Safety Devices In Air Compressors On Ships c2k27

Safety Devices in Air Compressors on Ships What is emergency air compressor ? 

It is a small compressor independently driven by a prime mover having power supply from emergency switch board. They are also driven by diesel engines.

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It must be fitted to press up the emergency air bottle and to start auxiliary engine of a dead ship.

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It has no connection between the main air bottle.

What are the safety devices in air compressors on ships ? 1. Bursting discs are fitted on the cooler shells (At water side). 2. Relief valves are fitted to discharge side for every stages. 3. Moisture drain valve (unloader) are fitted at each cooler side. 4. Cooling water failure alarm. 5. Low L. O pressure alarm and trip. 6. Delivery air high temperature alarm on after cooler outlet (Max 93° C) What are the normal parameters of air compressor ? 

LP discharge pressure: 4 bars

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HP discharge pressure: 30 bars.

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Intercooler inlet air temperature: 130 ° C

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Intercooler outlet air temperature: 35 ° C

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After cooler inlet air temperature: 130 ° C

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After cooler outlet air temperature: 35 ° C

Type of intercooler and after cooler ? 

Intercooler is single type

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After cooler is double U-tube type

Purpose of unloder valve (moisture drain valve) in air compressor ? 

At starting this valve must be opened, this reduced the starting torque for the machine and clear out any accumulated moisture and oil in the system.

What would be effect of suction valves of an air compressor having too much lift ? 

The valve will be late in closing and this would reduce the volumetric efficiency of the machine.

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The valve experience greater force and therefore are more liable to break.

Effects of reduced volumetric efficiency of air compressor ? 1. Greater bumping clearance. 2. Sluggish opening and closing of suction and delivery valves. 3. Insufficient cooling water that effect of high air temperature. 4. Dirty or partially chocked suction air fitter. Difference between relief valve, bursting disc and fusible plug ?

Pressure relief valve 

Excess pressure is released by opening the valve.

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It opens at 10% over working pressure.

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Valve lift is proportional to excess pressure build up.

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Valve setting pressure can be altered by spring tension.

Bursting disc 

Pressure is released by bursting the disc.

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It permanently damaged.

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It burst at setting pressure.

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Setting pressure cannot be altered in place.

Fusible plug

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When the air temperature from compressor is high (above 105 ° C) pressure is released by melting (fusing) the metal.

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It cannot be used next time. ( permanent damage)

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Release all content or pressure to empty.

Why multistage compressors are mostly used than single stage compressor ? 1. More stages are needed to increase the required final pressure. 2. Easier to control the air temperature. 3. Reducing in air compressor size. 4. Lubrication problem does not exit. 5. Reduced the thermal stress. 6. Lower work done to compressing air. 7. Improve compressor efficiency Advantages of inter cooling of air compressor ? 

To avoid excessive temperature rise associated with higher compression ratios, and to approach isothermal compression.

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Saving in power.

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Volumetric efficiency is increased.

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Reduced the volume of air delivered and also reduced the compressor size.

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It can reduce the air temperature.

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Due to less temperature suction & delivery valves remain cleaner without being fouled with carbonized oil.

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It can avoid a danger of an explosion takes place in compressor cylinder.

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It allows good lubrication of the compressor piston.

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Moisture separation is easier through inter cooler drains.

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It also enables to deal with a greater weight of air for the same energy expended.

Why intercooler is fitted in main air compressor on ships ? 1. Reduced air temperature, volume and increased air density for next stage 2. So increased volumetric efficiency and compressor efficiency. 3. Due to reduced temperature give better lubrication for cylinder and piston rings 4. Drain are fitted from which water and excessive oil can be drained out, to prevent air bottle corrosion and starting air explosion and fouling of inter coolers and pipe. 5. Save the work done. Advantages of after cooler in air compressor ? 

To reduce final discharge air temperature thus air bottle size can be reduced.

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To reduce air volume after it has been compressed to the final pressure.

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So greater amount of air could be stored in air bottle.

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Increase volumetric efficiency

How to start the air compressor manually on ships ? 1. Change the switch to manual position on the switch board. 2. Check the L.O sump level and condition. 3. Open the moisture drain valve. 4. Open the compressor discharge valve & charging valve of air bottle. 5. Open cooling water system valves. 6. Turn the compressor flywheel by hand (one turn). 7. Start the motor, after draining the moisture shut the drain valve. 8. Check the motor ampere consumed. 9. Check the pressure gauge readings.

