(1)
(2)(3)(4)(5)(6)(7)
(8)
(9)(10)(11)(12)(13)(14)(15)(16)
(17)(18)(19)(20)
From KAUSHAL KUMAR, 6280
For orals fn 4,6
AIR COMPRESSOR
Bumping clearance-
what is bumping clearance, why it is called so, would it increase with time or
decrease
(may increase or decrease)
,how to adjust in tandem type, why not adjusted by using metal shims
in palm end connection, effects of increased clearance, what was the value of bumping clearance on your
ship
( 1% of cyl. Bore, 1.8 mm(CYL bore 180mm ) n 1.4 mm(cyl. Bore 140mm))?
Does B/E bearing adjustment
in a/c affect the bumping clearance?
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 gauges
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 dead
centre 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 be
removed for the changing of the first stage suction and discharge valves. When the cylinder head is put back the
correct 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.
IMPORTANT
….
bump clearance or squish is most definitely done with the head gasket installed between head and cylinder.Use 2 pieces of lead. Put one piece of lead directly over each end of the wrist pin out near the edge of the piston but not under a valve. This will give you 2 measurements. 1. piston clearance or squish. 2.
Piston/cylinder angle relative to crank. This angle is important as it shows the cylinders relationship to the crankshaft. If the pieces of lead are too different in thickness, the piston can run out of available ring compression and wrist pin end travel and contact the cylinder(scuff) at top and bottom.
differential squish is how the Indians measure and determine the sum of machine errors and the need for
half gaskets under the cylinder base on engines that have alignment issues.
#4 lead shot is perfect for this measurement as it is a uniform size and crushes very consistently. A little dab of grease or drop of oil will hold them where you put them on top of the piston during the
measurement.
Q.
Relief v/v n fusible plug-
setting (10% above stage pressure), Reason for lifting of relief v/v of LP
stage and HP stage, where fitted? Why fusible plug is fitted, its material
(tin, antimony, bismuth
), what
temp blows(
121*C
)?how to test relief v/v(
by normal hydraulic p/p
)?
Reasons of LP stage relief v/v lifting- HP stage suction v/v or discharge v/v leaking, 2
ndstage suction n discharge v/v interchanged after over’hl.
Reasons of HP stage relief v/v lifting- delivery v/v shut, setting error of pressure switch,
delivery v/v which is SDNR type is fitted inverted.
Lubrication-
how it takes place in main/brg, crankpin bearing, upper n lower cyl. In case of tandem type,
how piston gets cooled? Pressure value n alarm value(2-4 bar, alarm at 2 bar)? Reasons….pressure suddenly
drops, pressure drops slowly
(increase in clearance of main brg or crankpin brg
), increased oil consumption?
Why Breather is provided in lub. Oil filling line? Is crankcase pressurized during running condition?
For main brg n crankpin brg. Lubrication normally thr is a shaft driven gear p/p.
For lower cyl. In tandem type- it’s by splash. For upper cylinder in tandem type thr is a supply line from the
gear p/p going to suction side of air which supplies small amount of oil mist with air n that mist lubricates the
upper cyl. Sometimes the supply is from drilled hole in con. Rod like we have in A/E.
Reasons oil pressure not rising- motor rotation direction reverse, oil line block due to rag, no oil in sump,
filter clogged, worn metal so increase of clearance.
Increased oil consumption- too much oil in sump( above level H), oil scraper ring wear out, worn piston and
liner.
Breather- it is used so that pressure or vacuum is not created inside crankcase. It has filter so moisture and dirt
don’t go inside and also has metallic plate on the inner side which don’t allow lub. Oil to come out.
Cooling line-
pressure( 0.2-2 bar), alarms(90*c), why bursting disc, its material( copper), action if it bursts
during maneuvering, at what pressure it bursts, why we prefer bursting disc over relief valve( no chance of
getting reset), purpose of intercooler n aftercooler, What if Main air compressor runs without cooling
water(may cause explosion)? Auto drain trap working?
ANS.
If bursting disc bursts during maneuvering- Inform the bridge about the problem and to give lesser kicks,
Start the stand by compressor, Isolate the compressor whose bursting disc is damaged, Change the bursting
disc, if available onboard, If Not available, then let the S.W go into the E/room bilges, otherwise Fresh water
cooled, then join a flexible hose and put into the expansion tank.
Suction n delivery v/v-
how u will come to know they r leaking( temp. increase of air, relief v/v lift),
its affects, What would be the consequences of too high valve lift in an air compressor( chances of damage
due to impact, decrease in vol. efficiency)? What would be the consequences of a high spring constant of
spring plates in an air compressor(open late n sit with higher impact which may cause damage)? Can we
interchange spring of suction n delivery v/v( no, delivery v/v spring stiffness is more)? parts of
v/v(remember,the suction n delivery v/v for first stage r in single set but for 2
ndstage they r different, the
v/v parts for both suction n discharge of 2
ndstage r same but arranged in opposite order)?
Starting-
checks before manual starting, current value of air compressor?(Starting
310Amps,full load 30A)
ANS.
1
. Lubrication: check the oil level in the sump
(b/w H n L)and in the lubricator tank.
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
pumps a visual check of the pump 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.
Why reciprocating type compressor(pr.ratio is higher )?why two stage, pv diag for you comp.
clearance volume?
each stage pressure(4-6 BAR, 25-30 BAR)? Can they vary from normal during
starting? unloader ….purpose, design? What is volumetric efficiency, free air delivery?
ANS.
Free air delivery- volume of delivered air is measured at 1 atm and 15*C, it’s called free
air.
If the valve has too much lift then the valve closes late and reduce volumetric efficiency and
also its causes valve to close with greater impact and hence liable to break.
Why 2 stage- first, bcoz we can’t give a pressure of 30 bars in single stage as the lub.oil will
start burning.
T2/T1=(P2/P1)^n-1/n where n is around 1.35 for air
Now for p2/p1=30/1
T2=450*C
And at this temp. lub. Oil will start burning. Flash point for lub.oil is 200*C. so we keep the
pressure ratio limited to 5:1.
Secondly, we want to save work by moving towards isothermal line by providing
intercooling b/w stages.
PURIFIER
Why we need to heat oil, purifier formula, why we need disc stack, use of gravity disc,
position of e-line?
ANS. For ans see mcgeorge mar. aux. pg-58-62.
Q. what to do if u want to change DO purifier for HFO purifier?
ANS.
adjust temp.(around 95*C),adjust feed rate(reduce), adjust desludge time(increase
desludge time as DO don’t have so much of impurities).NOW FOR GRAVITY DISC,SINCE
DENSITY IN DECREASING, so increase size of gravity disc.
Q. Purifier ……Starting n disludging ? Small fire in purifier trays...wt's ur action?? pairing disc?
(SEE MM,OM2)
.
Back Pressure: The back pressure should be adjusted after the purifier is started. The back pressure varies as
the temperature, density, viscosity of feed oil inlet varies. The back pressure ensures that the oil paring disc is
immersed in the clean oil on the way of pumping to the clean oil tank.
Throughput of oil feed: Throughput means the quantity of oil pumped into the purifier/hr. In order to optimize
the purification, the throughput must be minimum.
