Category: MEO ORALS

● In tankers during loading and discharge Tank vapours can be released and sent clear of the decks through high velocity vent.
●  It has a moving orifice , held down by a counter weight to seal around the bottom of a fixed cone.
●  Pressure build up in the tanks, as filling proceeds, and it causes moving orifice to lift. 
●  The small gap between orifice lip and fixed cone gives high velocity to the emitted vapour.
●  It is fitted minimum 2 meter above the deck.
●  Rate of gas venting should be 30meter/second. 
●  Each tank should have 1 high velocity vent.
 

•     Requirements of high velocity vent? (  Generally asked by surveyor)

Q.1) Describe the general layout of internal lubricating oil system for an auxiliary engine?

The lubricating oil system is based on wet sump lubrication. All moving parts of the engine are lubricated with oil circulating under pressure in a closed built-on system. The lubricating oil is furthermore used for the purpose of cooling the pistons.

System Flow
The lubricating oil pump draws oil from the oil sump and presses the oil through the cooler and filter to the main lubricating oil pipe, from where the oil is distributed to the individual lubricating points. From the lubricating points the oil returns by gravity to the oil sump.
The main groups of components to be lubricated are:
1.Turbocharger
2. Main bearings, big-end bearing etc.
3 .Camshaft drive
4 .Governor drive
5 .Rocker arms
6 .Camshaft

1) Turbocharger: For priming and during operation, the turbocharger is connected to the lub. oil circuit of the engine, the oil series for bearing lubrication. The inlet line to the turbocharger is equipped with a fixed throttle in order to adjust the oil flow and a non-return valve to prevent draining during stand-still. The non-return valve has back-pressure function requiring a pressure slightly above the priming pressure to open in normal flow direction. In this way overflooding of the turbocharger is prevented during stand-still periods, where the prelubricating pump is running

2) Main bearings: Lubricating oil for the main bearings is supplied through holes drilled in the engine frame. From the main bearings it passes through bores in the crankshaft to the connecting rod big-end bearings. The connecting rods have bored channels for supply of oil from the big-end bearings to the small-end bearings, which has an inner circumferential groove, and a pocket for distribution of oil in the bush itself and for supply of oil to the pin bosses and the piston cooling through holes and channels in the piston pin. From the front main bearings channels are bored in the crankshaft for lubricating of the pump drive.

3) Camshaft drive: The lubricating oil pipes, for the camshaft drive gearwheels, are equipped with nozzles which are adjusted to apply the oil at the points where the gear wheels are in mesh.
 
4) Governor drive: The lubricating oil pipe and the gearwheels for the governor drive are adjusted to apply the oil at the points where the gear wheels are in mesh.

5) Rocker arms: The lubricating oil to the rocker arms is led through pipes to each cylinder head. It continues through bores in the Cylinder head and rocker arm to the movable parts to be lubricated at rocker arms and valve bridge. Further, lub. oil is led to the movable parts in need of lubrication.

6) Camshaft: Through a bore in the frame Iub. oil is led to the first camshaft bearing and through bores in the camshaft from where it is distributed to the other camshaft bearings.
Q2.) Describe the essential components of the system?

Lubricating Oil Pump
The lubricating oil pump which is of the gear wheel type, is mounted on the front end of the engine and is driven by means of the crankshaft through a coupling or a gear wheel.
The pressure regulator forms part of the lubricating oil pump. Adjustment of the oil pressure is done by removing the cap nut and turning the adjusting screw.

Pre-lubricating Pump
As standard the engine is equipped with an electric-driven prelub. pump mounted parallel to the main pump. The pump must be arranged for automatic operation, ensuring stand-still of the prelubricating pump when the engine is running, and running during engine stand-still in stand-by position. Running period of the prelubricating pump is
preferably to be continuous. If intermittent running is required for energy saving purpose, the timing equipment should be set for shortest possible intervals, say 2 minutes of running, 10 minutes of stand-still, etc. Further, it is recommended that the prelub. pump is led from the emergency switch board thus securing that the engine is not started without prelubrication.

Lubricating Oil Filter
The lubricating oil filter is a double filter which is generally used with only one filter chamber being in operation, the other filter chamber being stand-by. If the filter chamber in operation needs to be serviced, the operation can be switched to the other filter chamber without any interruption in lubricating oil supply to the engine. Servicing is generally restricted to replacing of the paper cartridges, cleaning of the radial mesh insert and inspection of sealings , the latter to be replaced if damages observed.
Each filter chamber is equipped with 1 or 2 replaceable paper cartridges of fineness 10-15 microns. In the centre of each filter chamber a filter basket (central element) is situated. This filter basket is acting as a safety filter, having a fineness of about 60 microns. During operation an increased pressure drop across the filter will be observed as dirt particles will deposit on the filtration surfaces of the paper cartridges and thus increase the flow resistance through the fitter.
If the pressure drop across the fitter exceeds 2.0 bar, a release valve will open and by-pass the 10-15 microns filter element, and the engine will run with only the 60 microns safety filter. To ensure safe filtering of the lubricating oil, none of the by-pass valves must open during normal service and the elements should be replaced at a pressure drop across the filter of 1.5 bar.

