(a)
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As been depicted in the diagram when the flow comes below the valve lid, the fluid will lift the lid and pass but when the flow is in reverse direction the lid will sit on the seat and stop the flow.

On the other hand when the spindle is screwed down the lid will not open in any case. This is what is called SDNR and screw down lift valve.

b) Quick closing valves are fitted in Lube Oil and Fuel oil lines, generally at the tanks on the lines which take the suction from those tanks. It is used to cut-off the oil flow to those line in case of fire.

It could be mechanically or pneumatically activated and when activated it shuts the valve. The shutting of the valve is achieved by collapsing the bridge of the valve which has internal threads on which the treaded spindle of the valve move up and down.

Thus if this internal thread (fitted in the bridge of the valve) itself is brought down it will shut the valve even if it is in open condition.
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For reversing the Main engine first the engine has to be started in reverse firing order, this is achieved by the changing the cam direction in the mechanical pilot air distributor of the main engine, which is done by the engine's pneumatic system on receiving the appropriate Signal from Engine order telegraph operated from the ship's wheelhouse.

a) Three methods of reversing the main engine Aftyer the engine is started on air in reverse order as mentioned it can be run on fuel by following either of the three methods as following:-
1} Reversing the firing order of the fuel pump:- It means the sequence in which the fuel is injected to each unit of the Main engine is reversed by its cam drive (it could have a separate cam for each cylinder for reverse firing order or the cam has special heart shape which when rotates in reverse direction due to running of engine in reverse direction due to air will work for reverse firing order) or electrical signal(as in the modern electronic engines)
2} Reversing the Actuation of the exhaust valves:- In this method the actuation of the valve opening and closing is reversed, only. This method is old and can run the engine safely in reverse order for small RPMs only.
3} Reversing the Fuel pump and Exhaust valve actuation: This is the most commonly used system where above mentioned both methods are applied.

b) The lost motion is the turning of the cam by an angle with respect to the cam shaft (In this there is a small servomotor put inside the cam shaft which shifts the cam in its axis)so that when the cam shaft is rotating in the reverse direction the cams would be pushing the roller of the fuel pumps in different firing order or alternatively both the shapes are forward and reverse directions are combined together to create a heart shaped cam (as shown in the video below)
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a) Supercharging means, increasing the density of the air which is inhaled by the engine. This means more air is taken by the engine and thus more fuel can be burnt inside it, thus producing more power.

Supercharging can be achieved by putting a separate air compressor which could be electric motor driven or engine driven or it could be driven by any other primemover, which in most cases happen to be Turbine driven which runs by the kinetic energy of the Engine's exhaust gases and is called Turbocharger.

b) Turbo Charging means charging the compressed gas to the engine by an Exhaust gas turbine driven centrifugal compressor called Turbocharger.

c) 1.Fouling of the Air cooler:- Difference in the Temperature of cooling water inlet and outlet of the Air cooler, will reduce indicating the fouling of the Air-cooler.

2. Fouling of air intake filters This will indicated by the fouling of the differential pressure manometer fitted across the Air intake filters of the turbocharger.
It will also be indicated by decrease in the scavenge pressure at any particular RPM of the ME and increase in the Exhaust temperatures.
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1) Transferring of the Engine command is to be done only after FWE(finished with engine) has been conveyed to Engine room from bridge i.e. the bridge do not require the Main engines any more and the Main engine plant can be shut.

Second after transferring the control to Engine room, the engines will be lubricated of its liners and engine blown on air, for which the propellor clearance has to be taken while transferring the control.

2)After cylinder liner lubrication and blowing the engine on air, in order to prepare the main engine for maintenance, depending on the type of maintenance to be done engine's cooling water and/or lubricating oil can be stopped and drained accordingly. For example, if maintenance is just scavenge space cleaning then there is no need of stopping cooling water pump and L.O. Pumps, but say you need to change the fuel injectors you will be required to stop only F.O.Circulating pump but the C.W. & L.O.pump would be running as usual. But if need to do decarbonisation of any unit then you will have to stop all three pumps i.e. L.O,C.W. & F.O. Pumps.

