MEO Class 4 Oral QUESTIONS: The Best Guide of 2024

MEO Class 4 Oral QUESTIONS

Preparing for the MEO Class 4 oral examination can be a challenging task for aspiring marine engineers. This guide brings together the most essential questions and expert insights to help you excel. With a focus on practical knowledge and real-world scenarios, these questions are designed to boost your confidence and enhance your understanding of critical engineering concepts. Get ready to tackle the 2024 exam with the best preparation tips and key topics that matter most!

1. What is the SQUAT Phenomenon?

The SQUAT phenomenon occurs when a vessel moves through shallow water, creating a venturi effect that increases the ship’s draft. This results in higher engine load and reduced steering ability due to the vacuum created under the hull.

2. What is the Significance of Firing Order?

The firing order helps balance primary and secondary inertia forces, optimizes exhaust grouping, distributes stress evenly along the crankshaft, ensures proper bearing loading, and provides consistent firing intervals for smooth engine operation.

3. What is a Thermostatic Expansion Valve?

A thermostatic expansion valve regulates the flow of refrigerant from the high-pressure to the low-pressure side of a refrigeration system. This pressure drop lowers the refrigerant’s evaporating temperature below that of the evaporator. It prevents liquid refrigerant from returning to the compressor and ensures automatic expansion control while maintaining a superheat of 6-7°C.

4.What is the Function of an L.P Controller?

The L.P (Low Pressure) controller stops the compressor when the suction pressure drops, typically caused by the closure of compartmental solenoids. When the pressure in the compressor’s suction rises due to the solenoid reopening, the L.P controller restarts the compressor, ensuring efficient system operation.

5. What is the Function of an L.P Cutout?

The L.P (Low Pressure) cutout protects the compressor by shutting it down when suction pressure drops too low, often due to refrigerant loss or blockage. This prevents air and moisture from entering the system if the pressure falls below atmospheric levels.

6. Functions of Lube Oil in Refrigeration System

Lube oil in a refrigeration system serves multiple functions:

• Provides lubrication
• Seals clearance spaces between the discharge and suction sides of the compressor
• Acts as a coolant
• Actuates capacity control
• Reduces noise generated by the compressor.

7. Reasons for Foaming in Refrigeration Compressor Crankcase

Foaming occurs when refrigerant dissolved in the oil rapidly boils out due to a sudden pressure drop. When the compressor starts, excess refrigerant boiling out can be carried through the system. Key causes include:

• Liquid in the suction line (e.g., TEV stuck open, incorrect superheat setting, sensing bulb issues, overcharge)
• Crankcase heater malfunction
• High compressor capacity at startup
• Expansion valve providing too little superheat
• Insufficient oil charge

8. Why Use Concentric Springs in Cylinder Head Valves?

Concentric springs are used to prevent valve surging, which occurs when the spring’s natural vibration frequency matches the camshaft speed. By using two springs, one inside the other, with different vibration characteristics, surging is minimized. Additionally, these springs reduce valve rotation, as their opposing forces counteract each other, enhancing stability and reducing wear. If one spring fails, the other continues to hold the valve, preventing damage from piston contact. This design also allows for thinner springs and meets stiffness requirements in limited space, with the total stiffness being the sum of both springs.

9. Why is Starting Air Overlap Provided in a Diesel Engine?

Starting air overlap ensures positive starting in the correct direction, allows the engine to start from any position, and provides redundancy so the engine can still start if one valve malfunctions.

10 What is Ovality of Auxiliary Engine Crank Pin?

Ovality refers to the distortion of the crank pin due to the combined effects of reduced lubrication effectiveness and directional thrust from the connecting rod. This distortion is most pronounced around 45 degrees after top dead center (ATDC) and can result from uneven loading of engine units or overloading. The maximum allowed ovality is 1/4th of the bearing clearance.

Ovality can be corrected through in-situ grinding and polishing, with a reference taken from the crank web fillet. The maximum allowable grinding is 2mm, as grinding beyond this limit reduces surface hardness significantly. Ovality, along with bearing clearance issues and poor lubrication, can lead to bottom bearing damage.

11. What is Critical Temperature?

Critical temperature is the temperature above which a gas cannot be liquefied, regardless of the pressure applied during isothermal compression.

