Most blowout disks are green. The absence of the green disk indicates the relief valve has opened, and the cause should be investigated before flight. Page ▪ 12 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems and Components Continuous Flow Systems The regulator can be adjustable to provide varying amounts of oxygen flow to match increasing need as altitude increases. These regulators can be manual or automatic in design. Manual continuous-flow regulators are adjusted by the crew as altitude changes. A manual continuous flow oxygen Automatic continuous-flow regulators have a built in system may have a regulator that is aneroid. As the aneroid expands with altitude, a adjusted by the pilot as altitude mechanism allows more oxygen to flow though the varies. By turning the knob, the left gauge can be made to match the regulator to the users. flight altitude thus increasing and decreasing flow as altitude changes. Page ▪ 13 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems and Components Continuous Flow Systems The passenger section of a continuous-flow oxygen system may A passenger service unit (psu) is hinged over each row of seats in an airliner. Four consist of a series of plug-in supply sockets fitted to the cabin yellow continuous flow oxygen masks are walls adjacent to the passenger seats to which oxygen masks shown deployed. can be connected. Flow is inhibited until a passenger manually plugs in. When used as an emergency system in pressurized aircraft, depressurization automatically triggers the deployment of oxygen ready continuous-flow masks at each passenger station. A continuous flow of oxygen from the storage tank can be wasteful hence a rebreather apparatus be used. Oxygen and air that is exhaled still contains usable oxygen and by capturing this Rebreather face mask capture oxygen in the a bag or a cannula with oxygen absorbing reservoir exhaled oxygen to be inhaled on the reservoirs can be inhaled with the next breath hence reducing next breath. This conserves oxygen waste. by permitting lower flow rates in continuous flow systems. Page ▪ 14 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems and Components Demand Flow Systems (Diluter) Demand-flow systems are similar to continuous- flow systems. Demand-flow oxygen regulators differ significantly from continuous-flow oxygen regulators. When the user inhales, a slight negative pressure is created in the chamber to the right of the demand diaphragm. This pressure reduction cause the a negative pressure to be applied to the chamber under the Diluter-demand oxygen regulator reducing valve diaphragm, moving the diaphragm to the left. When the diaphragm moves to the left, the pressure-reducing valve is lifted off its seat, allowing oxygen to enter the regulator and flow towards the mask. Page ▪ 15 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems and Components Demand Flow Systems (Diluter) Continued from previous page The mixing of air with oxygen is caused by the aneroid in the mixing chamber. The aneroid is sealed metal bellows. At sea level the aneroid is compressed by atmospheric pressure so that the oxygen-metering port is closed and the air-metering port is open. As atmospheric pressure is decreased, aneroid expands , opening the oxygen-metering port and reducing the air metering port. Diluter-demand oxygen regulator At altitude of approximately 34000 feet, the air- metering port is completely closed and the user is receiving only oxygen Page ▪ 16 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems and Components Pressure Demand Oxygen System Pressure-demand oxygen systems operate similarly to diluter- demand systems, except that oxygen is delivered through the individual pressure regulator(s) under higher pressure. When the demand valve is unseated, oxygen under pressure forces its way into the lungs of the user. The demand function still operates, extending the overall supply of oxygen beyond that of a Diluter and pressure demand oxygen regulator continuous-flow system. The user may select position the selector switch to 100% or to emergency to delivers 100% oxygen delivery, but in a continuous flow as the demand function is bypassed. Pressure-demand regulators are used on aircraft that regularly fly at 40,000 feet and above. They are also found on many airliners and high-performance aircraft that may not typically fly that high. Forcing oxygen into the lungs under pressure ensures saturation of the blood, regardless of altitude or cabin altitude. Page ▪ 17 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems and Components Flow indicator Demand-flow oxygen systems usually have flow indicators built into the individual regulators at each user station. Some contain a blinking device that activates when the user inhales and oxygen is delivered. Flow indicators provide a quick verification that an oxygen system is functioning. Page ▪ 18 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems Servicing Servicing Gaseous Oxygen For gaseous storage bottles can be refill using a ground cart. Leak testing gaseous oxygen systems can be Oxygen Ground Cart performed using approved oxygen leak detection solution by applying it to the outside of fittings and mating surfaces. The formation of bubbles indicates a leak. Leak Detection Test Page ▪ 19 For Training Purpose Only  Official (Closed), Non-Sensitive Oxygen Oxygen Systems Servicing Prevention of Oxygen Fires or Explosions Precautions must be observed when working with or around pure oxygen. It readily combines with other substances, some in a violent and explosive manner. it is extremely important to keep distance between pure oxygen and petroleum products. When allowed to combine, an explosion can result. When working on an oxygen system, it is essential that the warnings and precautions given in the aircraft maintenance manual be carefully observed. Ensure that all tools and servicing equipment are clean and avoid power on checks and use of the aircraft electrical system. Page ▪ 20 For Training Purpose Only