Thermostatic Valve                                                                                                                                  
The thermostatic valve is designed as a T-piece with the inlet in the cover (A) under which the thermostatic
elements are located.
The outlet to the engine (by-passing cooler) is marked (13) and outlet to the cooler is marked (C). In the 
warming up period, the oil is by-passing the coder. When the oil worn the engine reaches the normal
temperature a controlled amount of oil passes through the cooler.

Q1.) Explain in detail, why is the adjustment of Pmax necessary and the procedure to be followed?
                                                                                                                                                                                    
Ans. If fuel oil valve, piston, inlet and exhaust valves, as well as turbocharger and charge air cooler, are working correctly and the compression pressure Pcomp is normal, the maximum combustion pressure Pmax will indicate the injection timing for the fuel oil pump.

If Pmax is too low it indicates that the injection timing is delayed.

If Pmax is too high it indicates that the injection timing is advanced.

The injection timing can be altered by inserting or removing shims under the thrust piece on the roller guide, thus changing the measure "X", see fig.

                                                                                                                                                                                
Thinner and/or fewer shims ( increase of the distance “X”) results in a delayed injection timing and aPmax. Thicker and/or  more shims (reduction of the distance "X”) results in an advanced injection timing and a higher Pmax.    

If the distance “X" is to be changed the trigger (1) is used for dismantling of the thrust piece (2), where after the thickness and/or the number of shims (3) can be changed.

By changing "X" with 0.10mm the maximum combustion pressure is changed with approx. 1 bar (depending on engine type). After replacement of shims the thrust piece is re-mounted in the roller guide (4) with a soft hammer (5). When changing "X" it must be ensured that the distance between the upper edge of the roller guide housing and the thrust piece on the roller guide is not exceeded, when the roller is resting on the circular part of the fuel cam.

                                                                                                                                                                                                                                                                                                                                                                
In all cases "X' must be checked and adjusted , if necessary, when fuel oil pump, roller guide, roller guide housing anchor camshaft section have been replaced/dismantled
Note: If several fuel oil pumps, roller guides, roller guide housings and/or camshaft sections are dismantled at the same time it is advisable to number the parts in order to facilitate remounting and adjustment.

Q. What Is A Compressor?
Ans: A Compressor Is A Machine Which Compresses The Air At Ambient Temperature(taken As 15 Deg C) And Atmospheric Pressure(1 Bar) To Higher Pressure Such That Its Density I.e Mass Per Unit Volume Increases.

Q. What Are The Types Of Compressor And Its Use Onboard?
Ans: Types Of Compresssors Used On Board:
1. Reciprocating Compressor: It Is A Piston-liner Assembly, Piston Is Attached To The Crankshaft Via A Connecting-rod. The Shaft Is Further Coupled To Motor Which Drives The Assembly. It Is Used Onboard To Fill Compressed Air Into Air Bottles Mainly To Supply Starting Air To Main And Auxiliary Engine, And For Other Subsidiary Purposes.

2.Centrifugal Compressor: It Consists Of A Rotary Wheel With Blades Mounted On Them, The Wheel And Blades When Rotated Develops A Negative Pressure, The Inducer Guides Air Into The Blades . Centrifugal Force Generated Due To Moving Blades Increases The Velocity Of Air. Furthur, The Air Is Guided To The Diffuser Which Acts As A Divergent Nozzle And Reduces The Velocity And Increases The Pressure. Thus, The Density Of Air I.e Mass Per Unit Volume Increases. It Is Used Onboard In Turbocharger , For Supplying Compressed Air For Combustion In Engine Cylinder.
Basically, We Will Be Dealing With Reciprocating Compressors Used For Supplying Compressed Air For Starting The Engine.

Q. What Do You Mean By Capacity Of A Compressor And What Is Required Capacity?
Ans: By Capacity Of Compressor We Mean That Amount Of Free Air Delivered By A Compressor In An Hour.
Free Air Delivery= Volume Of Air Delivered By Compressor At Higher Temperature And Pressure/ Volume Of Air At 15 Degree Celcius And 1 Atm Pressure.
As Per SOLAS , Each Compressor Used Onboard Must Be Capable Enough To Fill One Air Bottle In 60 Minutes. If Two Compressors Are Running Simultaneously, Must Fill One Air Bottle In 30 Minutes. The SOLAS Requirement For Compressed Air Bottle And Both The Compressors On Board Is That It Should Provide Sufficient Air For 12 Consecutive Start For Reversible Engine And 6 Consecutive Start For Non-reversible Engine.

