Category: MEO ORALS

What Is The Procedure For Handing Over A Watch?
The Engineer Should Not Vacate The Engine Room Until His Relief Arrives.
He Should Acquaint The Relieving Engineer Of Any Abnormal Operating Conditions That Have Occurred During The Watch.
Any Orders From The Bridge, Recorded In The Log Book Should Be Pointed Out.
Instructions From Senior Engineer Should Be Passed On.
Any Repairs Should Be Reported Together With Information On Any Machinery That Has Been Dismantled.
The Presence Of Any Other Members Of Ship's Staff In The Engine Room Should Be Reported.
The Engineer Must Ascertain That His Relief If Fit And Able Before Vacating The Machinery Space.
 
Explain The Bilge System From Bilge Wells To Overboard.
The Bilge Pump (Positive Displacement Pump) Takes Suction From The Bilge Well Via A Strum Box, Then Via A Strainer Before Entering The Pump Where It Is Then Discharged To The Bilge Holding Tank.
From The Bilge Tank The Oily Water Separator Takes Suction, Bilge Water Passes Through The Separator Before Being Discharged Overboard Via 15ppm Monitoring Unit, Which Will Automatically Stop The Oily Water Separator Pump And Give An Alarm If The Oily Water Mixture Exceeds 15ppm.
 
How Is The Signal From The Bridge When The Helm Is Moved Transmitted To The Hydraulic Rams In Steering Flat?
When The Helm On The Bridge Is Moved, Electrical Impulses Are Produced.  These Impulses Are Transmitted Via An Amplifier Or Control Unit To The Steering Flat.  In The Steering Flat, These Impulses Are Relayed To A Servomotor (telemotor) Which Drives An Adjusting Gear And Floating Lever Which Puts The Steering Gear Variable Delivery Pump On Stroke, Thus Creating Hydraulic Pressure In The System Which Moves The Rams, Thus Moving The Tiller And Rudder.
The Pump Is Only Required To Deliver Oil When The Helm Is Moved I.e. Once Rudder Has Matched The Helm Angle, The Control Lever Will Put The Pump Off Stroke.
 
Why Is A Gear Type Pump Used For Pumping Oil, While A Centrifugal Pump Is Used For Pumping Water?
A Gear Pump Is Used For Pumping Oil As It Has A High Suction Lift, Is Self Priming, Able To Produce The Discharge Pressure Required By The System And Can Handle Large Amounts Of Vapour Or Entrained Gases.  It Is Also Able To Pump High Viscous Fluids.
A Centrifugal Pump Is Used For Pumping Water, As It Is Unable To Pump High Viscous Fluids Such As Oil, The Centrifugal Pump Is Not Self-Priming.

What Would Happen To The Amps Of A Centrifugal Pump If It Were Run With The Discharge Valve Shut?
The Amps Would Drop, As There Would Be No Load On The Pump.
 
What Steering Gear Checks Would You Do Before Sailing?
Prior To A Ship's Departure From Any Port, The Steering Gear Should Be Tested To Ensure Satisfactory Operation.  These Tests Should Include:
Operation Of The Main Steering Gear
Operation Of The Auxiliary Steering Gear Or The Use Of The Second Pump Which Acts As The Auxiliary.
Operation Of The Remote Control Systems From The Main Bridge Steering Positions.
Operation Of Steering Gear Using The Emergency Power Supply.
The Rudder Angle Indicator Reading With Respect To The Actual Rudder Angle Should Be Checked.
The Alarms Fitted To The Remote Control System And Steering Gear Power Units Should Be Checked For Correct Operation. 
Steering Gear Header Tank Level Should Be Checked. 
During These Tests, The Rudder Should Be Moved Through Its Full Travel, In Both Port And Starboard And The Various Equipment Items, Linkages, Etc. Visually Inspected For Damage Or Wear.  The Communication System Between Bridge And Steering Gear Compartment Should Also Be Operated.
 
What Are Normal Jacket Water Temperatures And Pressures?
Normal Jacket Water Pressures Are Between 2-3 Bar, Temperatures 80-85°C, Alarm Point At 90°C And Shut Down At 95°C .
What Is The Correct Method Of Starting And Stopping A Centrifugal Pump?
The Correct Way To Start And Stop A Centrifugal Pump Is With The Discharge Valve From The Pump Closed, I.e. Less Load On The Motor When Starting And Stopping.
 
What Would You Do In The Event Of An Oil Spill?
Raise The Alarm, Inform Bridge And Chief Engineer. 
There Should Be A Set Drill For Oil Spills, Which Is Practised Regularly.
If Possible Contain The Spill On Deck And Start Clean Up Procedures Using Appropriate Oil Spill Equipment.
If The Oil Has Spilt Into The Sea:-  If In Port, Port Authorities Should Be Informed.  If At Sea, Coastguard Should Be Informed.
The Time Of Spill Should Be Recorded With The Place Or Position Of Ship At The Time Of Spill Along With Approximate Quantity And Type Of Oil.
Circumstances Of Discharge Or Escape Would Be Logged In Oil Record Book And Engine Room Log Book.
 
Why Are High And Low Suctions Fitted On Fuel Oil Service Tanks?
The High And Low Suctions Are A Safety Feature To Prevent Invertent Shut Down Of Main Engines, Generators And Boilers Due To Water Contamination Of The Fuel.  Normally The Low Suction Is Kept In Use.  If Any Water Should Find Its Way Into The Fuel And Service Tank, It Will Gradually Separate Towards The Tank Bottom.  When It Becomes Apparent Water Is Present By Finding It At The Tank Drains Or By Operation Of The Engine, It Is Possible To Bring The High Suction Into Operation And Avoid Shut Down.
 
