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What is ovality of auxiliary engine crank pin?

Combined effect of reduced effectiveness of L.O and directional thrust of the con rod. This is maximum at around 45 degree ATDC Uneven loading of units and overloading Max Allowed: 1/4th of the bearing clearance Removed By: Insitu Grinding and polishing Reference: Fillet of crank web Max. Allowed Grinding: 2mm, because after grinding 2mm or more surface hardness reduces drastically. Due to this maximum allowable grinding is 2mm. Bottom bearing damage reason is the ovality, bearing clearance and condition of L.O supply 2.

Why are concentric springs fitted for A/E cylinder head valves?

If the frequency of the natural vibration of air or exhaust valve springs is a harmonic of the camshaft speed, then the spring may vibrate axially and are said to surge. Surge can be avoided by modifying the sizes of springs by arranging the springs in pairs and fitting one inside the other. If one spring fails the valve is held up and is not damaged by striking the piston. The thickness of individual springs can be reduced as against original thickness. Normally two springs of different vibration characteristics are chosen. Moreover, the stiffness requirements and the space congestion at this place warrants a concentric springs arrangement. The net stiffness is equal to the sum of individual stiffness.

3.

What is SQUAT Phenomenon?

It is a venturi effect while vessel is moving on shallow water. A vacuum is created due to which the draught of the vessel is increased there by increasing the engine load. Steering ability of the ship is reduced as a result. 4.

What is a thermostatic expansion valve?

This is a regulator through which the refrigerant is metered from the high pressure side to the low pressure side of the system. The pressure drop causes the evaporating temperature (saturation temp.) of the refrigerant to fall below that of the evaporator. a. Avoids liquid refrigerant return to the compressor suction. b. Automatic expansion control and maintain 6 ~ 7 degree superheat. 5.

What is the function of an L.P controller?

The LP controller stops the compressor at low suction pressure caused by the closure of all compartmental solenoids. When the pressure in the compressor suction rises due to solenoid opening, the LP controller restarts the compressor. 6.

What is the function of an L.P cutout?

This is used to protect the compressor against the low suction pressure due to loss of refrigerant or blockage. If the a/c compressor suction pressure is allowed to fall below atmospheric pressure then there exists a risk of moisture and air ingress into the system.

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What is a Coalescer?

A device consisting of a material whose surface provokes coalescence. The process of combining of larger droplets of a liquid like oil into larger droplets is called coalescing.

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MEO Class 4 Oral Questions With Answers 8.

Why is there a starting air overlap provided in a diesel engine? a. To give a positive starting in correct direction. b. Starting ability from any position. c. If any one of the valve is malfunctioning. Engine can still be started.

9.

What is the significance of firing order? a. Balancing of primary and secondary inertia forces. b. To assist the exhaust grouping. c. For distribution of stress over the length of crankshaft and optimum bearing loading. d. A firing interval for even turning moment.

10.

What are the reasons for foaming in refrigeration compressor crankcase?

Due to rapid boiling out of the refrigerant dissolved in the oil when the pressure is suddenly reduced. When the compressor starts operating, if a large quantity of refrigerant has been dissolved, larger quantity of refrigerant boils out and can be carried through the refrigeration lines. Reasons: a. Liquid in the suction line (viz. TEV stuck open, incorrect super heat setting, sensing bulb not closing, overcharge etc.,) b. Crankcase heater not working. c. Compressor capacity too high at the start. d. Expansion valve giving too small superheat e. Oil charge is less. 11.

Explain the functions of lube oil in refrigeration system a. Lubrication b. Seal the clearance spaces between the discharge and suction sides of the compressor. c. Act as a coolant. d. Actuate capacity control. e. Dampen the noise generated by the compressor.

12.

What are the various windlass safeties?

ELECTRIC: a. Electromagnetic brake. b. Motor overload protection. c. Short circuit protection. d. Restart delay timer. e. A Restart stop. MANUAL: a. Manual brake / mech. Brake. b. Cable stopper. c. Slipping clutch (torque limiter).

Class4exam.com Register Yourself In Our Forums d. Relief valve. 13.

What are the steering gear motor safeties?

a. Overload alarm. b. 200% insulation in motor. c. High temperature alarm. d. Self-starting after power failure. e. Short circuit trip. f. Phase failure alarm. g. One of the steering motor is fed from the emergency bus. Hydraulic side there is two trips a. Low level cutout b. High lube oil temperature cutout. 14.

What are the overhead crane safeties?

Current to motor‟s field coils passes through solenoid coil of a brake which is magnetized and holds a brake against spring and releases the rotor. Incase of power failure the solenoid is demagnetized and brake is applied. SAFETY: a. Limit switch on the f‟wd, aft, port, s‟tbd, hoisting and lowering prevents movements more than the allowed limits. b. Overload trip. c. Dead man‟s handle. d. Guards over the pulley. e. Locking device on the lifting hook. f. Mechanical locking (to avoid crane movement during heavy weather)

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MEO Class 4 Oral Questions With Answers 15.

What is a critical pressure?

It is the pressure at which gas will just liquefy at its critical temperature. 16.

What is a critical temperature?

It is the temperature above which the gas cannot be liquefied under isothermal compression. 17.

What are the air bottle safeties? a. Relief valve b. Fusible plug c. Drain d. Low pressure alarm

18.

What happens if fuel pump leaks? a. Fuel quantity is reduced – loss of power, cylinder liner lubrication is affected. b. Loss of cylinder power. c. Late injection. d. After burning. e. High exhaust temperatures, smoky exhaust. f. Power imbalance among units.

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What are the constant tension winches?

It is a variation of the constant pressure and constant horsepower control for variable capacity pumps. It is used to achieve constant tension winch system. In this case the pump control is automatically operative across the neutral such that constant system pressure and hence a constant motor torque is maintained whilst both drawing in and paying out. 20.

What are the causes of turbocharger surging? a. Rapid variation (reduction) in load. b. Chocked exhaust and air passage like scavenge ports, valve or air cooler etc., c. Abnormal fuel system like a unit misfiring. d. Chocked air suction filter, fouling of the turbocharger, unbalanced output from the engine, damaged exhaust valve, scavenge fire.

21.

What are the causes of cylinder head cracking? a. Scale deposits b. Inefficient cooling water c. Uneven tightening of bolts and fuel valves d. Fluctuating cooling water temperature (excessive temperature gradient) e. Overloading or racing of engine f. Faulty relief valve g. Mechanical failure due to gas corrosion, acidic corrosion due to leaky exhaust valves h. Water side corrosion

22.

What is the normal relief valve setting of cylinder head in a diesel engine?

10 ~ 14.5% more than the working pressure about 120 bar (some what higher than maximum pressure) 23.