Q. List Various Components Of A Compressor?
Ans: 
Motor: The Driving Component, Attached To The Shaft.
Crankshaft: The Driven Unit, Produces The Rotary Motion.
Connnecting Rod: It Is Attached To Shaft, Translate The Rotary Motion Of The Shaft To Linear Motion Of Piston.
Piston: The Component That Moves Within A Liner, To Drive In The Air, Compress It And Deliver.
Intercooler: It Is Basically A Cooler Used Between Two Stages Of Compressor To Cool The Air After 1st Stage, To Bring Down Its Temperature To Ambient Temperature.
Aftercooler: Similar To Intercooler, It Is Used After The 2nd Stage Delivery, To Bring The Temperature.
Fresh Water/ Sea Water Cooling: The Cooling Line Is For Intercooler, Aftercooler, And Cooling Of Cylinder Head And Liner.
Suction/Delivery Valves: These Are Plate Type Valves , Suction Valves Open Inside Where As Delivery Valves Open Outside. They Are Plate Type Because Of Less Inertia Of The Valves, Which Is Quite High In Spring Loaded Valves. There Is No Problem Of Spring's Rententivity.

Q. What Is A Discharge Unloader And Describe Its Operaton?
Ans: One Of The Most Important Component, An Unloader Is Used For Unloaded Starting Of Compressor And Draining At Continuous Intervals. An Unloader Is Fitted At The End Of Drain Line From Inter And Aftercooler. It Is Basically A Solenoid Operated Spring Loaded Valve Arrangement. Unloader Has Two Lines Drain From Above And Delivery Air Pressure Of 1st Stage From Below. When Compressor Is Shut And Delivery Air Pressure Is Zero, The Drain Opens The Unloader Valve Against Spring Pressure, Thus It Is Always Open. When Started, Slowly The Delivery Pressure Rises And Tries To Shut The Valve, During This Time The Actuated Solenoid Valve Overcomes The Air Pressure And Keeps The Valve Open. The Solenoid Valve Is Operated By A Time Delay Circuit As The Time Span Of 10-15 Sec Gets Over The Solenoid Is Deactivated And The Unloader Valve Shuts. After Every 20-30 Mins., It Is Activated Again And Clears The Drain For 10-15 Secs, Then Deactivates. If The Unloaderdoes'nt Function Properly, There Is A Manually Operated Valve Just Before Unloader, Which Should Bebe Open Before Starting The Unloader.
Now, Why Is It So Important To Start The Compressor In Unloaded Condition?
It Must Be Unloaded Because When Started The Compressor Draws A Very High Current, If It Will Be Loaded I.e Valve Not Open. The Motor Which Is Driving The Machine May Get Overloaded.

Q. Enumerate The Safeties In A Reciprocating Compressor?
Ans:
1. Lubricating Oil Pressure Low Cut Out: It Is Provided Such That If Lub Oil Pressure Falls Down The Parts Which Are Lubricated Like Liner, Piston, Main Bearings, Bottom End Bearings Might Get Worn Out.

2. Bursting Disc: It Is Given In Intercooler And Aftercooler In The Water Side So That If Any Highly Pressurized Air Tube Bursts, The Cooler Shell Will Not Be Pressurized , Bursting Disc Will Burst And Liberate All The Water , Indicating Air-tube Burst. Generally Made Of Copper.

3. Non- Return Valve In Delivery Line: It Is Provided, So That The Air Once Delivered Does'nt Return Back To The Compressor In Case A Low Pressure Develops In Compressor Side.

4. Discharge Unloader: Already Explained Above.

5. Relief Valve On Intercooler: A Relief Valve With Setting 10% Above The 1st Stage Pressure Is Provided To Release Air If High Pressure Is Generated In 1st Stage Generally Due To Valve Malfunction.

6. Fusible Plug: Generally Made Of Tin, Antimony And Bismuth, Is Fitted In Inter And Aftercooler To Release Excess Air When Temperature Rises Upto 121 Degree Celcius Due To Rise In Pressure.

7. High Temperature Alarm: At Around 90 Degree Celcius, The Alarm Sounds Denoting The Rise In Air Temperature.

Q. What Is Multistaging In Compressor And Why Is It Done?
Ans: Multi-staging Is Conducting The Process Of Compression In More Than One Stagesi.e Air Is Compressed By Two Or More Pistons Before Delivery. Generally, Two Stage Reciprocating Compressors Are Used On Board. The Purpose Of Multistatgingis :-

1.If We Increase The Pressure Of Air Upto 30bar (pressure Of Air At 2nd Stage) In One Stage, The L.o Will Start Burning Due To Rise In Temperature. As Per The Thermodynamic Equation For A Polytropic Process,
T2/T1= (P2/P1)^(n-1/n )
Where N=1.35 For Air.
P2/P1= 30/1
T2= 450 Degcelcius.
At This Temperature L.o Will Burn As Flash Point Of L.o Is 200 Deg. Celcius. So We Keep The Pressure Ratio Limited To 5:1.

2. To Reduce The Work Done By Compressor In The Whole Process. The Compression Of Air To Higher Pressure And Lesser Volume Is A Reversible Adiabatic Process. I.e Change In Temperature Takes Place, If Change In Temperature Is Kept Minimum Or Zero , The Work Done By Compressor Will Be Minimum.

