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Mech Theory 4 > Mech theory 4 > Flashcards

Mech theory 4 Flashcards

1
Q

Describe the four components of the four part refrigeration cycle:

A
  1. Compressor – Pumps the refrigerant around the system
  2. Condenser – Uses sea water to cool the refrigerant changing its state from a Gas into a Liquid.
  3. TEV (Thermal Expansion Valve) – Controls the flowrate of refrigerant through the system. Increasing or decreasing the flow depending on the temperature of the refrigerant leaving the Evaporator.
  4. Evaporator – The refrigerant flowing through the Evaporator removes heat from the refrigerator / cold room. This action changes the state of the refrigerant from a Liquid into a Gas.
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2
Q

What is the condition of the refrigerant as it flows between the four components of the system?

A
  • Compressor to Condenser – Hot, High Pressure, Gas
  • Condenser to TEV – Warm, High Pressure, Liquid (Sub-cooled)
  • TEV to Evaporator – Very Cold, Low Pressure, Liquid
  • Evaporator to Compressor – Cool, Low Pressure, Gas (Super-Heated)
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3
Q

What are the three methods of defrosting and how often are they done?

A
  • Natural Defrost - carried out every 3 to 6 months
  • Hot Gas Defrosting – This is done for a maximum of 1 hour in 24 in 15 minute slots
  • Electrical Heating Coils – This is also done for a maximum of 1 hour in 24
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4
Q

What are the five methods of leak detection in the refrigeration system?

A
  • Oil slicks – where oil is leaking there will also be refrigerant leaking
  • IRLDS Infra-red leak detection system
  • Spectrolyne Dye and UV Lamp
  • Snoop (similar to soapy water)
  • Halogen Leak Detector (Hand held electronic device)
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5
Q

What does hygroscopic mean?

A

Absorbing of moisture from the atmosphere.

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6
Q

How do we add oil to the compressor?

A
  • Via Sump Filler Plug
  • By a Hand Pump
  • Through the use of a Dosing Pot
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7
Q

What is the montreal agreement?

A

Agreement to phase out harmful ozone depleting substances / refrigerants such as:
* CFCs
* HCFC
* Halons

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8
Q

What is the Kyoto agreement?

A

Agreement to reduce all Greenhouse gases:
o CO²
o HFC
o PFC
o Methane

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9
Q

What are the hazards of refrigerants?

A

They air is heavier than air so will displace oxygen, can be suffocating.
If exposed to higher temperatures they can produce Phosphene gas.
Can produce cold burns on exposed skin. (frost bite)
Decomposing fruit and veg can produce CO2.

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10
Q

What is the health and safety requirements when being exposed to refrigerant?

A

If refrigerant gets into eyes they need flushing with running water and then require medical treatment.
Refrigerant on the skin requires washing off immediately

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11
Q

What is the procedure for entering Refrigeration compartments?

A
  • The Rating in charge of the watch is to be informed that personnel are entering the compartment, and informed when the compartment is vacated
  • Breathing Apparatus is available at the machinery space access
  • The high and low exhaust fans are running
  • No smoking at any time in the refrigeration area. Any hot work is to be very tightly controlled
  • The Infra-Red Leak Detections System (IRLDS) is working correctly and indicating safe
  • The personnel trapped warning lamps are in working order
  • Any rating entering the room is to be accompanied by another rating who remains outside the room as a safety number
  • The internal door opening mechanism is in correct working order
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12
Q

What is the difference between a refrigeration and chilled water plant?

A

There is a water chiller instead of an evaporator.

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13
Q

What are the five uses of ventilation on ship?

A
  • Cooling of Electronic Equipment
  • CBRN
  • Habitability
  • Main Machinery Space Cooling
  • Galley Ventilation
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14
Q

Where is a fan supply and fan exhaust fitted?

A

Fitted where it is necessary to remove large quantities of Wild Heat, Moisture or Noxious Fumes coupled with the requirements to provide fresh air to personnel working in the compartment. E.g. Machinery spaces, Galleys, Laundries, WCs and Bathrooms

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15
Q

Where would you fit a fan supply and natural exhaust?