10.Frequently drain the moisture. 11.When charging full, open drain valve and stop the compressor How do you check compressor efficiency during running ? 1. Checked by filling time with the previous record and also check the first stage discharge pressure. If compressor efficiency is lower, compressor will run longer and compressor temperature will rise. 2. First stage and second stage pressure gauge must be correct and stable. 3. No escape of air from suction filter. 4. Intercooler and after cooler outlet air temperature should not be high. 5. If open drain valve nothing can be found. 6. Low L.O consumption. 7. Oily air mixture must not blow out from breather pipe. Safety devices on main air bottle ? 1. Pressure relief valve. 2. Fusible plug.(if safety valve is not directly fitted on the bottle) 3. Pressure gauge. 4. Low air pressure alarm. 5. Moisture drains valve. Where is the fusible plug fitted and its purpose ? 

Fusible plug is fitted under side of the pipe between relief valve and air bottle.

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It is fitted to release the compressed air in the event of abnormally high compressed air temperature.

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Fusible plug melt at 105 °C and release all content of air.

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It is made by 50% bismut, 30% tin, 20% lead.

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A fusible plug is fitted after the second stage cooler to limit the delivered air temperature and thus protect the compressed air reservoirs and pipe work.

Can you fit the relief valve at the space of bursting disc and why ? 

At the compressor, relief valve can not be fitted at the bursting disc, because of their difference operation.

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Bursting disc is fitted for totally release and stop operation circuit.

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Release valve opens excess pressure at compressor running and reset when pressure reduce or when the compressor is stopped. Thus cooling water can enter to compressed air space; it can cause water hammer when the next start of compressor.

Air Compressor

Image Credit: leelloyds.com Effects of leaking valves in Air Compressor: First Stage Suction: 

Reduce air delivery

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Reduce 2nd stage suction pressure

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Unload the compressor

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Increase running time.

First Stage Delivery:

1. Reduce air delivery 2. Increase discharge temperature 3. Less air drawn in, due to high-pressure air leaking back into cylinder. Second Stage Suction: 1. Reduce air delivery 2. High temperature & pressure in 2nd stage suction line 3. Increase running time Second Stage Delivery: 1. Reduce air delivery 2. Increase suction pressure in 2nd stage 3. Increase delivery pressure from 1st stage. 4. Back pressure from air bottle. How to check Air Compressor Efficiency? 1. Regular overhauling of valves done or not. 2. Check Air Bottle filling time. 3. Compare test results and records. How to check Air Compressor capacity is sufficient? 

Total no. of Air Compressors must be sufficient to fill the empty Air Bottle to maximum pressure within 1 hour.

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Must be sufficient to start at least 12 times for Reversible Engine, and at least 6 times for Non-Reversible Engine.

Bursting Disc: 1. Fitted on the shell of Intercooler at waterside. 2. Relieves pressure if the tubes burst.

3. Rolled Copper Alloy and relief pressure is set while the disc is at softest condition. 4. Material tends to harden due to time and surrounding temperature, and set pressure also increased. 5. Bursting Disc needed to be annealed, to regain correct relief pressure. Compound Valves, why used in Air Compressor? 1. Give large area of opening and small amount of valve lift. 2. Improve Volumetric Efficiency, as valve open and close in minimum time. 3. Reduce bumping clearance. 4. Reduce wear and tear. LP Relief Valve opening: Causes: 1. HP suction valve 2. Intercooler choked. 3. Relief valve, jammed by foreign particles, in open position. HP Relief Valve opening: Causes: 1. HP discharge valve, in closed position. 2. After cooler choked. 3. Relief valve, jammed by foreign particles, or spring sticking in open position. (Relief Valves opening pressure are set at ≯ 10% above stage pressure.) Why Intercooler is fitted? 1. Reduce air temperature and volume, and increase air density for next stage. 2. Increase Compressor Capacity and Volumetric Efficiency. 3. Better lubrication for cylinder and rings.