Q. What Is Bumping Clearance In Compressor And How Is It Measured?
Ans: Bumping Clearance As The Name Signifies Is A Clearance Given So That The Piston Of The Marine Reciprocating Compressor Would Not Bump Into Its Cylinder Head.
How To Check Bumping Clearance:-
1. In Case A Suitable Opening Is Available The Piston Can Be Barred To The Top Dead Centre And Then Feeler Gauge Can Be Put Inside And The Clearances Checked At Two Three Points.

2. The More Convenient Method Is To Take Lead Wire From The Engine Store And Make A Small Ball Based On The Expected Clearance And Put It Between The Piston And The Head From The Valve Opening. Then The Piston Is Slowly Turned To The Top Dead Centre With The Help Of A Tommy Bar. After That The Piston Is Again Turned Down And The Lead Wire Ball Is Extracted And The Thickness Measured With The Help Of A Micrometer. This Measurement Would Give The Bumping Clearance. The Caution Which Must Be Observed In These Methods Is That The Clearances Of The Main And The Crank Pin Bearing Have Not Been Taken Into Account. The Correct Method Is Thus That After Turning The Piston To Top Deadcentre The Piston Connecting Rod Must Be Jacked Up With The Help Of A Crow Bar. It Is Only After This Hidden Clearance Has Been Accounted For, Will The Correct Bumping Clearance Be Found.

How To Adjust The Bumping Clearance
3. The Cylinder Head Gaskets Can Be Changed To A Different Thickness Thus Altering The Bumping Clearance.
4. The Shims Between The Foot Of The Connecting Rod And The Bottom End Bearing Can Be Changed Thus Changing The Bumping Clearance. However After Adjusting The Bumping Clearance The Clearance Should Be Checked Once Again To Make Sure That There Is No Error And The Clearance Is Within The Range As Specified By The Manufacturers.

Change In Bumping Clearance
Wear At The Crankpin Bearing. The Crankpin Bearing Wears Down Due To Use And This Clearance Can Travel Right Up To The Piston And An Unloaded Piston Can Hit The Cylinder Head. This Type Of Wear Can Be Recognized When The Compressor Makes Impact Sounds Running Unloaded At The Starting And Stopping Operations. This Type Of Wear Would Also Be Accompanied By A Slow Decrease In Oil Pressure Over A Period Of Time.
Opening Up Of Cylinder Heads. In Certain Types Of Reciprocating Compressors The Cylinder Head Have To Beremoved For The Changing Of The First Stage Suction And Discharge Valves. When The Cylinder Head Is Put Back Thecorrect Thickness Of The Cylinder Head Gaskets Should Be Used Otherwise It Would Change The Bumping Clearance.
Wear On The Main Bearings. Over All Wear On The Main Bearings Would Lower The Crank Shaft And Would Thus Lower The Piston And Increase The Bumping Clearances.

Q. What Is The Type Of Cylinder Liner Lubrication In Compressor And How Is It Done?
Ans: For 2 Stage Compressors, Which Has Two Different In-line Cylinder Arrangement For Both Stages, Splash Lubrication Of Liner And Piston Takes Place. The L.o From Sump Is Splashed By The Movement Of The Shaft Into The Liner Walls And Is Scraped Back By The Oil Scraper Ring.
For Two Stage Tandem Type (in Which Only One Cylinder Liner Is Used And Both Pistons Are Connected), For 1st Stage Lubrication A Separate Line Is Connected To The Suction Side , As Air Is Drawn In For Compression, An Oil Mist Of L.o And Air Is Also Carried To The 1st Stage. Thus, Al.o Film Is Generated And Boundary Lubrication Takes Place. 2nd Stage Lubrication Takes Place By Splash Of L.o By The Crankshaft And Is Scraped Down By The Oil Scraper Ring.

Q. Name The Parts Of A Compressor Suction And Discharge Valve And How Is Its Overhaul Done?
Ans: Fig: Air Compressor Suction Valve
Overhaul Procedure:

1. Loosen The Castle Nut By Suitable Spanner.Image Text
2. Take Out The Split Pin.
3. Remove The Nut Washer.
4. Remove Buffer Plate.
5. Remove 3 Spring Plates.
6. Remove Damper Plate.
7. Remove Valve Plate And Guide Washer.
8. Remove Locating Pin(it Keeps The Valve Aligned ).Now All The Plates Are Checked For Proper Seating , If Valve Plate Does'nt Seat Properly, It Is Lapped By A Carborandum 500 (coarser) And Then Carborandum 200(finer ) Paste, Making A Figure Of 8 On A True Surface Plate. A Figure Of 8 Is Made Because An Even And Continuous Lapping Can Be Done Only By A Figure Of 8.

