Function of Thermostatic Expansion Valve in refrigeration system, Internal and external equalizing valve types with explanation and diagram.

Thermostatic expansion valve is a throttling device used for flow control of refrigerant in the refrigeration system. Throttling is done to reduce the boiling point of the liquid from the condenser. this is achieved by reducing the presure of the refrigerant as it is metered through the small orifice of the throttling device. As the pressure reduces, the boiling temperature of the refrigerant also reduces.

So the main functions of a TEV is to
- To meter the liquid refrigerant from liquid into the evaporator at a rate suitable to maintain the designed operating pressure at different load condition.
- To mainatain the difference of pressure between high and low pressure side of the refrigerant.
- to amintain a constant degree of superheat at the outlet of evaporator.

Systems using thermostatic expansion valves use basically one of two types of valves: internally equalized and externally equalized.  The two types of expansion valves are similar, but not interchangeable, both types of expansion valves are Installed in the system to lower the pressure before the refrigerant enters the evaporator.  The reduction in pressure is accomplished simply by passing the refrigerant through a small hole (orifice), but the opening and closing of the orifice must be controlled to compensate for changes in pressure and temperature, the temperature of refrigerant leaving the evaporator is sensed by a thermal bulb and capillary tube which moves the valve seat via a diaphragm and actuating pins.  Internally equalized expansion valves permit refrigerant pressure from the outlet side of the orifice to pass through an internal passage and push against the underside of the diaphragm.Externally equalized expansion valves have a line connected to the outlet side of the evaporator and refrigerant pressure passes through this line to push against the underside of the diaphragm

Internal Equalizing TEV

External Equalizing TEV

Three forces which govern the thermal expansion valve’s operation are
1) The power element and remote bulb pressure (P1)
2) the evaporator pressure (P2), and
3) the superheat spring equivalent pressure (P3).

We will deal with both types of TEV, 1) Internally equalized TEV 2) Externally Equalized TEV

1) Internal Equalized Expansion Valve
(Eventhough R12 is banned as per the montreal protocal, we have used R12 refigerant for the purpose of calculation)
Three conditions present themselves in the operation of this valve: first, the balanced forces; second, an increase in superheat; third, a decrease in superheat.  The remote bulb and the power element make up a closed system (power assembly), and in the following discussion, it is assumed that the remote bulb and power element are charged with the same refrigerant as that in the system.  The remote bulb and Power element pressure which corresponds to the saturation pressure of the refrigerant gas temperature leaving the evaporator, moves the valve pin in the opening direction.

Opposed to this opening force on the underneath side of the diaphragm and acting in the closing direction are two forces: (1) the force exerted by the evaporator pressure and (2) that exerted by the superheat spring.  In the first condition, the valve will assume a stable control position when these three Forces are in balance (that is, when P1 = P2 + P3).  In the next step, the temperature of the refrigerant gas at the evaporator outlet (remote bulb location) increases above the saturation temperature corresponding to the evaporator pressure as it becomes superheated.  The pressure thus generated in the remote bulb, due to this higher temperature, Increases above the combined pressures of the evaporator pressure and the superheat spring (P1 greater than P2 + P3) And causes the valve pin to move in an opening direction.  Conversely, as the temperature of the refrigerant gas leaving the evaporator decreases, the pressure in the remote bulb and Power assembly also decreases and the combine evaporator and Spring pressure cause the valve pin to move in a closing Direction (P1 less than P2 + P3).

For example, when the evaporator is operating with R12 at a Temperature of 40EF or a pressure of 37 Psig and the refrigerant gas leaving the evaporator at the remote bulb Location is 50EF a condition of 10EF superheat exists.

Since the remote bulb and power assembly are charged with the same refrigerant as that used in the system (R12), its Pressure (P1) will follow its saturation pressure temperature characteristics.  With the liquid in the remote bulb at 50ºF the pressure inside the remote bulb and power assembly will be 46.7 Psig acting in an opening direction.

Beneath the diaphragm and action a closing direction is the evaporator pressure (P2) of 37 Psig and the spring pressure (P3) for a 10EF superheat setting of 9.7 Psig (37 + 9.7 = 46.7) making A total of 46.7 Psig.  The valve is in balance, 46.7 Psig Above the diaphragm and 46.7 Psig below the diaphragm. changes in load, increasing the superheat, will cause the thermal expansion valve pin to move in an opening direction.  Conversely, a change, decreasing the superheat, will cause the thermal valve pin to move in a closing direction.