4. Water and excess oil can be drained out, preventing fouling of Intercooler and pipes, Air Bottle corrosion, and starting airline explosion. 5. Work done is saved. 6. Metal stresses reduced, due to control of temperature. Volumetric Efficiency: VE = (Volume of Air drawn into Cylinder) / (Stroke Volume of LP Piston) and VE = (Volume of Air discharged as ‘free air’) / (Stroke Volume of LP Piston) Why Multistage Air Compressor is built? 1. To obtain near to ideal isothermal compression, compressor is to be constructed of multistage with inter-stage cooling. 2. Inter-stage cooling reduces air temperature and volume after 1st stage compression, thus increase mass of air for 2nd 3. Workdone is saved and air compressor efficiency increased. Other advantages are: 1. Easy to get high final air pressure. 2. Easy to control air temperature. 3. Easy to maintain correct lubrication. 4. Better compressor balancing. 5. Reduction in size. 6. reduction in clearance volume loss. Capacity of air compressor: 1. Capacity is checked upon how much filling time is lowered. 2. Compressor should have enough filling capacity so that sufficient stopping time should be provided between fillings.

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12 consecutive starts in reversible engine and

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6 consecutive starts in non-reversible engine.

What is Free Air Delivery, FAD? 1. Capacity of Air Compressor is stated in of [ m³/ hr ]. 2. Volume of air actually discharged in 1 hour, that would occupy if expanded down to atmospheric pressure and cooled to atmospheric temperature. Safety devices on Main Air Compressor: 1. Bursting Disc on Intercooler: (At water side) 2. Bursting Disc and Fusible Plug (121°C) on Aftercooler 3. Relief valves on LP and HP stages. (Set to lift at 10% rise above normal stage pressure.) 4. Automatic Moisture Drain Valve. 5. Cooling water supply failure alarm. 6. Low LO pressure alarm. 7. Relief valve on crankcase LO pump. 8. Delivery air HT cut out and alarm on Aftercooler outlet. (Max. 93°C) 

LP discharge pressure 4 bars and HP discharge pressure 30 bar

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Intercooler inlet air 130°C and intercooler outlet air 35°C

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Aftercooler inlet air 130°C and Aftercooler outlet air 35°C:

Intercooler is single type: Aftercooler, double U-tube type:} Uses of Compressed Air: 

Engine Starting 20 to 25 bar

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Boiler Soot Blowing 20 to 25 bar

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General Service (Whistle, Pneumatic Tools, Lifeboat , service air for cleaning and Pilot ladder) 7 to 10 bar

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Instrumentation and Control 5 bar

Air Filter: 1. Material: Felt, Metal gauze or Nylon strands 2. Removes contaminants from air. Dirt and dust act as abrasives and increase wear. 3. Contaminant deposits on valves can become hot and source of ignition. Hazard of Dirty Filter: 1. Very dirty filter or muffling a filter results in large pressure drop. 2. Air has to be compressed over higher range. 3. In extreme case, discharge air temperature may exceed flash point, or auto-ignition temperature resulting in an 4. As a safety against explosion, air temperature is limited to 93° Fusible Plug (121°C) or a High Temperature cut out (93°C) is provided on Compressor. Pressure Test on Air Compressor: 

Cylinders, cylinder cover, Inter & After coolers are hydraulically tested to:

Air Side: 1.5 x max. Working Pressure. Water Side: 4 bar or 1.5 x max. WP (whichever is greater)

Air receiver: 

Total capacity of air receivers must be sufficient to give at least 12 starts for reversible engine, and at least 6 starts for non-reversible engine, without refilling the receivers.

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There must be two identical main air receivers and one emergency bottle for every vessel.

Mountings of Air receiver: 1. Fusible plug: 

composition – Bismuth 50%, Tin 30%, Lead 20%,

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Melting point: 220΄F (104.4΄C). Fitted at the reservoir’s bottom or on reservoir at ship side, when relief valve (safety valve) is not directly fitted on the reservoir.

2. Atmospheric relief valve: provided for back-up of fusible plug. In case of ER fire when CO₂ flooding is required, this valve is opened before evacuating ER. 3. Spring loaded safety valve: setting pressure: 32 bar (for 30 bar working pressure), with ≯ 10% rise in accumulation of pressure. May be fitted directly or with extension. 4. Compensation ring: when a hole is cut or machined in pressure vessel, higher stresses will subject to the material around the hole, and to reduce this, compensation rings are fitted. It is a flange on which a valve or fitting is usually mounted. 5. Manual Drain valve or Automatic Drain valve. 6. Pressure gauges. 7. Access doors. 8. Main starting air valve, auxiliary starting air valve, filling valve, service air or whistle air valve. Internal surface coating: Graphite suspension in water, Linseed oil, Copal vanish or Epoxy coating having basic properties of anti-corrosive, anti-toxic or anti-oxidation. Safety devices on Main Air Bottle: 1. Fusible plug. 2. Pressure Relief Valve 3. Atmospheric Relief Valve. 4. Low Air Pressure alarm. 5. Automatic or remote control Moisture Drain Valve. How does emergency alarm ring?