State the advantages of uniflow scavenging a. Simple liner construction b. Long skirt (for piston) not required c. Stroke length can be increased d. High scavenging efficiency e. High thermal efficiency f. Low grade of fuel can be burnt g. Uniform wear of piston rings and liner h. Less thermal stresses i. Less intermixing of scavenging air with the exhaust gas j. Exhaust valve can be made to open late – more work, close early – scavenge air is more utilized.

24.

Why cylinder liner wear is more at the top? a. High temperature exposure due to the combustion gases b. Loss of liner lubrication in low speed diesels c. Corrosion, predominantly acidic due to combustion products d. Fuel impingement, deposits e. Change of direction of the piston, which causes to a step like formation at the reversal point

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MEO Class 4 Oral Questions With Answers Class4exam.com Register Yourself In Our Forums 25.

What actions do you take incase of stern tube of the ship starts leaking? a. Maintain low head. b. Use higher viscous oil. c. Replenish periodically to counter for the oil loss. d. Drain off the water periodically. e. Try to remove foreign particles by changing direction of shaft.

26.

How do you test a fresh water generator plant for leaks? a. Close the outlet of the distillate pump, vacuum breaker valve, bottom blow off valve and feed water valve b. Inject air into the evaporator shell c. Keep the shell pressed up to about 1.0bar gauge d. Sprinkle soap solution on to the jointings, packings, and suspected areas of the shell

27.

What are the reasons for a piston crown to crack? a. Casting defect b. Thermal stresses due to cold starting air and scavenging air c. Scavenge fire d. Overheated piston(cooling failure, cooling side deposits due to oxidation of the cooling oil) e. After burning f. Faulty fuel injection system (more penetration or loss of atomization)

28.

What are the reasons for black smoke from a diesel engine? a. Poor combustion due to faulty injection system b. Low compression c. Insufficient scavenging air d. Fouled exhaust system e. Broken piston rings f. Ineffective lube oil seal g. After burning, bad fuel and other fuel assisted faults h. Faulty cylinder lubrication i. During starting, it is inevitable as the engine maker sets the starting fuel index to a fixed value. At this index there is insufficient air, low piston speed, cold combustion chamber, low fuel injection pressure etc., each compounding the cause for black smoke

29.

What are the critical speed effects?

Resonance, torsional vibration, fatigue failure of components Can be remedied by: a. Detuners b. Vibration dampers c. Electric vibration compensator unit

Class4exam.com Register Yourself In Our Forums 30. What are the types of vibration in a diesel engine and which is the most damaging? Types of vibration: a. Linear vibration b. Torsional vibration c. Resonant vibrations involving any two of the above or may be combinational Most damaging form of vibration is the torsional vibration mode, affecting crankshaft and propeller shafting. 31.

What is a node?

A node is found where the deflection is zero and the amplitude changes its sign in a vibrating medium. The more the nodes in a given length the higher the corresponding natural frequency. 32.

What is a forcing frequency?

W.r.t the crank shafts, the forcing frequencies are caused by the firing impulses in the cylinders.

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MEO Class 4 Oral Questions With Answers Firing impulses superimpose on one another and appear as a complex waveform represented by harmonics – 1x cycle frequency: first order harmonics of firing 2x cycle frequency: second order harmonics 3x cycle frequency: third order harmonics and so on… 33. How can the frequency of resonance, the forcing impulses and the resultant stresses adjusted? a. By adjusting shaft sizes b. Number of propeller blades c. Firing order d. Using viscous or other dampers e. Using balancing weights f. Detuning coupling 34.

What is balancing?

Balancing is a way of controlling vibrations by arranging that the overall summation of the out of balance forces and couples cancels out, or is reduced to a more acceptable amount.

35.

Explain the vibration characteristics of low speed 2-S engines a. External unbalanced moments b. Guide force moments c. Axial vibrations in the shafting system d. Torsional vibrations in the shafting system

36.

What is 1st order moment?

These moments acts in both vertical and horizontal directions. For engines with 5 cylinders or more, the 1st order moments are of rare significance to the ship but it could be of a

Class4exam.com Register Yourself In Our Forums disturbing magnitude in the 4 cylinder engines. Resonance with a 1st order moment may occur for hull vibrations with two and/or three nodes. 1st order compensator can be introduced in the chain tightener wheel. It comprises of two counter rotating masses rotating at the same speed as the crankshaft. 37.

What is a second order moment?

The second order moment acts only in the vertical direction and precaution needs only be considered for 4, 5 and 6 cylinder engines. Resonance with the 2nd order moment may only occur at hull vibrations with more than 3 nodes. A 2nd order moment compensator comprises two counter rotating masses running at twice the engine speed. 38.

What are the methods to cope up with the second order moments? a. A compensator mounted on the aft end of the engine driven by the main engine chain drive mechanism. b. A compensator mounted on the fore end driven from the crankshaft thus a separate chain drive. c. A compensator on both aft and fore end completely eliminating the external 2nd order moment.

39.

What is an electric compensator?

It is electrically driven compensator preferably located in the steering gear compartment, where deflections are the maximum and the effect of the compensator is maximum. Such a compensator is synchronized to the correct phase relative to the external force or moment and can neutralize the excitation. The compensator requires an extra seating to be fitted. 40.

What are guide force moments and their types?

The origin of the guide force moment is the angularity of the connecting rod. It is the vibration of the engine about the foundation bolts. Guide force moments are caused by the transverse reaction forces acting on the cross head due to the con rod crankshaft mechanism. Guide force moments may excite engine vibrations moving the engine top arthwartships causing a rocking (excited by the H moment) or twisting (excited by X moment) movement of the engine. Guide force moments are harmless except when the resonance occurs in the engine double bottom system. As a precaution, top bracing is installed between the engine‟s upper platform brackets and the casing side for all its 2S models. 41.

What are different types of the top bracing for a diesel engine? a. It comprises of the stiff connections (links) either with friction plates which allows adjustment to the loading conditions of the ship

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MEO Class 4 Oral Questions With Answers b. A hydraulic top bracing – by using the top bracing natural frequency will increase to a level where resonance will occur above the normal engine speed.

Class4exam.com Register Yourself In Our Forums 42. How are the axial vibrations caused in the crankshaft? How are they remedied? When the crank throw is loaded by the gas pressure through the conrod mechanism, the arms of the crank throw deflect in the axial direction of the crankshaft, exciting axial vibrations. These vibrations may be transferred to the ship‟s hull through the thrust bearing. Its remedy is to axially dampen the crankshaft vibrations. 43.

How is torsional vibrations generated?

The varying gas pressure in the cylinders during the working cycle and the crankshaft / conrod mechanism create a varying torque in the crankshaft. It is these variations that cause the excitation of torsional vibration of the shafting system. The torsional excitation also comes from the propeller through its interaction with the non-uniform wake field. Remedy: modify crankshaft natural frequency by adjusting the diameter. Use a torsional damper. 44.