A

Fitted where the supply of fresh air to compartments is the primary objective. E.g. Store rooms and Workshops

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16
Q

Where would you fit a natural supply and fan exhaust?

A

Fitted where the removal of noxious gases and flammable vapours is the primary object. E.g. Paint stores, Spirit rooms, Inflame stores

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17
Q

Where would fit a natural supply and natural exhaust?

A

In minor unoccupied compartments and lobbies

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18
Q

What are the common filters aboard ship?

A
  • PANEL FILTER: Re-circulating trunking associated with air conditioning systems
  • SUPPLY FILTERS: Polyurethane filters fitted in ATUs between the plenum chamber and the cooler
  • GREASE FILTERS: Fitted to exhaust canopies over deep fat fryers and ranges in galleys
  • LINT FILTERS: Fitted to prevent the accumulation of fluff and fibres in the exhaust trunking of the laundry
  • DUST FILTERS: Fitted to computer and sonar instrument spaces and sick bays
  • FLAMEPROOF GAUZES: Are fitted to inflammable stores, paint shops, hangers, vehicle decks and magazines
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19
Q

What areas have special requirements for ventilation?

A
  • Galleys – Have Fire Flaps fitted to their exhaust trunking
  • Store Rooms - subject to the build-up of toxic fumes (CO2) which is heavier than air.
  • Auxiliary Machinery Spaces - . To prevent any build-up of gas 50% of exhaust terminals will be found at deck level.
  • Sewage Treatment Spaces - These spaces require 15 air changes per hour with a separate exhaust system and a slight excess of exhaust capacity from that of the supply.
  • Magazines - fitted with their own air conditioning system which allows 100% treated fresh air
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20
Q

What percentage of fresh air and recycled air does ATU’s use?

A

33% fresh air, 67% recirculated

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21
Q

What does an AFU consist of?

A
  1. Pre-Particulate Filter – A paper filter which removes coarse particulate matter including radio-active fall-out
  2. Particulate Filter – Made of glass fibre; designed to remove particulate such as bacteria by entrapment
  3. Gas Filter – Designed to remove all known chemical warfare agents in the form of gases or vapours from the airstream by absorption in the activated charcoal filling
22
Q

How is the Citadel described?

A
  • As a whole ship chemical, biological and nuclear shelter
  • Formed by closing the ship down to an increased gas tight state
  • The Citadel works by increasing the atmospheric pressure within the ship above external pressure using air filtered by AFU units
23
Q

When and how often is the Citadel’s air tight state checked?

A
  1. Annually
  2. Prior to DED (Docking Extended Duration) to locate leaks and ensure that those beyond the capacity of Ship’s Staff are included in the Defect List
  3. During Harbour Acceptance Trials (HATS)
  4. During Sea Acceptance Trials (SATS)
  5. All ships will be required to carry out a Citadel Test during FOST Work-up
    For the Citadel to be effective a pressure of 2” WG is required during the test
24
Q

What is a crash stop?

A

Stops all fans immediately in an emergency.

25
Q

What is the definition for a fluid in a hydraulic system?

A
  • It is a substance that will readily take the shape of its container
  • It is capable of transmitting power
  • It can be a liquid or gas
26
Q

What are the advantages of hydraulics?

A
  • It is reliable
  • Simple and easy to understand
  • Infinite speed range
  • Easily reversed
  • Ability to withstand overload
  • No spark risks
  • High torque at low speeds
  • 1/12 size of equivalent electric motor
27
Q

What are the disadvantages of hydraulics?

A
  • Fire risk with mineral oil systems
  • Noise
  • Risk of contamination
  • Less efficient (85-95%)
28
Q

What PPE is needed when working with flourocarbon elastomers?

A
  • PVC gauntlets
  • Rubber boots
  • PVC coveralls
  • Full-face visor
29
Q

What are the two types of hydraulic liquids?

A

Petroleum based. Petroleum based oils are general purpose (inexpensive) mineral oils.
Synthetic based. Synthetic oils are man-made, for specific purposes.