Ans: Continuous ringing of bell. Emergency situation is explained at the muster situation. Pattern of Emergency signal is indicated on Muster list Q. Explain the Fire Tube and Water Tube Boiler.

Fire Tube Type: Due to simple design of the tubes effective heat transfer takes place, but periodical cleaning/maintenance is slightly difficult. Soot blowing is not effective for regular cleaning. Used with low pressure boiler

Water Tube type: In comparison to fire tube type heat transfer is not so so effective. Gas side cleaning is easier, sometimes fixed water spray design is used for cleaning. Soot blowing is effective , used with medium – high pressure boiler Q. What is Ogee ring?

Ans: Connects the bottom of the furnace to the boiler shell plating.

Q. How the boiler Gas side is cleaned during operation?

Ans: i. By means of steam, soot blowing ii. By injecting soot remover powder (chemical) to the system. Sketch a gauge glass and explain blow down procedure.

Ans: a) Close steam and water cock, open drain cock, nothing should come out the cocks are not leaking. 1. Open and close steam cock to check cock is clear. 2. Open and close water cock to check cock is clear. 3. Close the drain 4. Now open water cock, water should gradually rise up the top of gage glass. 5. Open the steam cock, the water should fall to the level of the water in the boiler. What is the consequence of low water level? What is your immediate action?

Ans: Boiler running without water will cause overheating the tubes, tube plates and shell, that will lead the boiler to face thermal over stress damage, crack or rupture to the tube, tube plates, shell plates. However, low water level alarm should be activated and boiler firing will shutdown. If the boiler water level found minimum at the water cock level it is safe to put feed water in the boiler. If the level is below this line care has to be exercised not to thermally stress boiler while putting water into boiler. What is the consequence of high water level? What is your action?

Ans: This will cause priming of the boiler, loss of heat from the heaters, possibly loss of steam pressure.

As per as possible steam heating to be minimized temporarily, carry out partial blow down to normal level. Then introduce normal heating again. What is the purpose of treating boiler water?

Ans: a) Prevent scale formation b) Prevent corrosion c) Control of sludge formation and prevent carry over to the system d) Prevent entry of foreign matters to the boiler. What type of chemicals are used to treat low pressure boilers?

Ans: Lime Ca(OH)2 and soda ash are used Na2CO3 are used to deal with calcium and magnesium compounds in the boiler water. MgCl2 + Ca(OH)2

Mg(OH)2 + CaCl2

CaCl2 + Na2CO3

CaCO3 + 2 NaCl

What is the problem if boiler water contaminated with oil?

Ans: i) Create layer on the boiler plates, tubes etc and reduces heat transfer and thermal stresses are induced. ii) initiates corrosion With regard to capacity state the regulation for steering gear?

Ans: A vessel at deepest draught and at maximum service speed should be able to move rudder angel from 350 one side and to 350 other side. It should be capable to move 350 one side to 300 other side within 28 seconds. The auxiliary steering gear should be able to move from 150 one side to 150 other side at half service speed or 7 knots whichever is greater in 60 seconds. Describe steering gears routine checks before departure and arrival ports.

Ans:

I) After prolonged use of auto pilot check remote/manual steering on arrival. ii) Check both steering gear power unit on arrival, run simultaneously on maneuvering channel. On departure from port within 12 hours: 

Check main and auxiliary steering gear

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Remote control system for steering gear

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Steering position on navigation Bridge

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Emergency power supply

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check com rudder angel position

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Alarms

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Auto isolation arrangements

How often the emergency steering drill is carried out? How you used to carry out in your last ship?

Ans: Every three months. Controlling the pumps in either direction by means of manual push buttons from steering gear room locally. What is the function of by valve and relief valves?

Ans: By valve are used to open circuit any particular unit. Relief valves are given to relief over pressure, especially during rough sea undue movements of rudder created extra oil pressure which is relieved by them to avoid any rupture, leakage, damage. Care and management of pumping systems: Candidates should remain aware of various pumps working principle. Q:

Classify pumps.

Ans: i) Positive displacement pumps e.g. reciprocating, screw, gear etc. ii) Rotor dynamic e.g. Centrifugal,

Q: A centrifugal pump not taking suction, what action you are going to take?