What is under critical running?

The natural frequency of the one node vibration is so adjusted that the resonance with the main critical order occurs about 35~45% above the engine speed at specified maximum continuous rating (MCR). The characteristics of an under critical system: a. Relatively short shafting system b. Probably no turning wheel c. Turning wheel with low inertia d. Large diameter of the shafting e. Without barred speed range 45.

What is overcritical running?

The natural frequency of the one node vibration is so adjusted that the resonance with the main critical order occurs about 30~70% below the engine speed at the specified MCR. The characteristics of the system are: a. Turning wheel may be necessary on the crankshaft b. Turning wheel with a relatively high inertia c. Shaft with relatively small diameter (shaft material has to be of high UTS) d. With a barred speed range of about +/- 10% w.r.t the critical engine speed 46.

If resonance occurs, what is the solution?

The following modification(s) have to be carried: a. Lanchester balancers, either on the engine or electrically driven units usually located in the steering flat, compensated for ships vibration caused by the 2nd order vertical moment b. Counter balancing weights on the crankshaft to be adjusted for compensating the first order vibrations c. Combined primary and secondary balancers d. Adjusting the side stays 47.

How to prepare a DB fuel oil tank for a survey/inspection? a. Empty the oil, strip with portable pumps if required

Class4exam.com Register Yourself In Our Forums b. Clean the tank with sea water and pump it through the oily water separator c.

Ventilate the tank(s) with a blower specially provided for the purpose, always cross ventilate i.e. there should be at least two openings, each for entry and exit for the air

d. Check the space for explosive gases at various points suitably, more sampling should be carried out at the corners at the bottom most part of the tank e. Obtain the necessary certificates and get the checklist completed

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MEO Class 4 Oral Questions With Answers 48.

Why are the CO2 bottles provided with dip tubes?

It is to ensure that only liquid is drawn during release. The liquid expands after the nozzles and assumes the gaseous state. This will prevent co2 freezing and blocking the nozzle Also it achieves the 85% discharge in 2 Minutes as liquid part represents a large volume of gas The materials used in its construction are copper, stainless steel 49. Why a crankcase relief door is not fitted in the refrigeration compressor crankcase? a. Possibility of the contamination of the refrigeration system by air by leaks b. Oxygen is not available in the compressor crankcase c. The incoming refrigerant temperature is low and chances of hot spots is low d. Crankcase forms the suction chamber of the compressor and chances exist that the compressor may draw in air and moisture 50.

Why heaters are provided in the crankcase of a refrigeration compressor? a. To avoid carry over of the lube oil because at low temperature, the separation of the refrigerant and the oil is difficult b. To condition the lube oil, by maintaining the viscosity so that the lubrication is effectively carried out. c. This prevents the lube oil achieving its floc point which may cause narrowing or chocking of the passages (flocculation)

51.

What are the causes of a centrifugal pump reduced output? a. Friction and leakage losses, loss of suction head, chocked suction filter, worn out wear ring, air ingress in the suction side b. Low voltage is applied to the pump motor c. Cavitations on the impeller d. Bad maintenance, incorrect fixing up of the parts after overhaul

52.

What are the causes of vibration in the vertical centrifugal pump?

Misalignment of the shaft, worn out bearing, foundation bolts loose, hydraulic clearances not proper on the impeller, coupling bolts / seating damaged, bottom bush worn out, heavy objects/debris deposits, and corrosion/erosion on the rotating parts 53.

What is volumetric efficiency of air compressors? Actual volume of air drawn in / swept volume

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What is compression ratio? (Swept volume + clearance volume)/clearance volume

55.

What is brake thermal efficiency?

Ratio of the energy developed at the brake to the energy supplied. Amount of heat liberated during the combustion to the heat equivalent at the brake 56.

What is the function of a Solenoid valve in the refrigeration system?

There is an electric signal actuated valve in the liquid line of the refrigeration system just before the thermostatic expansion valve. This is being actuated by the thermostat in the refer compartment. The solenoid shuts off the refrigerant supply if the compartment is sufficiently cooled to the lower set point of the thermostat. Also it connects the supply when the temperature of the compartment goes high i.e. above the thermostat higher set point

57.

What is the function of the back pressure valve in the refrigeration system?

Back pressure valve is fitted just at the exit of the refrigerant from the evaporator coil in a multi temperature rooms system. This being fitted at the exit of the compartments whose temperature is set higher (usually at about 4~5 degrees centigrade). The function of the valve is to maintain equilibrium of the system as the pressure of the gas at the exit of each compartment differs. More over the back pressure valve creates a back pressure on the evaporator coil and ensures that most of the liquid refrigerant is made available to the lesser temperature requirement compartments as their demand for the refrigerant is higher than the compartments being maintained at a higher temperature. It is spring loaded non return valve 58.

What is the function of a H.P cut out in a refrigeration system?

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MEO Class 4 Oral Questions With Answers This is a safety device (trip) provided in the discharge of the compressor. It functions to trip the compressor if the pressure in the HP side goes high above the working level 59.

What is the function of the driers in the refrigeration system?

The filter/drier is installed in the main liquid line of the system to absorb any moisture present in the refrigerant. It consists of activated alumina or silica gel in a renewable cartridge. It also accommodates the charging connection 60.

What are the usual stern tube bearing clearances? a. Water cooled stern bearing clearance: 8.0mm (8~12mm) b. Oil cooled stern tube bearing: 1.87~2.0mm

61.

What is a usual volumetric efficiency of a diesel engine? a. Naturally aspirated engine: 0.85~0.95 b. Supercharged engine: up to 4.0 c. For 2S engine: 0.85~2.5

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What is a usual propeller drop usual value? 1mm/160mm of the shaft diameter

63.

What are the advantages of a thin shell bearing? a. Increased fatigue resistant properties b. High load carrying capacities c. Embed ability d. Conformability e. Bedding not required f. Easy storage, easy fitting, light in weight g. Increased (enhanced) mechanical properties h. Better heat transfer due to reduced thickness and uniformity of the contact with the bearing housing

64.

What are the typical bearing failures? a. Fatigue failure (cracks) b. Tin oxide encrustation (black SnO2 ) c. Wiping damage of the bearing surface d. Tearing of the overlay e. Acidic corrosion f. Cavitations, erosion g. Dross inclusion h. Spark erosion i. Bacterial attack damage (honey colored deposits on the bearing surface)

65.

What are the advantages and disadvantages of the synthetic lube oils?

Advantages: a. Better low temperature fluidity and pump ability, due to nil wax content b. Better oil retention at high temperatures c. Lower friction losses d. Reduced thickening of the oil in service due to oxidation e. Lower deposits at higher temperature due to resistance to oxidation properties and thermal stability Disadvantages: a. b. Uses: a. b.

