The pressure of air decreases as ascend to upward from earth surface. Because force of gravity, temperature and another a few factors begins decrease as ascend to upward. Thus aırflow partıcles move to far from each other.
Therefore both pressure and quantıty of air will decrease . There are various gases create air. These as rate; %78 Nitrogen, %21 Oxygen and %1 other gases.
Rate of this gases always constant. But quantity of their are changing because of gravity and temperature.
The most aircrafts fly in high altitudes. Air pressure and quantity less in here. Therefore pressurizated air has pressing to into cabin of aircraft for protecting health of aircraft structures and people. Also pressurizated air regulates again according to change of altitude for same purpose.
This operations provide to increase quantity of oxygen in the air of cabin. Thus passengers easily breaths. So this operations provide to protect structure of aircraft against structural loads. But altitude of the aircraft changes throughout the flight. Therefore pressure of cabin air should be regulate according to pressure of atmospheric air.
Air condition and pressurization system performs all of these.
(This system gets air from bleed & pneumatic system. Bleed system is getting to air from compressor stages of engine. And it is regulating this air and it is deploying to other system)
When air condition and pressurization system gets air from bleed system, system has been regulating pressure and temperature of air by air condition pack, trim air temperature valve, trim air pressure modulating valve. And system has been pressing regulated air to cabin of aircraft. This air regulates again according to change of altitude with by pressurization system.
Pressurization system has been checking pressure of pressurizated air with by pressure controller, outflow valves, negative relief valve, positive relief valve, cabin altitude warning switch. Also system has been regulating pressure of air in same time.
Outflow valves adjust pressure of cabin air according to pressure of atmosphere air. Outflow valve has been awaiting in a spesific position.
Thus both pressure of cabin air wont very decrease and pressure of cabin air wont very increase. So pressure of cabin air will being within intended value.
If pressure of cabin air decreases, oxygen masks will drop after from a certain time. If pressure of cabin air is still decreasing, outflow valve will close as automatically after from a certain time. If pressure of cabin air still decreasing after from all these, negative relief valve will open in a particular time.
There are two notion as negative differential pressure and positive differential pressure. We have been calculating negative differential pressure by eliminating pressure of cabin air from pressure of atmospheric air. We calculate positive differential pressure by eliminating pressure of atmospheric air from pressure of cabin air.
We dont want very alteration within differential pressures. Differantial pressures can increase in some cases. When pressure of cabin air increases, positive differantial pressure has been increasing. When pressure of cabin air decreases, negative differantial pressure has been increasing.
When positive differential pressure reachs to 8.65 psi, positive relief valve opens and pressurizated cabin air drains to atmosphere by this valve. Thus prevents very pressure of cabin air. When negative differential pressure reachs to 1 psi, negative relief valve opens. This valve gets air to cabin of aircraft from atmosphere. Thus prevents low pressure of cabin air. We can think to relief valves as assistant of outflow valve. When the outflow valve is failure or it is not enough, relief valves will be opening after from a particular time. All these for protecting to health of aircraft structures and people… https://aircrafttechnic.com/