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Airframe Test > Environmental Systems > Flashcards

Environmental Systems Flashcards

1
Q

Describe Vapor Cycle Air Conditioning

A
  1. used on most non-turbine aircraft equipped
    with air conditions
  2. not a source of pressurizing air - it only cools
    the cabin
  3. it is a closed systems used solely for the
    transfer of heat from inside the cabin to
    outside of the cabin
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2
Q

Define Boiling Point

A
  1. the temperature at which a substance
    changes from a liquid to a vapor
  2. when pressure in liquid increases -the boiling
    point increases
  3. when pressure decreases - the boiling point
    decreases
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3
Q

What temperature does vapor condense into a liquid

A

Boiling Point

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4
Q

What are the 2 sides of the Vapor Cycle system?

A
  1. Low Side - this side accepts heat
  2. High Side - this side gives up heat

low and high refer to the temperature and
pressure of the refrigerant

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5
Q

List the 7 components of the Vapor Cycle Air Conditioning system

A
  1. Refrigerant
  2. Receiver Dryer
  3. Expansion Valve
  4. Evaporator
  5. Compressor
  6. Condenser
  7. Service Valves
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6
Q

Refrigerant - Things to know

A
  1. R12 - old refrigerant - used in older systems
  2. R134a replaced R12
  3. R134a is better for the environment
  4. R12 and R134a should not be mixed
  5. gloves, goggles, skin protection required when
    using
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7
Q

Describe the Receiver Dryer

A
  1. acts as the reservoir of the vapor cycle system
  2. located downstream of the condenser and
    upstream of the expansion valve
  3. when it is vey hot, more refrigerant is used
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8
Q

What is a stand tube used for?

A
  1. a stand tube is used to remove refrigerant
    that may enter the receiver dryer
  2. it runs to the bottom of the unit to ensure all
    liquid is withdrawn and sent to the expansion
    valve
  3. there is a sight glass at the top allowing tech
    to see the refrigerant - bubbles will show if
    low on refrigerant
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9
Q

What is the Expansion Valve?

A
  1. refrigerant exists the receiver dryer and flows
    to the expansion valve
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10
Q

How much refrigerant should the expansion valve release?

A

only the amount of refrigerant spray that can be completely converted to a vapor

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11
Q

What determines the amount of refrigerant the expansion valve should spray into the evaporator?

A

the temperature of the cabin air to be cooled

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12
Q

What can happen if too much refrigerant is released by the expansion valve into the evaporator?

A
  1. some of it remains liquid when it exists the
    evaporator - it is sucked into the compressor -
    could cause the compressor to break
    ** liquids are not compressible**
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13
Q

Describe an Evaporator

A
  1. made of copper or aluminum tubing coiled
    into a compact unit
  2. fins are attached to increase the surface area
  3. expansion valve located at evaporator inlet
    releases high pressure
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14
Q

What keeps condensed water from freezing in the Condenser?

A

the continuous movement of warm cabin air around the fins

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15
Q

What is the compressor?

A
  1. the heart of the vapor cycle air conditioning
    system
  2. it circulates the refrigerant around the vapor
    cycle system
  3. it receives low pressure, low temperature
    refrigerant vapor from the outlet of the
    evaporator and compresses it.
  4. it is the dividing point between the low side
    and the high side of the vapor cycle system
  5. modern compressors are either engine driven
    or driven by an electric motor
  6. it is usually a piston type pump
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16
Q

What is a Condenser?

A
  1. the final component in the vapor cycle
  2. it is a radiator-like heat exchanger situated so
    that outside air flows over it and absorbs heat
    from the refrigerant received from the
    compressor
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17
Q

What are Service Valves?

A
  1. used for servicing of vapor cycle air
    conditioning systems
  2. one valve is located in the high side and
    one valve is located on the low side of the
    system
  3. should always be capped when not in use
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18
Q

What is a common type of valve used in a vapor cycle system?

A
  1. Schrader valve
  2. operates with R12 refrigerant
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19
Q

What 2 other types of valves are used, besides a Schrader valve, in a vapor cycle system?

A
  1. R134a valve
    • fittings are different than Schrader valve
    • will not attach to Schrader valve threads
  2. Compressor Isolation Valve
    • serves 2 purposes
      1. permits servicing of the system with
        refrigerant
      2. can isolate the compressor so oil level can
        be checked
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20
Q

Describe a Compressor Isolation valve

A
  1. permits servicing of system with refrigerant
  2. can isolate the compressor so oil level can
    be checked
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21
Q

What equipment used for servicing Vapor Cycle Systems

A
  1. Manifold Set, Gauges, Hoses, and Fittings
  2. Full Service Refrigerant Recovery, Recycling,
    Evacuation, and Recharging Units
  3. Refrigerant Source
  4. Vacuum Pumps
  5. Leak Detectors
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22
Q