Ans:

Q:

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Check valves open

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Suction live have crack/leakage

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Air Ingress to check, primer to check

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Suction line ting to check

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check suction filter clogged

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should the above not complying check the wear ring clearance excessive

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may be the impeller securing arrangement detached. Why positive displacement pumps require relief valves?

Ans: with the pumping action, pumping rate is same but if the delivery is obstructed the pressure will be built up gradually, which will damage line, casing etc. To protect from above relief valves are required to be fitted. Q: What type of pump is used for Oily Water SWeparator? Is centrifugal pump is suitable for the above?

Ans: positive displacement pumps e.g. rotor line screw, reciprocating and gear pumps are used for the above. Centrifugal pumps are not suitable for above because they produce large quantities of small oil droplets. Q:

How the tubular coolers thermal expansion is allowed?

Ans: i) By means of expansion piece ii) by means of free end arrangements Q:

What for “bilge injection” v/v is used? What is relevant regulation?

Ans: Bilge injection valve is used for in case of serious flooding in the machinery space. Diameter of the valve should be 2/3rd of the diameter of main sea inlet, valve spindle should be clear of engine platform. What is the function of oil sensing probe in OWS?

Ans: The Capacitance probe in 1st stage senses and causes the solenoid to be energized through control switch. Hence control air access to the diaphragm controlled piston valve to drain oil to bilge oil tank.

Q:

what is the function of coalesce filter ?

Ans: Removes fine solids up to certain extent. Small drops of oil coalesce to form larger drops. These rise up to oil collecting space. Q: How to ensure no accidental discharge O/B will take place from O.W separator?

Ans: i) 15 PPM alarm monitor will activate and discharge P/P will stop automatically. ii) Three way valve will activate on reaching effluent content 15 PPM, will divert the flow to bilge water tank instead of O/B. Construction, maintenance and operation of fire fighting equipment, fire prevention:

detection and

Candidate should know the basic principle operation of portable extinguishers, fixed fire fighting installations and fire detector sensors.

Q:

With regard to capacity state the regulation for emergency fire p/p.

Ans: Capacity should be at least 40% of fire pumps but not less than 25m3/hour. To supply 2 jets 13 mm dia with a horizontal throw of 13 m. Q:

How does smoke detector works? How do you test it ?

Ans: smoke is sensed by the photo electric call, this signal is transmitted to trigger the alarm. It can be tested by (i) Smoke (ii) Spray can Q:

How does sprinkler system work? Where is it used ?

Ans: Sprinkler heads are fitted with quartzoid bulb. Heat expands the liquid and shatters the bulb. Water strikes a deflector to ensure a cover of floor area of 12m2. On dropping system pressure sprinkler P/P starts automatically. Used for accommodation, alleyways of enger ships and some cargo spaces. Q:

What is international shore connection?

Ans: It is to be provided to enable water to be supplied from another ship or from shore to the fire main.

PCD 132 mm, Outer dia of flange 178 mm, Bore (inner dia of flange) 64 mm. 4 bolts are required of 16 mm dia and 50 mm length. Q:

With regard to CO2 total flooding state the regulation?

Ans: 85%of the gas must be released within two minutes. The quantity of gas carried 1. must be sufficient to give a free gas volume equal to 40% of the volume of the space except where the horizontal casing area is less than 40% of the general area of the space. 2. Must give a free gas volume equal to 35% of the entire space whichever is greater. Q:

How the CO2 total flooding system is maintained?

Ans: CO2 room visual inspection is carried out regularly (say weekly), CO2 alarm checked on monthly basis and servicing and others checking of the system is carried out annually by authorized work shop. Modern vessels maintain routine check lists of weekly, monthly, quarterly, 6 monthly and annually. Q:

What is fireman outfit?

Ans: a) A safety lamp b) A fireman’s axe c) A breathing apparatus or ii. Smoke helmet, or A smoke mask. Q:

Before wearing a BA set, what would you check?

Ans: i) Pressure normal; 140-210 bar ii) Test alarm whistle working iii) Check mask “seals”, not leaking Alarm comes when air contents are brought about 80%.

Q:

State the procedure of CO2 flooding

Ans: On completion of assessment , permission granted by Master in consulting with chief engineer to carry out flooding: 

personnel counted

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all openings sealed including flaps, ducts for ventilation

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shut down all fans, blowers, pumps, purifiers, motors by remote stop device

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shut down fuel supply by quick closing valve operation

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follow operating instruction for operating pilot cylinder for gang release and there after the master valve

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use boundary cooling and observe fire and rescue procedure.