So it depends on the type and scope of maintenance, you have planned that will decide on the steps you have to take vis-a-vis Main engine.
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(A) Drop in suction pressure will lead to excessive carryover of crankcase oil or there could be leakage from the crankcase shaft seal.

(C) Causes of the excess icing in the Compressor suction are following:
1. Over charging of refrigerant.
2. Faulty Thermostatic expansion valve.
3. Blocked evaporator due to icing or under-size evaporator.
4. Faulty back-pressure valves of the Evaporators.

(D) Short cycling occurs in the compressor when a mechanical failure is causing the run times to terminate prematurely and since set point has not been achieved, it restarts shortly afterward, thus requiring more compressor ‘ON’ time to compensate. Short cycling is a symptom of a potentially wide range of causes.

Dirty condenser/automatic high pressure reset: A dirty condenser can severely limit your system’s ability to reject heat for regulating temperatures and pressures needed for cooling which can lead to compressor tripping on high head pressure. If the condenser has automatic high pressure reset it can result in short run cycles.

Pressure or temperature control differential is too small: When the pressure controller’s low pressure differential is set too tight, it can cause the compressor to short cycle. This can be observed during normal cooling when the low pressure setting is reached and the compressor cycles off until the pressure in the evaporator rises above the high side of the low pressure setting. This results in longer times to achieve set point and greater energy use.

Lack of operation time delay: While it’s certainly important to have a minimum and maximum run time in place for proper system performance, it’s equally important to have a minimum OFF time in the form of an operation time delay. This is arguably the most common cause of a short cycle. By having an effective time delay, you can potentially prevent other causes from infiltrating your system. For example, a proper time delay can keep the system from running due to discharged air still circulating in the system immediately after its operation. Another: it can allow the pressure controller to reset itself naturally while not calling for cooling as opposed to firing another cycle based on high pressure triggers due to compromised condensers.
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(a) Why turbulent flow:
A common situation encountered by an engineer is heat transfer to fluid flowing through a tube.

This can occur in heat exchangers, boilers, condensers, evaporators, and a host of other process equipment.

The study of heat transfer can be done either in laminar flow or in turbulent flow. Both conditions show different performance characteristics of the heat transfer.

Under turbulent flow conditions, the increase in heat transfer rate is more significant than that under laminar flow conditions.

This is due to the increase in the Reynolds number of the flowing fluid in turbulent flow.

Laminar flow develops an insulating blanket around the channel wall and restricts heat transfer. Conversely, turbulent flow, due to the agitation factor, develops no insulating blanket and heat is transferred very rapidly.

How the turbulent flow is achieved

1.Higher the velocity more the turbulent the flow will be.
2.The jumbled, tumbled flow pattern can disrupt much of the stationary fluid film. Built-in obstructions to flow, called turbulators, disrupt laminar flow, thereby improving heat transfer. Although these obstructions to flow increase pressure drop through the heat exchanger, the improvement in heat transfer more than compensates for the higher pressure drop.

(b) Impressed current corrosion protection system (ICCP) is used if there is no sacrificial anode fitted.

Impressed current cathodic protection works by delivering controlled amounts of DC current to the surfaces submerged in water with the aid of ultra-reliable zinc electrodes as well as combined anodes of metal oxide. The electrical current that is continuously regulated and monitored by the ICCP system helps prevent the electrochemical mechanism of galvanic corrosion prior to its attack.

(c)
A heat exchanger is a device for transferring thermal energy from one medium to another. It generally consists of two channels or system of channels, one for each medium, and separated from each other by partitions through which heat is transferred from the hot medium to the cold medium.

Most coolers used on board ship transfer heat from a hot fluid to sea water. For the main propulsion engine of the motor ship, the engine jacket water, lubricating oil and charge air must be cooled and generally also water or oil used in cooling the pistons.

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The flow path of the fluids are fixed by the division plates in the heat exchanger heads for the cooling fluid and the internal baffles or tube support shets within the body of the heat exchanger for warm fluid:
The division plates in the heads or boxes fix the position of the inlet and outlet branches for the fluid passing through the tubes.

The internal baffles fix the position of the inlet and outlet branches for the fluid passing through the body of the heat exchanger on the outside of the tubes.