Describe The Duties Of A Duty Engineer.
Regularly Check And Record All Pressures And Temperatures In The Engine Room Log.
Pay Attention To Readings For Deviation From Normal, Particular Attention Being Made To Exhaust Gas Temperature, Scavenge Temperatures And Pressures And Turbo Charger Revs.
Adjustments Should Be Made For Sea Water Temperature Changes To Keep Correct Temperatures And Pressures.
Checks Should Be Made On The Pressure Drops Across Fuel And Lubrication Filters To See That They Are Operating Within Required Limits.
Check All Oil Levels In Auxiliary Machinery:  Main Engine Sump Levels, Cylinder Lubricators, Turbo Charges, Governors.
Check Around All Bearings And Crankcase Doors Using Palm Of The Hand To Feel For Any Increase In Temperature.
Ensure That Fuel In The Daily Service Tanks Is At Correct Levels And That It Is Sludged And Drained Of Water.
Depending On Type Of Purifiers Fitted, Sludge And Drain, Check Oil Level, Signs Of Vibration And Clean If Required.
Carry Out All Routine Assignments As Recommended By Engine Builders Or The Company.
At All Times Use Sight, Smell And Hearing, As This Is Often The First Sign Of A Fault Developing In The Engine Room.
Check Bilge Levels, Stern Gland, Air Start Bottles And Maintain Correct Levels And Pressures.
Record And Fuel/Lub Oil Transfers And Any Irregularities In Log.
 
What Are The Uses Of Centrifugal Pumps, Positive Displacement Pumps And Gear Pumps On Board A Ship?
Centrifugal Pumps:  Seawater Cooling Pumps, Jacket Water Cooling Pumps, Boiler Feed Pumps (Multi Stage Pumps)
Positive Displacement Pumps:   Bilge Pumps, Steering Gear Pumps, Cargo Shipping Pumps.
Gear Type Pumps:   Fuel Oil Booster Pumps, Fuel Oil Transfer Pumps, Engine Lub Oil Pumps.
 
Why Are Weighted Cocks Fitted To Sounding Pipes Of Fuel Oil Tanks?
Weighted Cocks Are Fitted To Sounding Pipes Of Fuel Oil Tanks To Prevent Fuel Oil Spills From Overflows.  They Also Prevent Vapours Escaping From Tanks.
 
Describe Different Types Of Cooling Systems I.e. Seawater Cooling System And Central Cooling System.
A Seawater Cooling System Is An Arrangement That Uses Individual Coolers For Lub Oil, Jacket Water And The Piston Cooling System.  Each Cooler Being Circulated By Sea Water.
As Where Some Modern Ships Use A Central Cooling System With Only One Large Sea Water Circulated Cooler.  This Cools A Supply Of Fresh Water, Which Then Circulates To The Other Individual Coolers.  With Less Equipment In Contact With Sea Water, The Corrosion Problems Are Much Reduced In This System.
 
How Many Pumps Are There In The Engine Room That You Can Pump Bilges With?
A Bilge Pump Which Is Normally Positive Displacement.
The Others May Vary From Ship To Ship, But Can Be The Ballast Pump, General Service Pump And Main Sea Water Cooling Pump.  These Pumps Are Only Used For Pumping Bilges In The Event Of An Emergency And Have An Emergency Bilge Suction/Injection Valve Connected To Them.
 
Give Possible Reasons Why The Engine Room Bilge Pump May Not Be Able To Empty Bilges.
The Strum Box From The Bilge May Be Fowled.
Bilge Pump Suction Strainer May Be Blocked.
A Valve May Be Left Open From An Empty Bilge.
There Could Be A Hole In The System On The Suction Side Of The Pump.
Depending On Type Of Bilge Pump, The Pump Suction Or Discharge Valves May Need Overhauling.

Why Would The Bridge Need To Be Informed That The Engine Is About To Be Stopped?
The Bridge Would Need To Be Informed That The Engine Was About To Be Stopped To Ensure It Was Navigationally Safe To Do So, I.e. Not In Busy Shipping Lanes Or Near Land.

Centrifugal and positive displacement pumps, both used on board. Selection of these pumps basicaly depends on the behavior and ship board requirements. Centrifugal pumps are most common type of pumps on board ships. Almost all of the pumps on board for seawater or fresh water are of centrifugal type. positive displacement pumps are used for high pressure requirements, like FO supply pump, FO and LO transfer pump, sludge pump etc. Behaviour and performance of these pumps changes distinctly for any change in parameter like viscosity, presure head. Lets see how these pumps behave with the change through graphs.

Q. Describe camber, sheer, tumble home, Rise of floor.
Ans.
Camber:-The transverse curvature of the deck from the centerline down to the sides. This camber is used on exposed deck to drive water to the sides of the ship.
Sheer: The curvature of the deck in a fore & aft directions, rising from mid-ship to the maximum at the ends. It makes a ship more seaworthy by raising the deck at the fore & after ends further from the water and by reducing the volume of water coming on the deck.
Tumble Home: In some ships, the mid-ship side shell in the region of the upper deck is curved slightly towards the center line, thus reducing the width of the upper deck & decks above.
Rise of Floor: The bottom shell of ship is sometimes sloped up from the keel to the bilge to facilitate drainage. The rise of floor is very small.

Q. What is freeboard and reserve buoyancy?
Freeboard: It is the distance from the waterline to the top of the deck plating at the side of the deck amidships.
Reserve Buoyancy: It is the potential buoyancy of a ship and depends upon the intact, watertight volume above the waterline.
When a mass is added to the ship, or buoyancy is lost due to bilging, the reserve buoyancy is converted into buoyancy by increasing the draught. If the loss in buoyancy exceeds the reserve buoyancy the vessel will sink.

Q. Why do tankers have less freeboard?
Ans. The value of GM is greater compared to other types of ships, the openings in the tankers are small than of other ship & also the permeability is more.
      