Q:

what are the safety incorporated in co2 system? How it works?

Ans: 1) relief v/v on manifold, rupture dick for cylinders 11) interlock for fan, pump and purifiers stop 111) audio-visual alarm while operating lever box is opened. iv) overriding procedure for releasing, if pilot release fails

co2 cylinders are stored to maintain temp below 55ºc and at 52 bar. If pressure rise above 177 bar at temp 63ºc or above, rupture disk on cylinders opens. This gas is released through safety v/v on manifold. When the co2 cyl require recharging? How the content be checked?

Ans: Re-charge when weight reduce by 10% 

check by weighting, or radio active level indicator or ultrasonic gauging.

Codes of safety working practices: Candidates should be familiar with a book “code of safe working practices” available on board vessels. It is important to identify safeties to encounter hazards.

Q:

What precaution should be taken while entering a enclosed space?

Ans: To be complied with company check lists but in the general it will cover followings: 1. Assessment of atmosphere 2. Ventilation 3. Illumination (safety) 4. Permit to work 5. Self contained B/A set stand by 6. Ladder required as appropriate 7. Man standby at entry position 8. Communication should be established Q:

What precaution should be taken before decarbonizing a M/E unit?

Ans: Company policies are relevant. In general they are 1. Immobilization granted 2. Turning gear engaged 3. Starting air valve shut off 4. System, staring air line vented 5. Starting air distributor inlet valve shut 6. Appropriate notices given 7. Fuel, cooling etc relevant valves in appropriate position 8. Over head crane tested.

Methods of manicuring, including bridge control Systems and Variable pitch propellers.

Bridge Control Procedures:

Engine should be tested from ECR first to ensure safe operation. If satisfactory, control is change over to bridge and engine tested ahead and astern, telegraphic printer checked working Properly.

Bridge alarm checked, in order. During maneuvering speed program may be cancelled, while at full away condition load up program should remain on to speed up gradually. Maximum rpm can be limited from ECR. Variable pitch Propellers:

While testing engine/vessel ahead and astern movements, only propeller pitches are adjusted to get desired movements. Engine need not to stop for ahead/astern moves. Engine clutch/declutch mechanism can be utilized as appropriate. Hydro oil level, pressure, and pumps should be checked. Pitch control – tried out from bridge/control room as well from local control. Emergency Control: Q:

With respect to M/E , what is emergency control?

Ans: Should M/E remote operation is not working, it may be operated from emergency / local control stand which will cover following: 1. Manual Fuel Control 2. Manual Air control 3. Manual Reversing Q: What action you are going to take in the event of a black out/M/E failure?

Ans: 1. Inform bridge/chief engineer 2. Engineers alarm may be raised for additional help 3. Emergency lighting/emergency generator will be active 4. identify the problem, preferably start other generator which was not in service and restore power. 5. Run appropriate cooling P/Ps, reset all needful breakers, start all other plants 6. Prepare M/E and restore same after informing bridge 7. Check all Standby machineries and emergency equipments at ready mode.

Working principle and constructional details of a compressor, air receivers, and associated equipment:

Candidates should have understand the efficacy of inter coolers, P-V diagrams gain in efficiency. Q:

What is the working principle of a main air compressor?

Ans: Reciprocating motions are used to in conjunction with spring loaded non -return suction and delivery valves to achieve compressed air. Intercoolers are used to acquire gain in efficiency. Q: Describe the construction of a main air compressor you used in our last ship.

Ans: It was a in line reciprocating 2 stage compressor. 1st stage piston relatively larger and 2nd stage piston smaller in comparison, materials respectively aluminum and cast iron. Both stages were having spring loaded suction and discharge non-return valves. Inter stage cooler and after coolers were there. Q:

Other than in line, what different type of compressor is used?

Ans: Tandem type compressor are the other type commonly used. 1st stage piston relatively larger, 2nd stage piston exists on top of above relatively of smaller size. Q:

Why the bumping clearance is important?

Ans: Bumping clearance should be optimum. The more clearance volume increase, volumetric efficiency and hence capacity decreases. Q:

How do you take bumping clearance?

Ans: Remove suction or disch valve assy from the unit, place a small ball of lead wire on the piston edge. Then rotate the flywheel by hand and to take the piston at TDC. Remove and measure the thickness of lead wire ball. Q:

What is function of intercooler and after cooler?