12. What is Critical Pressure?

Critical pressure is the pressure required to liquefy a gas at its critical temperature.

13. What is a Coalescer?

A coalescer is a device with a material surface that causes small liquid droplets, such as oil, to combine into larger droplets. This process is known as coalescing.

14. What Are Constant Tension Winches?

Constant tension winches use variable capacity pumps with constant pressure and horsepower control. The pump automatically adjusts across neutral to maintain constant system pressure, ensuring steady motor torque when both drawing in and paying out, providing consistent tension.

15. What Happens if the Fuel Pump Leaks?

• Reduced fuel quantity leads to loss of power and affects cylinder liner lubrication
• Imbalance in power output among engine units
• High exhaust temperatures and smoky emissions
• Injection timing delays, causing late injection
• Afterburning issues
• Significant loss of cylinder power

16. What Are the Steering Gear Motor Safeties?

• Short circuit trip for protection
• Self-starts after a power failure
• High temperature alarm to prevent overheating
• 200% motor insulation for enhanced safety
• Overload alarm to detect excessive load
• Alarm for phase failure
• One steering motor connected to the emergency bus

Hydraulic Safeties:

• Low-level cutout to prevent damage
• High lube oil temperature cutout for protection

17. What Are the Overhead Crane Safeties?

• Limit switches prevent excess movement in all directions
• Overload trip to safeguard against excessive load
• Dead man’s handle for controlled operation
• Guards over pulleys to prevent accidents
• Locking device on the lifting hook for secure operation
• Mechanical locking to prevent movement in rough weather

18. What Are the Causes of Turbocharger Surging?

• Blocked air intake filter or fouled turbocharger
• Sudden reduction in engine load
• Restricted exhaust or air passages, such as clogged scavenge ports, valves, or air coolers
• Malfunctioning fuel system, such as a misfiring unit
• Unbalanced engine output, damaged exhaust valves, or scavenge fires

19. What Are the Various Windlass Safeties?

Electric Safeties:

• Short circuit safeguarding
• Electromagnetic braking system
• Prevents automatic restart
• Protection against motor overload
• Delay timer for restarting

Manual Safeties:

• Torque-limiting slipping clutch
• Pressure relief valve
• Hand-operated or mechanical brake
• Chain stopper for securing

20. What Are the Air Bottle Safeties?

• Relief valve to release excess pressure
• Fusible plug for temperature protection
• Drain to remove accumulated moisture
• Low-pressure alarm for early detection

21. What Are the Causes of Cylinder Head Cracking?

• Ineffective cooling water flow
• Scale buildup in the cooling system
• Excessive temperature fluctuations causing high thermal gradients
• Uneven tightening of bolts or fuel valves
• Engine overloading or racing
• Corrosion from gas or acid due to leaky exhaust valves
• Faulty relief valves
• Corrosion on the water side of the cylinder head

22. Advantages of Uniflow Scavenging

• Increased stroke length capability
• Simple liner construction
• No need for long piston skirts
• High scavenging and thermal efficiency
• Uniform wear on piston rings and liners
• Reduced thermal stresses
• Effective burning of low-grade fuel
• Minimal intermixing of scavenging air with exhaust gases
• Exhaust valve opens late for more work and closes early to maximize scavenging air use

23. What Is the Normal Relief Valve Setting for a Cylinder Head in a Diesel Engine?

The relief valve is typically set 10-14.5% above the working pressure, around 120 bar, slightly higher than the maximum operating pressure.

24. What Actions to Take If the Stern Tube of a Ship Starts Leaking?

• Use higher viscosity oil
• Maintain a low head pressure
• Replenish oil regularly to compensate for losses
• Periodically drain off water
• Reverse the shaft direction to dislodge foreign particles

25. What Are the Reasons for a Piston Crown to Crack?

• Thermal stresses caused by cold starting air and scavenging air
• Casting defects during manufacturing
• Scavenge fire incidents
• Overheated piston due to cooling failure or cooling side deposits from oil oxidation
• After burning in the combustion chamber
• Faulty fuel injection system causing excessive penetration or poor atomization

26. What Are the Effects of Critical Speed?

Critical speed can lead to resonance, torsional vibrations, and fatigue failure of components.