Increased cost of the lube oil (about 6~12 times) Poor availability

66.

What is the purpose of the lube oil analysis?

Air compressors Purifiers c. Hydraulic units

a. To determine any deterioration in lube oil properties or additives levels and assess its suitability for further service b. To determine the type and level of the contaminants held within the oil which indicate the rate of contamination and effectiveness of the purification process c. To predict the internal wear rate on the machinery components d. To lengthen the time between overhauls or surveys

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MEO Class 4 Oral Questions With Answers Class4exam.com Register Yourself In Our Forums 67.

When is the lube oil said have deteriorated? a. TBN reduces b. Viscosity reduces c. Flash point reduces d. Oxidation increases e. Water content high f. Insolubles increase g. Dispersancy increases

68.

What are the problems in cast iron welding? a. Brittleness (cracks easily) b. High carbon content in the form of graphite c. Close grain structure d. Poor thermal conductivity and differential cooling e. Possibility of stresses and distortion

69.

How is a propeller drop measured?

a. Turn the engine to coincide with the mark on the liner and the stern tube or normal reference is taken to be that the engine‟s unit 1 will be in TDC prior measuring the propeller drop This could be also arranged as with a designated blade of the propeller up wards while measuring this drop. Blades are assigned alphabets A, B, C, D and so on. b. Take the poker gauge reading and the compare with the previous reading c. Bearing clearance : 2mm (oil sealed) : 8mm (sea water lubricated) Bearing length is about 2xdia of the shaft for oil cooled stern tube bearing 4xdia of the shaft for sea water lubricated stern tube bearing 70.

Compare an engine flywheel and its governor a. A governor maintains the speed of the engine b. A flywheel controls the cyclic fluctuations of the engine RPM c. Flywheel works on the virtue of the inertia alone and the governor uses the inertia principle to actuate the fuel linkages to counter the changes in the engine RPM

71.

Why are tie rods provided?

Tie rods are provided to keep the whole engine structure in compression which: a. Increases the fatigue strength of the engine structure as it is the tensile stress which causes fatigue b. Maintain running gear alignment to avoid fretting The firing forces that press down the bearing saddle also attempt to push up the cylinder covers, the net effect being to put the whole engine structure into tensile loading. So the tie rods are tightened such that the engine structure is maintained in compression even during the peak firing conditions and that the engine is not subjected to the tensile loading.

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72.

Register Yourself In Our Forums Why tie rods are placed close to the centerline of the crankshaft?

During firing, the transverse girders are subjected to a bending moment as the saddle is pushed down by the crankshaft acting on the cylinder head. To limit this bending effect and consequent distortion of the bearing housing the tie rods are positioned as close as possible to the centerline of the crankshaft. 73.

Where is a thrust bearing installed in an auxiliary engine? And why?

Axial location of the crankshaft may be required if the coupling does not incorporate a thrust housing. This is achieved by forming white metal rings on the sides of one main bearing shell that allows the shaft to run with a small clearance between running faces on the two adjacent webs. In some engines a small collar may be provided at one side of the bearing. It is important to appreciate that only one such locating bearing should be fitted to any one shaft, otherwise the differential thermal expansions of frame and the crankshaft may cause problems.

74.

What are the environmental problems with the use of CFCs? a. CFC released into the atmosphere are broken down by pyrolysis to release chlorine atoms which catalytically destroy ozone layer.(this layer in the stratosphere acts

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MEO Class 4 Oral Questions With Answers as a filter to the UV radiation from the sun) b. Furthermore CFCs along with other greenhouse gases inhibit radiation from the earth‟s surface thereby contributing to the global warming. 75.

What is a pH value?

It is the logarithm of the reciprocal of the hydrogen ion concentration expressed in gram ion per liter. Pure water at 25 degree centigrade consists of equal concentration of the hydrogen and the -14 hydroxyl ions and equal to 10 gram ion per liter. If the hydroxyl ion concentration exceeds the hydrogen ion concentration then the solution is basic and vice versa is acidic in nature. pH value = log [1/H+] If the water temperature is increased, the concentration of the hydrogen ion increases and hence acidity. 76.

Why is a man hole door elliptical in shape?

Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole is lesser in size than the corresponding circular hole. More over it is prime concern to have a smoothed generous radius at the corners to eliminate stress concentration. Hence other geometrical shapes like rectangle and square are ruled out. To compensate for the loss of material in the shell due to opening, a doubler ring has to be provided around the opening. The thickness of the ring depends on the axis length along the direction in which the stresses are maximum and the thickness of the shell. It is important to align the minor axis along the length of the vessel, as the stress in this direction is maximum.

Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t= thickness of the shell plating Circumferential stress: Pd/4t More over a considerable material and weight saving is achieved as minor is along the direction of maximum stress.

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Why is the fridge compressor belt driven? a. A slight misalignment is a problem or vibration of the electric motor may lead to shaft seal leakage, leading to loss of the refrigerant. So minimize these the fridge compressor is belt driven. b. In case of the liquid entry into the refrigeration compressor, the belt drive gives a limitation of the damage owing to the slip in the belt and flexibility of the belt material.

78. Why intercooling is provided in an air compressor? And why is the compression distributed into stages? a. By employing the interstage cooling we are trying to achieve an isothermal compression cycle. So least work is expended in the process. b. The air outlet temperature after compression is lowered by intercooling. So oxidation of the lube oil is prevented. Also good lubrication is achieved. c. Lesser deposits in the air system. d. Intercooling increases the air density and hence reduced volume of the HP compression chambers is possible. e. It facilitates removal of moisture by condensation at the intercoolers. f. To facilitate intercooling the compression is distributed into stages. Also even load distribution is achieved over the cycle. 79.

What if the compressor motor connections are reversed after overhauling? a. The lube oil pressure will not be sufficient for lubrication so the compressor may trip on low lube oil pressure. The moving parts may get damaged due to the failure of the lubrication. b. The cooling water pump which is also shafted driven usually does not build up enough flow/pressure hence the compressor may trip of the cool water non flow or high air temperature.

80. If viscotherm is absent or damaged how do you maintain the fuel oil viscosity? The required viscosity prior injection and the viscosity of the fuel oil at 50°C are provided by the fuel oil analysis report. Basing on the viscosity nomogram the required fuel oil heating is determined. The steam inlet to the fuel oil heater is manually adjusted to maintain the temperature and a close observation has to be maintained on the steam pressure and temperature of the fuel oil at the outlet of the heater. 81. What are the reasons for the error between the helm order and the angle shown locally on the steering gear unit?

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MEO Class 4 Oral Questions With Answers a. Air in the hydraulic telemotor system b. Buffer spring too weak or stiff, faulty hunting gear c. Instrument error/defective d. Worn out linkages

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82.

