Mechanical Theory 1 Flashcards
What is the definition of the three tanks:
Header
Service
Tank
Header - used as a reservoir to top up a tank or system
Service - used as a reservoir of clean,water free supply of fuel
Tank - used to collect oil returning from a system
What are the main factors that will dictate the material a pipe is made of
Temperature
Fluid used
Pressure
What is an accumulator
A device which potential energy is stored
(Compressed gas)
(Spring loaded piston)
(Raised weight)
What is the operating principle used within a pressure gauge
Bourdon tube principle
Four uses of diesel engines in the RN
Motor / propulsion
Power generation
Compressors
Fire systems
What are the five materials used for piping and what for
Copper - fresh domestic water
Copper nickel - lubricating oil
Phosphor bronze - HPSW (salt water)
Brass - castings (valves / taps)
Plastic - sewage and pre-wet
What is the definition of a system
The organisation of components into a structure that provides a specific service and safely
What is fitted in within a system to remove coarse particles from a fluid
Strainer
What are the 3 main gauge types and what are they used for
Gauge glass - visual indication of how much fluid is left
Contents gauge - indicates how much fluid remains
Sounding tune - measure the depth of a tank (uses dip tape and conversion chart
what is the purpose of a flywheel
- promotes smooth running of the engine during non-power strokes
- uses stored inertia to power the crankshaft
what component connects the piston to the crankshaft
connecting rod
describe the induction stage on a 4 stroke cycle
- intake valve is opened
- piston moves from TDC to BDC which draws in air from the intake.
describe the compression stage on a 4 stroke cycle
- intake closes (both valves are closed)
- piston moves from BDC to TDC, before reaching the max travel,
- the injector shoots high pressure fuel into the cylinder.
describe the power stage in a 4 stroke cycle
- both valves closed
- piston hits max travel which causes the mixture to spark(explode).
- controlled explosion forces the piston back to the BDC
describe the exhaust stage on a 4 stroke cycle
exhaust valve opens allowing for the exhaust fumes to be drawn out of the cylinder
list the safety trips ans safety devices fitted to a diesel engine
- low oil pressure
- low coolant pressure
- high oil temperature
- high coolant temperature
- engine overspeed
what are the three oil properties that are checked on a oil test
- water
- acidity
- viscosity
what is used to connect the piston to the connecting rod
gudgeon pin
what are four functions of the cylinder head
- incorporates inlet / exhaust ports
- forms the upper part of the combustion chamber
- closes the top of the cylinder
- houses valves and injectors
what are the two types of systems
Open Loop system - the working fluid is consumed e.g. fuel system, HPSW
Closed Loop system - the working fluid is re-used e.g. fresh water-cooling system.
what are the main factors concidered for choosing the seal type
- the system working pressure
- the fluid being used
- the temperature involved
what are the four example of seals used on board ships
- Gaskets - (non-asbestos fibre, paper, leather, cork, copper, rubber)
- Mechanical seals – tend to be spring loaded seals with physically push the barrier closed (used on a rotating shaft)
- Keelering coupling
- Glandpacking
what is the main function of a valve
- Valves and cocks provide a way of controlling the flow of liquid or gas within a system.
- Valves further allow you to isolate systems. (direction of flow)
name the 8 types of valves used
- Globe valve – name from the shape, screw down valve, once shut the spindle is lowered.
- Gate valve – used in large bore systems
- Flap valve – non-return valve (like a diode)
- Saunders valve – fitted with a rubber diaphragm (used in water and fuel systems)
- Ball seated cock – bored through ball, turns 90degrees to open/close
- Relief valve – valve is consistently shut via a spring, however if the pressure has a stronger force then the spring, the valve will release the pressure (protects systems from over pressurisation)
- Reducing valve – valve reduces the pressure build up
- Non-return valve – prevents flow reversal using either piston or flap method (like a diode)
what are the two types of pumps
Positive
* physically displaces and moves the fluid along
* These pumps deliver high pressures and have the ability to self-prime as they physically pull the fluid from the tank
dynamic displacement
* moves a fluid by using the enrgy from the impeller withing the pump to accelerate the fluid
* These pumps are required to be primed before being used fully
what is bernoulli’s principle
the speed of a moving fluid increases as the pressure within the fluid decreases
what are the six pressure gauses and system indicates
- Pressure and vacuum gauges - as pressure increases the bourdon tube extends, moving the dial clockwise (measures pressure and vacuum)
- Manometer – provides a visual representation of pressure or vacuum
- Tachometer – measures rotational speed
- Thermometer – measures temperature
- Flow meter – measures rate of flow
- Voltage meter - measures the potential difference
what is a metallic filter
- made from wire wool, thin steel plates or gauze screens.
- They are used to remove coarser partials of contaminates from a system.
- When block it is required for them to be cleaned and returned.
what is a absorbent filter
- made from paper, cloth, felt and other fabrics.
- They are used to remove finer partials, used where higher standards of cleanliness is required.
- When serviced these filters are replaced with new ones.
what are pressure control valves
- Pressure control valves maintain system pressure at designated set levels.
- It will monitor outlet pressure and open/close as required to main a constancy
what is rod gearing
- Allows a valve to be shut manually from another location, if a space becomes unsafe to enter (flooding/fire/gas leak), these rods allow valves to be controlled from a safe location.
- Important for them to maintained to high standard as they are commonly used on emergency equipment.
what is the purpose of a pressure relief valve
what
Used to protect a system from over-pressurisation, put on outlet pump
what is a accumulator
- an energy storage device: a device which accepts energy, stores energy, and releases energy as needed.
- Common form are hydro-pneumatic types and used in fluid power systems.
- They can be used as a surge/pulsation dampener/absorber