It can be mitigated by:

• Vibration dampers
• Detuners
• Electric vibration compensator units

27. How to Test a Fresh Water Generator Plant for Leaks?

• Inject air into the evaporator shell
• Close the distillate pump outlet, vacuum breaker valve, bottom blow-off valve, and feed water valve
• Maintain shell pressure at around 1.0 bar gauge
• Apply soap solution to joints, packings, and suspected leak areas

28. Why Is Cylinder Liner Wear More at the Top?

• Corrosive wear, especially acidic corrosion from combustion byproducts
• Fuel impingement leading to deposits
• Exposure to high temperatures from combustion gases
• Piston direction change causing step-like wear at the reversal point
• Lubrication loss in low-speed diesel engines

29. What Are the Reasons for Black Smoke from a Diesel Engine?

• Low compression leading to poor combustion
• Faulty injection system causing incomplete combustion
• Insufficient scavenging air
• Clogged or fouled exhaust system
• Broken piston rings
• Ineffective lube oil seals
• After burning or use of bad fuel, along with fuel-related faults
• Faulty cylinder lubrication
• During starting, black smoke is common due to fixed starting fuel index, low air, slow piston speed, cold combustion chamber, and low fuel injection pressure

30. Why Is Cylinder Liner Wear More at the Top?

• Corrosive wear, especially acidic corrosion from combustion byproducts
• Fuel impingement leading to deposits
• Exposure to high temperatures from combustion gases
• Piston direction change causing step-like wear at the reversal point
• Lubrication loss in low-speed diesel engines

31. What Are the Types of Vibration in a Diesel Engine and Which Is the Most Damaging?

Types of vibration:

• Torsional vibration
• Linear vibration
• Resonant vibrations, which may involve either or a combination of both

The most harmful is torsional vibration, as it primarily impacts the crankshaft and propeller shafting.

32. What Is Forcing Frequency?

Forcing frequency, in relation to crankshafts, is caused by firing impulses from the cylinders. These impulses combine to form complex waveforms, represented by harmonics:

• 1x cycle frequency: first-order harmonic
• 2x cycle frequency: second-order harmonic
• 3x cycle frequency: third-order harmonic, and so on.

33. What Is a Node?

A node is a point in a vibrating medium where deflection is zero and the amplitude changes direction. More nodes in a given length indicate a higher natural frequency.

34. What Is an Electric Compensator?

An electric compensator, typically located in the steering gear compartment where deflections are greatest, neutralizes external forces or moments by synchronizing with the correct phase. It requires additional seating for installation to maximize its effect.

35. Types of Top Bracing for a Diesel Engine

• Stiff connections (links): Equipped with friction plates to adjust based on the ship’s loading conditions
• Hydraulic top bracing: Raises the natural frequency to prevent resonance within the engine’s normal operating speed range

36. What Is Balancing?

Balancing controls vibrations by ensuring that out-of-balance forces and couples are either canceled out or minimized to an acceptable level.

37. What Is a 1st Order Moment?

A 1st order moment acts in both vertical and horizontal directions. In engines with five or more cylinders, it generally has little impact, but in four-cylinder engines, it can be significant. Resonance with the 1st order moment may occur with hull vibrations involving two or three nodes. A 1st order compensator, consisting of two counter-rotating masses at crankshaft speed, can be added to the chain tightener wheel to counteract these effects.

38. What Is a Second Order Moment?

A second order moment affects only the vertical direction and is relevant for 4, 5, and 6-cylinder engines. Resonance with this moment may occur in hull vibrations with more than three nodes. A second order moment compensator, consisting of two counter-rotating masses, operates at twice the engine speed to counteract these effects.

39. Causes and Remedies of Axial Vibrations in the Crankshaft

Axial vibrations in the crankshaft occur when gas pressure on the crank throw, via the connecting rod, causes axial deflection. These vibrations can transfer to the ship’s hull through the thrust bearing. The remedy is to use axial dampers to reduce these vibrations.

40. How Are Torsional Vibrations Generated?

Torsional vibrations arise from fluctuating gas pressure during the working cycle and the crankshaft/conrod mechanism, creating varying torque. Propeller interactions with the uneven wake field also contribute to these vibrations.