Q. what do u mean by the stability of ship? How does stable Ship returns to the upright position if heeled by an external force?
Ans. STABILITY OF SHIP: The tendency of the ship to come back to its upright position when healed by external force is defined as the stability of the ship.
When a ship is healed, the centre of buoyancy shifts, this forms a righting lever, thus acting in the opposite direction to upright the ship.  

Q.What are tender and stiff ships?
Ans. Tender Ship: The ship with a small Metacentric height has a small righting lever at any angle & will roll easily is said to be a tender ship. In a tender ship, th

f Gravity lies above the transverse metacentre.
      

Q. What is the free surface effect? How is knowledge of free surface effect useful?
Ans. Free Surface Effect: When a tank of liquid is partially filled & the mass of liquid is moved. This movement affects the Metacentric height. This is called free surface effect.If free surface effects become more, then ship may capsize.

Q. What is the purpose of Collision bulkhead and what is it's  location?
Ans. Purpose:-
o    Avoid flooding of the ship in case of damage to bows.
Location
   o    The location is such that it is not so much forward as to get damaged on 

impact , Neither it should be too far aft so that compartment flooded forward causes extensive trim by head. As a rule located at a minimum distance to get maximum space for cargo.
   o   Minimum at 1/20 of ships length from forward perpendicular 
   o The collision bulkhead is continuous to uppermost continuous deck

   o    The collision bulkhead is 20% stronger than other bulkheads
   o    Collision bulkhead is 5 to 8 percent of ships length from forward.
 
Q. What are the types of bulkheads?
Ans.
a. Flat Bulkhead
b. Corrugated Bulkhead
c. Longitudinal Bulkhead
d. Transverse Bulkhead.
e. Watertight Bulkheadf. Non-Watertight Bulkhead
g. Fire Class A Bulkhead
h. Fire Class B Bulkhead
i. Fire Class C Bulkhead
j. Collision Bulkhead.

k. insulated bulkhead
 

Q. What are the methods of reducing rolling?
Ans. Various Methods of Reducing Rolling are:-
a. Fin stabiliser
b. Bilge keel

Q. How much length does bilge keel extends to?

Ans. It is half of the length of the ship, starting from mid-ship to fore & aft.
 

 

Q. What is an angle of loll?
Ans.
Angle of LOL: It is the angle at which the ship with initial negative Metacentric height will lie at rest in still water.
If the ship is further inclined to an angle more than angle of loll, the ship will sink.

Q. What is margin line?
Ans. Margin Line: It is the imaginary line which is drawn 75mm below the uppermost continuous deck. It denotes the limit, up to which vessel can be flooded/ loaded without sinking.

Q. What is block coefficient? If we say that block coefficient of one ship is 0.9 and the 0ther 0.95, what does it represent?
Ans. Block Coefficient:-It is the ratio of volume of displacement to the product of the length, breadth & draught.
Cb = Volume of displacement / (L x B x d)
When Block coefficient is more, it means Volume of displacement is more.

Q. What is the regulations for pumping out ER bilges in Special areas and outside special areas?

Ans. Pumping out ER Bilges outside special area:As per Marpol Annex I, Regulation 15.

Any discharge into the sea of oil or oily mixtures from ships of 400 GRT & above shall be prohibited except when all the following conditions are satisfied:-
1. The ship should be proceeding en route from Point A to point B.
2. The oily mixture is processed through an oil filtering equipment.
3. The oily content of the effluent without dilution does not exceed more than 15ppm.
4. The oily mixture does not originate from cargo pump room bilges on oil tankers.
5. The oily mixture, in case of oil tankers, is not mixed with oil cargo residues.
Pumping out ER Bilges inside special area.
1. The ship should be proceeding en route from Point A to Point B.
2. The oily mixture is processed through an Oil filtering Equipment approved by the Administration.
3. The oil content of the effluent without dilution does not exceed more than 15ppm.
4. The oily mixture does not originate from Cargo pump room bilges on oil tankers.
5. The oily mixture in the case of oil tankers, is not mixed with oil cargo residues.
6. Any discharge into the sea of oil or oily mixtures from any ship shall be prohibited in Antarctic area.

Q. Name special areas for MARPOL Annex I.
Ans. As Per MARPOL Annex 1, Regulation 1, the special areas are:-
1. Mediterranean Sea
2. Baltic sea
3. Black sea
4. Red Sea
5. Gulf area
6. Gulf of Aden area
7. Antarctic area.
8. North West European Waters
9. Oman area of the Arabian sea

Q. What do you mean by refrigeration? What is the principle of refrigeration?
Ans: Refrigeration is a process of moving heat from one location to another in controlled conditions. The work of heat transport is traditionally driven by mechanical work, but can also be driven by heat, magnetism, electricity, laser, or other means. 
The basic principle of refrigeration is simple. You simply pass a colder liquid continuously around the object that is to be cooled. This will take heat from the object due to the temperature difference.

Q. What is a thermostatic expansion valve?
Ans: A TEV 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.

Q. What is the function of an L.P controller?
Ans: It stops the compressor at low suction pressure caused by the closure of all compartmental solenoids. When the pressure in the compressors suction rises due solenoid opening, the LP controller restarts the compressor.

Q. What is the function of an L.P cutout?
Ans: 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.

Q. What is the function of a solenoid valve in the refrigeration system?
Ans: This is an electrical signal actuated v/v in the liquid line of the refrigeration system just before the TEV. 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.

Q. What is the function of back pressure valve in the refrigeration system?
Ans: Back pressure valve is fitted just at the exit of the refrigerant from the evaporator coil in a multi temperature room system. This being fitted at the exit of the compartments whose temperature is set higher (usually at about4~5 degrees centigrade). The function of the v/v is to maintain equilibrium of the system as the pressure of the gas at the exit of each compartment differs. Moreover, the back pressure v/v 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.

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

Q. What is the function of the driers in the refrigeration system?
Ans: 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.