Describe the manifold set

A
  1. contains 3 hose fittings, 2 O-ring sealed
    valves, and 2 gauges
  2. it is a manifold into which the gauges, fittings,
    and valves are attached
  3. all servicing operations are performed by
    manipulating the valves
  4. when not using manifold set - make sure
    hoses are capped
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23
Q

Describe the gauges on the manifold

A
  1. the gauges on the manifold are dedicated
  2. one for the low side of the system and one for
    the high side of the system
  3. the low pressure gauge is a compound gauge
    • indicates pressure above/below atmospheric
      pressure

Below atmospheric pressure
1. the gauge is scaled in inches of mercury down
to 30 inches - to indicate vacuum
2. 29.92 inches equals an absolute vacuum
(absolute zero air pressure)

Above atmospheric pressure
1. gauge pressure read in psi ranging from 1 - 60
psi ( some go go 150 psi)
2. high pressure gauge - range is 0-500 psi

24
Q

Describe modern refrigeration and recovery units

A
  1. they perform all of the servicing functions
    required for vapor cycle air conditioning
    systems
  2. All in one units that have the manifold set
    built into the unit
  3. Integral solenoid valves, reservoirs, filters, and
    smart controls allow entire servicing
    procedure to be controlled from the unit
    panel
  4. built-in compressor allows complete system
    refrigerant purging
  5. built-in vacuum pump performs system
    evacuation
25
Q

Refrigerant - things to know

A
  1. R134a comes in containers measured by
    weight of the refrigerant contained
  2. 12oz to 2 1/2 lb cans are common for adding
    refrigerant
  3. 30 and 50lb cylinders with shutoff valves are
    used to charge an evacuated system / used in
    shops that service vapor cycle systems
26
Q

Describe Vacuum Pumps

A
  1. used with a manifold set or as part of a
    service cart
  2. connected to the vapor cycle system so the
    system pressure can be reduced to a near
    total vacuum - this removes all water from the
    system
27
Q

What can happen if water is left in the vapor cycle system?

A
  1. water can freeze causing the system to
    malfunction
  2. water can combine with the refrigerant to
    create corrosive compounds
28
Q

Describe the types leak detection in vapor cycle systems

A
  1. Electronic leak detectors
  2. soapy solution applied to fittings
  3. special leak detection dyes can be injected
  4. visual inspections
29
Q

What 8 tests/steps are performed when servicing a Vapor Cycle Air Conditioning System?

A
  1. Visual inspection
  2. Leak Test
  3. Performance Test
  4. Feet Test
  5. Purging the System
  6. Checking Compressor Oil
  7. Evacuating the System
  8. Charging the System
30
Q

During the visual inspection - what should you pay special attention to?

A
  1. Evaporator Fins - should be checked - clean,
    unobstructed, and not folded from impact
  2. Condenser - check for debris that may restrict
    airflow / make sure fan operating correctly
  3. Hinged Units - check for security and wear
  4. Capillary Temperature Feedback Sensor -
    make sure securely attached to evaporator
    outlet
  5. Evaporator - check for ice
  6. Fan Blower - make sure rotates freely
31
Q

What are the signs/indications that there is a leak in Vapor Cycle Air Conditioning system?

A
  1. low refrigerant
  2. bubbles in sigh glass
32
Q

How do you locate the leak point in a Vapor Cycle Air Conditioning system?

A
  1. partially charge system with refrigerant -
    about 50 psi in the high and low sides
  2. by introducing refrigerant into the high side,
    pressure indicated on the low side gauge
    verified the orifice in the expansion valve is
    not clogged
33
Q

When all refrigerant is lost in a Vapor Cycle system - what should be done?

A

A full system evacuation must be performed after the leak is found and repaired

34
Q

What happens when a Vapor Cycle air conditioning system loses all of its refrigerant charge?

A
  1. air and water can enter the system
  2. a full system evacuation is required after the
    leak is found and repaired
35
Q

Performance Test of the Vapor Cycle air conditioning system - things to know

A
  1. involves operating the system and checking
    parameters to ensure they are in normal
    range
  2. A key indication of performance is the
    temperature of the air that is cooled by the
    evaporator - this can be measured at the air
    outflow from the evaporator - thermometer
    should read 40-50 degrees
  3. Pressures can also be observed
    a. low side pressure is normally 10-50psi
    b. high side pressure is 125-250psi
  4. all system tests are performed at a specified
    engine rpm
36
Q

Feel Test on a Vapor Cycle air conditioning system - things to know

A
  1. components and lines in the high side (from
    compressor to expansion valve) should be
    warm or hot to the touch - lines on both sides
    of the receiver dryer should be the same temp
  2. Low side lines and the evaporator should be
    cool - no ice should be visible
37
Q

Purging the Vapor Cycle air conditioning system
- what does it mean
- things to know

A

Meaning: Purging the system means emptying of
its refrigerant charge
1. A service cart is required since the refrigerant
must be captured
2. vapor cycle systems must be properly purged
before opening for maintenance or
component replacement

38
Q

Describe the process for purging a vapor cycle air conditioning system

A
  1. Connect hoses to the high side and low side
    service valves
  2. Select recover, cart solenoid valves position so
    that a system pursing compressor pumps the
    refrigerant out of the vapor cycle system and
    into a recovery tank
39
Q

Evacuating a vapor cycle air conditioning system
- what does this mean
- when is this done

A

Meaning: water is removed from the system - also known as pumping down the system

When done:
1. anytime the system refrigerant charge falls
below atmospheric pressure
2. the refrigerant charge is lost
3. the system is opened

40
Q

What 2 types of oxygen systems are used on civilian aircraft?