2)External Equalized Expansion Valve
When the pressure drop through the evaporator is of any consequence, i.e., in general a pressure drop equivalent to 3 degrees in the air-conditioning range, 2 degrees in the commercial temperature range, and 1 degree in the low temperature range, it will hold the thermal expansion valve in a relatively "restricted" position and reduce the system capacity, unless a thermal expansion valve with an external equalizer is used.  The evaporator should be selected for the operating conditions and the thermal expansion valve selected and applied accordingly.

For example, an evaporator is fed by a thermal expansion valve with an internal equalizer, where a sizeable pressure drop of 10 Psig is present. The pressure at point "c" is 27 Psig or 10 Psig lower than at the valve outlet, point "a"; however, the pressure of 37 Psig at point "a" is the pressure acting on the lower side of the diaphragm in a closing Direction.  With the valve spring set at a compression equivalent to 10EF superheat or a pressure of 9.7 Psig, the required pressure above the diaphragm to equalize the forces is (37 + 9.7) or 46.7 Psig.  This pressure corresponds to a saturation temperature of 50EF.  It is evident that the refrigerant temperature at point "c" must be 50EF if the valve is to be in equilibrium.  Since the pressure at this point is only 27 Psig and the corresponding saturation temperature is 28EF a superheat of 50EF - 28EF or 22 Degrees is required to open the valve.  This increase in superheat, from 10 to 22 degrees make it necessary to use more of the evaporator surface to produce this higher superheated refrigerant gas.  Therefore, the amount of evaporator surface available for absorption of latent heat of vaporization of the refrigerant is reduced; the evaporator is starved before the required superheat is reached.  Since the pressure drop across the evaporator, which caused this high superheat condition, increases with the load because of friction, this "restriction" or "starving" effect is increased when the demand on the thermal valve capacity is greatest.

In order to compensate for an excessive pressure drop through an evaporator, the thermal expansion valve must be of the external equalizer type, with the equalizer line connected either into the evaporator at a point beyond the greatest pressure drop or into the suction line at a point on the compressor side of the remote bulb location.

In general and as a rule of thumb, the equalizer line should be connected to the suction line at the evaporator outlet.  If the external equalizer type of thermal expansion valve is used, with the equalizer line connected to the suction line, the true evaporator outlet pressure is exerted beneath the thermal valve diaphragm, the operating pressures on the valve diaphragm are now free from any effect of the pressure drop through the evaporator, and the thermal valve will respond to the superheat of the refrigerant gas leaving the evaporator.

When the same conditions of pressure drop exists in a system with a thermal expansion valve which has the external equalizer feature, the same pressure drop still exists through the evaporator; however, the pressure under the diaphragm is now the same as the pressure at the end of the evaporator, point "c", or 27 Psig.

The required pressure above the diaphragm for equilibrium is 27 + 9.7 or 36 Psig.  This pressure, 36.7 Psig, corresponds to a saturation temperature of 40EF and the superheat required is now (40EF - 28EF) 12 degrees.  The use of an external equalizer has reduced the superheat from 22 to 12 degrees.  Thus, the capacity of a system, having an evaporator with a sizable pressure drop, will be increased by the use of a thermal expansion valve with the external equalizer as compared to the use of an internally equalized valve.  As pointed out Earlier the external equalizer line must be installed beyond the point of greatest pressure drop.

So external equalizing line is used when there is a marginal pressure drop inside the evaporator, so we can avoid starvation of refrigerant

How Bulbous bow increases the efficiency of a ship and what are its major functions and advantages?

Bulbous bow reduces the Hull wave making resistance of a ship, which is the major residuary frictional resistance of a ship. It reduces the bow wave, due to the wave generated by the bulb itself, making the ship more efficient in terms of energy. Here Blue and Green lines shows the wave generated by the bulbous bow of the ship and stem of the ship respectively. The Red line shows the resultant wave, which is reduced in amplitude due to the interference of one on other. Thus the hull wave making resistance is reduced. So more efficient and lesser fuel oil consumption.