Pre-checks before starting a Purifier
1. If the Purifier is started after a overhaul, then check all fittings are fiited in right manner. The bowl frame
hood locked with hinges.
2. Check the Oil level in the gear case. Ensure that it is exactly half in the sight glass. Also ensure the sight
glass is in vertical position, as there is a common mistake of fixing it in horizontal position.
3. check the direction of rotation of the seperator, by just starting and stopping the purifier motor. 4. Check
whether the brake is in released position.
•
Starting the Purifier
1. Ensure the lines are set and respective valves are open. Usually the lines are set from settling tank to service tank.
2. Start the purifier feed pump with the 3-way re-circulation valve in a position leading to settling tank.
3. Open the steam to the heater slightly ensuring the drains are open so that the condensate drains. close the drains once
steam appears.
4. Start the Purifier. 5. Check for vibrations, check the gear case for noise and abnormal heating.
6. Note the current (amps) during starting. It goes high during starting and then when the purifier bowl picks-up speed and
when it reaches the rated speed, the current drawn drops to normal value.
7. Ensure the feed inlet temperature has reached optimum temperature for separation as stated in the Bunker delivery note
and nomogram (can get the separation temperature and gravity disc size from the nomogram)
8. Now check whether the bowl has reached the rated speed by looking at the revolution counter. The revolution counter
gives the scaled down speed of the bowl. The ratio for calculation can be obtained from the manual.
9. Now, after the bowl reaching the rated RPM, check for the current attaining its normal value.
•
De-sludge Procedure
10. Open the bowl closing water/operating water, which closes the bowl. (Ensure sufficient water is present in the
operating water tank)
11. Now after 10 seconds, open the sealing water to the bowl.
12. The sealing water should be kept open till the water comes out of the waste water outlet.
13. Once the water overflows through the waste water outlet, stop the sealing water.
14. Now open the bowl opening water. (This is done to ensure the bowl has closed properly). During de-sludge we can
hear a characteristic sound at the opening of the bowl.
15. Repeat the steps 10, 11 ,12 & 13.
16. Open the 3-way re-circulation valve such that the dirty oil feed is fed into the purifier.
17. Wait for the back pressure to build up.
18. Check for overflowing of dirty-oil through waste water outlet & sludge port.
19. Now adjust the throughput to a value specified in the manual. Correspondingly adjust the back pressure, too.
20. Now the purifier is put into operation. Change over the clean-oil filling valve to service tank.
Q. purifier rpm not coming, reasons, Explain about purifier drive mechanism….how you will
check that ?when you will change it(see MM p4-12,change spiral gear if wear down is more
than 3mm,change friction block lining if wear is 3mm,change pulley if wear is 1mm,change
brake lining if wear is 5 mm). When d motor attains full speed does d horizontal shaft rotates
at d same speed of motor?
Q. why frictional clutch in purifier??
ANS. 1.
it gives less staring current for motor, also
2.worm and worm wheel arrangement will break due to high starting torque.
REFRIGIRATION SYSTEM
T
ROUBLEP
OSSIBLEC
AUSEC
ORRECTIVEM
EASUREH
IGH CONDENSING PRESSURE.
I
NLET WATER WARM.
I
NCREASE QUANTITY OF CONDENSING WATER.
A
IR ON NON-
CONDENSABLE GAS IN SYSTEM.
P
URGE AIR FROM CONDENSERI
NSUFFICIENT WATER FLOWING THROUGH CONDENSER.
I
NCREASE QUANTITY OF WATER.
C
ONDENSER TUBES CLOGGED OR SCALED.
C
LEAN CONDENSER WATER TUBES.
T
OO MUCH LIQUID IN RECEIVER,
CONDENSER TUBES SUBMERGED IN LIQUID REFRIGERANT
.
D
RAW OFF LIQUID INTO SERVICE CYLINDER.
L
OW CONDENSING PRESSURE.
T
OO MUCH WATER FLOWING THROUGH CONDENSER.
R
EDUCE QUANTITY OF WATER.
W
ATER TOO COLD.
R
EDUCE QUANTITY OF WATER.
L
IQUID REFRIGERANT FLOODING BACK FROM EVAPORATOR.
C
HANGE EXPANSION VALVE ADJUSTMENT,
EXAMINE FASTENING OF THERMAL BULB.
L
EAKY DISCHARGE VALVE.
R
EMOVE HEAD,
EXAMINE VALVES.
R
EPLACE ANY FOUND DEFECTIVE.
F
ROSTING OR SWEATING OF A LIQUID LINE.
R
EFRIGERANT LINE RESTRICTION.
C
HECK FOR PARTIALLY CLOSED STOP VALVE,
OR STUCK SOLENOID VALVE.
S
YSTEM LOW ON REFRIGERANT.
C
HECK FOR LEAKS,
ADD REFRIGERANT.
H
IGH SUCTION PRESSURE.
C
OMPRESSOR CRANKCASE SWEATINGO
VERFEEDING OF EXPANSION VALVE.
R
EGULATE EXPANSION VALVE,
CHECK BULB ATTACHMENT.
L
EAKY SUCTION VALVE.
R
EMOVE HEAD,
EXAMINE VALVE AND REPLACE IF WORN.
L
OW SUCTION PRESSURE.
R
ESTRICTED LIQUID LINE AND EXPANSION VALVE OR SUCTION SCREENS.
R
UMP DOWN,
REMOVE,
EXAMINE AND CLEAN SCREENS,
I
NSUFFICIENT REFRIGERANT IN SYSTEM.
C
HECK FOR REFRIGERANT STORAGE.
T
OO MUCH OIL CIRCULATING IN SYSTEM.
C
HECK FOR TOO MUCH OIL IN CIRCULATION.
R
EMOVE OIL.
I
MPROPER ADJUSTMENT OF EXPANSION VALVESA
DJUST VALVE TO GIVE MORE FLOW.
DEAD OR WEAK ELEMENT
.
C
OMPRESSOR SHORT CYCLES ON LOW-PRESSURE CONTROL
.
L
OW REFRIGERANT CHARGE.
L
OCATE AND REPAIR LEAKS.
C
HARGE REFRIGERANT.
T
HERMAL EXPANSION VALVE NOT FEEDING PROPERLY.
a. D
IRTY STRAINERS.
b. M
OISTURE FROZEN IN ORIFICE OR ORIFICE PLUGGED WITH DIRT.
c. P
OWER ELEMENT DEAD OR WEAKA
DJUST,
REPAIR OR REPLACE THERMAL EXPANSION VALVE.
a. C
LEAN STRAINERS.
b. R
EMOVE MOISTURE OR DIRT(
USE SYSTEM DEHYDRATOR).
c. R
EPLACE POWER ELEMENT.
W
ATER FLOW THROUGH EVAPORATORS RESTRICTED OR STOPPED.
E
VAPORATOR COILS PLUGGED,
DIRTY,
OR CLOGGED WITH FROST.
R
EMOVE RESTRICTION.
C
HECK WATER FLOW.
C
LEAN COILS OR TUBES.