Register Yourself In Our Forums Why are the accumulators used in the hydraulic systems? a. To absorb shock due to load variation or sudden change in the direction of flow, impact loading b. To maintain the circuit pressure by compensating for the loss due to leaks or pressure increase due to rising temperature c. To supplement the pump delivery where multiple circuit operations have wide flow variations with a short term peak demand in excess of the pump capacity. Accumulator charge can take place during low demand periods to meet maximum demand later

83.

Explain the cross head slipper lubrication a. The lubricating oil is fed to the guide shoes by a pipe from the main lube oil system b. The lubricating oil may also be fed from the drilled passages in the pin to the slipper faces

84.

What is the material of the CO2 bottle and its accessories?

CO2 bottle: solid drawn seamless manganese steel Cable: phosphor bronze Seal/bursting disc: thickness 0.3mm, phosphor bronze Pipeline: solid drawn MS galvanized Siphon tube: copper tube Cutter: 120° /travel 19mm 85. How will you decide for reentry into the engine room after flooding it with CO2 Re-entry is determined by a. Heat build up due to the scale of the fire and the elapsed time after release b. Has the fire been extinguished or chances of a smoldering fire exists c. Ship‟s position, condition and the prevailing weather (ship may be listing to the angle of progressive flooding etc.,) d. The location of the entry point e. Risk analysis outcome 86. What is the quality of the vapor coming back to the compressor suction in the refer system? In addition, how will you ensure that the vapor has adequate degree of superheat? a. The condition of the vapor coming to the compressor suction line should have adequate degree of superheat b. The condition is checked by reading the pressure of the returning vapor and its corresponding temperature from the P-T chart provided for the specific refrigerant. This temperature is compared with that of the evaporator outlet and the degree of super heat is expressed as the difference in the temperature. 87.

What is the length of the crank web?

Length of the crank web = stroke length/2

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What is lignum vita?

In the traditional sea water lubricated stern tubes the bearing material consisted of the staves of the wood called lignum vitae. This has a property of lubrication in the presence of sea water. They are fitted with the grains in the axial direction for economy and are shaped with V or U grooves between them at the surface to allow for access to water. They also

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MEO Class 4 Oral Questions With Answers act as a debris collector points. The staves are held in place in the bronze boss by bronze keys attached to the bush by counter sunk screws. Bearing length is equal to 4times the shaft diameter. 89.

What are the safeties in the fridge system? a. HP cut out b. Differential lube oil pressure cutout c. LP cutout d. Relief valve in the condenser e. Belt driven f. Cylinder head relief valve g. Cooling water low flow/high temperature alarm h. Motor overload i. Oil separator j. Drier k. Mech. Seal l. Unloaders /capacity controllers m. Non return shut off valves n. Sensors – temperature, pressure

90. How will you know the presence of air in the refrigeration system? Explain the procedure for purging air a. High condenser pressure b. Small bubbles in the sight glass c. Compressor discharge pressure high/running hot d. More superheat e. Pressure fluctuations f. Inefficient working PROCEDURE FOR PURGING AIR a. In the normal operation of the system, measure the liquid refrigerant pressure, temperature at the outlet of the condenser/reservoir b. Check the corresponding saturation temperature for the recorded pressure of the liquid refrigerant from the P-T chart for the same refrigerant c. Compare the measured temperature with the determined saturation temperature for any sub-cooling and adjust the flow of the cooling water through the condenser to achieve near saturation condition inside the condenser, Then, d. With the condenser liquid refrigerant outlet valve closed, circulate cooling water, start the compressor and pump down the liquid to the condenser/reservoir, checking the pressure in the suction line. If this pressure is allowed to drop down below the atmospheric pressure then there could be chances of air ingress into the system e. Circulate the cooling water till the cooling water outlet and the inlet temperatures equal, a check to ensure complete pump down operation f. Check the condenser sea water out let temperature, check the refrigerant pressure corresponding to its temperature from the P-T chart of same refrigerant

Class4exam.com Register Yourself In Our Forums g. Due to the presence of air they don‟t agree h. Release air from the condenser, through the vent cock until the pressure of the refrigerant in the condenser corresponds to the saturation pressure at the sea water outlet temperature 91.

What is the material of the boiler gauge glass?

The material used in the gauge glass is a special toughened glass containing a. Silicon oxide or magnesium oxide b. Borosilicate or lime soda glass 92.

What is the material of a boiler tube?

Low carbon alloy steels containing chromium, nickel, molybdenum 93.

What is the material of the ship side valve?

BODY: Nickel-Aluminium bronze / cast steel Stem/Seat/Disc: Monel metal (cupro nickels of varying proportions are used popular being a Cu:Ni = 2:1) The cupronickels are known for their great resistance to the sea water corrosion, erosion by the particles in the sea water, and strength. 94.

What is the material of the propeller material? a. Nickel aluminium bronze (nickalium) Copper: 55~62%, Aluminium: 0.5~2.2%, Nickel: 0.5%, Manganese: 0.5~1.0%, Iron: 0.4~1.5%, balance is Zinc b. Manganese bronze Copper: 58%, Iron: 1%, Aluminium: 1%, Manganese: 1%, Nickel: 0.5%,

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MEO Class 4 Oral Questions With Answers Zinc: 38%, Tin: 0.5% 95.

What is the general composition of the stainless steels?

Chromium: 18%, Nickel: 8%, Carbon: 0.12% 96. What is the material of the 4S engine conrod? a. Forged steel: Open hearth plain carbon steel UTS: 432~494 MN/m2 % Elongation: 25~30% Fatigue limit: 208 MN/m2 (push pull) b. Nickel steel, 3%Ni UTS: 695 MN/m2 %Elongation: 20% Fatigue limit: 309 MN/m2 (push pull) METHODS OF TIGHTENING: a. Measuring the extension of the bolts b. Use of the calibrated torque wrenches c. Hydraulic tensioning d. Angle tightening

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What is the material of the foundation bolts?

High tensile steel 98.

What is the material of the tie rod?

High tensile steel 99.

What is the material of the double bottom plug?

Silicon steels 100.

What is the material of the crankshaft?

Forged low carbon alloy steel. Carbon: 0.12% and less 101. What are the materials used for the diesel engine’s liner and piston rings? State their principle differences Generally the materials used for the piston rings are harder than the liner material. This is due to the fact that the rings are subjected to wear always during their operation but only the portion of the liner in contact with the rings wears. Material used for the liner is generally the nodular cast iron, which is tailored to have expansion along the length and negligible expansion circumferentially. Alloying materials are added to improve certain characteristics like vanadium and titanium. Piston rings are cast and machined from graphite grey cast iron. This ring may include chromium, nickel & copper as alloying substances. The prime property which distinguishes it from the liner material is that it has to flex circumferentially. This is of primary concern for running in and to match the contour of the wearing liner surface. Also they have to form an effective sealing of the combustion gases. 102.