So the major functions and advantages of a bulbous bow ships are

• Reduces the bow wave, due to the wave generated by the bulb itself, making the ship more efficient in terms of energy
• Increases the ship’s waterline length, slightly increasing the ship speed, reducing the installed power requirements and so the fuel oil consumption
• Works as a robust “bumper" in the event of a collision
• Allows the installation of the bow thrusters at a foremost position, making it more efficient
• Allows a larger reserve of flotation 
• A larger ballast capacity of fore peak tank
• Extra protection for panting and pounding

Ship's different movements in sea - explanation with diagram - Surging, Swaying, Heaving, Rolling, Pitching and Yawing -

Here is the answer for the question ' What are the different types of movements or motions of ship at sea?'

Ship has 6 motions at sea- 3 linear motions and 3 angular or rotational motions

Linear motion Rotational motion

Surging is motion along the longitudinal axis. 

Rolling is motion around the longitudinal axis.

Swaying is motion along the transverse axis

Rotational Motions

Pitching is motion around the transverse axis.

Heaving is motion along the vertical axis.

Yawing is motion around the vertical axis.

Function of PV Breaker (Pressure Vacuum Breaker) in Inert Gas (IG system) line onboard ship

Pressure Vacuum Breaker or usually known as PV Breaker is a safety measure used in the IG line on deck. The major functions of a PV breaker are

1) Abnormal rise of Pressure in Cargo tanks when loaded specified rate of gas outlets
2) Abnormal rise of Pressure in Cargo tanks when cargo is unloaded beyond specified rate of the inert gas blower
3) Abnormal rise or drop of pressure in cargo tanks when the breather valve doesnot operate properly for the fluctuation of the pressure in cargo tanks due to variation in atmospheric and sea water temperatures

Operation

1) When Pressure Rises
When the pressure in the cargo oil tanks rise, the seal liquid rises in the inner pipe. At this time , if the pressure beyond the specific capacity of the breaker, the seal liquid will push out of the pipe to let the pressure inside the be out

2) When Pressure drops
When the pressure in the cargo oil tanks fall, the seal liquid rises in the outer pipe. If the pressure beyond the specific capacity of the breaker, the seal liquid is drown into the cargo oil tanks, and atmospheric air will be inhaled in the tank

Set 1 - MEK Motor important questions from E Pariksha online exam for MEO class 4 exam

1. When fuel is injected late into a diesel engine cylinder,
choose one the exhaust will be clear fuel consumption will be low all the fuel will be burned at top dead center fuel consumption will be high

2. As a thumb rule, ovality in crankpins of medium speed engines should not exceed _____________ of bearing clearance.
choose one 10% 15% 25% 30%

3. On small diesel engines, a noticeable decrease in the time interval between the replacement of the lube filter cartridge indicates –
choose one piston ring blow-by dirty air filter excessive oil pressure excessive oil temperature

4. Modern marine turbochargers use a ___________ type of compressor
choose one Radial flow Axial flow Mixed flow Turbulent flow

5. During inspection of the crank bearing for one of the units in the main engine, the bearing shell was found as follows: Surface of the white metal was black and very hard. Patches of black incrustations have worn grooves in the journal. What was the cause?
choose one Dirt in the lubricating oil Wrong casting of bearing shell Water in the lubricating oil during service Bearing shell service time exceeded

6. A large change in ambient temperature, or using an oil of a viscosity different than the one recommended by the manufacturer in a mechanical hydraulic governor, will result in the need to adjust the
choose one pilot valve opening compensating needle valve Droop oil pressure

7. Fuel oil penetration into the cylinder of a diesel engine is
choose one dependent on air turbulence reduced by finer atomization increased by finer atomization non-existent in the precombustion chamber system

8. An individual injection pump is designed for variable beginning and constant ending of injection. For diesel engines operating at constant speeds, the start of injection will
choose one advance as the load increases retard as the load increases remain unchanged regardless of load always occur at top dead center

9. The amount of fuel injected in a particular time, or degree, of crankshaft rotation is termed
choose one metering timing rate of injection rate of distribution

10. In a diesel engine, late fuel injection is indicated by black or gray exhaust smoke with ______________.
choose one low firing pressure low exhaust temperature mechanical knock in each cylinder fuel knock in each cylinder