Question Answer For Marine Engineering Practise (MEP) 

What Are The Alarms And Trips On A Lub Oil System For The Main Engine?
Alarms And Trips On A Lub Oil System On A Main Engine Are As Follows:
High Lub Oil Temperature Alarm
Low Lub Oil Pressure Alarm
High Lub Oil Filter Differential Alarm
Low Lub Oil Sump Level Alarm
Low Lub Oil Pressure Shut Down Alarm
Stand By Lub Oil Pump Cut In Alarm.

What Interlocks Are There On The Start Air System?
An Interlock To Prevent Fuel Being Injected
An Interlock On Turning Gear And
An Interlock CCP System, Pitch Has To Be On Zero Before Starting Engine.

Why Is Simultaneous Injection Of Fuel Oil And Starting Air Into A Main Engine Cylinder Undesirable And How Is It Prevented?
Simultaneous Injection Of Fuel And Starting Air Into A Cylinder Is Undesirable As It Could Lead To An Explosion In The Start Air System.  
It Is Prevented By Means Of Interlock, Which Prevents Fuel Being Injected When The Air Start Auto Valve Is Open.  
The Interlock Operates A Stop Solenoid, Which Keeps The Fuel Rack At Zero Position. 

Name Main Engine Shutdowns.
Low Lub Oil Pressure
High Jacket Water Temperature
High Main Bearing Temperature
Overspeed
Oil Mist Detection

How Does The Overspeed Trip Work?
The Overspeed Trip Works By Shutting The Fuel Off To The Engine.
There Are Various Types Of Trips, Mechanical Types, Which Work On The Principle Of Fly-weights, Or Electrical Types, Which Work On The Principle Of A Speed "pick-up" Operating A Stop Solenoid.

How Does An Oil Mist Detector Work?
The Oil Mist Detector Uses A Photoelectric Cell To Measure Small Increases In Oil Density.  A Motor Driven Fan Continuously Draws Samples Of Crankcase Oil Mist Through A Measuring Tube.  An Increased Meter Reading And An Alarm Will Result If Any Crankcase Sample Contains Excessive Mist When Compared To Either Clean Air Or To The Other Crankcase Compartments.  The Rotary Valve, Which Draws The Sample, Then Stops To Indicate The Suspect Crankcase Compartment.
The Alarm Will Cause An Engine Slow Down Or Shut Down.

What Is The Critical And Barred Range On An Engine?
This Is Where The Speed Of An Engine In Rpm, At Which The Resonant Condition Occurs, And Is Referred To As Critical Speed.
The High Stresses Associated With Resonant Condition Start To Build Up As Critical Speed Is Approached And Do Not Come Back To A Safe Value Until Speed Is Beyond Critical Speed.  The Unsafe Stresses Either Side Of Critical Speed Are Known As Flank Stresses, This Is Known As The Barred Speed Range.
The Engine Must Not Be Continuously Operated At Speeds Within The Barred Range.

What Is The Purpose Of The Crankcase Oil Mist Detector?
The Purpose Of The Oil Mist Detector Is To Detect The Building Up Of Oil Mist In The Crankcase, Generated From A Hot Spot.  The Detector Will Then Give An Alarm, Either Shut Down Or Slow The Engine Down And Give Indication Of Which Unit The Oil Mist Is Generated.

What Is Crankcase Inspections Frequency, Procedure And Reasons They Are Carried Out?
The Frequency May Vary From Different Engine Manufacturers But Is Roughly Around 5000 Hrs.
Also Inspections Are Carried Out After Any Work Has Taken Place In The Crankcase.
Procedure Is As Follows:
Remove Crankcase Doors From Both Sides Of The Engine.  Relief Valves Can Be Checked At The Same Time As The Doors Are Off.
Inspect Condition Of All Bolt Locking Devices, Replace Any Damaged Components.
Turn Engine Over Using Turning Gear, ENSURE NO-ONE Is In Crankcase While Doing This And That The Indicator Cocks Are Open, Check Condition Of Camshaft Drive Gears. 
Start Main Lub Oil Pump And Check Oil Flow From Bearings And Piston Cooling Parts.  Check For Any Leakage From Internal Oil Pipes And Galleries.
Check For Any Damage Of Camshaft Lobes
Check For Any Evidence Of Water Leakage From Lower Cylinder Liner "O" Rings.
Replace Any Damaged Crankcase Door Joints.
Record Any Defects.

What Safety Devices Are Fitted To The Main Engine Crankcase?
Explosion Door/Relief Valves, Bearing Temperature Sensor And Oil Mist Detectors.

What Are Crankcase Pressure Relief Valves For?
These Valves Act As A Safeguard To Relieve Excessive Crankcase Pressures, Which May Occur From Oil Vapour Igniting In The Occurrence Of An Engine Component Overheating.  They Also Prevent Flames From Being Emitted From The Crankcase And Must Also Be Self Closing To Stop The Return Of Atmospheric Air Into The Crankcase.   