Remedy: Adjust crankshaft diameter to modify its natural frequency or use a torsional damper.

41. Causes of Reduced Output in a Centrifugal Pump

• Cavitation on the impeller
• Friction, leakage losses, loss of suction head, clogged suction filter, worn wear ring, or air ingress in the suction side
• Low voltage supplied to the pump motor
• Poor maintenance or incorrect reassembly after overhaul

42. Solutions for Resonance Issues

When resonance occurs, the following modifications can be made:

• Lanchester balancers: Installed on the engine or as electrically driven units in the steering flat to compensate for ship vibrations caused by the second-order vertical moment.
• Counterweights on the crankshaft: Adjusted to counter first-order vibrations.
• Primary and secondary balancers: Combined to manage both types of vibrations.
• Adjusting side stays: To help minimize the effects of vibration.

43. Vibration Characteristics of Low-Speed 2-Stroke Engines

• Unbalanced external moments
• Guide force moments affecting engine dynamics
• Axial vibrations in the shafting system
• Torsional vibrations within the shafting system

44. Methods to Manage Second Order Moments

• Compensator on the fore end driven directly from the crankshaft with a separate chain drive
• Compensator on the aft end driven by the engine’s chain drive mechanism
• Compensators on both aft and fore ends to fully eliminate external second order moments

45. How to Adjust Resonance Frequency, Forcing Impulses, and Resultant Stresses

• Modify shaft sizes
• Change the number of propeller blades
• Adjust the firing order
• Implement viscous or other dampers
• Use balancing weights
• Detune the coupling

46. What Are Guide Force Moments and Their Types?

Guide force moments originate from the angularity of the connecting rod and are caused by transverse reaction forces on the crosshead. These moments result in engine vibrations around the foundation bolts. There are two types:

• H moment: Causes a rocking motion of the engine top arthwartships.
• X moment: Leads to a twisting motion of the engine.

47. What Is Over-Critical Running?

Over-critical running occurs when the natural frequency of one-node vibration is adjusted so that resonance with the main critical order happens 30-70% below the engine’s MCR. Characteristics of this system include:

• High-inertia turning wheel
• Barred speed range of approximately +/- 10% around the critical engine speed
• A turning wheel may be required on the crankshaft
• Small-diameter shaft (material with high UTS required)

48. What Is Under-Critical Running?

Under-critical running occurs when the natural frequency of one-node vibration is adjusted so that resonance with the main critical order happens 35-45% above the engine’s maximum continuous rating (MCR). Characteristics of an under-critical system include:

• Short shafting system
• Large shaft diameter
• Low-inertia turning wheel or no turning wheel
• No barred speed range

49. Steps to Prepare a DB Fuel Oil Tank for Survey/Inspection

• Ventilate the tank using a blower, ensuring cross ventilation with at least two openings for air entry and exit.
• Empty the oil and, if necessary, strip with portable pumps.
• Clean the tank with seawater and pump the contents through the oily water separator.
• Test for explosive gases at multiple points, especially in the corners and bottom of the tank.
• Complete the necessary checklist and obtain required certificates for the inspection.

50. Why Isn’t a Crankcase Relief Door Fitted in Refrigeration Compressor Crankcases?

• There’s a risk of air leaking in, contaminating the refrigeration system.
• Oxygen is absent in the compressor crankcase.
• The refrigerant’s low temperature reduces the likelihood of hot spots.
• As the crankcase acts as the compressor’s suction chamber, there’s a chance it could draw in air and moisture.

51. Why Are Heaters Installed in Refrigeration Compressor Crankcases?

• To maintain oil viscosity for effective lubrication.
• To prevent refrigerant and oil separation issues at low temperatures, reducing oil carryover.
• To avoid the lube oil reaching its floc point, which could lead to passage narrowing or blockage due to flocculation.

52. Why Are CO2 Bottles Fitted with Dip Tubes?

Dip tubes ensure that only liquid CO2 is drawn during release, which expands into gas after passing through the nozzles. This prevents freezing and blockage while achieving 85% discharge within 2 minutes, as the liquid represents a larger gas volume.

53. What Is Compression Ratio?

The compression ratio is the ratio of the total volume (swept volume + clearance volume) to the clearance volume.