If the heat exchanger heads do not contain any division plates, he fluid passing through the tubes enters at one end of the heat exchanger and leaves at the other. This arrangement is referred to as a single pass heat exchanger. If the heat exchanger is a double pass type, a division plate is fitted in one head. The inlet and outlet connections for the fluid passing through the tubes are fitted on this head. The division plate prevents the fluid bypassing and causes it to pass through half the tubes in the heat exchanger which is referred to as the inlet bank. After the fluid passes through the inlet bank it enters the other head which is just a bobbin piece and a cover. The direction of fluid flow is reversed in this head or box and it passes back through the outlet bank of tubes and leaves at the outlet branch. The fluid has passed through the tubes in two different paths from which it gets the name two pass, or double pass.

In recent designs, the guided flow concept has been introduced, i.e. a secondary cooling surface in the form of radial fins integral with the tubes between which flow is guided radially, alternately out and in from section to section. This gives better heat transfer surface and better heat transfer, lower metal surface temperature and increase performance.

(d)
In a multipass shell and tube heat exchanger, the problem of differential expansion between the shell and tube passes is taken care of by using a U-bend or floating head tube sheet.
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(a) wpe9232052_06.png

(b) When we measure pH, we’re measuring the power of Hydrogen. The number refers to the relative concentration of hydrogen (acid) and hydroxide (base) ions in solution.

It comes into play with steam boilers because a pH between 7 and 9 (slightly alkaline) is just right.

If the pH is lower than that, the water will start eating the pipes. If it’s higher than that, the water won’t corrode metal, but it may begin to foam, and that’s not good.

Say, you’re on a job and you have a steam boiler that’s taking on a lot of feed water because the system has leaks.

Here’s the real problem for that: Fresh feed water brings with it carbonates and bicarbonates, which are both natural and normal. The challenge starts when the water boils because carbonates and bicarbonates break down and leave the boiler as carbon dioxide. This gas flows through the system with the steam, and if you’re not venting the system well, the condensate will absorb the carbon dioxide as the steam gives up its latent heat to the pipes and the radiators. We call that Henry’s Law.

The system winds up with carbonic acid in the returns and that’s bad news because carbonic acid removes the thin film of rust that naturally forms on the insides of steel pipes. That mild rusting is a good thing to have because it helps protect the underlying metal from further corrosion. By stripping away the surface rust, the acid makes more fresh metal available for munching. Before long, you have leaks.

This is why it’s good to insulate the return lines in any steam system. The cooler the water gets, the more it will absorb gases such as carbon dioxide (Henry’s Law). Keep the condensate as hot as possible; it will be less acidic and the return lines will last longer. The boiler system will also use less fuel.

And even if you fix the leaks in the system, you still have to keep an eye on the pH of the water because many people add chemicals to their boilers to avoid corrosion. These chemicals shove the pH toward the alkaline side of the scale. When the pH reaches 10, corrosion becomes impossible. That’s what makes chemical drain cleaners safe for pipes. That nasty stuff has a very high pH (think lye).

The trouble really starts when someone gets overenthusiastic with the chemicals and the pH reaches 11. At that point, the water will foam, and that leads to wet steam, which wastes fuel because it robs the steam of its latent heat. The steam boiler has to run his burner longer to heat the building, and with lousy results.
Use litmus paper to check the pH whenever you blow down a low-water cutoff. It’s a simple test and easy to do, and by getting the water’s pH just right, you can solve a lot of problems that are costing money.

And please keep in mind that all steam systems are open to the atmosphere (through the Hotwell), so there’s always going to be some evaporation and a need for feed water. But steam boilers that do only space heating reuse nearly all of the water because the condensate returns to the boiler from the piping and radiators. You shouldn’t have to add too much water to these systems unless they’re leaking.

Feed water is cold and contains lots of oxygen. People who maintain boilers deal with that oxygen by passing the feed water through a deaerator, but you’ll rarely see a deaerator on a space-heating boiler.

Henry’s Law tells us that gases dissolve in liquids in direct proportion to pressure and temperature. So the colder the water, the more oxygen it will contain. That oxygen comes out of solution as the water boils, and it can eat holes in the boiler, right at the boiler’s waterline.