D
EFECTIVE LOW-
PRESSURE CONTROL SWITCH.
R
EPAIR OR REPLACE LOW-
PRESSURE CONTROL SWITCH.
C
OMPRESSOR RUNS CONTINUOUSLY.
S
HORTAGE OF REFRIGERANT.
R
EPAIR LEAK AND RECHARGE SYSTEM.
L
EAKING DISCHARGE VALVES.
R
EPLACE DISCHARGE VALVES.
C
OMPRESSOR SHORT CYCLES ON HIGH-PRESSURE CONTROL SWITCH
.
I
NSUFFICIENT WATER FLOWING THROUGH CONDENSER,
CLOGGED CONDENSER.
D
ETERMINE IF WATER HAS BEEN TURNED OFF.
C
HECK FOR SCALED OR FOULED CONDENSER.
D
EFECTIVE HIGH-
PRESSURE CONTROL SWITCH.
R
EPAIR OR REPLACE HIGH-
PRESSURE CONTROL SWITCH.
C
OMPRESSOR WILL NOT RUN.
S
EIZED COMPRESSOR.
R
EPAIR OR REPLACE COMPRESSOR.
C
UT-
IN POINT OF LOW-
PRESSURE CONTROL SWITCH TOO HIGH.
S
ETL.
P.
CONTROL SWITCH TO CUT-
IN AT CORRECT PRESSURE.
H
IGH-
PRESSURE CONTROL SWITCH DOES NOT CUT-
IN.
1
.D
EFECTIVE SWITCH.
2.
E
LECTRIC POWER CUT OFF.
3.
S
ERVICE OR DISCONNECT SWITCH OPEN.
4.
F
USES BLOWN.
5.
O
VER-
LOAD RELAYS TRIPPED.
6.
L
OW VOLTAGE.
7.
E
LECTRICAL MOTOR IN TROUBLE.
8.
T
ROUBLE IN STARTING SWITCH ORC
HECK DISCHARGE PRESSURE AND RESETP.
H.
CONTROL SWITCH.
1.
R
EPAIR OR REPLACE SWITCH.
2.
C
HECK POWER SUPPLY.
3.C
LOSE SWITCHES.
4.
T
EST FUSES AND RENEW IF NECESSARY.
5.
R
E-
SET RELAYS AND FIND CAUSE OF OVERLOAD.
6.
C
HECK VOLTAGE(
SHOULD BE WITHIN10
PERCENT OF NAMEPLATE RATING).
7.
R
EPAIR OR REPLACE MOTOR.
8.
C
LOSE SWITCH MANUALLY TO TEST POWER SUPPLY.
I
FOK,
CHECK CONTROLCONTROL CIRCUIT
.
9.
C
OMPRESSOR MOTOR STOPPED BY OIL PRESSURE DIFFERENTIAL SWITCH.
CIRCUIT INCLUDING TEMPERATURE AND PRESSURE CONTROLS
.
9.
C
HECK OIL LEVEL IN CRANKCASE.
C
HECK OIL PUMP PRESSURE.
D
ECREASED CAPACITY OF THE COMPRESSOR.
H
IGH VAPOR SUPERHEAT.
A
DJUST OR REPLACE EXPANSION VALVE.
S
UDDEN LOSS OF OIL FROM CRANKCASE.
L
IQUID REFRIGERANT SLUGGING BACK TO COMPRESSOR CRANK CASE.
A
DJUST OR REPLACE EXPANSION VALVE.
C
APACITY REDUCTION SYSTEM FALLS TO UNLOAD CYLINDERS.
H
AND OPERATING STEM OF CAPACITY CONTROL VALVE NOT TURNED TO AUTOMATIC POSITION.
S
ET HAND OPERATING STEM TO AUTOMATIC POSITION.
C
OMPRESSOR CONTINUES TO OPERATE AT FULL OR PARTIAL LOAD.
P
RESSURE REGULATING VALVE NOT OPENING.
A
DJUST OR REPAIR PRESSURE REGULATING VALVE.
C
APACITY REDUCTION SYSTEM FAILS TO LOAD CYLINDERS.
B
ROKEN OR LEAKING OIL TUBE BETWEEN PUMP AND POWER ELEMENT.
R
EPAIR LEAK.
L
OW DISCHARGE PRESSURE WITH HIGH SUCTION PRESSURE.
D
ISCHARGE RELIEF VALVE LEAKING BACK TO THE SUCTION SIDE.
R
EPLACE RELIEF VALVE.
C
OMPRESSOR CONTINUES TO OPERATE UNLOADED.
P
RESSURE REGULATING VALVE NOT CLOSING.
A
DJUST OR REPAIR PRESSURE REGULATING VALVE.
C
OMPRESSOR OIL BROWNISH IN COLORC
OPPER PLATING CAUSED BY MOISTURE IN THE SYSTEM.
C
HANGE FILTER DRIER,
OR DEHYDRATOR.
C
OMPRESSOR OIL GRAY OR METALLIC.
C
OMPRESSOR BEARING WEAR OR PISTON SCORING.
R
EPLACE OR OVERHAUL COMPRESSOR.
C
OMPRESSOR OIL BLACKC
ARBONIZATION RESULTING FROM AIR IN THE SYSTEM.
R
EMOVE AIR FROM SYSTEM.
REFRIGERATION SYSTEM WORKS ONFIRST LAW OF THERMODYNAMICS
,
REVERSE CARNOT CYCLE.
COP
=
Q/
W1
TON REFRIGERATION CAPACITY=
RATE OF HEAT TRANSFER IN FORMING I TON OF ICE AT0*
C FROM WATER AT0*
C.
ADVANTAGE OF UNDERCOOLING=
INCREASE REFRIGERATION EFFECT BY REDUCING AMOUNT OF FLASH OFF AT EXP.
V/
V.
NAMING OF REFRIGERENT
-
1
ST DIGIT FROM LEFT IS ONE LESS THEN NUMBER OF C ATOMS.
2
NDIS ONE MORE THEN H ATOM
Q.
PURPOSE F BACK PRESSURE V/
V IN REFER OF REFRIGRENT JUST AFTER EAVPORATER.
H
OW DIFFERENT ROOM TEMP R MAINTAINED IN REFRERATION SYSTEM?
ANS.
B
ACK PRESSURE V/
V-
TO KEEP DIFFERENT TEMP OF DIFFERENT ROOMS.
WE USE IT IN VEG.
ROOM.
W
E SET BACK PRESSURE,
SO IT INCREASE THE BACK PRESSURE IN VEG ROOM LINE.
AND SO THE SATURATION TEMP.
INCREASE.
S
ITUATED AT VEG ROOM DICHARGE.
back pressure valve is fitted at the outlet of veg room. the reason being that the veg room is maintained at a
temperature of +4 -5 degress while fish room is at about -12 to -15 degrees and the flow and amount of
refrigerant at fish room and meat room is greater as compared to that of veg room. hence if back pressure
valve is not fitted then when refrigerants will come at the outlet of all the three rooms then the refrigerant will
tend to flow towards veg room. hence to avoid it a back pressure valve is fitted which will allow refrigerant to
flow out only if the pressure inside the veg room outlet will be greater than the outlet from the main line.