What are the liner wear rates? And how is it achieved?

Old engines: 0.1mm/1000hrs Modern engines(2S): 0.03mm/1000hrs Modern engines(4S): 0.12mm/1000hrs This is achieved by: a. Highly alkaline lube oil b. Load dependant jacket cooling water temperature control c. Good quality of cast iron with a hard face d. Careful design of the piston ring profile e. Improvement in lube oil f. Multilevel cylinder lubrication g. Condensate separation from the scavenging air h. By use of the anti-polishing ring or the piston cleaning 103.

Explain why stainless steel is resistant to corrosion?

Stainless steel depends on the formation of a protective oxide film, tenacious chromium oxide for resisting corrosion. This film is formed spontaneously on exposure to air or well aerated water.

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MEO Class 4 Oral Questions With Answers Class4exam.com Register Yourself In Our Forums Without this oxide film, their corrosion resistance is only slightly better than other engineering steels. 104.

What is the material of the fuel valve needle and body? Needle: high speed steel Body: case hardened steel

105.

What is the material of the chain and its tightener arrangement? High tensile steels

106.

Quote some important clearances in the rudder system Jumping clearance: 6mm Clearance at raphson slide mechanism: 16~19mm Propeller drop: 1mm/160mm diameter of the tail shaft Pintle clearance: 1.1mm~3.3mm

107.

What are the usual pressures to which the boilers are tested? New boilers, if > 6.9bar working pressure, 1.5xdesign pressure If < 6.9bar working pressure, 2.0xdesign pressure After major repair, 1.25~1.5x working pressure, duration of the testing: 30Min.

108.

Explain the purpose of the hunting gear

a. To put the pump on stroke gradually b. To stop the pump at the end of the stroke gradually c. To lock the rudder at desired position till further movement is given at helm d. To transmit movement of telemotor to pump e. Spring in the hunting gear store extra control movement to ensure that the pump operates at the maximum capacity for major part of the turning operation 109. Differentiate between the terms priming and foaming with reference to their occurrence in a steam boiler Both refer to the carry over of water into the steam outlet. Priming is due to the mechanical/physical aspects and the foaming refers to certain insouble/solubles in the boiler water, which by the principle of increased surface tension cause priming. The various reasons for priming: a. High water level in the boiler b. Rapid changes in the steam demand c. Safety valve lifting frequently due to its malfunction d. Rough weather causing heavy rolling/pitching e. Rapidly raising steam f. High salinity of the boiler water Foaming is the formation of unbroken chain of bubbles on the surface of boiler water. A common cause of the same is the oil contamination. 110. Mention some important mechanical properties of metals a. Elasticity:

Class4exam.com Register Yourself In Our Forums b. Hardness: Resistance to abrasion c. Plasticity: d. Toughness: Ability to absorb maximum energy before fracture e. Ductility: Ability of the metals to deform plastically under tensile force f. Stiffness: Ability to withstand deformation g. Malleability: Ability of the materials to deform plastically under compressive force as in forging or rolling h. Resilience: Resist shock and impact i. Brittleness: Tendency of the material towards brittle fracture. Brittle fracture is the failure of the material without plastic deformation j. Creep: Plastic flow under constant load application or heat k. Weld ability: l. Endurance: Ability to withstand alternating stresses m. Cast ability: n. Strength: Ability to withstand rupture 111. What is a tie rod bolt pinch screw? And what is its purpose? Pinch screw is normally provided at the foot of the engine cylinder jacket to stop the tie rod from vibrating during the normal service of the engine.

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MEO Class 4 Oral Questions With Answers The pinch screw is fitted at the antinodal point of the tie rod to limit its transverse vibration amplitude, thereby preventing its fracture due to vibrations. These can be arranged as a group of three screws positioned equilaterally at the antinodal point. Each screw consists of a stud, which is hand tightened by screwing the outer sleeve and held in place by a lock nut which is tightened to a torque specified by the manufacturer. 112. What is the course of action after finding that a bottom end bolt is slackened? a. Check the length of the bolt b. Check whether it is within the limits c. Check for cracks / surface finish. Check the threads d. The tie rod can be rolled over a flat surface coated with Prussian blue. Any twists in the rod are revealed by the Prussian blue lines on the tie rod which get adhered along the twisted plane e. If found alright, tighten the bolt and check the remaining bolts 113.

Define higher calorific value and the lower calorific value

[H2O formed by the hydrogen in the fuel oil cannot exist as water at the high temperatures in an internal combustion engines. The water formed by the combination of hydrogen and oxygen absorb the heat from the combustion and forms steam. Therefore, some amount of available energy is lost in converting water into steam. This energy is not available to the engine. Therefore, the calorific value of the fuel reduced by this amount presents the actual calorific value available to the engine.] - Æ This definition is given by reeds and I feel this has to be altered after looking into the MANBW manual, which provides a graph to calculate the Lower calorific value based on the Specific Gravity and Sulfur content. Therefore, the amount of heat loss due to the inclusion of sulfur, which cannot be separated by normal fuel oil treatment and its subsequent oxidation to SOx warrants the entire calorific value to include correction for corresponding fuel content in a specific mass of fuel sample

Class4exam.com Register Yourself In Our Forums and the energy loss due to sulfur oxidation. Corrections should also include for ash & water content. Therefore, to get the practical scenario two specific calorific values are mentioned Lower calorific value and the higher calorific value. Lower calorific value = higher calorific value – the energy loss in converting the mass of the [water into steam] + sulfur to sulfur oxides + Loss of specific enthalpy due to ash content present in unit mass of fuel. 114.

Explain gear pumps w.r.t the materials used and the clearances

Rotors and shafts are integrally forged of Nitraalloy steel. Gears are case hardened, medium carbon steel. They are hardened all over and ground finished after hardening Casing and bearing housing are close grained grey cast iron Shafts are supported by white metal bearing or roller bearings or bronze bushes on the free ends Liquid being pumped is forced out after being carried around the gear teeth between the gear teeth and the casing. Backflow is limited by: a. Minimizing the radial clearances between the teeth of the gears and the housing b. Increasing the number of teeth c. Optimizing the side tolerances /play Gear pump suitable for operating up to 25bar and can achieve displacement volume of 0.35~1.0 liters/revolution Clearances between the gear teeth and the housing are of the order 0.02~0.03mm 115.

What are the advantages and disadvantages of resin chocks?

ADVANTAGES: a. 100% contact on uneven surfaces b. Cheaper to install as no hand fitting is required c. Don‟t corrode and are resistant to most of the chemicals d. As they achieve good contact, there is little chance of fretting, thus cheaper, shorter, non resilient bolts can be used. These permit a reduction in the bolt tension by a factor of 4 e. Avoid vibrations DISADVANTAGES: a. Overstressing of the bolts causes the resin to shatter and break b. Maximum temperature is limited to about 80°C 116.