What Would Cause A Crankcase Explosion?
A Crankcase Explosion Could Be Caused By The Formation Of A Hot Spot I.e. The Overheating Of A Bearing, Which In Turn Could Cause An Oil Mist To Be Generated.  If This Oil Mist Is Allowed To Build Up, An Explosive Condition Could Occur Where The Oil Mist Can Be Ignited By Piston Blow By Or The Hot Spot Itself.

What Would You Do In The Case Of A Crankcase Explosion?
When The Alarm Sounds, The Engine Speed Must Be Reduced To Slow And Permission Obtained To Stop The Engine.
Inform Chief Engineer.
When An Engine Has Stopped Under Alarm Conditions Under No Circumstances Must Any Doors Or Inspection Windows Be Opened.
Oil Should Continue To Be Circulated And Time Allowed For The Hot Spot To Cool.
The Early Opening Of Doors Could Cause An Explosion Due To Ingress Of Air.
During Cooling Down Period, The Engine Room Staff Must Keep Clear Of The Side Of The Engine Fitted With Explosion Doors.
After A Period Of At Least 20 Minutes, Stop The Lubricating Oil Pump, Cut Off All Air And Engage Turning Gear.
The Access Doors Should Then Be Opened And Personnel Must Keep Clear Of Possible Flames.  Under No Circumstances Should Naked Lights Be Used Nor Should Anyone Be Permitted To Smoke.
Examination Should Then Take Place For Any Squeezed Out Bearing Metal Or Loose Bearing Metal In The Crankcase.  Heat Discoloured Metal Parts Or Blistering Of Paintwork Must Be Investigated.  The Ceiling Of The Crankcase And Guide Bars Should Also Be Observed.  If The Crankcase Is Clear, The Camshaft Drive And Main Thrust Bearing Should Be Inspected For Signs Of Overheating.

Question Answer For ME Frequently Asked In MEP Orals

How Would You Prepare A Main Engine For Sea?
This May Vary From Engine To Engine.
Have A Visual Check All Round The Engine.
Start The Engine Lub Oil Pumps, Engage Turning Gear And Turn The Engine Ensuring Indicator Cocks Are Open.
Jacket Water Heating Should Be On Ensuring The Engine Is Warmed Through, Circulated By Circulating Pump. 
The Fuel Oil Booster Pumps Should Also Be Running, Circulating Fuel Around The System.
Note:  If Manoeuvring On High Viscosity Fuel Oil, The Fuel Should Be Heated And Circulated Around The Injectors To Give The Correct Viscosity For The Grade Of Fuel In Use.  Ensure Fuel Injectors Are Vented And Primed.
Drain Any Water From Air Start Receivers And Starting Air Manifold, Also Control Systems.
Check Jacket Heater Tank Level.
Check All Oil Levels, Sump, Governor, Turbocharger, Cylinder Lub Oil Tank, Rocker Arm If On 4-stroke.
Operate Cylinder Lubricators By Hand.
Check Fuel Oil Service Tank, I.e. Drain Off Water/sludge
Disengage Turning Gear.
Inform Bridge That You Are About To Blow The Engine Over On Air.  Open Air Start Valve From Receiver.
Once Engine Is Blown Over On Air, Close Indicator Cocks, Start Jacket Water Pumps, Shut Off Jacket Heating And Circulating Pump.
If Two Stroke Engine, Start Auxiliary Blower.
Inform Bridge You Are Ready To Start Engine.
Start Engine And Seawater Cooling Pump, Have A Good Visual Check Around The Engine And Check All Parameters Are Correct.
Inform Bridge That You Are Ready For Stand-by.

Explain A Main Engine Lub Oil System?
Lub Oil For An Engine Is Stored At The Bottom Of A Crankcase Known As The Sump, Or In A Drain Tank Located Beneath The Engine.  The Oil Is Drawn From This Tank Through A Strainer By One Of Two Pumps In Parallel, One Pump Being On Stand-by.  The Pump Discharges The Oil Into One Of A Pair Of Fine Filters, It Is Then Passed Through A Cooler Before Entering The Engine And Being Distributed To The Various Branch Pipes.  The Branch Pipe For A Particular Unit May Feed The Main Bearing, For Instance.  Some Of This Oil Will Pass Along A Drilled Passage In The Crankshaft To The Bottom End Bearing And Then Up A Drilled Passage In The Con-rod To The Gudgeon Pin In A Trunk Piston Engine Or Crosshead Bearing In A Crosshead Engine.
An Alarm At The End Of The Distribution Pipe Ensures That Adequate Pressure Is Maintained, By The Pump.  Pumps And Fine Filters Are Arranged In Duplicate With One As Standby.  After Use In The Engine, The Lub Oil Drains Back To The Sump Or Drain Tank For Re-use.