Q:
W
HAT IS THE DIFFERENCE BETWEEN THE"
AUTOMATIC EXPANSION VALVE"
AND THE"
THERMOSTATIC EXPANSION VALVE"?
T
HE AUTOMATIC EXPANSION VALVE WAS THE FIRST VALVE DEVELOPED TO PREVENT MANUAL ADJUSTMENT OF THE FLUID METER,
THEN USED AS EXPANSION VALVE
.
T
HE VALVE IS DESIGNED TO KEEP CONSTANT PRESSURE IN THE EXPANSION VALVE OUTLET.
O
N KEEPING CONSTANT PRESSURE,
IT ALSO INDIRECTLY CONTROLS THE TEMPERATURE,
HOWEVER,
IT DOES NOT ASSURE OVERHEATING,
WHICH WILL PROTECT THE COMPRESSOR
.A
S THE EVAPORATOR CAPACITY IS REDUCED,
THERE IS LESS FLUID EVAPORATION,
ON THE OTHER HAND,
BECAUSE THE VALVE MAINTAINS THE PRESSURE,
IT ALSO MAINTAINS THE VALUE OF THIS FLOW.
O
N DOING SO,
HOWEVER,
EXCESS REFRIGERANT STILL IN LIQUID STATE IS FED INTO THE EVAPORATOR,
WHICH RESULTS IN ITS RETURN TO THE COMPRESSOR,
WITH HUGE MECHANICAL LOSS.
A
LTERNATIVELY,
IF THERE IS INCREASE IN LOAD,
THERE WILL BE GREATERFLUID VAPORIZATION AND IF THE VALVE MAINTAINS THE FLOW
,
IT WILL INCREASE OVERHEATING OF THE GAS AND LITTLE USE OF THE HEAT EXCHANGE SURFACE.
U
NFORTUNATELY,
THIS RESULTS IN OPERATION OF THE EVAPORATOR CONTRARY TO THE PRODUCTION OF COLD,
WHEN ITS LOAD IS HIGHER.T
HESE COUNTERPARTS RESULTED IN REPLACEMENT OF THE AUTOMATIC EXPANSION VALVE BY THET
HERMOSTATICE
XPANSIONV
ALVE IN MOST APPLICATIONS.
T
HET
HERMOSTATICE
XPANSIONV
ALVE CORRESPONDS TO THE OVERHEATING AT THE EVAPORATOR OUTLET AND,
AS A RESULT,
THIS RESPONDS BETTER TO THE ACTUAL LOAD,
RESULTING IN A MORE EFFICIENT SYSTEM.
Q.
REFER COMPRESSOR CHARGING LIQUID AND GAS?
WHERE U CONNECT THE CHARGING CONNECTION?
WHY WE TAKE PURGE AIR IN A SEALED CONTAINER?
N HOW U WL COME TO KNOW DAT SYSTEM IS ENOUGH CHARGED WITHOUT WEIGHING BOTTLE(
SEE IN GAUGE GLASS)...
ANS.
L
IQUID CHARGE-
CONNECTION IS B/
W CONDENSER AND DRIER.
BEFORE DRIER BCOZ MOISTURE MAY ENTER DURING CHARGING,
SO IT WILL BE ABSORBED
.
AFTER CONDENSER BCOZ BEFORE CONDENSER ALL IS GAS.
F
OR CHARGING CONNECT CYL.
T
O A BOTTLE,
PURGE,
THEN CONNECT TO CHARGING POINT.
W
G
AS CHARGING-
CONNECTION IS IN SUCTION SIDE,
JUST LITTLE BEFORE SUCTION LINE.
R
EMEMBER,
REFRIGERANT COMES TO CRANKCASE FIRST THEN IT GOES TO SUCTION SIDE OF1
ST CYL.
C
HARGING CYL.
H
AS2
V/
V-
ONE RED IS CONNECTED TO DIP TUBE AND IS FOR LIQUID CHARGING.
A
ND A BLUE V/
V IS FROM TOP AND DON’
T HAVE DIP TUBE AND IT IS FOR GAS CHARING.
IN BOTH CONDITION CYL.
W
E KEEP CYL.
U
PRIGHT.
I
F ONLY ONE V/
V THEN WE NORMALLY WE DON’
T HAVE DIP TUBE AND IN THIS WHEN LIQUID THEN TURN DOWN BY HEAD.
GAS CHARGING OF REFRIGERATION PLANT:
FOR GAS CHARGING, A SPECIAL T PIECE VALVE BLOCK WITH MOUNTED PRESSURE GAUGE IS PROVIDED
TO COMBINE THREE CONNECTORS INTER-CONNECTING:FOLLOWING STEPS ARE TO BE TAKEN FOR CHARGING GAS INTO THE REEFER PLANT:
1. CONNECT GAS BOTTLE OR CHARGING CYLINDER, VACUUM PUMP AND CHARGING POINT IN THE REEFER
SYSTEM TO THE VALVE BLOCK.2. THE DISCHARGE OF THE VACUUM PUMP IS TO BE CONNECTED IN THE EMPTY RECOVERY BOTTLE
3. FIRST OPEN THE VALVE BETWEEN VACUUM PUMP AND CHARGING BOTTLE LOCATED IN THE VALVE
BLOCK WITHOUT OPENING THE MAIN VALVE OF THE CHARGING CYLINDER. THIS WILL REMOVE ALL THE AIR INSIDE THE PIPE. ONCE VACUUM IS REACHED, CLOSE THE VALVE OF CHARGE CYLINDER IN THE VALVE BLOCK4. NOW OPEN THE VALVE OF THE CHARGING POINT PIPE IN THE VALVE BLOCK AND RUN THE VACUUM
PUMP UNTIL THE VACUUM IS REACHED. THIS WILL REMOVE THE TRAPPED AIR FROM THIS PIPE. THEN SHUT THE VALVE IN THE VALVE BLOCK5. NOW KEEP THE SYSTEM IDLE FOR 5 MINUTES TO CHECK THERE IS NO PRESSURE DROP. THIS WILL
ENSURE THERE ARE NO LEAKAGES IN THE SYSTEM6. NOW OPEN CHARGING BOTTLE PIPE VALVE AND THE CHARGING POINT PIPE VALVE LOCATED IN THE
VALVE BLOCK. THIS WILL SET THE LINE FOR CHARGING. ENSURE THAT THE VACUUM PUMP VALVE IS SHUT7. NOW OPEN THE MAIN VALVES IN THE CHARGING CYLINDER AND CHARGING POINT OF THE REEFER
SYSTEM8. DO NOT OVERFILL THE SYSTEM. MAKE SURE THE RECEIVER HAS 5 % SPACE FOR EXPANSION
ENSURE THAT NO REFRIGERANT IS LEAKED OUT IN THE ENVIRONMENT AS THESE EFFECTS THE OZONE
LAYER IN THE ATMOSPHERE.Q.
AIR,
MOISTURE,
OIL,
OVERCHARGING,
UNDERCHARGING?
INDICATION,
HARMS,
ACTIONS?