54. What Is Brake Thermal Efficiency?

Brake thermal efficiency is the ratio of energy developed at the brake to the energy supplied, comparing the heat liberated during combustion to the energy output at the brake.

55. Typical Volumetric Efficiency of a Diesel Engine

• Supercharged engine: Efficiency can reach up to 4.0
• 2-stroke engine: Efficiency ranges between 0.85 and 2.5
• Naturally aspirated engine: Efficiency typically ranges from 0.85 to 0.95

56. What Is Volumetric Efficiency of Air Compressors?

Volumetric efficiency is the ratio of the actual volume of air drawn into the compressor to the swept volume.

57. Causes of Vibration in Vertical Centrifugal Pumps

Shaft misalignment, worn bearings, loose foundation bolts, improper hydraulic clearances, damaged coupling bolts/seating, worn bottom bush, debris buildup, and corrosion or erosion on rotating parts.

58. Function of the Back Pressure Valve in Refrigeration Systems

A back pressure valve, located at the evaporator coil exit in multi-temperature systems, maintains system balance by managing pressure differences. It ensures liquid refrigerant is prioritized for compartments requiring lower temperatures and acts as a spring-loaded non-return valve.

59. Function of H.P Cut-Out in Refrigeration Systems

The H.P cut-out is a safety device on the compressor’s discharge side, tripping the compressor if the high-pressure side exceeds the normal operating limit.

60. Function of Driers in Refrigeration Systems

Driers in the liquid line absorb moisture from the refrigerant using a renewable cartridge filled with activated alumina or silica gel, ensuring efficient system operation. It also includes a charging connection.

61. Function of a Solenoid Valve in a Refrigeration System

A solenoid valve, controlled by the thermostat, is placed in the liquid line before the thermostatic expansion valve. It shuts off refrigerant flow when the compartment reaches the lower temperature set point and opens when the temperature rises above the upper set point.

62. Typical Stern Tube Bearing Clearances

• Oil-cooled stern tube bearing: Clearance ranges from 1.87 to 2.0 mm
• Water-cooled stern bearing: Clearance is typically 8.0 mm (range 8 to 12 mm)

63. Usual Propeller Drop Value

The standard propeller drop is typically 1 mm for every 160 mm of shaft diameter.

64. Common Bearing Failures

• Wiping damage on the bearing surface
• Fatigue failure, resulting in cracks
• Tin oxide encrustation (black SnO₂ formation)
• Tearing of the overlay layer
• Acidic corrosion leading to surface damage
• Cavitation and erosion of the bearing material
• Dross inclusion within the bearing
• Spark erosion causing localized damage
• Bacterial attack with honey-colored deposits on the surface

65. Advantages of Thin Shell Bearings

• Better heat transfer due to reduced thickness and uniform contact with the housing
• Increased mechanical properties for better performance
• High load carrying capacities to handle heavy loads
• Fatigue resistance for longer bearing life
• No bedding required, simplifying installation
• Conformability and embed ability for better adaptability
• Lightweight, easy to fit, and store

66. Advantages and Disadvantages of Synthetic Lube Oils

Advantages:

• Excellent low-temperature fluidity and pump ability due to no wax content
• Better oil retention at high temperatures
• Lower friction losses, enhancing efficiency
• Reduced thickening during use from oxidation resistance
• Fewer deposits at high temperatures thanks to thermal stability and oxidation resistance

Disadvantages:

• Higher cost, approximately 6-12 times more expensive
• Limited availability in some regions

Uses:

• Air compressors
• Purifiers
• Hydraulic units

67. Purpose of Lube Oil Analysis

• Assess contaminant levels to evaluate contamination rates and the effectiveness of purification
• Monitor deterioration in lube oil properties or additives to ensure suitability for continued use
• Predict internal wear rates on machinery components
• Extend time between overhauls or surveys, improving maintenance intervals

68. When Is Lube Oil Considered Deteriorated?

• Increased water content
• Reduction in TBN (Total Base Number)
• Decreased viscosity
• Lower flash point
• Increased oxidation levels
• Higher insolubles content
• Increased dispersancy

69. Challenges in Cast Iron Welding

• High carbon content in the form of graphite
• Brittleness, making it prone to cracking
• Close grain structure, complicating the welding process
• Poor thermal conductivity, leading to uneven cooling
• Potential for stresses and distortion during welding

70. Comparison Between an Engine Flywheel and Governor

• Governor: Regulates the overall engine speed.
• Flywheel: Manages cyclic RPM fluctuations.
• Flywheel relies solely on inertia, while the governor uses inertia to adjust fuel linkages and stabilize RPM changes.