What Action Would You Take In The Event Of The Main Engine Oil Sump Level Rising?  What Could Be The Problem And How Would You Fix It?
The Action To Be Taken Would Depend On How Fast The Level Was Rising And What Was Causing It To Rise.
It Could Be Due To The Lub Oil Filling Valve Being Left Open.
But, If It Were Due To Water Or Fuel Entering The Sump, The Engine Would Have To Be Stopped As Soon As It Was Safe To Do So.
Tests Would Be Carried Out To Tell If It Were Water Or Fuel.
If It Were Fuel, You Can Normally Smell This In The Oil, But A Flow Stick Test Can Be Done.
Water Has A Tendency To Form The Colour Of The Oil, Depending On Extent Of Contamination.
If It Were Fuel, The Most Likely Cause Would Be A Faulty Injector; Therefore It Would Be Changed.
If It Were Water, It Could Be Coming From A Cracked Liner Or Liner 'O' Rings, Therefore Possible Liner Change To Solve The Problem.
The Oil May Have To Be Changed, Depending On Extent Of Contamination, But The Lub Oil Purifier May Be Able To Cope With It. 

What Is The Purpose Of A Volute Casing In A Turbo Charger?
The Purpose Of A Volute Casing In A Turbo Charger Is To Change The Air Velocity In To Pressure.  It Also Ensures A Constant Velocity Of Air Leaving The Turbo Charger By Accommodating For The Gradual Increase In Quantity Of Air That Builds Up At The Circumference Of The Compressor.

What Would Cause Excessive Exhaust Temperatures?
On A Single Cylinder, It Could Be An Incorrect Fuel Pump Timing I.e. Late Injection Causing After-burn,  too Much Fuel, Leaking Fuel Injector Or Burnt Out Exhaust Valve.  If All Exhaust Temperatures Were High, It Could Be Due To High Scavenge Temperature, Charge Air Cooler Fouled, Turbo Charger Air Filters Dirty Or Fouled, High Engine Load. 

How Would You Know If You Had A Cracked Liner Or Cylinder Head?
Your Jacket Water Header Tank Would Start To Fall.
Possibly Higher Temperatures On That Unit
On A Medium Speed 4 Stroke Engine, If The Liner Was Cracked, You Would Get Water Contamination Of The Sump.
On A 2 Stroke Engine There Would Be Possible Water Leakage From Stuffing Box Drains.

Why Is Overlap Necessary On Air Start Valves?
Overlap Is Necessary As If There Was No Overlap It Would Be Possible For The Engine To Stop In A Position Where No Valves Are Open, I.e. Unable To Start.

How Can Exhaust Valve Leakage Be Confirmed?
Exhaust Valve Leakage Can Be Confirmed By Taking An Indicator Card, The Card Should Be Taken With Fuel "On" And "Off" The Unit.  If The Valve Is Leaking, The Compression Pressure And Maximum Pressure Will Be Low..

What Are You Looking For When You Pull A Piston?
When You Pull A Piston, You Are Looking For Any Damage To The Piston Crown, Including Cracks.
The Condition Of Piston Rings Are Checked, Plus Piston Ring Grooves.
Check For Any Scuffing Of Piston Skirt
Check Condition Of Top End Bearing Bush And Gudgeon Pin, Plus Clearance Between Pin And Bush.
Check Lubrication Bores Are Clear On Under Side Of Piston.
What Is The First Indication Of A Leaking Exhaust Valve?
The First Indication Of A Leaking Exhaust Valve Is A Rise Of Exhaust Gas Temperature At The Outlet Of The Valve.

Give A Rough Indication Of Engine Speed Ranges I.e. Slow, Medium And High Speed.
Slow Speed:       100-150 Rpm
Medium Speed:     300-850 Rpm
High Speed:       850-3000 Rpm

How Many Starts Do You Require To Get From An Air Receiver Without Recharging?
On A Reversible Engine:   12 Starts
On Engines With CPP Propellers:   6 Starts.

What Would You Do If You Found That You Had A Cracked Liner Or Cylinder Head?
Inform The Bridge That Engine Would Have To Be Stopped And Of The Situation, Also Inform Chief Engineer And Repair The Unit As Soon As It Is Safe To Do So.

How Is Leakage In The High Pressure PipeLine Between The Fuel Pump And Injector, Detected?
Leakage Between The Double Skin/Wall Of The High Pressure PipeLine Between The Fuel Pump And Injector Is Detected As This Space Between The Double Skin/Walled Pipe Is Led Via Drain Line To A Small Tank Fitted With A Level Alarm.

What Should You Do To Ensure That There Is No Water Leakage Into The Engine Cylinder Before Preparing Main Engine For Sea?
The Engine Should Be Turned Using Turning Gear With Indicator Cocks Open, Keeping A Close Eye On The Cocks For Any Signs Of Water Discharge.
Immediately Prior To Starting, The Engine Should Be Kicked On Air.
Note:  2 Stroke Engines Should Be Turned At Least One Revolution, Where A 4 Stroke Should Be Turned Two Revolutions.

What Is An Indication In The Exhaust Gas Of Good Combustion?
Grey Smoke Indicates Good Combustion.

How Would You Know An Air Start Valve Was Leaking Or Passing?
The Adjacent Start Air Line For That Valve Would Become Very Hot.

