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پستهای کانال
| 2 | The information was related to Saacke boiler on board but may slightly differ with the make of the boiler and the piping system and automation on board. | 290 |
| 3 | What To Do During Marine Auxiliary Boiler’s Flame Failure or Fuel Pump Tripping?
Marine auxiliary boiler is only used in port and the exhaust boiler caters for all heating and steam needs while at sea. Generally if the burner routines are carried out religiously and the filters are cleaned, there is no major maintenance or routine that needs to be done
In this article the author is relating a problem faced on one ship and the troubleshooting done.
Scenario
One day the boiler shut down after flame failure alarm came. After many futile attempts to restart the boiler on HFO, the boiler was changed over to diesel and manually fired. The auto firing mode was non operational and the FO pressure low alarm was coming and fuel pumps stopping.
The following checks were done that helped to restart the boiler:
*Correct pressure setting of the boiler: Generally the Fuel Oil pressure at the burner must be between 2 to 4 bars. In case the pressure is too high more fuel will be sent and the air fuel ratio disturbed. Less fuel pressure will give a lean mixture and flame will be unsteady and fail.
*The fuel pump might trip on overload. Check the pump for mechanical damage and jamming. It should be free to turn by hand.
*The over current relay may be at fault. Check the OCR setting and try increasing it if not correct. There is generally a test lever at back of OCR for testing.
*The fine filter also called as dirt trap on the burner may be dirty.
*The pressure transmitter may be giving wrong pressure feedback, check the wires.
*The pressure transmitter for DO is normally different from FO line, Check this pressure transmitter.
*The PLC will give command to stop due to pressure transmitter fault. Try calibrating the transmitter with the Master calibrator and check output. Output should be between 4 to 20 mA.
*The fuel oil line may be choked and blocked. This can be ascertained by high back pressure.
*The fuel oil temperature should be around 90 deg C.
Check heater for correct functioning. High temperature can cause vapor lock that can lead to ignition failure.
*The PLC (Programmable Logic Controller) has a reset buttons and resetting it restores the default values, often solving the problem.
*Check any error code flashing on the display of the PLC or logic module and consult the manufacturer.
*If a fuel oil (FO) low pressure alarm is generated it may be due to restriction in the line going to the pressure transmitter. There are also valves for isolation, they must be open.
*Local FO pressure gauge may be replaced with a new / calibrated one to get correct picture.
*If the boiler is firing on diesel oil (DO) then the burner should be generally ok, however if filters are partially dirty or the nozzle is partially choked, it may lead to this problem. Overhauling the burners may give correct picture. If the nozzle is choked it will create a back pressure.
*There are two fuel oil (FO) pumps, try starting the second pump.
*Check supply and return lines for correct functioning of valves.
*Check the megger reading of the pump motor.
*Check the suction line change over and return line change over valves.
*In case the system includes separate pressure control valves for HFO and MDO, change over the three way valve from MDO position to HFO position or close the stop valve before the MDO pressure control valve.
*Near the FO change over valves and near the burner assembly, there are pressure regulating valves on MDO and HFO line, try to adjust the pressure within 3 to 4 bars for HFO. Moreover there may be another pressure regulating valve near the pressure gauge of burner assembly. Use this for fine adjustment.
*If the fuel pumps are tripping in manual firing then there is pump problem or back pressure.
In manual mode PLC should not be involved and as still pump is tripping there is some other fault.
*Check the input voltage to the pump and also the current by clamp meter.
*If both the pumps are tripping then it indicates Pressure switch or back pressure problem. | 280 |
| 4 |  +1بدون متن... | 335 |
| 5 | +9 بدون متن... | 248 |
| 6 | Fuel dribble (dripping) after injection
This occurs when the fuel supply is not precisely cutoff at the end of fuel injection and fuel particles are accumulated on the tip of the nozzle. If fuel dribble occurs after fuel injection, the fuel in the cylinder will not burn completely. This will result in the emission of black or white smoke being exhausted. To prevent fuel dribble, the relief valve of the delivery valve is designed to draw back any fuel that may drip out of the nozzle after injection. Fuel dribble occurs if there is any failure in the delivery valve or injection nozzle, as the residual pressure remains in the injection pipe after fuel injection.
Diesel EngineBleeding Air for the Fuel System
1. Bleeding the air between the fuel tank and the injection pump (low pressure side)
(1) Repeatedly push down and release the pump handle.