71. Purpose of Tie Rods in an Engine

Tie rods maintain the engine structure under compression, which:

• Increases fatigue strength, as tensile stress is the primary cause of fatigue
• Maintains alignment of the running gear to prevent fretting

During firing, forces attempt to push up the cylinder covers and press down the bearing saddle, inducing tensile stress. Tie rods are tightened to keep the engine structure in compression, even under peak firing conditions, preventing tensile loading.

72. Where and Why Is a Thrust Bearing Installed in an Auxiliary Engine?

A thrust bearing is installed at one main bearing location if the coupling lacks a thrust housing. White metal rings or a small collar are added to control axial movement, allowing minimal clearance between the shaft and adjacent webs. Only one such bearing is used per shaft to avoid issues from differential thermal expansion between the frame and crankshaft.

73. Why Are Tie Rods Positioned Close to the Crankshaft Centerline?

Tie rods are placed near the crankshaft centerline to minimize bending moments on transverse girders during firing, reducing distortion of the bearing housing caused by crankshaft forces on the cylinder head.

74. How Is Propeller Drop Measured?

• Align the engine: Rotate the engine to align a mark on the liner with the stern tube, or position unit 1 at TDC. Alternatively, use a designated propeller blade (A, B, C, D, etc.) facing upwards.
• Take poker gauge readings: Compare these with previous measurements.
• Bearing clearances: 2 mm for oil-sealed, 8 mm for seawater-lubricated systems.
• Bearing lengths: 2x shaft diameter for oil-cooled, 4x shaft diameter for seawater-lubricated systems.

75. Environmental Issues Caused by CFCs

• Ozone depletion: CFCs, when released, undergo pyrolysis and release chlorine atoms, which catalytically destroy the ozone layer. This ozone layer in the stratosphere acts as a shield against harmful UV radiation.
• Global warming: CFCs, along with other greenhouse gases, trap radiation from the Earth’s surface, contributing to the greenhouse effect and global warming.

76. What Is pH Value?

pH is the logarithm of the reciprocal of the hydrogen ion concentration in a solution. Pure water at 25°C has equal concentrations of hydrogen and hydroxyl ions (10⁻¹⁴ g ions/L). A solution is basic if hydroxyl ions exceed hydrogen ions and acidic if the opposite. The pH formula is: pH = log [1/H⁺]. Higher temperatures increase hydrogen ion concentration, raising acidity.

77. How to Maintain Fuel Oil Viscosity Without Viscotherm?

Refer to the fuel oil analysis report for viscosity data at 50°C and desired injection viscosity. Use a viscosity nomogram to determine required heating. Manually adjust steam inlet to the fuel oil heater, closely monitoring steam pressure and outlet temperature to maintain proper viscosity.

78. Why Is Intercooling Provided and Compression Staged in an Air Compressor?

• Achieves isothermal compression: Intercooling reduces the work needed for compression.
• Lowers outlet temperature: Prevents lube oil oxidation and ensures better lubrication.
• Reduces deposits: Minimizes buildup in the air system.
• Increases air density: Allows smaller HP compression chambers.
• Removes moisture: Intercooling facilitates moisture condensation and removal.
• Even load distribution: Staging the compression ensures balanced loads throughout the cycle.

79. Why Is a Manhole Door Elliptical in Shape?

Elliptical openings in pressure vessels are smaller than circular ones, minimizing material removal while allowing entry. The smooth, rounded edges reduce stress concentration, unlike rectangular or square shapes. A doubler ring is added around the opening to compensate for material loss, with its thickness based on the axis length and shell thickness. The minor axis is aligned with the vessel’s length, where stress is highest, optimizing weight and material savings.

• Longitudinal stress: Pd/2t
• Circumferential stress: Pd/4t

80. What Happens if Compressor Motor Connections Are Reversed After Overhaul?

• Insufficient lubrication: Low lube oil pressure can cause the compressor to trip, and moving parts may suffer damage due to inadequate lubrication.
• Cooling issues: The shaft-driven cooling water pump may not generate enough flow, leading to a trip due to insufficient water flow or high air temperature.