How Would You Test For A Leaking Air Start Valve In Port?
First Ensure All The Engine Indicator Cocks Are Open For All Cylinders, Then Isolate The Air Supply To The Timing Valves, This Will Ensure No Pilot Air Is Supplied To The Air Start Valves When The Auto Valve Is Opened.
Then Operate The Auto Valve, Any Air Discharge From The Indicator Cocks Will Indicate A Leaking Or Passing Air Start Valve.

How Would You Get Water In The Combustion Spaces?
From Cracked Exhaust Valve Cages
Cracked Cylinder Head Or Liner
Fuel Contamination Via Fuel Injector
Undercooling Of The Charge/Scavenge Air.

What Is The Diffuser Plate In A Turbocharger?
The Diffuser Plate In A Turbocharger Is Found On The Compressor Side, It Converts The Velocity/Kinetic Energy From The Compressor Into Pressure. 

What Would Cause The Level Of The Lub Oil Sump Or Drain Tank To Rise?
Water Entering The Oil, Or Fuel Or Even A Lub Oil Filling Valve Passing. 

What Would You Do If Lub Oil Temperature Started To Fall?
Reduce Sea Water Cooling Flow Through The Lub Oil Cooler By Throttling The Sea Water Discharge Valve From The Cooler.

What Would You Do If You Had High Jacket Water Cooling Temperatures?
Inform Bridge And Then Reduce Engine Load And Investigate Problem:
Which Could Be Insufficient Flow Through Cooler Due To Fouled Cooler Or Faulty Thermostatic Valve.

What Would You Do If You Had A High Chloride Level In The Boiler?
To Reduce The Chloride Level In The Boiler, The Boiler Would Be Blown Down, Thus Allowing Fresh Feed To The Boiler.

What Type Of Safety Valve Is Fitted To A Boiler And At What Pressure Does It Lift? 
The Type Of Safety Valves Fitted To Boilers Are High Lift Safety Valves And Are Designed To Operate At 10% Boiler Working Pressure And Must Also Be Capable Of Releasing All The Steam The Boiler Can Produce Without The Pressure Rising More Than 10% Over A Set Period:  15 Min For Tank Boilers And 7 Mins For Water Tube.  The Spring Pressure, Once Set, Is Fixed And Sealed By A Surveyor.
Note:  The Above Test Is Known As The Accumulation Of Pressure Test.

What Is The Purpose Of The Scum Valve On A Boiler?
The Scum Valve On A Boiler Is Connected To A Shallow Dish Positioned At The Normal Water Level Of The Boiler And Enables The Blowing Down Or Removal Of Scum And Impurities From The Water Surface.

What Type Of Water Tests Would You Do On A Low Pressure Auxiliary Boiler/Economiser?
Chlorides Test
PH-alkalinity Test
Total Dissolved Solids Test – Using Hydrometer
Phenolphthalein Alkalinity Test
Hardness Test
Phosphate Reserve.

How Would You Blow Down A Boiler Gauge Glass?
Close The Water And Steam Cocks On The Gauge Glass And Open The Drain.   
Then Open The Steam Cock – A Strong Jet Of Steam Should Be Seen From The Drain.
Close The Steam Cock.
Open The Water Cock – A Strong Jet Of Water Should Be Observed From The Drain.
Close The Water Cock And Then Close The Drain.
Then Open The Water Cock, The Water Will Rise In The Gauge, Above Normal Level.
Then Open The Steam Cock, The Water Should Then Settle Down, Finding Its Correct Level.

Why Purge A Boiler Furnace?
A Boiler Furnace Is Purged Before Burner Operations To Ensure That There Is No Unburned Fuel Or Gases In The Furnace, Which May Cause A Blowback.  Purging Should Be Carried Out For At Least Two Minutes.

Describe The Boiler Hot Well And Cascade Tank.  Why Is It Fitted And How Would You Trace An Oil Leak?
The Boiler Hot Well Is Where The Condensate Drains Return From The Condensor.  This Condensate May Be Contaminated As Some Of The Drains Are From Fuel Oil Heating Systems Or Tank Heating Systems. Normally These Drains Will Pass To The Hot Well Via An Observation Tank, Which Permits Inspection Of Drains And Their Discharge To An Oily Bilge If Contaminated.  The Hot Well Tank Is Also Arranged With Internal Baffles To Bring About Preliminary Oil Separation From Any Contaminated Fuel Or Drains.  The Feed Water Is Then Passed Through Charcoal Or Cloth Filters To Complete The Cleaning Process.  Any Overflow From The Hot Well Passes To The Feedwater Tank, Which Provides Additional Feedwater To The System When Required.  Feed Pumps Take Suction From The Hot Well To The Boiler.
To Trace An Oil Leak To The System, Various Heating Coils To Tanks Would Be Shut Off In Turn Until The Leak Stopped, Thus Indicating Which Heating Coil Was Leaking.