Q. Why is fridge compressor belt driven?
Ans:
a. A slight misalignment is a problem or vibration of the electric motor that may lead to shaft seal leakage, leading to loss of the refrigerant. So, to minimize this, 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.

Q. 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?
Ans:
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.

Q. What are the safeties in the fridge system?
Ans: Safeties in fridge system are:
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

Q. How will you know the presence of air in the refrigeration system? Explain the procedure for purging air.
Ans:
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 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.

Q. What are the air bottle maintenance and inspections?
Ans: 
a. Regularly drain the bottle of water and oil
b. Regular inspection to ensure that the internal condition of the bottle is good
c. Check for corrosion both externally and internally
d. Inside coating, COPAL varnish condition to be checked to ensure that it is unbroken and no peeling is taking place
e. Welding seem to be checked, carry out dye-penetrant test at suspected areas.
The tell-tale hole between the lap welding seams of the doubler plate / ring to be checked for leaks in service to ensure that the internal welding is intact
g. Face of the man hole to be checked for pitting marks
h. Drain should be clear
i. All points of high stress and corrosion are to be thoroughly checked viz. welds, supports braces, the bottom of the bottle where water/oil is collected. Pay attention to the zone of water line.
j. Check for leaks at the mounted valve glands/flanges, carry out inspection of the valve face and seat for wire drawing effect
k. A timing check with the air bottle completely charged and isolated will give a good idea of the intactness of the pressure vessel
l. The safety/relief valve setting to be inspected as per the class requirement
m. Regularly check the alarms and monitoring equipment for proper functioning

Q. Explain the air bottle entry procedure.
Ans: 
a. Inspection is to be carried out when the receiver capacity is not required for maneuvering
b. Receiver properly isolated, depressurized and notice pasted
c. The internal pressure is to be checked by the pressure gauge and by opening the drain valve
d. Open the manhole door carefully and ventilate the air bottle
e. Obtain an enclosed space permit and comply with it
f. Ventilation is to be maintained during the entire time of enclosed space entry

Q. What action should be taken in case of corrosion/wasting observed on air bottle?
Ans:
MINOR: Clean the site of corrosion, observe the varnish manufacturer instructions for surface finishing prior applying the coat. Apply new coat of the varnish.

MAJOR: The site has to be cleaned and re-varnished as above. The air bottle has to be derated.
In case of excessive the entire bottle has to be replaced.
The derating procedure should be carried out as follows:
a. The extent of the derating is determined by the class surveyor to a value which ensures the safe limit of the hoop stress at this reduced thickness of the shell plating
b. The derating should not violate the starting air requirements for consecutive starts of the main propulsion engine
c. The setting of the safety/relief valve, should be set not exceeding 10% of the maximum working pressure after derating
d. The cut in and cut out pressure switches for compressor automation should be readjusted

For these reasons the air pressure vessels on board ship are fabricated to allow for derating in future still complying with the consecutive start requirements of the propulsion engine.

Question Answer On The Topic Scavenging And Scavenge Fire

What Is Scavenging?
The Process Of Exchanging Gases Present In The Combustion Spaces After Combustion With The Charged Fresh Air Is Called Scavenging.
 
What Is Uniflow Scavenging?
With Uniflow Scavenging, The Incoming Air Enters At The Lower End Of The Cylinder And Leaves At The Top. The Advantage Of Uniflow Is The Simple Design Of The Liner, Plus It Is The Most Efficient.

What Is Cross Flow Scavenging?
In Cross Flow Scavenging, The Incoming Air Is Directed Upwards, Pushing The Exhaust Gases Before It.  The Exhaust Gases Then Travel Down And Out Of The Exhaust Port.  Advantage Is No Exhaust Valve.
 
What Is Loop Scavenging In A 2-Stroke Engine?
Loop Scavenging Is Where The Incoming Air Passes Over The Piston Crown, Then Rises Towards The Cylinder Head Forcing Exhaust Gases Down And Out The Exhaust Ports, Just Above The Inlet Port.  The Advantage Of Loop Is That No Exhaust Valve Is Required.
 
What Is Compression And Explain Why Compression Is Required?
Compression Is Where The Air That Is Drawn Into The Cylinder Is Compressed On The Upward Stroke Of The Piston, Both Inlet And Exhaust Valves Being Closed On This Stroke.  As The Air Is Compressed By The Rise Of The Piston, The Air Temperature Is Consequently Raised.  As The Piston Reaches The TDC, Fuel Is Injected, Causing Ignition And Very Rapid Rise In Pressure Of The Gases Forcing The Piston Down.
 
 
What Could Start A Scavenge Fire?
The Main Cause Of A Scavenge Fire Is The Fouling Of Scavenge Spaces By The Blow By Of Products Of Incomplete Combustion Caused By Incorrect Cylinder Lubrication, Faulty Fuel Injection Equipments, Accumulation Of Such Mixtures In The Scavenge Space Can Be Set Alight By Sparks Or Flame Blow By.
 
What You Can Do To Prevent Scavenge Fires?
Conscientious Maintenance Of The Engine And Regular Inspection And Cleaning Of Scavenge Air Spaces Will Help Prevent Scavenge Fires.
 
What Are The Symptoms Of A Scavenge Fire?
When A Scavenge Fire Has Broken Out, The Scavenge Air Temperature And The Exhaust Temperature Of The Unit In Question Will Increase Considerably And In Some Cases The Turbocharger May Start Surging.  Even Hot Spots On The Scavenge Trunking Can Be Found.
 