(2) Gradually the pump handle resistance will become higher, and the pump will seize to operate. Then the air flows with the fuel into the fuel tank via the return pipe.
(3) Bleeding the air is completed when the pump handle becomes hard to operate.
SERVICE HINT:
In following cases, bleed the air between the injection pump and injection nozzle (high pressure side).
When the engine does not operate properly after the engine is warmed up
When a part on the high pressure side of the fuel system are replaced
2. Bleeding the air between the injection pump and the injection nozzle (high pressure side)
(1) Loosen all injection pipe union nuts on the nozzle holder side.
(2) Crank the engine to force the fuel out of the injection pipe and bleed the air.
(3) Tighten the injection pipe union nuts.
NOTICE:
In the case of the common-rail type, use the hand-held tester and operate the injector to bleed the air. Do not bleed the air with the injection pipe union nuts loosened. | 227 |
| 7 | +6 بدون متن... | 272 |
| 8 | 10 Precautions to Take Before Operating Controllable Pitch Propeller (CPP) on Ships
The driving force of a ship comes from the rotation of propeller(s), which is attached to the main engine of the ship. The two main types of propellers that are used in merchant vessels are:
1. Fixed Pitch Propeller (FPP)
2. Controllable or Variable Pitch Propeller (CPP)
As the name suggest, in fixed pitch propeller, the blades are fixed with the propeller boss and hence their pitch cannot be changed. However, in Controllable or Variable Pitch Propeller (CPP), the propeller blades are attached to the boss and their pitch can be altered via the hydraulic system.
Both the types of propeller systems have their own advantages and disadvantages.
In Controllable Pitch Propeller (CPP), the main engine can be started with blade pitch set to 0. This decreases the fuel consumption and also reduces the load on various engine bearings and its shafting during the starting procedure.
If you are working on a ship with a Controllable Pitch Propeller (CPP) drive, do ensure to take the below mentioned precautions before operating it:
1. Operation from Remote Position: Operate the CPP from Remote control position for ahead, astern and stop position and check the pitch position indicator located near the stern shaft.
2. Operation from Emergency Position: Operate the CPP from Emergency control position which is located near the stern shaft for ahead, astern and stop position and check the pitch position indicator.
3. Check for Leakages: Ensure their is no oil leakage from the system. Even a small leakage can lead to failure of the system at later stage of operation.
4. Maintain the oil level: Check and maintain the oil level in the hydraulic tank of the system at all times. Also, ensure that all the alarms in the tanks are in working condition.
5. Check the pressure: Ensure their is no loss of pressure once the desired angle of pitch is achieved.
6. Start The Engine At Zero Pitch Angle: Always start the main engine at zero pitch angle as their will be a zero propeller resistance during the start, leading to less load on the shaft bearings.
7. Check all the Parameters: Check all the parameters of the main engine are within limits and check the temperature of all bearings including the shaft bearings.
8. Carry out Hydraulic Oil Analysis: Analysis of hydraulic oil used in the Controllable Pitch Propeller (CPP) system to be carried out onboard to check the condition and water intrusion.
9. Run Engine At Constant Speed: If shaft generator is fitted with power Take off/ Gear constant ratio for power production, the engine with CPP should be run at constant speed even at reduced load. This will ensure the efficiency of Controllable Pitch Propeller (CPP) and engine is maintained.
10. Perform Frequent Overboard Checks: Frequent overboard checks near the stern area to be performed during starting of the Controllable Pitch Propeller (CPP) for oil leakage from the sealing ring.
Controllable or Variable Pitch Propeller (CPP) eases the use of other fuel efficient machinery such as shaft generator and also reduces load on the ship’s engine. It is a complex and expensive installation as compared to the Fixed Pitch Propeller (FPP) and hence engineer officers onboard must be skilled enough to ensure no breakdown takes place by knowing the system inside-out. | 261 |
| 9 | +2 بدون متن... | 273 |
| 10 | +9 بدون متن... | 243 |
| 11 | +9 بدون متن... | 152 |
| 12 | Stuffing Box Tank:
The main engine stuffing box scraps the impure lubricating oil, which is collected in a separate tank known as stuffing box tank.
Stern tube gravity tank:
The stern tube system oil is circulated in the system by means of two tanks, lower gravity and upper gravity tanks.
Waste oil tank:
The waste oil tank is a separate tank used to collect waste and impure oil produced onboard ship.