A
  1. Gaseous
  2. Solid oxygen (oxygen generators)

Can be built-in o portable oxygen systems

41
Q

Gaseous Oxygen Systems - things to know

A

TYPES:
1. can be a small carry-on portable cylinder w/ a
single mask (found on light aircraft)
2. can be a larger carry-one portable cylinder
fitted with a regulator that divides flow to 2-4
people (found on light aircraft)
3. can be be a built in system with a distribution
system to multiple breathing stations (high
performance and light twin engine aircraft)
4. Transport aircraft may use elaborate built in
gaseous system as a backup system to cabin
pressurization

42
Q

How is oxygen stored on aircraft for gaseous oxygen systems?

A
  1. oxygen is stored as a gas at atmospheric
    temperature in high pressure cylinders
43
Q

Describe Oxygen Storage Cylinders

A
  1. traditionally heavy steel tanks rated for 1800-
    1850 psi & capable of maintaining pressure up
    to 2400 psi
  2. some newer cylinders made of lightweight
    aluminum shell wrapped with Kevlar are being
    used - can carry same amount of pressure as
    steel tanks, but much lighter
  3. Heavy walled all aluminum cylinders are
    commonly used for portable carry on tanks
  4. certified to DOT specifications
  5. must be hydrostatically tested periodically
  6. cylinders must be removed from service after
    a specified number of filling cycles or calendar
    age
  7. most commonly used heavy duty steel
    cylinders used are 3AA and3HT
  8. oxygen cylinders are considered empty when
    the pressure inside drops below 50 psi
44
Q

When should oxygen cylinders be removed/replaced?

A

cylinders must be removed from service after
a specified number of filling cycles or calendar
age

45
Q

What are the most commonly used heavy duty steel oxygen cylinders?

A

3AA and 3HT

46
Q

When are oxygen cylinders considered empty?

A

oxygen cylinders are considered empty when
the pressure inside drops below 50 psi

47
Q

The design of various oxygen systems used in aircraft depends on what?

A
  1. its operational requirements
  2. whether the aircraft has a pressurization
    system
48
Q

How are oxygen systems characterized?

A

By the type of regulator used to dispense the oxygen
1. continuous flow system
2. demand flow system

49
Q

Describe the continuous flow sytem

A
  1. Once the valve is opened, the flow of oxygen
    is continuous until the valve is closed
  2. A portable oxygen setup for a light aircraft is
    an example of a continuous flow system
  3. Some more advanced systems use a regulator
    that is adjustable - provides varying amounts
    of oxygen based on altitude increases
  4. The regulators can be manual or automatic
  5. many systems include a fixed location for the
    oxygen cylinders w/ permanent delivery
    plumbing installed to all crew and passenger
    stations
50
Q

How are manual continuous flow regulators adjusted

A

They are adjusted by the crew as altitude changes

51
Q

Describe automatic continuous flow regulators
How do they work?

A
  1. have a built in aneroid
  2. as the aneroid expands with altitude, a
    mechanism allows more oxygen to flow
    through the regulator to the users
52
Q

Describe fully integrated oxygen systems and how they work

A
  1. usually have separate, remotely mounted
    components to reduce pressure and regulate
    flow
  2. A pressure relief valve, a filter, and a gauge to
    indicate amount of oxygen pressure remains
    in the cylinder
53
Q

Describe a built-in continuous flow gaseous oxygen system and how it works

A
  1. accomplishes a final flow rate to individual
    user stations through the use of a calibrated
    orifice in each mask
  2. Larger diameter orifices are usually used in
    crew masks to provide greater flow than to
    passengers
54
Q

What is a demand flow oxygen system?

A
  1. oxygen is delivered only as the user inhales
  2. used most frequently by the crew of high
    performance and air transport category
    aircraft
  3. Similar to continuous flow systems, except the
    demand flow oxygen regulators differ
    significantly
55
Q

Describe how a demand-flow oxygen system works

A
  1. The pressure reducing valve (pressure
    regulator) lowers the oxygen pressure from
    the storage cylinder(s) to 60-85 psi and
    delivers to individual regulators
  2. A pressure reduction also occurs at the inlet
    of the individual regulator
56
Q

What are the two types of individual regulators

A
  1. diluter-demand type
  2. pressure-demand type
57
Q
A

Airframe Test (11 decks)

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