What Would You Do In The Event Of A Scavenge Fire?
If A Scavenge Fire Were To Start, The Two Main Objectives Are To Confine The Scavenge Fire To The Scavenge Space And To Minimise Damage To The Engine.
In The Event Of The Fire Breaking Out, Inform Bridge That The Engine Is To Be Brought To Dead Slow Ahead And Also Inform The Chief Engineer.
The Fuel Should Be Cut Off To That Particular Cylinder.  The Cylinder Lub Oil Should Be Increased To Prevent Seizure And Wear.
If Fixed Fire Fighting Equipment Is Attached To The Scavenge Trunking, This Can Be Brought Into Operation, Depending On Severity Of Situation.  But In Most Cases The Fire Will Generally Subside Within 5-15 Minutes.
Once The Fire Is Out And Navigational Circumstances Allow It, The Engine Must Be Stopped.
Do Not Open Scavenge Space Doors Or Crankcase Doors Before Site Of Fire Has Cooled Down.  When Opening Up, Care Must Be Taken To Keep Clear Of Any Flame.
After Opening Up, All Scavenge Spaces Must Be Thoroughly Cleaned And All Debris Removed.  The Piston Rods And Cylinder Liner Should Be Examined For Surface Blemishes, Straightness, Etc., And The Diaphragm Glands (Stuffing Box) Examined To Ensure That They Are Operational And Not Damaged.
Also Piston Rings Should Be Checked, As Blow By May Have Been The Ignition Source Of The Fire.  If Possible The Piston Head In Question Should Be Renewed At The Earliest Possible Moment And The Damaged Unit Overhauled.
On Engines Fitted With Tie Bolts, It May Be Necessary To Re-tighten The Bolts Adjacent To The Fire.
When Starting The Engine Again, Care Must Be Taken After Switching On The Fuel To The Cylinder In Question, And That Also The Cylinder Lub Oil Quantities Are Reduced To Normal.
What Is Scavenging?
The Process Of Exchanging Gases Present In The Combustion Spaces After Combustion With The Charged Fresh Air Is Called Scavenging.
 
What Is Compression And Explain Why Compression Is Required?
Compression Is Where The Air That Is Drawn Into The Cylinder Is Compressed On The Upward Stroke Of The Piston, Both Inlet And Exhaust Valves Being Closed On This Stroke.  As The Air Is Compressed By The Rise Of The Piston, The Air Temperature Is Consequently Raised.  As The Piston Reaches The TDC, Fuel Is Injected, Causing Ignition And Very Rapid Rise In Pressure Of The Gases Forcing The Piston Down.

What Is The Primary Function Of The Expansion Valve In A Refrigeration System?
The Primary Function Of An Expansion Valve In A Refrigeration System Is To Regulate The Flow Of Refrigerant From The H P Side To The L P Side Of The System.  
The Pressure Drop Causes The Saturation Temperature To Drop, Enabling It To Boil Off At The Low Temperature Of The Evaporator.

What Is The Function Of An Evaporator In A Refrigeration System?
The Function Of The Evaporator Is To Boil Off The Liquid Refrigerant, At The Same Time Cooling The Air.  The Design Of The System And Evaporator Should Be Such That All Liquid Refrigerant Is Boiled Off And The Gas Slightly Superheated Before Returning To The Compressor.

What Is The Function Of The Condenser In A Refrigeration System?
The Function Of A Condenser In A Refrigeration System Is To Condense And Sub Cool The Refrigerant Below Saturation Temperature. 

What Would Cause An Excessive High Pressure In A Refrigeration System?
High Pressure Could Be Caused By Lack Of Cooling Or A Fouled Condenser Or Even Overcharge, But This Is Usually Unlikely.
How Do You Purify HFO?
Heavy Fuel Oil Is Purified Using A Centrifugal Separator, Which Operates By The Principle Of Centrifugal Force Separating Two Liquids, In This Case Fuel Oil And Water By Means Of A Cylindrical Interface Between The Two.  The Positioning Of This Interface Being Very Important For The Correct Operation.

What Is The Difference Between A Clarifier And A Purifier?
A Purifier Removes Water As Where A Clarifier Removes Solid Impurities.
In Some Cases, Both Are Used For Separation Purposes, Firstly The Oil Is Purified, Then Clarified.

What Is The Regulation Regarding Use Of FWG Inshore?
Evaporators Should Not Be Used Within 20 Miles From Shore, Due To Risk Of Pollutants Being Taken Into The Freshwater System.

How Is 15 Ppm Reached In An Oily Water Separator?
15ppm Is Achieved In An Oily Water Separator By Normally Passing Through A Two Stage Separator Where In The First Stage Oil/Water Is Passed Into The Coarse Separating Compartment. Here Some Oil Will Rise To The Top Of The Compartment Due To Its Lower Density, Heating Coils May Aid This.  The Remaining Oil/Water Will Flow Down Into The Fine Separating Compartment And Moves Slowly Between Catch Plates.  More Oil Will Separate Out Onto The Underside Of These Plates And Travel Outwards Until Free To Rise To The Oil Collecting Space.  The Almost Oil Free Water (usually Being At 100ppm At This Stage) Will Then Pass To The Second Stage Of The Separator, Which Is A Filter Unit Comprising Of Two Filter Units.  The First Filter Stage Removes Physical Impurities Present And Promotes Some Fine Separation.  The Second Stage Filter Uses Coalescer Inserts To Achieve The Final De-oiling, Oil/Water Mixture Leaving This Stage At Less Than 15ppm.

What Safety Devices Are Fitted To A Start Air Line? 
Non Return Valve, Flame Traps/Arrestors, Bursting Discs And Safety Valves.

What Fittings Would You Expect To Find On A Start Air Receiver?
Fittings Found On A Receiver Are:  Safety Valve, Fusible Plug, Isolating Valve To Main Air Start System, Filling Valve From Compressor, Drain Valve, Valve To Control Air, Valve To Whistle, Pressure Gauge.

What Are The Safety Devices Fitted To An Air Compressor? 
Low Lub Oil Pressure Shut Down
High Air Temperature Shut Down
1st Stage Relief Valve
2nd Stage Relief Valve
A Fusible Plug Is Fitted After The 2nd Stage Cooler, Set At 120°C
If Water Cooled, A Busting Disc Is Fitted.