Soot collecting tank:
When the economiser tube washing is done, the soot water is collected in a soot collecting tank.
Sewage holding tank:
The sewage produced from the onboard crew is collected in a common tank known as sewage collecting tank. The sewage plant takes intake from the sewage holding tank.
Expansion tanks:
The jacket water system of main engine, auxiliary engine and some times main air compressor are provided with individual expansion to provide provision to compensate change in volume and maintaining positive pressure.
Jacket water drain tank:
When any maintenance is to be done on the main engine, the jacket water is drained and collected into the jacket water drain tank.
Rocker arm tank:
Many diesel generators are provided with separate rocker arm lubricating oil tank to avoid contamination. | 152 |
| 13 | List of Important and Not-So-Famous Tanks on a Ship
Fuel oil, diesel oil, and lubricating oil tanks are the names of tanks everyone is aware of. But there are several tanks apart from them which also play an important part in the overall working of the ship. Moreover, there are also tanks of which many people are not aware of. In this article we will have a look at some important and some not-so-famous tanks present on the ship.
1. Hydraulic Oil Tanks
Hydraulic oil tanks for valves:
Separate tanks are used to store oil which is used for different valves on the ship. Valves such as ballast valves, fuel valves etc. are remotely operated by hydraulic oil.
Hydraulic oil tanks for Winches:
Tanks for hydraulic oil are located outside the engine room to store winches oil.
Hydraulic oil tanks for Steering gear:
Steering gear hydraulic oil tank is normally located in the steering room and is used as a storage tank to receive bulk oil.
2. Water tanks
Fresh water tanks:
Fresh water tanks present onboard may be two or more in numbers, depending upon the size of vessel. They are used to store sanitary water for accommodation, engine room and deck use.
Drinking water tank:
A separate drinking water tank may be present to store drinkable water received from shore or to store water produced by fresh water generator (F.W.G).
Distilled Feed water tank:
A ship’s boiler needs distilled water to produce steam, and therefore water from fresh water generator (F.W.G) is stored in distilled water tank.
Boiler feed water tank:
The boiler feed water system consist of a separate tank which receives water from distilled water tank.
Cascade tank:
Cascade tank, also known as hot well, is a part of boiler feed water system. Water is pumped into the cascade tank from the feed water tank. The boiler water is treated in the cascade tank and the return from the steam heating system is also connected to the hot well.
Ballast water tanks:
Ballast water tanks are present all over the ship for ballasting and de-ballasting purpose for stabilizing the ship and for acquiring correct draught for port and canal crossing etc. Double bottom tanks are generally located outside the engine room.
Stern tube cooling water tank:
This tank is located around the stern tube of the propeller and acts as a cooling media for the same. It can be used as a fresh water water tank of the ship.
3. Slop tank
Slop tank in tanker:
Slop tanks are present onboard tanker to store oily water mixture from cargo tank washing. The number of slop tanks depends on the Dead weight Tonnage (DWT) of the vessel.
Sludge tank:
Located in engine room, this tank is used to store sludge produced after treating fuel or lube oil through purifiers.
Bilge tank:
The water and oil leakage in the engine room is collected in bilge wells and this oily water mixture is then transferred to primary bilge tank or bilge holding tank, where the mixture is settled down and then is transferred to secondary bilge tank.
The oily water separator is supplied through secondary or separated bilge tank and a shore connection is also connected to this tank to dispose off all the collected bilge to shore.
Scavenge drain tank:
The sludge produced by the main engine in the scavenge area is collected in the small capacity scavenge drain tank.
Oily Water Separator (O.W.S) Sludge tank:
When oily water separator operates, it separates oil from water and that oil is collected and discharged into a separate tank known as O.W.S sludge tank.
4. Other Not-So-Famous yet Important Tanks
Drain tank:
The drain tank is located in the engine room. All drip trays and other drains are connected to this tank.
Leak off tank:
This is a small tank separately fitted in the main engine and all auxiliary engines to detect any fuel leakage. The tank consists of an orifice and a float. If the leak is very small, it will pass through the orifice; but if leakage increases, the oil will not be able to pass through the orifice and tank level would increase, rising the float and thus giving an alarm. | 181 |
| 14 | +7 بدون متن... | 279 |
| 15 | Air Compressor Unloader Valve: Its Purpose
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A reciprocating air compressor is a positive displacement mechanical device that relies on a cylinder and crankshaft-driven piston to produce compressed air. An unloader valve is one of the many small but essential parts and components that ensure the effective, efficient operation of a reciprocating compressor.