Score =
Correct answers:

Set 26 - MEK Motor multiple choice online exam questions

1. What ensures correction axial location of a thin shell bearing in its housing, for correct alignment of the oil holes ?
choose one The nip or crush of the bearing Location tangs or pegs Dowels or keys None of the above

2. Economisers are built up with
choose one Copper tubes Plain steel tubes Stainless steel tubes Steel tubes fitted with shrunk on C.I. grills

3. Constant pressure turbocharging is ______________ efficient compared to that of pulse pressure turbocharging .
choose one Equally Less Slightly More Very highly

4. Only a pre determined fixed amount of water should be used during:
choose one Water washing of the turbine side of a turbocharger Water washing of the blower side of a turbocharger Water washing of both blower and turbine sides of a turbocharger. Exhaust gas boiler water washing

5. A non water-cooled turbocharger offers which of the following advantages?
choose one More heat is available for waste heat boilers Corrosion problems of internal surfaces due to formation of sulfuric acid are eliminated Improved thermal efficiency of turbocharger All of the above

6. Post Nox emission test bed trial and approval of an engine, periodic Nox emission limit verification is normally done by:
choose one Emission tests at regular intervals Engine parameters/settings check method By running the engine at full load and sending a sample of exhaust gas for analysis None of the above

7. An auxiliary engine under load continuously fluctuates even with a steady load. The fault you diagnose could be owing to
choose one the quality of fuel the quality of servicing of the governor in the last port. the supply of charge air the overhaul of fuel injectors done in the last decarbonisation

8. Which of the following factors affect penetration of fuel droplets during injection?
choose one Quality of atomization Injection temperature Scavenge air pressure All the above

9. Which of the following is the primary advantage of supercharging the air quantity in a diesel engine, by means of a turbocharger?
choose one It leads to considerable gain in thermal efficiency. It increases the maximum pressure generated in a cylinder appreciably. It improves the power to weight ratio of the engine All of the above.

10. The maximum amount of liner wear occurs at—
choose one top of liner 1/ 3 downward from top centre midway bottom of liner

Score =
Correct answers:

Set 25 - Motor E-Pareeksha unsolved questions

Share your knowledge to help your friends. Here are some important questions to which candidates have many answers. So if you have the answer with any reference, please help others by giving the answers in the comment box below. It will be helpful for others.

 1) The main requirements which a fuel injection system must fulfil are
a) accurate metering of small amount of fuel oil.
b) control of quality of fuel injection
c) proper timing of the fuel injection
d) selective distribution of the fuel in the combustion space.

 2) Which of the following layers of a thin shell bearing gives it its fatigue strength?
A.The overlay
B.The interlay
C.The backing
D.The barrier layer

 3) Prompt correction of speed of diesel engines driving alternators, without having massive fluctuations is ensured by incorporating:
A.Load limiting devices
B.Load sharing devices
C.Load sensing devices
D.Load shedding devices

 4) The use of ball and roller bearings in internal combustion engines is becoming more and more popular for some or all of the following
(a) The low coefficient of friction
(b) The absence of wear under favorable conditions
(c) The independence in lubrication
(d) The extreme reliability of such bearings

 5) An auxiliary engine turbo-charger makes strange noises when the load changes. The engine parameters however are absolutely fine. An external examination of turbocharger parameters as stated in the manual also reveals nothing. Would you
a) continue to run the engine and wait for some time
b) stop the engine for a while and make some checks
c) reduce the load of the engine
d) run it on steady load to make some checks.

 6) In modern marine 2-stroke diesel engines, ________________ is sometimes used as a coating on the underside of the exhaust valve disc, to reduce the rate of hot corrosion.
A.Monel
B.Chromium
C.Inconel
D.Cermet

 7) Which of the following types of damages are metal seatings of a valve subject to?Choose the correct alternative.
A. Corrosion, Erosion, Abrasion, Deformation
B. Corrosion, Fatigue failure, brittle fracture, caustic cracking
C. Erosion, caustic cracking, brittle fracture, Cloverleafing
D. None of the above

 8) Which of the following is one of the disadvantages of cast iron chokes, used in holding down arrangement of engines?
A. Poor compressive strength
B. Poor vibration damping
C. Cast iron is brittle and prone to crack
D. All of the above