What Is The Maximum Compressed Air Temperature That Should Leave An Air Compressor?
93°C

What Is The Purpose Of A Fusible Plug On An Air Receiver And At What Temperature Is It Designed To Melt?
The Purpose Of The Fusible Plug Is To Act As A Safety Feature To Release Compressed Air From The Receiver In The Event Of A Fire In The Vicinity.  The Fusible Plug Is Designed To Melt At 150°C.

Explain How You Would Start An Air Compressor And Stop It (after Overhaul)
Check Oil Level In Crankcase.
Then Ensure All Drains Are Open, I.e. Intercooler Drains And Also Unloaders.
Check Air Intake Filter Is Clean.
Ensure Oil Pressure Gauge Is Open And That Air Pressure Gauges I.e. 1st And 2nd Stage, Are Partially Open To Stop Gauge Fluctuation.
If Water Cooled, Check Valves Are Open And Cooling Is Supplied.  Also Check Header Tank.
Bar Machine Over By Hand To See If It Is Free To Turn.
Start The Machine, Check There Are No Unusual Noises Or Vibrations And Oil Pressure Is Correct.
Then Close Drains And Unloader.
If All Seem Okay, Run For 30 Minutes, After Which, It Can Be Stopped, Covers Removed And Bearings Checked.  If Okay Machine Can Be Started On Automatic And Run.
To Stop The Machine, Always Make Sure The Machine Is Unloaded And Drains Opened Before Stopping, Unless Automatic Drains And Unloaders Are Fitted.

Name The Two Most Common Types Of Coolers Used On Board?
Shell And Plate Type Coolers
Shell Being Where A Tube Stack Is Used And Fitted Into A Shell And Closed At Either End With End Covers.
Plate Type Being Made Up Of A Number Of Pressed Plates Surrounded By Seals And Held Together In A Frame.

How Do You Start Up, And Parallel A Generator?
First Check Engine Oil Levels, Such As Lub Oil Sump, T/C Oil Level, Governor Oil Level, Rocker Arm Bank Oil Level (if Fitted).
Check Jacket Water Header Tank Level
Ensure Indicator Cocks Are Open, Start Lub Oil Priming Pump Then Bar Engine Over (ensure Turning Bar Is Removed).
Kick Engine On Air.  Close Indicator Cocks.
Start The Engine.
Check All Parameters Are Correct:  Lub Oil Pressure/Temperature, Jacket Water Temperature/Pressure, Check Sea Water Cooling Pressure And Rocker Arm Lub Oil Pressure.
Allow Engine To Warm Up And When Satisfied That Everything Is Okay, Engine May Be Paralleled As Follows:
Ensure The Voltage Of The Machine To Be Paralleled Is The Same As The Bus-bar Voltage.  Ensure The Frequencies Of Both Machines Are The Same (the Frequency Of The Incoming Machine Can Be Adjusted Using The Speed Control).
Select The Machine To Be Paralleled On The Synchroscope Selector.
The Synchroscope Should Then Start To Rotate, It Should Be Rotating In A Clockwise Direction Slowly.  If It Is Rotating In An Anti-clockwise Direction, This Means The Speed Of The Incoming Machine Is Too Slow Or If It Is Rotating Fast Clockwise, The Speed Of The Incoming Machine Is Too Fast, This Is Adjusted Using The Speed Control.
When The Needle Of The Synchroscope Is Rotating In The Clockwise Direction Slowly, The Breaker Of The Incoming Machine Should Be Closed.  When The Needle Of The Synchroscope Is At The Five To Twelve Position, This Will Allow The Incoming Machine To Take A Slight Amount Of Load When Coming On The Switchboard And Also Prevent The Machine Tripping On Reverse Power.
The Load Is Then Shared Equally Between Both Machines.

What Is The Purpose Of Rocker Gear On An Engine?
The Purpose Of The Rocker Gear Is To Operate The Inlet And Exhaust Valves On The Cylinder Head.

What Trips Are There On A Generator?
The Trips On A Generator Are:  Lub Oil Low Pressure Shut Down, Jacket Water High Temperature, Overspeed Shut Down.

Q. Why Cylinder Lubrication Is Required?
Ans:  Cylinder Lubrication Is Required To Develop An Oil Film Between Piston Rings And Cylinder Liner To Avoid Metal To Metal Contact. In Latest Engines, With Higher Peak Pressure And Cycle Temperature Good Quality Of Cylinder Oil Is Required To Maintain An Oil Film Between The Rings And The Liner For A Long Period Of Time. Apart From Lubrication Its Other Properties Enhance Engine Performance.

Q. State, With Reasons, Five Desirable Properties Of Cylinder Oil Used For An Engine Which Is Burning Residual Fuel.
Ans: Five Desirable Properties Of Cylinder Oil Used For An  engine Which Is Burning Residual Fuel Are;
It Must Effectively Neutralise The Corrosive Effect Of Suphuric Acids Formed During Combustion Of Fuel.
It Must Prevent The Build Up Of Deposits In The Ring Grooves And In Ports Of Port Exhausted Two Stroke Engines.
It Must Be Able To Burn Cleanly, Therefore Leaving As Little As Possible Soft Deposits.
It Must Pocess Adequate Viscosity At High Working Temperatures.
It Must Form An Effective Seal In Conjunction With Piston Rings To Prevent Blow By.