O
IL IN THER
EFRIGERATIONS
YSTEMINDICATION:
•
T
EMPERATURE IS NOT DROPPING IN THE COLD ROOMS AS NORMAL,
DUE TO FACT THAT OIL ACT AS INSULATION IN THE EVAPORATOR.
•
I
T MAY CAUSE EXCESSIVE FROST ON THE SUCTION LINE.
•
R
EFRIGERANT COMPRESSOR RUNS FOR THE EXTENDED PERIOD OF TIME.
•
L
UBRICATING OIL LEVEL IN THE COMPRESSOR WILL DROP.
•
R
EFRIGERANT LEVEL WILL FALL IF OIL HAS CAUSED BLOCKAGE.
CAUSES:
•
T
HIS MAY HAPPEN IF THE OIL SEPARATOR IS NOT WORKING PROPERLY.
•
O
IL MAY CARRY OVER FROM THE COMPRESSOR AND MAY NOT COME BACK TO THE COMPRESSOR DUE TO BLOCKAGE IN THE SYSTEM.
•
D
EFECTIVE PISTON RINGS OR WORN OUT LINER OF THE COMPRESSOR MAY CAUSE THE OIL TO CARRY OVER ALONG WITH THE REFRIGERANT.
•
C
OMPRESSOR MAY TAKE HIGH CAPACITY CURRENT DURING STARTING.
ACTION:
•
C
HECK THE OIL SEPARATOR FOR PROPER FUNCTIONING.
•
C
HECK THE DRIER FOR PROPER CLEANING AND IF ITS REQUIRE CLEANING CLEAN IT•
E
VAPORATOR COIL SHOULD BE DRAINED TO REMOVE ANY TRACE OF OIL.
•
I
F THERE IS OIL IN THE COOLING COILS,
INCREASE THE CONDENSER AND EVAPORATOR TEMPERATURE DIFFERENTIALS AND REMOVE EXCESS FROST ON THESUCTION PIPE.
•
H
EAT PIPES WITH BLOW TORCH.
A
IR IN THES
YSTEMINDICATION:
•
T
HIS MAY CAUSE THE REFRIGERATION COMPRESSOR TO OVERHEAT,
WITH A HIGH DISCHARGE PRESSURE AND NORMAL CONDENSING TEMPERATURE.
•
T
HERE ARE POSSIBILITIES OF SMALL AIR BUBBLES IN THE LIQUID SIGHT GLASS OF THE CONDENSER.
•
C
ONDENSING PRESSURE OF THE REFRIGERANT IN THE CONDENSER MAY BE HIGH.
•
I
F THERE IS EXCESSIVE AIR,
IT MAY REDUCE THE COOLING CAPACITY OF THE SYSTEM,
MAKING THE COMPRESSOR TO RUN FOR THE EXTENDED PERIOD OF TIME.
•
I
T MAY CAUSE THE GAUGE POINTER OF THE CONDENSER TO JUMP INDEFINITELY.
CAUSES:
•
D
URING CHARGING,
AIR MAY ENTER IN TO THE SYSTEM.
•
I
FF
REON-12
IS USED AIR MAY LEAKS IN TO THE SUCTION LINE BECAUSE THE WORKING PRESSURE OF THEF
REON-12
REFRIGERANT IS LESS THAN THE ATMOSPHERIC PRESSURE.
ACTION:
•
A
IR IN THE SYSTEM CAN BE REMOVED BY COLLECTING THE SYSTEM GAS IN THE CONDENSER,
LEAVING THE CONDENSER COOLING WATER ON AND VENTING OUT THE AIR FROM THE TOP OF THE CONDENSER BECAUSE AIR WILL NOT BE CONDENSED IN THE CONDENSER BUT REMAINS ON TOP OF THE CONDENSER ABOVE THE LIQUID REFRIGERANT.
•
C
ONNECT THE COLLECTING CYLINDER TO THE PURGING LINE OF THE CONDENSER,
OPEN THE VALVE,
AND COLLECT AIR IN THE CYLINDER.
•
A
FTER PURGING THE AIR FROM THE SYSTEM DON’
T FORGET TO SHUT THE PURGING VALVE.
• PUMPING DOWN
,
CLOSE CONDENSER INLET VALVE,
COOLING WATER AT FULL FLOW,
WHEN CW INLET AND OUTLET TEMP BECOME EQUAL,
SEE WHAT IS THE CONDENSING PRESSURE AND FROM COMPRESSOR SUCTION GAUGE FIND OUT SATURATION TEMP AT THAT CORRESPONDING CONDENSING PRESSURE,
IF IT IS EQUAL TO CW TEMP THEN IT MEANS AIR HAS BEEN REMOVED.
R
ESTART THE COMPRESSOR WITH ALL SAFETY PRECAUTIONS.
•
U
NDERCHARGING OFR
EFRIGERATIONS
YSTEMINDICATION:
•
C
OMPRESSOR IS RUNNING HOT AND PERFORMANCE OF THE COMPRESSOR FALLS OFF DUE TO HIGH SUPERHEAT TEMPERATURE AT THE SUCTION SIDE OF COMPRESSOR.
•
S
UCTION AND DISCHARGE PRESSURE OF THE COMPRESSOR IS LOW.
•
L
ARGE VAPOR BUBBLES IN THE LIQUID SIGHT GLASS.
•
L
OW GAUGE READINGS IN THE CONDENSER.
•
A
MMETER READING FOR THE COMPRESSOR MOTOR IS LOWER THAN NORMAL.
•
R
ISE IN ROOM TEMPERATURE WHICH IS TO BE COOLED.
•
C
OMPRESSOR IS RUNNING FOR EXTENDED PERIOD OF TIME.
CAUSES:
•
L
EAKAGE OF REFRIGERANT AT THE SHAFT SEAL,
FLANGE COUPLINGS,
VALVE GLAND ETC.
•
E
XPANSION VALVE MAY BE BLOCKED AT THE STRAINER.
•
P
ARTIAL BLOCKAGE OF REFRIGERANT AT THE FILTER OR DRIER OR EVAPORATOR MAY CAUSE UNDERCHARGING.
ACTION:
•
I
DENTIFY AND RECTIFY THE LEAKAGE OF REFRIGERANT FROM THE SYSTEM.
•
C
LEAN THE FILTER AND DRIER.
•
C
HARGE THE SYSTEM WITH FRESH REFRIGERANT AS REQUIRED.
•
O
VERCHARGE OFR
EFRIGERATIONS
YSTEMINDICATION:
•
T
HE LIQUID LEVEL IN THE CONDENSER IS TOO HIGH(
HIGH CONDENSER GAUGE READING).
T
HIS WILL REDUCE THE AVAILABLE CONDENSING SURFACE,
WITH CORRESPONDING INCREASE IN THE SATURATION TEMPERATURE AND PRESSURE.
•
H
IGH PRESSURE SWITCH OF THE REFRIGERANT COMPRESSOR ACTIVATES AND STOPS THE COMPRESSOR.
•
T
HE SUCTION AND THE DISCHARGE PRESSURES ARE HIGH.
