general me ft Flashcards
Describe the air flow through a GT
The gas turbine air flow is separated into 5 sections, induction, compression, combustion, power and exhaust. In the induction stage air is drawn into the engine. It then goes into compression which is divided into LP and HP compressors, the air is drawn in at atmospheric pressure into the LP compressor where the LP air rotates a series of blades with divergent passages. The LP compressed air then enters the HP compressor with more blades, increasing the air pressure squeezing the air, by slowing down the air in divergent passages creates more pressure. Combustion begins when the compressed air enters the combustion chamber where atomised fuel is injected a long with a igniter to provide the initial start up. Combustion cans 2 and 8 create the initial ignition. Not all air is used for initial combustion, majority of it is for cooling down the chamber. Power then happens when the hot gases leave the chamber and drive the LP and HP turbines which in turn rotate the compressors as they are connected, making the turbine self sustained when up to speed. The remaining energy passes through the power turbine causing it to turn, driving the gearbox etc
Describe the shaft line and shaft brake checks
The shaft line is a long metal shaft that starts at the gear and ends at the propellor with a multitude of components in between which stabilise the shaft in different ways. The shaft is separated into 3 sections, Thrust shaft, intermediate shaft and tail shaft. The thrust shaft contains the thrust collar which links the gearbox to the intermediate shaft which contains the thrust block, bulkhead glands, plumber block, stern seal, intermediate A bracket. The tail shaft contains the SKF coupling which disconnects the tail from the intermediate, the main A bracket and the propeller.
Shaft break checks:
Shaft break on:
Pads are applied, no risks and the shaft is not rotating
Shaft off:
Pads are clear of the shaft, shaft is rotating and no fire risks or damage.
Engineering standards? watch routines?
Ensure all equipments and systems are safe, efficient and reliable and are operated the maintained for optimum performance by properly trained personal in a clean and safe environment.
Watch keeping is enforced to maintain engineering safety and reliability, doing rounds to ensure all machinery is safe and working. Looking for fires, gases, floods, fumes, noise, injury and built up dust in filters.
Describe the refrigeration cycle
Compressor acts as an axial pump for the system, pumping the refrigeration round. It comes out the compressor as a HP hot gas and enters the condenser where it gets cooled via sea water, it then leaves the condenser as a HP warm liquid, the cooling changes the state of the gas to a liquid. It then goes to the thermal expansion valve which controls the flow rate of the refrigerant dependant on the temperature leaving the evaporator. The liquid leaves the TEV as a very cold LP liquid and then enters the evaporator where it becomes a gas as it removes the heat from the cold room. The gas then returns to the compressor and the cycle continues again.
Describe the 4 stroke cycle
The 4 stroke cycle is the function of a diesel engine. The 4 strokes are induction, compression, power and exhaust. In induction the inlet valve is open and air is drawn into the cylinder as the pistol moves from TDC to BDC. Compression is where both valves are closed and the pistol moves from BDC towards TDC compressing the new air in the cylinder, as the air is compressed towards the end of the stoke it gets hot, measured atomised fuel is injected via the injector. Power happens after ignition delay, the atomised fuel ignited with the hot compressed air creating combustion, this forces the pistol from BDC to TDC. Exhaust is where the pistol returns back to TDC with the exhaust valve open, purging all the remaining exhaust gases out,
Describe the hydraulic system
A pump forces oil round a system creating pressure, pressure is then controlled by a directional control valve. The oil is filtered, cooled and monitored, the energy from the pressure is turned into mechanical motion.
How do you turn sea water into fresh water
Sea water is converted to fresh water using a reverse osmosis plant. Sea water passes through pre-filters before it reaches the semi permable membranes which dilute the salt solution reducing salt concentration using osmotic pressure. It passes through multiple membranes and if the reverse osmosis is successful it enters a made water line however if it doesn’t filter correctly it goes back overboard, being controlled by a concentration control valve.
How do we make LP/HP air and what is used for?
LP air is typically created by hydrovane compressors which are single stage, oil sealed, rotary sliding cane compressors. The LP air is used for pneumatic tools, radar waveguides, emergency inflation stern seals and pneumatic surveillance panels.
HP air is created by HAMWORTHY compressors where air is compressed into 4 stages at 4, 17.5, 68 and 276 bar. Pistols are driven by a crankshaft using connecting rods. HP air is used for DG/GT starting, siren startup, BA charging, WE system and air driven machinery.
What are the hazards associated with STPs
Dangerous chemicals such as calcium hypochlorite
Raw sewage can give you typhoid, hepatitis and gastroenteritis.
Dangerous gases can be produced such as Methane and hydrogen sulphide, these gases are harmful to the body and flammable. Medical precautions are in place to prevent these hazards such as medical protection, PPE, person hygiene standards and monitoring the atmosphere for gases.
What do you know about condition based monitoring?
Condition based monitoring is regularly monitoring the performance of machinery and equipment to extend its lifetime, measuring things such as vibration doing vibration analysis to ensure the machinery isn’t damaged and if it is it indicates and allows you to find the problem and fix it, prolonging it’s life.
What tests do we carry out on oil and fuels and other fluids?
The tests for fuel are:
Visual test, DFTK, water reaction test and colour test.
For oil the tests are:
insolubles, vescosity, water in oil and acidity
tests for coolant are:
acidity, density and salinity
Why do we have the tag out procedure, how is it used?
The LOTO procedure is in place to enforce health and safety at the highest standard and to prevent damage to the ship or injury to crew. It also logs down all maintenance, including times, locations and job descriptions. It allows the person conducting work to safety isolate and work on their equipment without hazard. It is conducted using a LOTO log book which contains all the information to perform a LOTO. You first gain permission, then inform those affected by the LOTO, then you fill out the index sheet up to the correct point, fill out the labels and put them in place, return the index sheet to the log book and carry out work, on completion you close the LOTO and remove the labels and open the system up.
What do you understand by SHIPHAZ and permits to work?
SHIPHAZ is the event of a hazardous task being conducted on ship like working aloft or divers down beneath the ship. SHIPHAZ enforces the health and safety in regards to these jobs, removing hazards and making the task more safe. Permits to work requires you to get official permission to conduct a job with higher risk than usual, such as docking up for shore supply.
What precautions must you follow when working aloft?
When working aloft you must follow the following precautions:
Sentry is set at the bottom of where you are working with a hard hat, you are to wear an in date harness attached to a safe point, your tools must be secured, slip proof boots must be worn, no loose objects and overalls worn and tucked in.
What precautions must be follow when working in a confined space?
When working in a confined space you should monitor the air constantly in case dangerous gases emerge, you must wear PPE, have a sentry at the access, no smoking, personal life line and BA available for sentry, person conducting work medically fit.