Ans: Intercooler:

i) Decreases air temp

ii) Reduces work done iii) Maintains safe lubrications iv) Increase compressor efficiency After-cooler:

i) Separate oil and water from compressed air

ii) Reduces air temperature before the filling receiver Q:

What mounted safeties are incorporated with a main air compressor?

Ans: i) Relief valves are fitted at the discharge of each stage

ii) incorporated discharge non return valve iii) Bursting discharges are fitted with intercoolers to protect from over pressure due to tube leakage iv) Un-loader/drain valves Q:

What safeties are incorporated for compressor protection?

Ans: i) Low pressure alarm, stop for lube oil ii) Jacket high temperature/air discharge high temperature, alarm, stop. Q:

Describe the special features for main air receivers?

Ans: i) Manhole door elliptical, for the ease of opening and consider strength of the pressure vessel ii) Circumferential and longitudinal welding seams are existing. iii) Relief valve fitted (if isolated from relief valve, fitted with fusible plug, melting point 1500 C.) iv) Drain valve, pressure gauge v ) Pressure switch for cut in /cut off air compressor auto running.

Operations, Testing Power, the running adjustment to maintain performance: Candidates should know how to use indicator machine, taking power cards, draw cards etc and know how to measure engine power. Q: If an individual unit of M/E shows high exht temp, what should you do ?

Ans: i) If the parameter goes beyond limit, that case engine power/rpm may have to be reduced informing bridge and chief engineer. Need to find out fault. ii) check the funnel smoke and check the pyrometer is correct, fuel rack in order.

iii) Fuel injection equipment, – fuel valve, fuel P/P may be faulty. Take power card to understand fuel injection, all units peak pressure may be compared iv) Compression pressure can be checked from above, to have an idea about liner wear/piston rings. v) Exhaust valve operation can be checked visually (through glass) or light spring card can be taken to ensure the problem with exhaust valve or not. vi) check particular unit scavenge drain line vii) Should all above are in order, consider mistiming for late injection or mistiming of early opening. Q:

M/E all units exhaust temps are high what could be the reason?

Ans: Consider it is a common problem for all, hence it can be of followings: 1. Faulty governor or fuel linkage 2. Fuel quality to be assessed 3. Problem with T/C, scavenging not enough 4. T/C Air filter dirty 5. Scav. Air temperature high 6. Residual temperature low, responsible for incorrect injection 7. check fuel load, if the vessel at shallow water 8. Ships hull fouled 9. in worst case due bad quality fuel injection equipment may be worn. Q:

How do you calculate POWER in a conventional method?

Ans: – take power card (in-phase diagram) Where: PmLAN in KW = POWER ……………… (1) Pm = MEAN EFFECTIVE PRESSURE

, L= STROKE LENGTH, A= AREA OF PISTON , N= REVS NO.

Calculate area of the diagram by using planimeter, check length of diagram

Calculate the mean height of diagram, which is n = area (mm²)/ length(mm) Now the MEP= h (mean height, mm) x spring scale (bar/mm) i.e MEP found in bar or, MEP is (barx10²) kN/m² from (1) we get power= PmLAN kW for one cylinder. For total engine, the result of other cylinders to be ed for. Q: What was the main Engine Type in your last ship? How did you calculate engine power?

Ans: Engine Type SULZER5RTA48T Power of first estimation was P1(KW) can be read from the graph read by (Fn-F0)×N from Where

Fn = Load indicator pos

F0 = 1.22 (mean), pos of load indicate pos corresponding to FO P/P idle stroke N = Engine speed (rpm) r

Hu

Effective Power 818.70

N=

P1×—————-×————- KW

42.50

r = Specific gravity of FO at engine inlet temp r`= 8.18.7 kg/m3 FO used during trial (at engine inlet temperature) Hu= Lower catorific value of fuel oil Hu`= 42.50MJ/Kg (lower cal. Value of DO used during trial) Safe and efficient operation and maintenance of marine diesel Engine

candidates should remain aware of the working principles of various main and auxiliary machineries. Should know how to decarb a particular 2 stroke/4 stroke engine unit and relevant inspections. To be familiar with operation recommended by the manufacturer, specially while during operation with defective components.

What is the indication of black/blue smoke?

Ans: Black smoke indicate incorrect /incomplete combustion. Blue smoke indicates of LO with the combustion. Smoke should be clear.

burning

What are the causes of scavenge fire?