Explain the cavitation in the bearings

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MEO Class 4 Oral Questions With Answers Vaporization due to oil pressure falling locally below vapor pressure causes bubbles in the oil, which when goes to higher pressure region, collapses and shock wave is generated causing heavy impingement. The causes: a. High oil temperature b. Low oil pressure c. Vibration d. Oil contamination

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What are the Nimonic and Stellite coatings?

These are considered to be the hardened materials by the process of metallic cementation Nimonic: carbon, chromium, Titanium, Aluminium, Cobalt, Molybdenum, Iron, Nickel There could be other constituents such as Manganese, copper, silicon Stellite: They are alloys of Cobalt, and Chromium, with the addition of varying amounts of tungsten and other elements They are very resistant to corrosion and abrasion. Retain their hardness at a red heat Since they cannot be forged, they must be cast direct to shape or deposited by welding 118.

Why is an equalizing line provided in the refrigeration system?

It is used in the installations where a large drop in pressure occurs in the evaporator. In the expansion valve, the pressure acting outside (top) of the bellow corresponds to the saturation pressure plus the degree of superheat of the refrigerant leaving the evaporator. This pressure is trying to open the valve against the spring force from below the diaphragm. The external equalizer connection has a saturation pressure of the refrigerant leaving evaporator, to act below the diaphragm. Therefore the saturation pressure from the external equalizer connection balances the saturation pressure of the sensing bulb leaving only the pressure due to degree of super heat only to oppose the spring force. Therefore, this degree of superheat is supposed to open the expansion valve. By this method, we are getting a control over only the degree of superheat of the refrigerant leaving the evaporator coil. This is important to ensure proper utilization of the refrigerant and that no liquid refrigerant reaches the suction of the compressor. 119.

What are the reasons for short cycling of a refrigerant compressor? a. Refrigerant charge is too low b. Frosting or clogging of the evaporator c. Dirty suction strainer d. Low pressure control differential too small e. Wrongly adjusted capacity regulator f. Refrigerant vapor in the liquid line g. Too much cooling water h. TEV faulty i. Too high compressor capacity

120. What is viscosity? Differentiate between the kinematic viscosity and the dynamic viscosity Defined as the resistance of fluids to change of shape, being due to the internal molecular friction of molecule with molecule of the fluid producing the frictional drag effect. Absolute (Dynamic) viscosity is numerically equal to the force to shear a plane of fluid

surface of area of a unit square meter, over another plane surface at the rate of one meter per sec, when the distance between the surfaces is one meter. Kinematic viscosity is the ratio of the absolute viscosity to the density at the temperature of viscosity measurement. Viscosity index is a numerical value which measures the ability of the oil to resist the change in viscosity with the change in temperature. A high viscosity index shows a good resistance to the change in viscosity with change in temperature.

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What is an Otto cycle or the constant volume cycle?

This is the constant volume cycle. Although no actual engine cycle operates strictly following this ideal cycle, the analysis of this cycle provides a tool for comparison of performances of actual engines under different operating conditions.

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MEO Class 4 Oral Questions With Answers The most important noted difference between this ideal cycle and the normal cycle is that this is a non-flow cycle involving an ideal gas whereas the actual cycle is a flow process and the gases are real. This cycle is explained as follows: At the beginning of the process the cylinder is assumed to be full with a charge of fresh air. γ The air is compressed isentropically following the law PV = constant. Heat is then added to the same mass of air at constant volume. This point represents the maximum pressure and temperature in the cycle. From here the air is expanded isentropically to the initial volume and then the heat is rejected at the constant volume.

122.

What is a Diesel cycle?

This thermodynamic cycle is first analyzed by Rudolph Diesel. This is a slight variation of the above constant volume cycle, the difference being that the heat addition in the cycle takes place at constant pressure. The other processes during compression, expansion, and heat rejection remain same as with the constant volume cycle. 123.

What actions do you take incase of an EGB Soot fire?

The oxygen levels in the EG Boiler/Economizer is about 14~16%, so this can support combustion. The nature of combustible deposits include soot from the combustion of fuel in the plant as well as some amount of unburnt oil (fuel and lube oil), particularly at low loads. Ignition of soot may arise at sufficient high temperature of the layer of the soot whose surface temperature may go up to 300~400˚C, but presence of unburnt oil may lower this temperature to about 150˚C and under favorable conditions to about 120˚C. SMALL SOOT FIRES: Mainly occurs during maneuvering with the engine being operated at prolonged low loads. The situation may arise even at short low load running if the fuel is bad. Indications: a. High economizer exhaust gas outlet temperature b. Sparks from the funnel c. Engine running parameters showing deviations due to increased exhaust back pressure d. High steam pressure or outlet temperature from the super heater section if fitted How to deal with this situation: a. Stop the main engine so that the oxygen levels can be brought well below the fire sustenance levels b. Carry out the boundary cooling c. Fire watch to be kept on deck due to the risk of the funnel sparks, fire hoses to be kept charged d. Continue running the circulating water pump e. Never use the soot blowers for fire fighting f. Stop the auxiliary blowers g. Ensure that all the exhaust valves are positively closed (check the spring air pressure)

Class4exam.com Register Yourself In Our Forums If the soot fire has now turned into metal fire (identified immediately by the loss of the circulating water of the economizer), stop the circulating water pump. Carry out the boundary cooling. If means are provided, deluging the economizer fires with copious amounts of water should be carried out to the seat of the fire. This is essential because, if lesser amount of water used the fire is additionally supported by the production of steam sourcing hydrogen for the situation to get worse. Hydrogen fire: Occurs because of dissociation of water (steam) into hydrogen and oxygen or carbon in connection with carbon monoxide and hydrogen This occurs only above 1000˚C Iron fire: Oxidation of the iron at high temperature occurs at a rate sufficiently high to make the amount of hest release from the reactions sustain the process. These reactions may take place at a temperature in excess of 1100˚C 124. How do you identify the symptoms of a crank case explosion? What action would you take to minimize the hazard? a. Engine noise b. Oil mist detector alarm c. High bearing temperature (alarm if fitted) d. In case of minor explosions the crank case relief door releases the pressure ACTION: a. Slow down the engine, inform the bridge b. Take permission from the bridge for stopping the engine c. Continue running the engine lube oil pumps d. In severe cases, it is prudent to open the engine room skylights and other vents and

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MEO Class 4 Oral Questions With Answers abandoning the engine room. The doors from the engine room to the accommodation should be kept shut. Return to the engine room only after carrying out risk assessment e. Turn the engine by turning gear with the indicator cock opened to prevent seizure of the hot spots f. Stay clear of the crank case specially in the region of the relief door to the turbocharger suction g. Don‟t open the crank case door until sufficient time has elapsed 125.