Set 24 - Motor important questions and answers for class 4 exam in India

1. An advantage of aluminium pistons compared to cast iron pistons is:
choose one greater high temperature strength better heat conductivity greater weight per cubic cm increased resistance to wear

2. Which engine component increases air density and helps to improve engine operating efficiency
choose one impeller compressor aftercooler exhaust diffuser

3. An electric heater built into the cylinder water jacket would be used to
choose one raise lube oil viscosity for easier starting in cold weather increase air inlet temperature increase compression ratio increase water temperature for easier starting in cold weather

4. Which is found with both mechanical and hydraulic governors?
choose one direct linkage between the ball head and fuel rack a servomotor a compensating device flyweights

5. Which of the following design features will reduce the possibility of overheating the top compression rings of a cast iron piston?
choose one The top ring is located as close to the piston as possible The inside surface of the piston head is rounded into the ring belt A nickel-bearing insert is cast into the top ring groove A heat dam design is sometimes used in the piston head

6. The purpose of heat dam used in some diesel engine cast iron pistons is to a)concentrate all heat in the piston crown
choose one increase the distance of travel for heat from the crown to the top ring groove concentrate all heat in the piston crown ensure that all heat in the piston crowns is conducted to the top ring )provide a short direct path for heat to flow from the crown to the top ring

7. Valves used in diesel engine fuel oil pressure piping are to be
choose one installed to close against flow solenoid released upon the failure of engine lubrication either of the gate or globe valve type forge constructed under the approval of the Marine Inspector

8. Cast iron pistons used in large propulsion engines are constructed with
choose one no taper whatsoever the skirt being tapered and smaller than the crown the skirt being tapered and larger than the crown the crown being tapered and smaller than the skirt

9. The diameter of a piston is usually less at the crown than at the skirt, in order to
choose one facilitate the installation of piston rings allow for the expansion of the piston during operation prevent crankcase vapors from entering the combustion chamber reduce wearing of the upper cylinder liner

10. Which of the following manufacturing methods is recommended for diesel engine fuel injection line piping?
choose one Cold rolled Electric resistance welded Seamless drawn Straight seam

Score =
Correct answers:

Set 23 - Class 4 motor paper previous asked important questions

1.The purpose of a temperature sensing device installed in the stack of a small automatically fired auxiliary steam boiler is to secure the oil burner _______________.  

A.        in the event of a flame failure                        

B.         in the event of a stack fire                              

C.         when the water level reaches the crown sheet 

D.        when the feed pump discharge pressure drops to a preset minimum                                                      ANS – A

2.         In a diesel engine, late fuel injection is indicated by black or gray exhaust smoke with ______________.   

(a)        low firing pressure                                          

(b)        low exhaust temperature                                 

(c)        mechanical knock in each cylinder                 

(d)        fuel knock in each cylinder

ANS – A

3.         Which of the following actions takes place in the control circuit of an automatically fired auxiliary boiler when the desired steam pressure is obtained?                      

(a)        A temperature sensing device opens the circuit breaker in the burner motor. 

(b)        The high limit control secures power to the entire oil firing system.               

(c)        The stack relay actuates the low limit control which breaks the ignition circuit.         

(d)        The stack relay secures power to the high voltage side of the ignition transformer.

ANS B

4 An auxiliary engine under load continuously fluctuates even with a steady load. The fault you diagnose could be owing to

(a)        the quality of fuel

(b)        the quality of servicing of the governor in the last port.

(c)        the supply of charge air

(d)        the overhaul of fuel injectors done in the last decarbonisation

ANS A

5 Which of the following actions takes place in the control circuit of an automatically fired auxiliary boiler when the desired steam pressure is obtained?                

(a)        A temperature sensing device opens the circuit breaker in the burner motor.             

(b)        The high limit control secures power to the entire oil   firing system.                                     

(c)        The stack relay actuates the low limit control which breaks the ignition circuit.                                 

(d)        The stack relay secures power to the high voltage side of the ignition transformer.                