81. Why Is the Fridge Compressor Belt Driven?

• Minimizes misalignment and vibration: Direct misalignment or motor vibration could lead to shaft seal leaks and refrigerant loss, so a belt drive helps reduce this risk.
• Limits damage from liquid entry: In case of liquid entry into the compressor, the belt can slip, reducing potential damage due to its flexibility.

82. Causes of Error Between Helm Order and Steering Gear Angle

• Worn out linkages affecting accurate transmission of movement
• Air in the hydraulic telemotor system leading to improper signal transmission
• Weak or stiff buffer spring or faulty hunting gear disrupting the system’s responsiveness
• Instrument errors or defects causing inaccurate readings

83. Quality of Vapor Returning to Compressor in Refrigeration System

• Vapor should have sufficient superheat when returning to the compressor suction line.
• Ensure proper superheat by checking the vapor pressure and corresponding temperature using the refrigerant’s P-T chart. Compare this temperature with the evaporator outlet temperature, and the degree of superheat is the difference between these values.

84. Why Are Accumulators Used in Hydraulic Systems?

• Absorb shock from load variations or sudden flow changes, preventing impact loading
• Maintain circuit pressure by compensating for leaks or pressure changes due to temperature fluctuations
• Supplement pump delivery during peak demand that exceeds pump capacity, with the accumulator charged during low-demand periods for later use

85. Crosshead Slipper Lubrication Explained

• Lubricating oil is supplied to the guide shoes via a pipe connected to the main lube oil system
• Oil may also be fed through drilled passages in the pin, delivering lubrication to the slipper faces

86. Criteria for Re-Entry into the Engine Room After CO2 Flooding

Re-entry is based on:

• Heat buildup and time elapsed after CO2 release, considering the fire’s intensity
• Confirmation that the fire is extinguished or if there’s a risk of smoldering
• Ship’s condition and position, including potential listing or flooding
• Location of the re-entry point for safe access
• Risk analysis outcome determining the safety of re-entry

87. CO2 Bottle and Accessories Material

• CO2 bottle: Seamless manganese steel
• Cable: Phosphor bronze
• Seal/bursting disc: 0.3mm phosphor bronze
• Pipeline: Galvanized solid drawn mild steel
• Siphon tube: Copper
• Cutter: 120° angle, 19mm travel

88. Crank Web Length

The length of the crank web is half the stroke length, or:
Crank web length = stroke length / 2.

89. What Is Lignum Vitae?

Lignum vitae is a wood traditionally used as bearing material in seawater-lubricated stern tubes. It provides natural lubrication in seawater and is arranged with axial grain direction for durability. V or U grooves allow water access and collect debris. The staves are secured in a bronze boss with bronze keys and screws, and the bearing length is typically four times the shaft diameter.

90. Safety Features in a Refrigeration System

• High Pressure (HP) cutout
• Low Pressure (LP) cutout
• Differential lube oil pressure cutout
• Relief valve in the condenser
• Cylinder head relief valve
• Cooling water low flow/high temperature alarm
• Motor overload protection
• Belt-driven system
• Oil separator
• Drier
• Mechanical seal
• Unloaders/capacity controllers
• Non-return shut-off valves
• Temperature and pressure sensors

91. Detecting Air in Refrigeration System and Purging Procedure

Signs of Air in the System:

• High condenser pressure
• Bubbles in the sight glass
• Compressor running hot with high discharge pressure
• Increased superheat
• Pressure fluctuations
• Inefficient system performance

Procedure for Purging Air:

• Measure liquid refrigerant pressure and temperature at the condenser/reservoir outlet during normal operation.
• Check the P-T chart for the corresponding saturation temperature of the refrigerant at the measured pressure.
• Compare the actual temperature with the saturation temperature to determine sub-cooling and adjust cooling water flow to maintain near-saturation conditions.