CAUSES:
•
I
T MAY BE DUE TO THE REASON THAT EXCESSIVE REFRIGERANT HAS BEEN CHARGED IN THE SYSTEM.
•
A
IR IN THE SYSTEM MAY ALSO CAUSE OVER CHARGING INDICATION.
•
I
T MAY ALSO BE DUE TO THE FORMATION OFFICE ON THE REGULATOR.
•
R
EMOVE THE REFRIGERANT FROM THE SYSTEM.
T
HIS IS DONE BY CONNECTING A CYLINDER TO THE LIQUID LINE CHARGING VALVE,
STARTING THE COMPRESSOR,
AND THEN OPERATING THE CHARGING VALVE.
•
P
URGE THE AIR FROM THE SYSTEM AND MAINTAIN EFFECTIVE COOLING.
•
R
EMOVE ICE FROM THE REGULATOR BY USING ANY OF THE DEFROSTING METHODS.
•
M
OISTURE IN THES
YSTEMTHIS NORMALLY COMES WITH THE INGRESS OF AIR IN THE SYSTEM. MOISTURE MAY FREEZE AT THE
EXPANSION VALVE, GIVING SOME OF THE INDICATION OF UNDER CHARGING. IT WILL CONTRIBUTE TO THE CORROSION IN THE SYSTEM. IT MAY CAUSE LUBRICATION PROBLEMS AND BREAKDOWN OF THE LUBRICATING OIL IN THE REFRIGERANT COMPRESSOR.ACTION:
•
R
ENEW SILICA GEL IN CASE OF MINOR MOISTURE.
• COLLECT REFRIGENANT AND REMOVE ALL AIR AND MOISTURE BY VACUUM PUMP IF THE AMOUNT IS HUGE
.
69. recharging LO in refrigerant compressor.
- Collect the refrigerant into the condenser by shutting off the condenser outlet valve. - Stop the compressor and shut off the inlet and outlet valves of compressor. - Open the oil filling plug and start filling the oil slowly.
- Start the compressor momentarily(0.5- 0.6 seconds) to facilitate speedy charging. - After charging to the correct level, tightened up the oil plug.
- Bleed off air in the compressor casing by slightly opening the suction valve and loosening connecting caps from the high pressure gauge (In case connection fittings for vacuum pump are provided, use the vacuum pump to extract the air from the compressor crankcase).
Extracting Oil
- i. Pump down the refrigerant into the compressor only. Ensure that refrigerant - pressure is higher than the atmosphere.
- ii. Loosen the oil drain plug in the compressor crankcase and extract the amount oil. Precautions:
- 1.) Care to be taken when charging oil so that no air will be trapped in the - compressor crankcase.
- 2.) Ensure to bleed off air every after charging and extracting refrigeration oil.
Q. bulb in thermostatic exp v/v has come off...what will be the effect??reasons 4 icing on
expansion v/v?
Q.what is short cycling OF REFRIGIRATION, reasons and what u will do? Refrigration system LO
properties. recharging LO in refrigerant compressor? 2.what is the function of condenser..what is
sub cooling..?what will u check to insure that condenser is working properly...what will happen if temp diff
between inlet and outlet of cooling sea water is increasing(cooling water flow is less or chocked) or
decreasing(scaling,) and how will u make sure that it is being restored? Changing of filter drier of ref.
comp?
ANS. For changing filter drier. We can do this when plant is running. Open bypass v/v. close
inlet outlet of drier. Change drier. open inlet outlet n close bypass.
Q. Tev equalising connection. Why?
ANS. We use where evaporator is large. So we have different pressure at inlet and outlet. Act as
second line of defense. That is if bulb comes out then.
Q. Did refrgrt’n compressor have relief door?(NO) Why not?(crankcase doesn’t have o2,so
chances of fire is very less.temp. so less bcoz of cool refrigerant .and. also vol. of crankcase is
less so no need as per regulation)
Q. refrigeration oil separator working, type complete...why required?
ANS. Impingement type- fitted in discharge line. Its a closed container fitted with a series of
baffle. As vapour enters the oil separator, there is reduction in velocity due to larger area of
separator. Since oil particles have greater momentum, they impinge on the baffles. And later
gets drained to crankcase through a float valve.
3. What is suc. Press. of refer and AC plant....is thr any diff ..if yes y?
AIR
.
CONDITIONING
WHAT IS SPECIFIC HUMIDITY
,
RELATIVE HUMIDITY
,
SENSIBLE HEAT
,
WET BULB TEMP
,
PSYCHOMETRIC CHART
,
HOW TEMP
.
IS CONTROLLED IN AIR CON
.
SYSTEM
,
LIGIONILA BACTERIA
,
MAIN ENGINE AND AUX. ENGINE FULL FORM
Q. Make and type of a/e and m/e with meanings. Alarms,interlocks, trips on that.
ANS. M/E-MAN B&W 6S46MC-C
MAN-MASCHINEN FABRIK AUGSBERG NURMBERG (DENMARK), BURMEISTER AND WEIN (GERMANY)
6-NO. OF CYLINDERS , S-SUPERLONG STROKE,APRROX. S/B RATIO-3.8 AND ABOVE(OTHER IS L,LONG STROKE-3.2 AND SHORT STROKE ,K,S/B RATIO-UPTO 2.8)
46-CYLINDER BORE IN cm , M-ENGINE PROGRAMME
C-CAMSHAFT CONTROLLED(OTHER USED IS E-ELECTRONICALLY CONTROLLED)
C-COMPACT, In 1996 and onward the MC-C versions of the small and medium bore engines were added to the programme. In this case the -C stands for "compact", as the engines were intended to be lighter, cheaper and yet more powerful. They feature an integrated camshaft housing, simplified cross-head and a variety of other smaller changes to facilitate the "compact" concept. In exchange the fuel injection system was simplified and the VIT system was made an option. The small and medium bore MC-C engines are thus best suited to vessels operating for prolonged periods at the power at which the engines are optimised.
AUXILLARY ENGINE - 5H 21/32
5-NO. OF CYLINDERS, H-HYUNDAI’s HIMSEN(HIMSEN STANDS FOR-Hitouch and Hitech Medium Speed Engine) 21-CYLINDER BORE IN cm , 32-PISTON STROKE IN cm
MAIN ENGINE AND A/E
STARTING AIR SYSTEM
How starting air system works, interlocks, function of …..air distributer(to select timing n
sequence), master starting v/v, safeties provided, why bursting disc or flame arrestor….their
working, regulation (for cyl. Bore 230 mm or more+reversing then on all cyl.)and construction,
what action if…..bursting disc bursts during maneuvering, starting air v/v gets stuck, how you
will come to know, what extra precaution if m/e running with one starting v/v isolated, why
negative cam for air distributor, crash maneuvering how, how starting and reversing takes place
in MAN B&W n sulzer, regulations regarding reversing capacity of engine, why air bottle v/v is
slow opening type, regulations regarding size of air bottle, material of….. air bottle(seamless low
carbon manganese steel), starting air line, starting air v/v(cast steel body, stainless steel v/v n
spindle), why overlap is necessary, timing dig. For uniflow, loop, and 4-st naturally n
supercharged engines, how starting air is introduced in ME type engine(starting v/v is solenoid
controlled,no air distributer), is thr a drain line in starting air line (yes, at lowest point in the
pipe), starting difficulties,what starting arrangement on A/E, why not air kick started,
ANS. In cases where the starting air supply has to be cut off to some cylinders, starting in all
crankshaft positions cannot always be expected. If the engine does not turn on starting air in a certain
crankshaft position, it must immediately be
started for a short period in the opposite
direction, after
which reversal is to be
made to the required direction of rotation. Should this not give the desired
result, it will be necessary to turn the engine to a better starting position, by means of the turning
gear. Remember to cut off the starting air before turning, and to open the indicator cocks.