ANS B

6.         A diesel engine should not be operated at low loads for long  periods of time because _____________.

(a)        heavy carbon deposits will buildup on the valves and in the exhaust 

(b)        fuel dilution is increased at low load              

(c)        exhaust valves may be damaged                     

(d)        all of the above                                               

ANS D

7.         The major cause of fuel pump and injection system problems is _____________.    

(a)        improper adjustments                         

(b)        contaminated fuel                                           

(c)        kinked fuel lines                                             

(d)        excessive engine vibration                              

Briefly Justify Your Answer

ANS B

8.         A dirty fuel oil filter element can be detected by ________.

(a)        visual inspection of the element                                 

(b)        the pressure drop across the filter                   

(c)        high fuel oil tank temperature                         

(d)        increase flow rate from the filter                                

ANS B

9.         In a two-stroke/cycle diesel engine, the process of scavenging begins as the ________.                    

(a)        piston nears and passes TDC                          

(b)        early part of the upstroke                                

(c)        piston passes BDC                                          

(d)        early part of the downstroke                           

ANS B

 10)   A large, low-speed, main propulsion diesel engine uses sea water to directly cool the

a)cylinder heads

b)exhaust valves

c)scavenging air

d)injectors

ANS- C

Set 22 - MEK Motor multiple choice questions of MEO class 4 exam

1. In case of 2-stroke marine diesel engines, the top part of the liner forming the combustion chamber experiences very high pressure induced mechanical stresses as well as high thermal stresses. Which of the following is a correctly designed liner for catering both the above stresses ? \

A. Thick top portion with jacket cooling to take care of both the high mechanical and thermal stresses

B. Thick top portion to take care of high mechanical stresses while bore cooling to reduce thermal gradients

C.Thin top portion to reduce thermal gradients and hence thermal stresses while supporting ribs to take care of mechanical stresses

D. Thick top portion to take care of high mechanical stresses with jacket cooling combined with allowance for thermal expansion to minimize the thermal stresses

ANS B

2 In a direct connected or geared main propulsion diesel engine would be fitted with a:

A. Isochronous hunting governor

B. Rotating governor disc

C. Variable speed govener

D. Constant frequency governor

ANS C

3) The light and medium fuels utilized in internal combustion engines provide a source of

a)lubrication for pistons and rings

b)food for microbiological organisms

c)gases most detrimental to the ozone layer of the atmosphere

d)all of the above

ANS B

4. A very sudden rise in pressure during combustion accompanied by a metallic, hammer like sound is called knocking of the unit or detonation and usually occurs

a) Near the end of the pressure rise after ignition of fuel charge.

b) Just before the fuel charge is about to ignite.

c) Immediately after the unit reaches peak pressure and before ignition of fuel charge.

d) At any stage of the combustion process.

5) Which of the following functions is done by a cam operating an exhaust valve ?

A.It governs the timing of opening and closing of the valve .

B.It governs the speed at which the valve operates

C.It governs the amount of opening of the valve

D.All of the above

ANS  D

6. In modern marine 2-stroke diesel engines, ________________ is sometimes used as a coating on the underside of the exhaust valve disc, to reduce the rate of hot corrosion.

A.Monel

B.Chromium

C.Inconel

D.Cermet

7. when m/e is running in emergency condition which of the alarms can't be bypassed

1.LO low pressure

 2.jacket water high temp

3.piston cooling water high temp

4.all the above

ANS A

8 What to check if Engine is not taking load.?

a. Water tightness to be checked.

b. Air to be removed from jacket water outlet line.

c. Priming lube oil pump to run before starting the engine.

d. Check the lube oil level.

e. Check the flow of lube oil.

f. Blow through the engine before starting

9 An auxiliary engine turbo-charger makes strange noises when the load changes. The engine parameters however are absolutely fine. An external examination of turbocharger parameters as stated in the manual also reveals nothing. Would you

a) continue to run the engine and wait for some time

b) stop the engine for a while and make some checks

c) reduce the load of the engine

d) run it on steady load to make some checks.

ANS A OR C

10 The main requirements which a fuel injection system must fulfil are

a) accurate metering of small amount of fuel oil.

b) control of quality of fuel injection

c) proper timing of the fuel injection

d) selective distribution of the fuel in the combustion space.

Set 21 - E Pariksha MEK Motor previous asked questions

1) Which of the following statements is true?