What Is the Unloader Valve?
A compressor unloader valve is a small part, typically measuring approximately 4-5 inches in length and width. It performs the critical function of releasing trapped air inside the tank, enabling the motor to restart. An unloader valve malfunction is one of the more common air compressor issues. If the trapped air cannot escape, the accumulated pressure may be enough to keep the motor from restarting.
The type of unloader valve found in an air compressor depends on the machine’s make and size. Some operate via a toggle switch on the side of the unit’s pressure switch. Others have an integral valve installed under the pressure switch.
What Is the Purpose of an Unloader Valve?
During the operation of a typical reciprocating air compressor, the machine’s electric motor-driven tank fills with air. The device contains a pressure switch that responds to the air accumulation by shutting off the motor’s power supply. The compressor pump, which is attached to the motor shaft, also stops.
When the motor attempts to restart, the air trapped inside the cylinder generates a load that makes it more challenging to execute the task. By venting the air, the unloader valve reduces the load over the piston, facilitating the restarting process.
Where Is the Unloader Valve Located?
If you own a smaller reciprocating air compressor, you’ll likely find the unloader valve mounted on or inside the pressure switch. When the switch shuts the compressor off, it actuates the valve. A small tube or pipe runs from the check valve, a device that keeps the entire tank from draining, to the unloader valve.
A larger air compressor often features a more sizeable unloader valve controlled by air pressure emanating from a smaller pilot valve. In this arrangement, the valve typically sits next to the compressor.
How Does an Unloader Valve Work?
When the air pressure inside the compressor’s tank reaches the pressure switch’s cut out pressure (the point when air is no longer delivered), the switch automatically trips off and interrupts the power supply to the motor. This process causes the unloader valve to open and vent the accumulated air.
When the tank pressure drops back down to the predetermined setting on the pressure switch, it causes the switch to trip again. This action results in the release of the unloader valve’s pin, preventing the escape of compressed air into the atmosphere.
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| 16 | +7 بدون متن... | 248 |
| 17 | Reasons for Failure and Misalignment of Crankshaft in Marine Engines
Crankshaft is the intermediate part of a marine engine, which transfers the power of a firing cylinder from the reciprocating piston to the rotating propeller (or alternator in case of a generator).
The working of other components of the engine depends upon the correct rotation of the crankshaft such as camshaft for fuel timing, firing order of units etc. Failure of a single part of the crankshaft can stall the engine as well as the ship.
As a marine engineer working on a ship, one should know various reasons which can lead to failure of this important component.
Reasons for failure of crankshaft
*Fatigue Failure: Majority of steel crankshaft failure occurs because of fatigue failure, which may originate at the change of cross-section such as at the lip of oil hole bored in the crankpin.
*Failure due to Vibration: If the engine is running with heavy vibration especially torsional vibration, it may lead to crack in the crankpin and journal
*Insufficient lubrication: If the lubrication of bearing in the crankshaft is starved, it may lead to wipe out of the bearing and failure of the crankshaft
*Over Pressurised Cylinder: It may happen that there is hydraulic lock (water leakage) inside the liner and due to extreme pressure the crankshaft may slip or even bent (if safety valve of that unit is not working).
*Cracks: Cracks can develop at the fillet between the journal and the web, particularly between the position corresponding to 10 o’clock and 2 o’clock when the piston is at T.D.C.
-Reasons for Crankshaft Misalignment
Crankshaft of a marine engine is a massive component when fully put together in the engine. Initially the complete crankshaft is aligned in a straight line (connection drawn from the centre of the crankshaft makes a straight line) before setting it on the top of main bearings.
But with time due to various factors, the straight line may deviate and misalign. A degree of misalignment is acceptable within limits but if the value goes beyond that rated by the manufacturer; it may lead to damage or even breakage of the crankshaft.
Following are the reasons for misalignment of crankshaft-
*Damage or wipe-out of the main bearing
*Loose engine foundation bolt leading to vibration
*Deformation of ship’s hull
*Crack in the bearing saddle
*Loose main bearing bolt leading to damage of main bearing
*Very high bending moment on the crankshaft due to excessive force from piston assembly
*Grounding of the ship
*Crankcase explosion or fire
*A defective or worn out stern tube or intermediate shaft bearings
*Loose or broken chokes in the foundation
*Bearing pockets cracked
*Bedplate deformed – transverse girder damaged
*Tie bolts slack or broken
*Weakening of structure due to corrosion | 233 |
| 18 | +6 بدون متن... | 216 |
| 19 | 11. It is important to check the tension of the garter springs using a spring balance, or by hanging the spring with a known weight attached and measuring the extension.