For checking- close master v/v, engage turning gear, open indicator cock, bring that piston to tdc,
open master v/v, if air coming from indicator cock that means leaking.
When an engine is in operation leakage of starting air valves is shown by overheating of the branch pipe connecting the starting air valve to the starting air rail. The heating occurs due to the leakage of hot gases from the engine cylinder into the starting air line connected to the starting air rail. During periods of manoeuvring the temperature of each supply pipe from the air rail to the starting air valve should be checked by feeling the pipe as close to the valve as possible.WHAT SHOULD I DO IF AN AIR START VALVE JAMS OPEN WHILST MANOEUVRING?
The fuel pump should be lifted (fuel rack zeroed, puncture valve operated or whatever) on the affected unit and the bridge informed. The load should be kept at a minimum, as one unit is now out of operation. As soon as safe to do so, the engine should be stopped and the air start valve replaced.
ANS. BODY REQUIREMENTS FOR A REVERSIBLE ENGINE
The main propulsion machinery is to be capable of maintaining in free route astern at least70% of the
ahead MCR revolutions for a period of at least 30 minutes.
The reversing characteristics of the propulsion plant are to be recorded during trails.
The power developed in astern direction should be 60 %of ahead.
SOLAS Requirements: Chapter Two (Reg. 28 & 03)
1. Sufficient power for going astern shall be provided to enable proper control of the ship in all circumstances.
2. Machinery should be able to reverse the direction of thrust of the propeller to bring the ship to rest from
maximum ahead service speed in sufficient time and reasonable distance. This shall be shown and
recorded.
11. Crash-Stop
(FPP-Plants and Reversible CPP-Plants)
The procedure is valid for:
!
Control Room Control. See Items 8.2, 9.2 and 10.2.
!
Control from Engine Side. See Items 8.4, 9.2 and 10.4.
Regarding crash-stop during Bridge Control,see the special instruction book for the Bridge Control System.
1. Acknowledge the telegraph.
2. Give the engine a
STOPorder.
The engine will continue to rotate (at slowly decreasing speed), because the velocity of the ship through the
water will drive the propeller, and thereby turn the engine.
3. Check that the limiters in the governor are not cancelled.
4. When the engine speed has fallen to the
REVERSING-
LEVEL(15-30% of MCR-speed, depending on engine
size and type of ship,
see Plate 70305):
!
Give
REVERSINGorder.
!
Give
STARTorder.
5. When the
START-
LEVELis reached in the opposite direction of rotation (8-12% of MCR-speed)
!
Give order to run on fuel.
CRANKCASE EXPLOSION, SCAVENGE FIRE, EGB FIRE
CRANKCASE EXPLOSION
-Safeties provided in crankcase, regulations, at what
pressure crankcase door lifts, how many doors, total area of escape in relief door, how do
u test the v/v, OMD alarm , what will u do ? How to check it’s false alarm, What are
different types of oil mist detectors and where are they used and why? How oil mist
formed in crankcase and what safeties provided and maintenance on them? Do all
crankcase doors in A/E have relief v/v? What to conclude if fitted in alternative doors or
only in fwd n aft? Why no crankcase relief v/v in air compressor and reefer compressor.
SCAVENGE FIRE
-reasons(give at least 6), indications, action to be taken when passage
through a narrow seaway, what if major fire takes place, what extinguishing arrangements
is there, how to use that?
WHAT PRECAUTIONS WHEN ENGINE IS RUNNING on less number of
units?
ANS. MANUAL 704.
Cyl. Oil properties( oilyness is imp.)? After how many cycle alfa lubricator injects fuel?( every 4th cycle)
Why exhaust gas temp. is less at exhaust v/v(320*c) but more at entry to turbine(380*c)??pressure of exhaust gas after turbocharger(0.3 bar).
Ans. Its bcoz of intermolecular collision. Also at nozzle the pressure decreses which increases the velocity. Now PV=NRT. As p decreses, t decreses.
Can you change the fuel injection timing or stop the fuel flow in one of the 3 injectors in a single unit in RT-flex.
Yes, we can stop the fuel through any one injectors at a time. WECS can give signal to any one of the rail valve separately and hence
the particular injection control valve will operate and the particular fuel injector will inject the fuel. This improves the injection pressure at low rpm and loads and hence improve combustion.
Main brg, x-head brg seizure…action?
How to know that there's an instrumental error from the crankweb deflection readings or we have
not taken reading correctly?
to know dat error... We add p+s reading nd f+a reading..nd diff shuldn't vary much...if it vry much den may
be dere s problem in gauge... or we have not taken reading correctly, also the reading on both sides around
bdc shud come zero.
6. How to cut off a fuel pump? Why not cut off by closing fuel inlet valve to that
cylinder? ANS. MANUAL 704 AND VOL 2,909-16.
Q. water cooled piston vs. oil cooled piston adv & disadv. & why oil cooled piston were not used earlier if they
r have so many advantages? Bore cooling? advan.?
ANS. Water- advan- specific heat more than oil so less amount of water is needed, easily available n cheap,
we can keep water temp. as high as 90*C so temp. diff is low whereas in case of oil upper temp. Limit is 65*C
to prevent oxidation.
Disadvan- chances of mixing with crankcase oil, need separate system with p/p etc.
Bore cooling-advan- max. temp at piston surface can be reduced to 400*C from 500*C as in case of cage type
cooling, problems with castings of internal ribs r not thr.in bore system cooling takes place by jet n shaker
effect.
Q. A/E cyl. head has been removed. What all checks to be carried out? what on piston?
ANS. Cracks, distortion, corrosion, cooling water side corrosion n scale etc.
Q.after taking liner calibration f-a readings are more and p-s readings are less.... What is this
phenomenon... And y does it happen?
ANS. Trim is more, ship is moving too much in ballast condition.
Q. How to take cylinder liner calibration for M/E n A/E(both have same method)?consquences
of operating with worn liner? how to calibrate template?
max. wear(0.7% of cyl.
bore
).honing(gulia244)?running in(
done for matching to reduce adhesive wear
)(r.sen41)?liner
material(gulia p249), antipolising ring(material is steel, r.sen70)?
Q. is crankshaft able to move axially ,if it does what prevents it, how is thrust taken;full
description? What is axial and torsion vibrations how they are reduced in engine? Moment
compensator everything?
ANS
.Axial Damper: The Axial damper is fitted on the crankshaft of the engine to dampen the
shaft generated axial vibration i.e. oscillation of the shaft in forward and aft directions, parallel to the
shaft horizontal line.