Then:

• Close the condenser liquid refrigerant outlet valve, circulate cooling water, and start the compressor to pump down the liquid to the condenser/reservoir while monitoring suction line pressure. Ensure it doesn’t drop below atmospheric to avoid air ingress.
• Continue circulating cooling water until the inlet and outlet temperatures match, confirming a complete pump-down.
• Check the condenser sea water outlet temperature, and verify the refrigerant pressure using the P-T chart.
• If air is present, the pressure and temperature won’t match.
• Vent air from the condenser using the vent cock until the refrigerant pressure aligns with the saturation pressure at the sea water outlet temperature.

92. Material of Tie Rods

Tie rods are made from high tensile steel to ensure durability and strength in load-bearing applications.

93. Material of Boiler Gauge Glass

The boiler gauge glass is made of special toughened glass, commonly containing:

• Silicon oxide or magnesium oxide
• Borosilicate or lime soda glass

94. Material of Boiler Tubes

Boiler tubes are made from low carbon alloy steels, typically containing chromium, nickel, and molybdenum for enhanced strength and durability.

95 Material of Ship Side Valve

• Body: Nickel-Aluminium bronze or cast steel
• Stem/Seat/Disc: Monel metal (Cupronickel, typically in a 2:1 ratio of Cu
  ) known for high resistance to seawater corrosion, erosion, and strength.

96. Material of Propeller

• 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 Zinc
• Manganese Bronze:
  • Copper: 58%, Iron: 1%, Aluminium: 1%, Manganese: 1%, Nickel: 0.5%, Zinc: 38%, Tin: 0.5%

97. Material of Crankshaft

Crankshafts are made from forged low carbon alloy steel, with carbon content of 0.12% or less for strength and durability.

98. General Composition of Stainless Steel

Stainless steel typically contains:

• Chromium: 18%
• Nickel: 8%
• Carbon: 0.12%

99. Material of 4-Stroke Engine Connecting Rod

• Forged steel (Open hearth plain carbon steel):
  • UTS: 432-494 MN/m²
  • Elongation: 25-30%
  • Fatigue limit: 208 MN/m² (push-pull)
• Nickel steel (3% Ni):
  • UTS: 695 MN/m²
  • Elongation: 20%
  • Fatigue limit: 309 MN/m² (push-pull)

Tightening Methods:

• Measuring bolt extension
• Using calibrated torque wrenches
• Hydraulic tensioning
• Angle tightening

100. Material of Foundation Bolts

Foundation bolts are made from high tensile steel for strength and durability.

101. Material of Double Bottom Plug

Double bottom plugs are typically made from silicon steel for durability and corrosion resistance.

102, Materials of Diesel Engine Liner and Piston Rings

• Liner material: Typically nodular cast iron, designed for longitudinal expansion with minimal circumferential expansion. Alloying elements like vanadium and titanium enhance specific properties.
• Piston ring material: Made from harder graphite grey cast iron, often alloyed with chromium, nickel, or copper for improved performance.

Principal Differences:

• Piston rings are harder than liners as they endure continuous wear, whereas only part of the liner is worn.
• Piston rings flex circumferentially, crucial for running in, sealing combustion gases, and conforming to the liner’s surface.

103. Why Is Stainless Steel Corrosion Resistant?

Stainless steel resists corrosion due to a protective chromium oxide film that forms spontaneously when exposed to air or aerated water. Without this film, its corrosion resistance is only slightly better than regular steels.

104. Liner Wear Rates and How They Are Achieved

• Old engines: 0.1mm/1000 hours
• Modern 2-stroke engines: 0.03mm/1000 hours
• Modern 4-stroke engines: 0.12mm/1000 hours

Achieved by:

• Highly alkaline lube oil
• Load-dependent jacket cooling water temperature control
• Improved cast iron quality with hard facing
• Optimized piston ring profile design
• Enhanced lube oil formulations
• Multilevel cylinder lubrication
• Condensate separation from scavenging air
• Use of anti-polishing rings or piston cleaning techniques

105. Material of Fuel Injector Needle and Body

• Needle: High-speed steel
• Body: Case-hardened steel

Conclusion

Preparing for the MEO Class 4 Viva can be challenging, but with the right guidance, you can approach it confidently. This guide provides a comprehensive collection of essential questions to enhance your knowledge and readiness. By focusing on key topics and practical insights, you’ll be well-equipped to excel in your 2024 examination. Best of luck!