Ans: i) Blow past through liner and piston rings ii) Due to incorrect fuel injection iii) Due to lack of cooling, breaking of Cylinder LO film iv) Excessive cylinder lubrication give undue fuel and cylinder film breakage will cause hot gas to blow by, consequence scavenge fire. What action you are going to take with above?

Ans: i) Inform bridge/chief engineer officer ii) Slow down engine to extinguish fire iii) Scavenge drain can be checked carefully iv) shut off fuel to the particular unit v) Increase cyl lubrication to give adequate sealing vi) check funnel, scav drain, scav temp if satisfactorily return to normal with appropriate rpm. vii) if above are not successful, not extinguished, stop engine, engage turning gear, mask T/C air filter, use fixed CO2 / steam to extinguish. viii) On completion, inspect, rectify the fault then start engine.

Candidates to know starting air explosion and c/case explosion, causes, remedy and action. What inspection is carried out on piston ring?

Ans:

i) Axial clearance . ii) Butt clearance iii) Ring thickness iv) Radial thickness v) ring tension What inspection should carry out with cylinder liners?

Ans: i) Check the ridge on top, remove by grinding if any 1. ii) check for crack, oilyness

iii) Check lubricators, condition of retaining Cylinder LO iv) Check for wear (gauging), ovaliti v) Scuffing vi) Abrasive wear vii) Corrosion What is thrust block?

Ans: This makes use of the engine bedplate and seatings to distribute the propeller thrust to the ships structure. What is the function of flywheel?

Ans: i) Store energy while acceleration and releases while deceleration, smooths out fluctuation of engine speed. 1. ii) Turns the engine for maintenance

iii) Used as pointer of engine position What are the TBN values for C/C oil of cross head engines and trunk piston engine?

Ans: Engine using residual fuel, C/C oil to be alkaline.

For X-head engine 10-15 TBN For trunk piston engines up to 40 TBN What is microbial degradation? Ans: It is a infection of C/Case oil by micro organism. This live by consuming hydrocarbons in the base oil together with nitrogen, sulpher and phosphorus from additives. Cooling water etc. leakage are responsible for depleting the above situation. Safeties during working shipboard electrical system:

Electrical shock and fire can cause loss of life and damage to the equipment, hence in general following should be complied : 1. To be familiar with ship electrical equipment and diagram. 2. Operate as makers instructions 3. Maintain as per makers instruction 4. Guards, covers, doors etc securely tightened 5. While shutting off the power, inform duty officer/engineer of the watch 6. While maintenance being done, remove fuse etc. 7. Before working with the equipment confirm circuit is dead. 8. Do not leave live conductors or rotating parts exposed 9. Avoid overloading equipment 10.Use appropriate warning notices What are the conditions of electric shock?

Ans 

: Minimum 15 mA AC or DC current is enough to cause an electric shock. Circuit may be from hand to hand or hand to foot. Shock current is related to the applied voltage and body resistance. Unfortunately if the applied voltage goes up, body resistance goes down, that means shock current is further increased.

What are the safety of the boards?

Ans:



Guarded



Insulated barriers



Some board cannot be opened unless the breaker is off



Adjacent floor covered by insulated mats.

During a watch you find low insulation resistance alarm, what is your action?

Ans: Inform chief engineer officer and electrical engineer officer. Meanwhile take following actions to find detect the faulty equipment. 

Isolate/change the running motor and check megger



If not found, check galley, laundry equipments



Deck crane electrical motor



Fwd/aft electrical equipments

After the faulty equipment is isolated, insulation indicator will restore back to normal. How do you check insulation resistance?

Ans: i) Phase to phase ii) Phase to earth. In dry dock while connecting shore electrical power, what will you check?

Ans: i) Check supplied voltage ii) Frequency iii) Phase sequence ( specially check at least one E/R exhaust fan that it is rotating in normal direction). iv) If shore supply is earthed neutral, the ships body has to be earthed. v) Check the capacity of the circuit breaker.

What is the sequence method synchronizing ? if synchroscope and light methods are out of order how do you parallel generator?

Ans: Two lights bright and one light goes out (dark), synchronizing method is sequence method.

Same phase of the bus bar and incoming generator are connected across a 500 V voltmeter. When voltmeter indicates 0 to maximum slowly and when voltmeter shows at zero, breaker to be closed. This is the point where they are in correct phase sequence.