It consists of a damping flange integrated to the crankshaft and placed near the last main bearing
girder, inside a cylindrical casing. The casing is filled with system oil on both side of flanges supplied
via small orifice. This oil provides the damping effect.
When the crankshaft vibrates axially, the oil in the sides of damping flange circulates inside the
casing through a throttling valve provided from one side of the flange to the other, which gives a
damping effect.(see r.sen 13.10)
Q .How was your engine piston cooling …line diagram, temp. and pressure, how is the
telescopic pipe arrangement…how will make sure proper cooling .. a very important alarm
on it? Explain crosshead lubrication. What modification ..(SEE 904,708,r.sen26)Why oil is
supplied to shoes, not guide in xhead lubrication?bore relief? tangential
runout?clearance(
m/b 0.4-0.6,crankpin0.2-0.4,crshd0.2-0.3
? Main engine's main bearing
clearance. BOTTOM END BEARING CLEARANCE?
ANS. it will make the system complex bcoz then we will have to make quills like
arrangement at many points. Also we have to make lub. Oil enter crosshead at last so
supplying to shoes is better.
Q.excessive liner lubrication in main engine? EFFECTS? desired properties of cylinder lube
oil(oilyness,viscosity, tbn, viscosity index)? Where r quill. If at bottom what happen, why
thr(p152 r.sen)how lub oil spreads on cylinder....what is clover leafing?
3. Types of indicator cards, purpose if each, draw all diagrams on single ordinate and abscissa with
timing diagram for 2 stroke engine, which diagram suggests error in ir indicator instrument, how to
take atmospheric line, what is 90 deg in phase and 90 deg out of phase, draw power card and draw
card at a situation when you are taking card and engine tripped
on
some mechanical trip? what will
be the maximum
pressure you vil get then..? What is mean effective pressure..how to find
out mip?why we do not use indicator instrument for A/E(see sanyal p309?
Why draw card is called 90 degree out of phase?
In books it is written that ... draw card is taken with indicator drum 90 degree out of phase
with the piston stroke, so it is called out of phase diagram..
My DOUBT...while taking draw card the indicator drum is rotated manually with the help of
string attached to it.So if the rotation of the indicator drum is controlled by us,then how come
it is said to be exactly 90 degree out of phase.
this is purely on experience...nothing else....people took draw cards on experience and after so
many trail and error practices nothing else...
Q
. why tappet clearance...what u check before tappet clearance(engine cold, n piston on
firing tdc).... procedure... what is tappet clearance, what is its effect if increased or
decreased? adjustment, tappet on my generators(0.4 in inlet n 0.9 on exhaust), how will u
remove exhaust valve of generator. Tappet adjustment in engine having two inlet and
exhaust v/vs(first balance yoke then adjust tappet)? what checks you will make on inlet and
exh v/vs springs during overhaul(check length,twist). how they held in position?
Q.
what is viscosity? Types? Viscosity index? SFOC and hw to calculate? cetane no,what if
less?
Fire point, ignition point, flash point, pour point,oiliness?
Fuel knock and how u
know it(by Fluctuation in rpm, after burn(spark from the funnel, smoke from exhaust). ignition
delay.def.wt governs it?hw it can b minimised?what property of fuel oil is responsible for it?
Q. expansion tank purpose (give six)..why we call it expansion tank? It is also called
compensation tank.
ANS.1. SINCE IT IS SITUATED AT HIGHEST POINT IT MAINTAINS
CONSTANT HEAD
ON THE SYSTEM AND SO
REDUCE
CHANCES OF
AIR INGRESS OR STEAM FORMATION
. 2.ALLOW FOR
EXPANSION. And place for adding
chemical
for treatment.
3.PROVIDE A PLACE FOR ADDING
MAKE UP FEED
,BCOZ OF LEAKAGE AND
EVAPORATION.
1.T/C lubrication(manual708)?what is surging....and hw it occur? and what will u do if
continuous surging takes place? outboard bearing inboard bearing? From main lub oil
system? In case M/E z stopped ….what provision z provided for its lubrication? T/C MAKE
(met type)water n dry washing (see r.sen,tur. Side dry 24-48 hrs n wet every week) kab karte
h. running indications dat it cleaned? pressure of exhaust gas after T/C(
0-350mmWC).function
of inducer(guide air smoothly to centre of impeller) and impeller(p181r.sen). P-V diagram of
impeller.,inducer, diffuser, locking of t/c, blade fixing.
Q. Butt clearance will increase or decrease after 8000 hrs? What about stuffing gland rings?
ANS. Butt clearance of piston ring (intial 0.5-1% cyl. Bore)will increase and those of stuffing
box rings( 3 and 4 mm) will decrease with time. When butt clearance of stuffing gland
becomes zero then we change the ring.
Q. Uniflow scavenging, name other 2, which 1 is better and why, which 1 has more power
stroke and why?
ANS.LOOP FLOW and cross flow. Uniflow is better because there is less intermixing of
scavenge air and exhaust gas.BecOz there is no change in the direction of scavenge air in the
cylinder.and when cyl. Length is more than loop n cross scavenging becomes difficult. Uniflow
has more power stroke bcoz of better scavange efficiency and use of super long stroke.
Q. why is a balance weight fitted ? why not in main engine?
ANS. balance weight r fitted only in a/e bcoz during exhaust stroke piston tries to fly out n also
to reduce 1
storder moment. In m/e 1
storder moment r compensated by providing idle gear in
chain drive arrangement.2
ndorder moment is also compensated by providing a smaller idle gear
which rotate at double the engine rpm and is fitted at chain drive.
Q. what is difference between valve rotocap and spinner and why rotocap on A/E and spinners on M/E, what is
the driving force in both of them..Maintenance and parts of valve rotocap..?no. of cotter and why only
those no. of pieces, purpose of cotter??
ANS.SPINNER ARE JUST VANES,NORMALLLY 6-8 IN NUMBER. M/E EXHAUST V/V IS BIG.AMOUNT OF
EXHAUST IS MUCH MORE SO IT CAN ROTATE THE V/V.BUT IN A/E AMOUNT OF EXHAUST IS LESS SO IT IS
NOT POSSIBLE TO ROTATE SPINNER BY EXHAUST IN A/E SO WE USE ROTOCAP. Cotter is In a/e, it holds
the exhaust v/v spindle, its in 2 pieces held in place by a cir-clip.
Q. why 2stroke engines for propulsion and 4stroke engines for power generation..?CAN WE PUT PROPELLER
IN FWD OF SHIP (propeller efficiency will increase but hull efficiency will decrease)?
ANS. M/E SHUD BE SLOW SPEED ENGINE FOR BETTER HULL EFFICIENCY. N 2ST engine are more efficient at
slow rpm. At high rpm scavenging becomes difficult. GIVE LONG STROKE CONCEPT, TWO ST. MORE POWER
PRODUCED.
Q.LO tests ( all five with name and how pensky martin test carried out ).
83. with respect to A/E Piston what is the name of the top most piston ring? How will one identify which piston ring goes in which groove if the rings get intermixed????
