Chapter 14 - Cabin atmosphere control

Question 1

What are the 4 types and characteristics of oxygen systems?

Answer 1

1. Gaseous - 1800 to 2400 psi

• ICC/DOT 3AA 1800 - tested with water pressure of 3,000 psi every 5 years
• ICC/DOT 3HT 1850 - tested with water pressure of 3,000 psi every 3 years; taken out of service every 24 years or 4380 refills
• DOT-E-8162 (composite) - tests are the same as 3HT; taken out of service every 15 years or 10,000 refills
  2. Liquid systems - 70 psi
• 1 liter = 860 gaseous liters
• kept in a dewar flask
  3. Chemical oxygen systems
• contains oxygen candles with sodium chlorate. When it burns, chemical reaction releases oxygen
  
  4. Mechanically-seperated systems
• has a “molecular sieve” filter that seperates nitrogen and other gases from the oxygen in the air.

Question 2

How do you lubricate and seal tapered pipe threads on the oxygen systems?

Answer 2

Lubricate

• Use lubricates that meets specification MIL-G-27617
• Threads may be wrapped with teflon tape
• NEVER use petroleum based products

Seal

• seal with protective caps or plugs
• never use tape to seal the lines and fittings

Question 3

How do you determine the amount of oxygen in the bottle?

Answer 3

The pressure guage.

The system is considered to be empty when the pressure gets down to 50-100 psi

Question 4

Contamintated oxygen systems gets purged with what?

Answer 4

Continous flow system

• oxygen masks are plugged into each of the outlets and the oxygen supply valve turned on. Oxygen should be allowed to flow through the system for about ten minutes

Diluter demand and pressure demand systems

• purged by placing the regulators in the EMERGENCY position and allowing the oxygen to flow for about ten minutes

New lines should be flushed with stabalized trichlorethelene, acetone, or some similar solvent and dried with dry air or nitrogen

Question 5

When servicing an oxygen bottle, what should you check on the bottle before servicing?

Answer 5

Check to see if there is a stamp near the filler neck with the approval number, date of manufacturer, and the dates of all of the hysrostatic tests

Question 6

Where do you find the specifications for the bottle?

Answer 6

MIL-G-27617

bottle manufacturer

Question 7

Oxygen systems of unpressurized aircrafts are of what type?

Answer 7

FAR part 91 requires most executive aircraft that operate at high altitudes to be equipped with diluter or pressure demand oxygen regulators for the flight crew and a continuous flow system for the occupants.

Aircraft operating at altitudes above 40,000 feet will utilize the pressure demand systems for crew and passengers

Question 8

On a diluted demand regulator, what is the purpose of the aneroid bellows?

Answer 8

A diluter demand regulator dilutes the oxygen supplied to the mask with air from the cabin.

The barometric control bellows expands with an increase in altitude, opening the oxygen passage while closing off the air passage. At 34,000 feet, the air passage is completely closed off.

Question 9

What is the difference between aviators breathing oxygen and other oxygen bottles?

Answer 9

Aviators breathing oxygen is 99.5% pure

Has less than 2ml of water vapor per liter

Question 11

Round disk blowouts are caused by what?

Answer 11

A thermal discharge caused by too much pressure to too high of a temperature

Question 12

On oxygen gaseous systems, how is pressure reduced for breathing?

Answer 12

Through a pressure reducer that reduces the pressure down to about 15 psi

Question 13

With a diluter demand regulator, what does the demand valve control?

Answer 13

The demand valve shuts off all flow of oxygen to the mask until the wearer inhales and decreases the pressure inside the regulator. This decreased pressure moves the demand diaphram and opens the demand valve so oxygen can flow through the regulator to the mask

Question 14

With the continuous flow system, what controls the amount of oxygen delivered to the masks?

Answer 14

refiller bag

Question 15

IF the pressure in a oxygen bottle drops below a predetermined amount, what may happen?