Q. How An Effective Film Can Be Obtained Over The Entire Liner Surface?
Ans: An Effective Oil Film Can Be Obtained Over The Entire Surface Of The Liner By Means Of Cylinder Lubrication.
Oil Is Injected Through A Number Of Holes Drilled In The Liner, Usually Six Or Eight Of These Displaced Circumferentially Around The Liner At A Chosen Vertical Position Within The Piston Stroke. Oil Is Supplied By Pressure Pulses From Positive Displacement Mechanical Lubricators Driven From The Engine Camshaft And Regulated To Deliver Oil At A Given Rate.
Lubricator Quills Are Connected To Each Oil Hole And Contain A Non-return Valve To Prevent Blowback. To Assist In Distribution Of Oil Around The Liner Circumference, Oil Gutters Adjacent To Lubricator Points Angled Downwards To Assist Flow By Gravity Are Fitted. Lubricating Oil Is Spread Over The Length Of The Liner By The Piston Rings During Their Stroke. 

Q. How It Can Be Ensured That The Correct Quantity And Quality Of Cylinder Lubricating Oil Is Being Used?
Ans: It Can Be Assured That The Right Quantity And Quality Of Cylinder Lubricating Oil Is Used By;
The Quantity Is Controlled By Linking The Pump Drive To The Engine Throttle Setting Levers, The Oil Quantity Then Being Regulated To The Power Produced. To Ensure The Quality Of The Oil Used Is Maintained For Lubrication And Not Burnt By Hot Gases, An Accumulator Can Be Fitted To The Cylinder Lubricator Quills So That A Quantity Of Oil Will Enter Each Time The Cylinder Pressure Drops Below That In The Accumulator, Thus Ensuring Oil Does Not Enter The Cylinder When Exposed To Hot Gases.

Q. How A Representative Sample Of Lubricating Oil Is Obtained From The Main Engine System For Analysis?
Ans: To Obtain A Representative Sample Of Lubricating Oil From The Main Engine System; A Clean Sample Bottle Must Be Used, The Sample Must Be Taken From An Area On The System Where There Is A Good Flow, Not From Filters Or The Sump.
The Best Place For The Sample To Be Taken, Would Be From The Lubricating Oil Rail / Supply Line, Ideally The Sample Point Should Be A Dedicated Sample Point To Avoid Accidents. 

Q. Describe Three On Board Tests For Lubricating Oil?
Ans:
The Flow Stick Test: This Is Where The Viscosity Of The Lubricating Oil Is Tested. Two Samples Of Oil Are Used For This Test, One From The System, And The Other, Fresh New Oil. The Flow Stick Contains Two Reservoirs, One For The System Sample And One For The New Fresh Oil, These Reservoirs Are Filled And The Samples Are Allowed To Reach The Same Temperature.The Flow Stick Is Then Tilted From The Horizontal And The Oil Flows Down Two Parallel Chanels, When The Fresh Oil Reaches A Reference Point, The Flow Stick Is Returned To The Horizontal.The Distance Traveled By The Used System Oil Is Compared To That Of The New, Fresh Oil And If The Used Oil Is Between The Two Used Oil Comparison Points, The Used System Oil Is Still In Good Condition.

Water In Oil Test: The % Water In Oil Test Is Used To Give An Indication If Any Of Water In The Lubricating Oil, Here A Fixed Amount Of Oil Is Sampled From The System, Which Is 5ml And Placed In A Capsule Where There Is A 15ml Solution Of White And Reagent. A Lid Incorporating A Pressure Gauge That Is Calibrated To Read % Water In Oil Is Then Screwed Onto The Capsule To Form An Air Tight Seal. The Capsule Is Then Shaken Vigorously For 1 Minute, Then Left To Stand, Any Water In The Lubricating Oil Will React With The White Spirit And Reagent Causing A Rise In Pressure That Will Be Read On The Pressure Gauge As % Water In The Lubricating Oil

Microbiological Degradation Of Oil Test:  This Test Will Give An Indication Of An Infestation Of Microbiological Organisms In The Lubricating Oil. The Test Makes Use Of Slides That Are Coated With A Special Gel, Which Is Dipped In The Sample Of Lubricating Oil, The Slide Is Then Placed In A Test Tube, Sealed And Left To Incubate, Any Growth That Comes About In The Incubation Period Is Then Compared To A Chart To Indicate Any Infestation By Microbiological Organisms.

Q. If No Testing Equipment Was Available, Explain How The Condition Of Lubricating Oil Could Be Assessed On Board?
Ans: If No Test Equipment Is Available On Board, Lubricating Oil Condition Can Be Determined By A Few Simple Tests:
Crackle Test For Water, This Is Where A Sample Of  lubricating Oil Is Take And Placed In A Test Tube, The Test Tube Is Then Heated, Any Water Droplets Will Make A Crackling Noise Due To The Formation Of Bubbles, This Will Only Detect Small Amounts Of Water, For Larger Amounts, A Simple Settling Test Can Be Used.

TBN Can Be Tested By Placing A Drop Of Indicator Solution On To Blotting Paper, This Being Followed By A Drop Sampled Lubricating Oil In The Centre Of The Blotting Paper. A Colour Change Should Take Place Around The Surrounding Area Of The Drop I.e. If The Colour Is Red, This Shows Acid Is Present, Green / Blue Show S Alkaline Presense.
Note: Filters Will Also Give A Good Indication Of The Lubricating Oil Quality.

Q. What is volumetric efficiency of air compressors?
Ans: Actual volume of air drawn in / swept volume.

Q. What is compression ratio?
Ans: (Swept volume + clearance volume)/clearance volume

Q. What is free air delivery?
Ans: Volume of delivered air measured at 1 atmospheric pressure and 15*C is called free air delivery.

Q. What is bumping clearance? How do you measure it?
Ans: Clearance volume or bumping clearance is the space between the top of the piston and the cylinder head of an air compressor. This clearance is an important aspect of the compressors and should be as less as practically possible to improve the volumetric efficiency of the compressor. The clearance volume should not be too less or too more. Moreover, it affects the efficiency of the machinery and thus should be checked at regular intervals of time.
Significance and Effects of Bumping Clearance
In an air compressor, when the discharge valve closes in the end of the compression cycle, a small amount of high pressure air is trapped in the clearance volume.
Before again taking suction, the air trapped in the clearance volume must expand below the suction pressure i.e. below the atmospheric pressure.
The expansion of this trapped air in the clearance volume causes effective loss of stroke due to which the volumetric efficiency of compressor drops. Therefore, the clearance volume has a significant effect on the efficiency of the compressor.

