Environmental Systems Flashcards
How is a vapor-cycle cooling system checked for refrigerant leaks?
Hold the probe of an electronic leak detector below any suspect fitting or component. If there is a leak, the tone of the sound produced by the detector will change.
What safety equipment should be worn when charging a vapor-cycle cooling system?
A safety face shield that protects the entire face.
What are two types of air conditioning systems that may be installed on an aircraft?
Air-cycle systems and vapor-cycle systems.
What are three ways supplemental oxygen can be carried in an aircraft?
As a high-pressure gas, in its liquid form, and as a solid in the form of a chemical candle.
What is a continuous-flow oxygen system?
An oxygen system that continuously flows a metered amount of oxygen into the mask.
What is a pressure-demand oxygen system?
An oxygen system that flows oxygen to the mask only when the wearer of the mask inhales. Above a specified altitude, the regulator meters oxygen under pressure into the mask when the wearer inhales.
How is the heat removed from an aircraft cabin with a vapor-cycle air conditioning system?
The cabin heat is absorbed by the refrigerant in the evaporator, then carried outside the aircraft where it is given up to the outside air in the condenser.
What produces the cool air in a vapor-cycle air conditioning system?
Warm cabin air is blown across the evaporator, where its heat is transferred into the refrigerant. The air that leaves the evaporator is cool.
What is used as the refrigerant in a vapor-cycle air conditioning system?
A Freon-type liquid refrigerant known as Refrigerant 12, or the more environmentally friendly R-134a.
What is the state of the refrigerant as it leaves the compressor?
It is a high-pressure gas.
What is the state of the refrigerant as it leaves the condenser?
It is a high-pressure liquid.
What is the state of the refrigerant as it leaves the thermostatic expansion valve?
It is a low-pressure liquid.
What is the state of the refrigerant as it leaves the evaporator?
It is a low-pressure vapor.
How is the compressor lubricated?
Refrigeration oil is mixed with the refrigerant and it circulates through the compressor and the entire system.
What is the function of the thermostatic expansion valve?
It meters just enough liquid refrigerant into the evaporator that all of it will be evaporated by the time it leaves the evaporator coils.
How is refrigerant put into the system?
It is put into the system through service valves on the low side of the system using a manifold gauge set.
How should the components in the low side of a properly operating vapor-cycle cooling system feel?
They should feel cool.
How is cabin pressure controlled in a pressurized aircraft?
More pressure than is needed is pumped into the aircraft cabin, and the pressure controller modulates the outflow valve to maintain the correct pressure in the cabin.
What is the function of the cabin outflow valve on a pressurized aircraft?
The cabin outflow valve, which is controlled by the pressure controller, maintains the correct amount of pressure inside the cabin.
What is the function of the cabin pressure safety valve on a pressurized aircraft?
The cabin pressure safety valve prevents cabin pressure from exceeding the maximum allowable differential pressure.
Why must pressurized aircraft have a negative pressure relief valve?
The structure of an aircraft cabin is not designed to tolerate the inside pressure being lower than the outside pressure.
What keeps the cabin of a pressurized aircraft from being pressurized when the aircraft is on the ground?
A squat switch on the landing gear holds the safety valve open when the aircraft is on the ground.
