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Tomislav Skračić, MA Undergraduate English Course for MARINE ENGINEERS 5th Semester Essential reading: SPINČIĆ, A., PRITCHARD, B., An English Textbook For Marine Engineers 2., Pomorski fakultet, Rijeka 2009. LUZER, J., SPINČIĆ, A., Gramatička vježbenica engleskog jezika za pomorce, Pomorski fakultet, Rijeka 2003. Lesson 15 STARTING AIR SYSTEM Lesson 15 – Starting Air System KEY WORDS starting air system - sustav uputnog zraka admit (v.) - dovoditi, pustiti receiver / bottle - spremnik / "boca" stlačenog zraka bore (n.) - provrt, otvor, kalibar large bore pipe - cijev velikog promjera air starting valve - uputni ventil, v. uputnog zraka pilot air system- sustav upravljačkog (sekundarnog) zr. pilot air control valve - ventil upravljačkog zraka starting (air) lever - ručka zraka za upućivanje starting air distributor - razvodnik zraka za upućivanje ahead / astern - naprijed (forward) / natrag (backward) timing valve - fazni ventil cam (n.) - brijeg camshaft (n.) - bregasta (razvodna) osovina Lesson 15 – Starting Air System KEY WORDS gear drive - zupčani prijenos interlock valve = blocking device - ventil uređaja za blokiranje remote operating valve line - daljinski upravljana veza ventila remote operating non-return valve - nepovratni ventil s daljinskim upravljanjem turning gear - uređaj / sprava za okretanje, "prekret" flame trap - odvajač / prigušivač plamena relief valve - odušni ventil starting air main - glavna linija uputnog zraka burst (v.) - prsnuti, puknuti unidirectional engine - istosmjerni motor pilot air - sekundarni zrak on the very bottom - na samom dnu the very man - baš taj čovjek ● Marine diesel engines are started by admitting compressed air to the cylinders at the appropriate point in the cycle. The air is stored in receivers which are charged by compressors. A pressure of about 28 bar is usual. ● Compressed air from the receivers is supplied by a large bore pipe to an automatic or remote operating non-return valve and then to the cylinder air starting valve. Opening of the air starting valve will admit compressed air into the cylinder. The opening of the remote operating valve and the air starting valve is controlled by a pilot air system. The pilot air is drawn from the large bore pipe and passes to a pilot air control valve which is operated by the engine starting air lever. ● When the starting lever is moved, part of the pilot air flows to the automatic or remote operating valve causing it to open. Another supply of pilot air for the appropriate direction - ahead or astern- is passed to the air distributor. This device consists of timing valves synchronized with the engine position in order to provide air to operate each starting valve in the correct order and timing as the engine rotates. Timing is controlled by cams or gear drive from the engine camshaft. ● The air strating valves are held closed by springs when not in use and opened by the pilot air enabling the compressed air from the recievers to enter directly the engine cylinders. An interlock is fitted to the remote operating valve line to stop the valve opening when the engine turning gear is engaged. The remote operating valve prevents the return of air which has been further compressed by the engine into the system. ● Lubricating oil from the compressor will under normal operations pass along the air lines and deposit on them. In the event of a cylinder air starting valve leaking, hot gases would pass into the air pipes and ignite the lubricating oil. If starting air is supplied to the engine, this would further feed the fire and could lead to an explosion in the pipelines. ● In order to prevent such an occurrence, cylinder starting valve should be properly maintained and pipelines regularly drained. In an attempt to reduce the effects of an explosion, flame traps and relief valves are provided in the pipelines. In addition, an isolating non-return valve is fitted to the system. ● Compressed air systems are liable to contain a certain amount of water which is a result of condensation in the process of compression and cooling. Most of the water condenses out in the air receivers and it can be drained from the recievers by internal pipes so arranged as to blow any water from the very bottom of the receiver. Exercise 1 – QUESTIONS & DISCUSSION 1. How is starting of marine diesel engines effected? 2. What is compressed air made to pass through before entering the cylinders? 3. What pipelines does the starting system consist of? 4. Say what occurs when the starting lever is operated. 5. What is the function of the air distributor? 6. What is the air distributor driven by? 7. What is the purpose of the remote operating valve? Exercise 1 – QUESTIONS & DISCUSSION 8. Why is a blocking device (interlock) fitted in the remote operating valve line? 9. What conditions may lead to an explosion in the starting air pipelines? 10. What precautions are adopted to prevent or minimize the danger of explosion? 11. Why must air receivers be fitted with drains? Exercise 2 – Say which of the following statements are TRUE and which are FALSE. If FALSE, state why. a) b) c) d) e) f) g) h) All engines are started by compressed air admitted to the cylinders. The cylinders are directly charged with starting air by compressors. The compressed air from the bottle is necessary to ignite the fuel. Valves, operated by a mechanism, control the admission of starting air to the working cylinders. The starting air valves are kept closed by means of spring when the engine is running. An automatic or remote control operating valve is fitted to each cylinder and each valve is connected to the starting air main. When the pilot air is admitted to the remote operating valve, it opens and allows air to be supplied to the starting valves. The air starting valve also acts as a non-return valve to prevent high pressure from the working cycle in the cylinder entering the starting system.