What are the various IG plant alarms and trips?

ALARMS: a. O2 content high b. Scrubber tower water level low c. Deck seal water level high d. Deck seal water level low e. IG pressure low f. IG pressure high g. IG temperature high h. Boiler uptake soot level high (Ringlemann) TRIPS: a. Scrubber tower water level high b. Venturi water pressure low c. Low IG cool sea water pressure

Class4exam.com Register Yourself In Our Forums Scrubber cool sea water pump abnormal stop Power failure Incorrect mode of the boiler (mode set to NAV, GF.. etc) IG temperature high high (more than alarm level) IG blower abnormal stop Deck seal water low flow IG deck main extreme high pressure 126. Reciprocating pump is getting over heated, what checks should be carried out? a. Inlet and outlet valves are to be examined b. Inspect the seat and lapping should be done if required c. Valve lift should be checked d. Inspect piston and piston rings e. Spring (valves should be checked for tension and springing action) f. Liner wear down should be checked g. Driving belt should be checked for wear down or damage 127.

Explain the various rudder inspections and testing in the dry dock

a. Visual examination of the rudder plating for cracks and distortion b. Air plugs and drain plugs are to be opened in the presence of the class surveyor, repair superintendent and chief officer. Water draining out indicates a breached rudder and the breach to be located by air pressure testing and applying soap solution, repairs to be planned c. Check the rudder drop in the steering gear compartment (trammel gauge) d. Check the pintle clearances, jumping bar clearance and the palm coupling bolts tightness to be checked e. Check the rudder stock for corrosion, erosion and any damage f. The inspection plates in the way of the upper, the lower pintle to be cut open, and the pintle nuts checked for proper securing. Later the plates to be welded and tested. g. Hydraulic test the rudder for a static head of about 2.45m of sea water h. After draining and re oiling the internals, plug the drain and check the effectiveness by a vacuum check and cement the plug i. The rudder stock gland packing has to be checked and renewed 128. What is caustic cracking or embrittlement? What is its cause? Suggest remedy This is a form of intercrystalline/intergrannular cracking and occurs when a specific corrodent and sufficient tensile stress exists. Iron consists of ferritic granules bonded by iron carbide so this gives a scope of the intergrannular corrosion. This can be found in water tubes, super heater, reheat tubes, and in stressed components of the water drum. The stress may be due to thermal, bending or residual stress (due to welding). This usually occurs as a localized attack in the combination of NaOH, some soluble silica and a tensile stress. The mechanism begins with the accumulation of the corrodent NaOH due to – 143. DNB (departure from nucleate boiling) 144. Deposition 145. Evaporation at the water line 146. Small leakage 147. High heat flux (rapid evaporation) 148. High pressure

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MEO Class 4 Oral Questions With Answers Class4exam.com Register Yourself In Our Forums This corrosion below 149˚C or with NaOH concentration below 5% is rare. Increased susceptibility occurs at about 20~40%. This corrosion is difficult to identify in the beginning and ND testing has to be carried out at the suspected areas. At some time after the initial start of the corrosion, this manifests as a whitish highly alkaline deposits or sparkling magnetite. COUNTER MEASURES: a. Applying heat treatment process to relieve stresses after fabrication/repairs (welding etc) b. Correct and accurate boiler water treatment c. Avoid DNB d. Avoid accumulation of the deposits e. Prevent leakage of corrodents f. Prevent carryover g. Use of rifling in the water tubes 129. A shell & tube type cooler tubes are leaking, what is the procedure to rectify the leaks? Before jumping to any conclusions it is prudent to check where the leaks are from. It could be from the breach on the tube (a hole etc) or from the origination of small gaps between the tube plate and the expanded portion of the tube. The procedure should to be based on the findings. A holed tube should be plugged from both the sides; the plugs can be of cork, wood, rubber, brass, or copper as supplied by the manufacturer. Care should be taken when plugging with the metal plugs, not to damage the tube plate. If the leaks are from the gaps between the tube plate and the tubes, slight flaring of the tube may help preventing the leaks however this flaring, if excessive will damage the tube plate and also the tube itself. Alternative methods are available by carrying out surface preparation and applying metal repair putty, like Devcon‟s brush able ceramic repair putty. In the above process, if the plugging of the tubes is about 10% the tubes have to be renewed. 130. Explain a tube renewal process To remove the tube, first remove the flare on the tube by chiseling off the flare flush with the tube plate and then split the tube taking care not to damage the tube plate. The tube can then be cut by a tube cutter to drop the tube inside the shell. Fitting of a new tube is carried out by first positioning the tube in place between the end tube plates and flaring to the correct amount by a flaring tool after fixing the other end by a brass wedge. It could by either hand operated, pneumatic or motor operated. The tube should have a protruding part about 1/4”~1/8” and the flaring should be to about 1/8” + tube diameter at the tip. 131.

What is a phosphate reserve? Why is it important in high-pressure boilers?

A reserve of phosphate should be present in the boiler water to neutralize any hardness salts, which may enter. These salts would deposit as a scale on the heating surface if reserve were too low while, too high a reserve leads to foaming and possible excess production of sludge. It also gives alkalinity.

Class4exam.com Register Yourself In Our Forums 3CaCO3 + 2Na3PO4 ----Æ Ca 3 (PO 4 )2 + Na2CO3 3CaSO4 + 2Na3PO4 ----Æ Ca 3 (PO 4 )2 + Na2SO4 3CaCl2 + 2Na3PO4

----Æ

Ca 3 (PO 4 )2 + 6NaCl

MgSO4 + 2Na3PO4

----Æ

Mg (PO 4 )2 + 3Na 2 SO 4

Precipitates as Sludge

At high pressure and temperature, reaction from left to right will be more. Therefore, it is very important in high pressure boilers to keep the reserve level up to required concentration to avoid excessive caustic alkalinity and thus caustic cracking. Na2CO3 + H2O Å --- Æ

2NaOH + CO2

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MEO Class 4 Oral Questions With Answers In high pressure boilers where there is a risk of caustic concentration and subsequent caustic attack it is common to apply a coordinated or congruent phosphate control programme. These control methods are based on the hydrolysis of tri-sodium phosphate (TSP) and disodium Phosphate (DSP) in the boiler water. Na3PO4 + H2O Å ----- Æ Na2HPO4 + NaOH Å ---- Æ

Na2HPO4 Na3PO4

+ NaOH + H2O

The objective is to maintain a desirable pH without the presence of free OH alkalinity. The desired conditions are obtained by maintaining the relationship of the pH to phosphate concentration in the boiler water at less than that of the equivalent stochiometric solution of Na3PO4 (