A.The rotary vane type steering gear generally operates at higher oil pressures than the ram type .

B.The ram type steering gear generally operates at higher oil pressures than the rotary vane type .

C.Both ram type and rotary vane type steering gears generally operate at similar oil pressures

D.None of the above

ANS- B

2) Modern marine turbochargers use a ___________ type of compressor

A.Radial flow

B.Axial flow

C.Mixed flow

D.Turbulent flow

ANS- A

3) Which of the following is a disadvantage of water as cooling medium for pistons, when compared to oil?

A.Chemical treatment is required

B.Higher thermal stresses in piston

C.Piston of more complicated design

D.All of the above

ANS D

4) How is the concentration of dissolved oxygen in the feedwater of an auxiliary boiler maintained at acceptable limits?

A.Feedwater is cycled through a DC heater.

B.Feedwater is treated with phosphates.

C.Oxygen is liberated in the three-stages of feedwater preheating.

D.Oxygen is liberated by maintaining the highest practical feedwater temperature

ANS D

5) In a 2-stroke marine diesel engine if the o-ring for Jacket cooling water sealing is leaking then:

A.The water will leak directly into the crankcase

B.The water will leak into the underpiston space

C.The water will come out through tell-tale hole provided between the two o-rings

D.The water will come out from the top of cylinder jacket

ANS C

6) The lube oil pump used in a diesel engine is a

A.volute pump

B.centrifugal pump

C.diaphragm pump

D.gear pump

ANS D

7) Prior to lighting off a cold automatically fired auxiliary boiler, you should

A.check and regulate the water level

B.close the air cock once fires are lit

C.blowdown the gage glass

D.crack the steam stop to assure protective steam flow

ANS A

8) Steam temperature control for the ESD-II boiler is achieved by :

A.Fitting a de-superheater between 1st & 2nd passes of superheater

B.Fitting an attemperator between 1st & 2nd passes of superheate

C.Gas dampers in boiler uptake

D.Bypassing the superheater

ANS C

9) The ash content of a fuel oil is significant to the operating engineer because it

A. is an indication of the amount of noncombustible material present in the oil

B. indicates the quantity of energy released by burning a unit amount of the fuel

C. is useful for determining proper atomization temperatures

D. reflects the overall thermal efficiency of the fuel oil service system

ANS A

10.  Which of the following design features will reduce the possibility of overheating the top compression rings of a cast iron piston?

A. A nickel-bearing insert is cast into the top ring groove

B. A heat dam design is sometimes used in the piston head

C. The top ring is located as close to the piston rim as possible

D. The inside surface of the piston head is rounded into the ring bell

ANS B

Marine Engineering Knowledge (Motor) E Pariksha online exam questions and answers for MEO class 4 exam

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Set 20 MEK Motor

1. Use of Halon as fire extinguishing medium has been discontinued because________________
It is highly toxic
It is expensive
It has high Ozone depleting potential
It leads to acid rains

2. The purpose of an air cooler in a supercharging system is to
Reduce temperature of supercharged air in order to condense and remove maximum possible moisture from the air prior entry to the engine
Reduce the temperature of the supercharged air in order to increase the density & also to cool down below dew point to remove moisture from air prior entry to the engine
Cool supercharged air to increase its density such that the dew point is not reached to avoid entry of moisture into the engine
Cool supercharged air to increase it???s density and also to keep the peak temperature and exhaust gas temperature within limits

3. In order for microbiological growths to thrive in a fuel tank it is necessary for
high temperatures to exist
low temperatures to exist
small amounts of water to be present
large amounts of water to be present

4. In comparison to exhaust valves, intake valves of diesel engines may be fabricated from low-alloy steels because
the beveled edges of the intake valves provide forself-centering during seating
intake valves utilize stellite-coated valve seat insertswhich reduce wear
the volume of air passing through intake valves is less than the volume of air passing through exhaust valves
intake valves are less affected to the corrosive action of exhaust gases

5. Why is it essential to renew turbocharger bearings after a preset number of hours of running even if the bearings are in seemingly perfect condition?
Because they are prone to failure due to prolonged exposure to high temperature conditions.
Because they are subject to cyclic loading and are prone to failure due to metal fatigue.
It is not essential to renew if condition monitoring suggests perfect condition.
Lube oil contamination is bound to occur and affect the condition of the bearings.