Effects Due to Less Clearance
Small clearance volume may result in piston banging or colliding to the cylinder head.
This is dangerous when the compressor when is running in unloaded condition without any resistance to the movement of the piston.

Effects Due to Large Clearance
Large bumping clearance retards the formation of vacuum on the suction stroke and thus less air is drawn inside for compression and accordingly the weight of the air delivered is reduced proportional to the clearance volume. Compressor has to run for a longer period to provide the necessary compression pressure.

Reasons for Change in Clearance Volume
During overhauls of the air compressor, if the gasket fitted between the cylinder head joints is of the wrong type, then the bumping clearance will increase, resulting in wear down of bottom bearings or wrong bearings are put in place.
How Bumping Clearance is checked?
Bumping clearance is checked by putting a lead ball or plastic gauges over the piston and then turning the compressor one revolution by hand.
By doing this the lead ball will compress and the thickness obtained is the clearance volume.
This thickness is measured with Vernier caliper or micrometer and is then compared with the manufacturer’s value. Adjustments are made in case there is an offset in the value.

Adjustment of bumping clearance
Bumping clearance can be adjusted with the help of inserting shims (thin metallic plates) in the bottom bearings. Inserting shims will move the connecting rod and the piston which will change the clearance.
What should be the Bumping Clearance?
Generally bumping clearance depends on the manufacturer but as a thumb rule it should be between 0.5% to 1% of the bore of the cylinder.

Q. What are the reasons of HP stage relief v/v lifting?
Ans: 
a. Delivery v/v shut.
b. Setting error of pressure switch.
c. Delivery v/v which is SDNR type is fitted inverted.

Q. What are the reasons for LP stage relief v/v lifting?
Ans: 
a. HP stage suction v/v or discharge v/v leaking.
b. 2nd stage suction n discharge v/v interchanged after overhaul.

Q. How lubrication takes place in main bearing, crankpin bearing, upper & lower cylinder in case of tandem type air compressor?
Ans: 
a. For main brg & crankpin brg- pressure lubrication provided by shaft driven gear p/p.
b. For lower cyl. In tandem type- it’s by splash.
c. For upper cylinder in tandem type- there is a supply from drilled hole in con. Rod which is scraped down by scraper ring into the lube oil sump.

Q. What are the reasons for low L.O pressure in an air compressor?
Ans: 
a. Motor rotation direction reversed.
b. Oil line blocked due to rag/dirt.
c. No oil in sump.
d. Filter clogged.
e. Worn metal of the bearing=> more clearance=> low oil pressure.

Q. What are the reasons for increased lube oil consumption in an air compressor?
Ans: 
a. Excess oil in sump (above level H).
b. Oil scraper ring worn out.
c. Worn piston and liner. 

Q. What checks do you make if a compressor trips on low lube oil pressure?
Ans: In case of reciprocating compressor
a. Direction of rotation, in case the motor is overhauled or some maintenance carried on the motor.
b. Suction filter should be cleaned.
c. Check the pressure switch.
d. Inspect the lube oil pump
e. Check if any lube oil pipe is holed
f. Check for excessive foaming

In case of rotary compressor,
a. Check whether the lube oil pump is rotating with the compressor
b. Check the condition of vanes and the elliptical casing for scoring damage
c. Check the compressor is free to turn, no seizure of rotor, no wear on the vanes and the casing.
   
Q. What is the purpose of breather in an air compressor?    
Ans: Breather- it is provided so that pressure or vacuum is not created inside crankcase. It has filter to prevent moisture and dirt from going inside the crankcase and also has metallic plate on the inner side which doesn’t allow lube Oil to come out.

Q. Why intercooling is provided in an air compressor? And why is the compression distributed into stages?
Ans: 
a. By employing the inter stage cooling we are trying to achieve an isothermal compression cycle in order to minimize the work done 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 chamber 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.
 
What would be the consequences of too high valve lift in an air compressor?
Ans: 
a. Chances of damage due to impact.
b.Decrease in vol. efficiency.
 
Q. What would be the consequences of a high spring constant of spring plates in an air compressor?
Ans: 
a. Valve will open late.
b. It will close with higher impact which may cause damage.
c. It also reduces volumetric efficiency.
 
Q. Can we interchange spring of suction & delivery v/v?
Ans: No.Delivery valve’s spring stiffness is more.

Q. What are the necessary checks before manual starting of an air compressor?
Ans: 
1.  Lubrication: check the oil level in the sump ( between H & L )and in the lubricator tank(if provided) .
2. Unloading: the valves in the unloading lines must be open.
3. Pressure gauge cocks: the cocks must be slightly open to avoid excessive pressure fluctuations which can damage the pressure gauges.
4. Air filter: check that the air intake filter is clean.
5. Cooling: check that the Cooling water pressure is correct (0.2-2bar) and in the case of attached pump a visual check of the pump to be carried out and all the valves in the line must be open.
6. Relief valves: some relief valves have hand testing levers given for testing, the same can be done.
7. Air-line piping: check that all the valves in the discharge piping are open and correctly lined up.
8. Final check: the compressor can be turned a few revolutions with a turning bar to check for the free movement.

Q. What if the compressor motor connections are reversed after overhauling?
Ans: 
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 shaft driven usually does not build up enough flow/pressure hence the compressor may trip because of the cooling water non flow or high air temperature.

Q. What are the reasons of piston seizure in a reciprocating air compressor?
Ans: 
a. Insufficient lubrication.
b. Lack of cooling water.
c. Valve part broken and fallen into the chamber.
d. Piston ring broken.