30
Q

What are the requirements of a hydraulic fluid?

A
  • The main requirement of a hydraulic fluid is for the transmission of power
  • The fluid must flow easily through lines
  • It must be as incompressible
  • Lubrication is another important requirement
  • Sealing Properties
  • Cooling is another role for hydraulic fluid.
31
Q

What are the most common causes of contamination in hydraulic fluids?

A
  • Airborne particles and moisture
  • Construction dirt
  • Dirt in new fluid
  • Dirt produced by wearing in new system
  • Dirt from human sources
32
Q

What are the methods of reducing contamination in hydraulic systems?

A
  • Good system design
  • Filtration and filter maintenance
  • Operation of filter and clogging indicators
  • Good working practices
  • Use of Guardian filter pack
  • Caps should be fitted to open pipework
  • Clean working area
33
Q

What are the different types of hydraulic pumps?

A
  • Internal gearwheel type
  • External gearwheel type
  • Vane type
  • Lobe type
  • Radial piston type
  • Axial Piston Pump (These types of pump use a Swash Plate)
34
Q

What are axial piston pumps used on?

A
  • Stabiliser systems
  • CPP systems
  • Steering systems
35
Q

Explain heat transfer

A

Heat transfers from hot to cold. In solids it travels by conduction. In liquid it travels by convection. In gases it travels by radiation.

36
Q

Explain the purpose of the compressor, condenser, Thermal expansion valve and evaporator.

A
  1. Compressor – Pumps the refrigerant around the system
  2. Condenser – Uses sea water to cool the refrigerant changing its state from a Gas into a Liquid.
  3. TEV (Thermal Expansion Valve) – Controls the flowrate of refrigerant through the system. Increasing or decreasing the flow depending on the temperature of the refrigerant leaving the Evaporator.
  4. Evaporator – The refrigerant flowing through the Evaporator removes heat from the refrigerator / cold room. This action changes the state of the refrigerant from a Liquid into a Gas.
37
Q

What are the three oils used in refrigeration systems?

A

OM70, SW68, Suniso 3GS

38
Q

What systems are supplied with chilled water?

A

Weapon systems, Radars, Ships main computer,

39
Q

When will phophene gas be created?

A

When refrigerant is heated to a high temperature.

40
Q

What should you do if you get refrigerant in your eyes?

A

Wash them with water

41
Q

State four uses of ventilation.

A
  • Cooling of electronic equipment
  • CBRN
  • Habitability
  • Main machinery space cooling.
  • Galley ventilation.
42
Q

State four types of filter

A

Panel filter, Supply filter, Grease filter, Lint filter, dust filter

43
Q

What are hydraulic O rings made of and at what temperature do they start to produce Hydrogen flouride?

A

They are made from fluorocarbon elastomers and above 300 degrees.

44
Q

What are the advantages of hydraulic systems?

A
  • They are reliable
  • Simple and easy to understand.
  • Infinite speed range.
  • Easily reversed.
  • No spark risk
  • Ability to withstand overload.
  • They have a high torque at low speeds.
  • 1/12 of the size of electric motors.
45
Q

What does demulsibility mean?

A

To not mix with water/ emulsify into oil.

46
Q

What are the six hydraulic pumps that are commonly used?

A
  • Internal gearwheel type
  • External gearwheel type
  • Vane type
  • Lobe type
  • Radial piston type
  • Axial piston pumps
47
Q

What does an actuator do and what types are available?

A
  • Actuators convert hydraulic energy (system pressure) into mechanical motion
  • Linear and Rotary.
  • Linear actuators can be single or double acting.
48
Q

State four spaces that require special filters:

A
  • Galley
  • Inflam stores
  • Magazines
  • Sick bays
  • Laundry
  • Sewage treatment plants
  • Auxillery machinery spaces
49
Q

Briefly explain the requirements of a ventilation for the STP:

A

Its completely independent from all other ventilation systems.

50
Q

What tests are performed on fresh water?

A
  • Taste
  • Visual
  • Chemets

Mech Theory 4 (1 decks)

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