12. If they have weakened then the ring segments will not be held against the surface of the rod with enough force to enable the sealing and scraping function, and new springs should therefore be fitted.
13. When fitting new ring segments or lamellae then sharp edges should be removed by rubbing the segment against a piece of Emery cloth taped to the piston rod.
14. Ensure the ring sets have their gaps offset when reassembling.
15. When the diaphragm gland is replaced in the engine and the engine is running examine the tell tale drain from the gland.
16. There should only be a slow drip of oil, Too much oil leaking out indicates defective scraper rings, while air blowing out indicates faulty sealing ring sets.
17. As an additional measure monitor crankcase oil consumption and crankcase pressure to ensure gland is operating effectively | 206 |
| 20 | STUFFING BOX
What is a Stuffing Box?
Stuffing Box is a sealing gland, having numerous applications on a ship. It is kind of a packing material used to seal pump, valve , stern-tubes etc. It is also used in boats, where the propeller shaft it protrudes out of the hull.
Stuffing box serves two main purposes:
It act as a sealing material to prevent leaks
It keeps the system operational and in cool condition.
Stuffing Box Arrangement
In most of the pumps, and even in the ship’s propeller shaft , the stuffing box consists of a stack of packing rings or a short square cross sectional rope made of greased flax. The material is closely packed or wound tightly around the propeller or pump shaft with threaded nut or spacer compressing it in place. There are also hose clamps attached to the stuffing box, which are then attached to a short piece of heavy duty rubber hose. The rubber hose is clamped around the place where the propeller opens in the ship’s hull.
Stuffing box is also seen in steam engines , at the place where the piston rod reciprocates with the cylinder cover, which helps in preventing leakage of steam from the cylinder.
In diesel engines , stuffing box is found in the bore for the piston rod in the bottom of the scavenge air box. The stuffing box prevents the entry of lubricating oil from the crankcase into the scavenge air space. It also prevents the leaking of air from scavenge space to the crankcase.
Construction of a Diesel Engine Stuffing Box:
The whole arrangement is distributed into two parts, put together by a flanged joint. The housing generally consists of five ring grooves of which, the two uppermost grooves accommodate sealing rings to prevent blowing down of scavenge air along the piston rod. The bottom groves are fitted with scrapper rings in order to scrap the lubricating oil on the piston rod. The oil enters and leaves the housing through bores. The two sealing rings are generally made of brass while the scrapper rings are made of steel.
In between the two types of rings , a cofferdam attached with connecting pipes and bores is provided, which communicates with a control clock fitted on the engine. It is used to monitor the performance of sealing and scrapper rings
Special Features:
All the stuffing boxes packed with flax rings are specifically fitted to allow a bit of leakage. The sealing is adjusted to receive a few drops of fluid per minute to maintain lubrication and subside the heat generated due to continuous motion of the shaft. This amount of water is not considered leakage and seldom creates a problem. Few other types of sealing arrangements such as mechanical face seal and lip seal use materials or lubrication systems which are more technically advanced. There are also drip-less seals made of Teflon or carbon.
Stuffing box overhaul
1. The diaphragm gland is overhauled at the same time as the piston when it is withdrawn from the engine.
2. The housing is mounted on a table clamped to the piston rod and then it is separated into its two sections by removing the clamping bolts.
3. After removal of one half of the casing access to the rings and garter springs is now possible.
4. During overhaul the axial clearance between rings and housing should be checked.
5. This should be in the region of 0.1 - 0.2mm for a large slow speed engine.
6. If too large the rings will hammer the seatings and also tend to tilt during operation, leading to inefficient scraping & sealing function.
7. To Check the butt clearances the ring segments on each set should are pushed together & the one gap measured.
8. The butt clearance should not be allowed to generally fall below 50% of its normal clearance, when the rings are new if the rings are going to last until the next overhaul.
9. Springs & ring segments can now be removed taking care to keep the individual ring sets separate.
10. Scraping function can be restored on some type of scraper rings by replacing the cast iron lamellae which slide into the scraper ring steel backing segments. | 192 |