Answer 15

moist air might enter into the bottles, freeze, and shut off air flow to the masks

Question 16

How to you test an oxygen bottle for leaks?

Answer 16

A non-oily soap solution should be spread over every fiting and every place a leak could possibly occur. The presence of bubbles will indicate a leak.

Question 17

Which type of system uses a plastic bag and a oronasal mask?

Answer 17

Continuous flow regulators - uses a oronasal & rebreathable bag

Question 18

What is the combustion air used for in a combustion heater?

Answer 18

USed to heat that air that is going to the cabin.

Question 19

What is ventalating air used for in a combustion heater?

Answer 19

• It operates while the aircraft is on the ground
• used as a back up in the even of a crack in the combustion chamber, ventilating air will flow into the combustion chamber rather than allowing the combustion air that contains carbon monoxide to mix with the venilating air
• cools the combustion chamber and initiates the thermostate to open the solenoid valve.

Question 20

In a combustion heater, what does the thermostat control?

Answer 20

When the thermostat calls for heat, a fuel selenoid valve opens and allows fuel to be sprayed into the combustion chamber for burning. As soon as the thermostat reaches its temperature value, the fuel solenoid valve de-energizes, shutting off the fuel to the heater

Question 21

In an ACM, where does the coldest air come from?

Answer 21

Outside ram air, which is used to cool the hot bleed air.

Question 22

In an air cycle machine, where does the first and last stage of cooling occur?

Answer 22

First stage

• The primary heat exchanger is a radiator through which cold ram air passes over the radiator’s fin like tubes to cool the engine bleed air

Last stage

• The expansion tube. Large pressure drop = large temperature drop.

Question 23

In a vapor-cycle air conditioning system, what serves as the reservoir?

Answer 23

The receiver-dryer

Question 24

What is the state and pressure of refrigant when entering the condenser with the vapor cycle?

Answer 24

A hot high-pressure vapor

Question 25

What is downstream and upstream of the compressor?

Answer 25

Upstream - evaporator

downstram - condenser

Question 26

What is the purpose of the evaporator?

Answer 26

The evaporator is the unit in an air-conditioning system that produces the cold air. Warm air is is blown through the thin metal fins that fir over the eveporator coils. This heat is absorbed by the refigerant, and when the air emerges from the evaporator, it is cool. When the heat is absorbed by the refrigerant, it changes from a liquid into a gas without increasing its temperature.

Question 27

In a vapor cycle system, what gives off and absorbs heat?

Answer 27

The evaporator unit absorbs heat, gives off cool air, and turns into a gas

The condenser unit absorbs cool air, gives off heat, and turns into a liquid

Question 28

What is almost universally used in aircraft a/c systems as a coolant?

Answer 28

Dichlorodifluromethane aka Freon-12

Question 29

The ______ is the control devise which meters the correct amount of refrigerant into the evaporator.

Answer 29

Thermal expansion valve

Question 30

What is the purpose of the safety valve in pressurized aircrafts?

Answer 30

The safety valve functions as a backup for the outflow valve in the air and to dump pressurization when the wheels arew on the ground.

Question 31

What component ensures that the cabin pressure alt is much lower than the outside pressure alt?

Answer 31

Outflow valve

Question 32

What is the order of the vapor-cycle air conditioning?

Answer 32

Thermal expansion valve

low pressure liquid

evaporator

low pressure vapor

compressor

high pressor vapor

condensor

reciever dryer

high pressure liquid

(back to the top)

Question 33

What are the three modes of pressurization?

Answer 33

Unpressurized

Isobaric - within limits of normal range (8,000ft)

Differential - Outside vs inside cabin

Question 34

What is standard day at sea level?

Answer 34

Pressure

• 29.92 inHg
• 1013.2 mb
• 14.69 psi

Temp

• 15 degrees C
• 59 degrees F

Question 35

What component in the air-cycle conditioner system raises the temperature?

Answer 35

The secondary heat exchanger as a by-product of the increase in pressure.