Feed water also contains suspended solids. The more feed water you allow in, the more solids you’re going to get. The solids collect on the surface of the water as it boils. They surround the steam bubbles as they form, making them tougher. Tough bubbles resist breaking, and that also leads to foaming and wet steam. The finer the suspended particles are, the more they will collect in the bubbles, and the worse the foaming will be. You probably can’t see these solids but they’re there, and this is why you must keep the feed water to a minimum. Fix those leaks.

(c)
Electrochemical corrosion is practically the simplest and the most common corrosion process that is observed. Generally seen in metals.

You can define it as a process of individual metal forming its salt byproducts.

For this few things are needed. An agent (which is most commonly water) and a depolariser. This dipolariser can be anything from oxigens to a free anion available in acids to a another positive ( in comparison ) metal. Nitrogen is almost and inert gas.

The basic equation is simple.

M (metal) - M+ + e.

This free electron is released from the outermost atom and goes to join the electron deficient depolariser. Forming salts/ oxides etc.
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(a) The cooling water temperature of an engine is to be kept within a certain range for following reasons:
1. To maintain the efficient combustion, the cylinder's temperature has to be kept above 80 deg. Celsius.Excessive low temperature of cooling water will lead to heat loss and thus lower the thermal efficiency.
2. To avoid thermal shock due to heat of combustion, the cylinder is to be kept above the certain temperature.
3. To prevent cold corrosion of the combustion space it is required to be kept above 75 deg. Celsius.
4. To avoid the excessive heating and thus undue expansion of the engine parts (which will lead to leakages) the cooling water temperature is kept below the 90 deg. celsius.

(b) The principle of the working of the centrifuge is the principle of gravity which separates the water from oil. If this gravitational force can be increased the rate of separation will also increase. The centrifugal force created by the high rotational speed of the centrifuge creates separation force of about 1000 times to the gravity and thus accelerates the separation of water from the oil.

Below is the sketch to describe the principle:

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(a)

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(b) operating principle: As shown in image above there are two meshing gear inside the casing. One gear is driven from external power, while the other is driven by that gear. As the external rotary motion is applied both the gears rotate opposite to each other's direction and the from the casing side, the gear teeths carry oil as they rotate.
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(A) Four safety devices fitted in the Boiler and their working:

1. Water low-low alarm: This is independent to the water level controlling system in a boiler and it activates a separate electrical relay which activates the main relay for deactivating the contactor of the Burner. Thus this device directly shuts down boiler burner on being activated.

2. High steam pressure cut-off: This device has pressure setting higher than the auto-operation's high limit pressure setting and lower than the safety valves' pressure setting. It stops the Burner with the same type of circuitry as described in point 1 above.

3. Burner door interlock : This device senses if burner door has opened, which could fire up the whole machinery spaces. It shuts down burner immediately.

4. Boiler's Safety valve: This is the ultimate pressure relieving mechanical device. It is kept shut by a set spring pressure and opens at a particular pressure, while it sits back at a much lower pressure(then the lifting pressure). It thus make the steam pressure at a safe range before stopping its function.

( Simple sketch of a water level gauge

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(C) Boiler troubleshooting:

1. The cause could be due to:
a) lock out will happen, if oil temperature/pressure is not within limit values.
b) Damper motor fault
c) Pilot valve/ignition terminal energized
d) Main oil valve terminal energized
e) Internal system fault
f) Faulty gas pressure sensor

The engineer needs to look into above points and restore the fault.

2. This will happen due to following:

a) the air gap of igniter probes is incorrect.
b) The ignition transformer is at fault.
c) Time sequence control has a fault.

3. This will happen due to following:
a) If pilot oil comes for ignition then no pressure in pilot oil supply(check its line filer first)
b) The arc which is developing is too far from the "oil cone" to catch fire (adjust ignitor orientation)
c) Fuel is not getting atomised properly ( check oil line filters, clean nozzle or atomising cup.
d) Water in the fuel( check for it and drain water from the service tank, purge out full fuel line to boiler.

4. Only one cause at this stage:
The flame eye(sensor) is dirty or malfunctioning.(Clean the flame eye, which is fitted in the burner and check its electrical circuit)
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