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Set 19 MEO class 4 exam MEK Motor online questions

1. Irregular circumferential wear of liner due to diminishing neutralizing capacity of cylinder oil away from lubricating holes is known as:
choose one Micro seizure Scuffing Scoring Clover leafing

2. Which standards govern the specifications for supply of Residual Marine Fuels and Distillate Marine Fuels onboard merchant ships?
choose one ISO 3012:1999 ISO 3648:1996 ISO 8216-1:2010 ISO 8217:2010

3. Crank web deflection readings will give a positiveindication of
choose one worn main bearing journals torsional stress deformation slack thrust bearings bearing shells shim dimensions

4. ESD stands for which type of boiler
choose one External superheater D-type Emergency shutdown Boiler Extreme Superheat type External Superheat De-superheater type

5. Which of the following is an example of a solid bearing?
choose one Piston pin bushing Turbo-generator turbine bearing Spring bearing Thrust bearing

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Set 18 - E Pariksha MEK Motor MEO class 4 questions

1. The main function of tie rods in the construction of large, low speed diesel engines is to
stiffen the bedplate in way of the main bearings to increase the engine's longitudinal strength
accept most of the tensile loading that results from the firing forces developed during operation
mount the engine frame securely to the hull to prevent shaft coupling misalignment
connect the crosshead solidly to the piston rod

2. The fall in speed that occurs in a diesel engine equipped with governor, on increase of load is called:
Offset
Speed drop
Speed droop
Speed offset

3. What do you mean by surge limit of a turbocharger ?
Characteristic curve of a turbocharger
Portion of compressor characteristic curve which lies on the left side of the point of maximum pressure
A line joining all the points of maximum pressure on compressor characteristic curves , drawn at various speeds of operation
Maximum rpm limit of T/C above which surging will start

4. In case of 2-stroke marine diesel engines, the top part of the liner forming the combustion chamber experiences very high pressure induced mechanical stresses as well as high thermal stresses. Which of the following is a correctly designed liner for catering both the above stresses ?
Thick top portion with jacket cooling to take care of both the high mechanical and thermal stresses
Thick top portion to take care of high mechanical stresses while bore cooling to reduce thermal gradients
Thin top portion to reduce thermal gradients and hence thermal stresses while supporting ribs to take care of mechanical stresses
Thick top portion to take care of high mechanical stresses with jacket cooling combined with allowance for thermal expansion to minimize the thermal stresses

5. Which of the following is a reasonable statement about water washing of turbine side of a T/C ?
It leads to thermal shock and reduces the life of the T/C
It leads to thermal shock and not so effective as solid washing
If properly carried out keeping rpm , load ,temperature limits & other factors into account , it is quite safe and more effective than solid washing
It should never be carried out as most of the engine manufacturers recommend against the same

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Set 17 Marine engineering Knowledge (Motor) online MCQ questions with answers

1. It is a known fact that centrifugal pumps require priming for pumping liquids , as they cannot handle air and will lose suction due to air entry . But on the other hand T/Cs use centrifugal compressors for supercharging . Which of the following do you think makes a centrifugal compressors to pump air and behave differently than the centrifugal pumps?
choose one Presence of air cooler Presence of Labyrinth seal High speed of rotation , very fine internal clearences and large impeller diameters Difference in principle of operation

2. If an operating auxiliary boiler has a water pH reading of 7, you should
choose one bottom blow the boiler treat the water with caustic soda treat the water with chemical scavengers reduce the water alkalinity to recommended readings

3. Even if there is an oil mist concentration inside a crankcase, and there is also a hot spot, crankcase explosion will only take place when_________________
choose one The hot spot provides the ignition temperature for the oil mist concentration When the oil mist - air mixture is in the flammable range Both A and B None of the abov

4. Which of these fuel oil impurities can cause maximum abrasive damage?
choose one Weter Ash Catalytic Fines Sodium

5. Steam temperature control for the ESD boiler is achieved by :
choose one Fitting a de-superheater between 1st & 2nd passes of superheater Fitting an attemperator between 1st & 2nd passes of superheater Bypassing the superheater Gas dampers in boiler uptake

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