Sanjeev Kumar Windlass Safety devices are :-
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In this Article, I have Explained Why discharge valve closed during starting of centrifugal pump ? Or Why centrifugal pump started with closed discharge valve ?
Why centrifugal pump started with closed discharge valve ? |
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Let Us First Understand through Characteristics Curve of Centrifugal Pump. A centrifugal pumps usually started with discharge valves shut. Considering the properties of centrifugal pump by operating characteristic curve it is clearly found that; when the amount of water delivered is zero, the power available is at minimum. So discharge valves valve remains shut off throughout the beginning to take care of low power demand by the pump on its motor having low power output at the beginning. This helps stabilizing pumps at the starting. When the pump is stable the discharge valves opened and high power avaibility meets the high power demand; which might be not possible for the motor to fulfill for the starting 4-5 seconds. |
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Or, It is a very common practice to start large capacity centrifugal pump with the closed discharge valve . If the characteristic curve for a centrifugal pump are examined it will be seen that when the quantity of water discharged is zero the power required by the pump is zero or very small amount. by starting the pump with discharge valve closed the power demand made by the pump on the pump motor is kept to very minimum after the pump has started and the momentary high motor current demand has stabilized the discharge valve is opened. |
Why centrifugal pump started with closed Discharge valve |
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By closing the discharge valve, the starting current can be reduced. As we know, at the start of any motor, the current will be high. When we start the pump with an open discharge valve, the discharge head will act on the pump, i.e. more resistance, so that the motor has to give more starting torque to the pump, which means more current is drawn by the motor. If we start the pump with discharge valve closed, it means there no discharge head and minimum resistance to the pump and so current drawn is minimum. Although the current taken during startup of motor is more than normal, but by closing the discharge valve of centrifugal pump we can avoid extra load act on the pump. If there is a check valve, then the discharge valve can be opened. Without having a check valve, we need to have the discharge valve closed if there is pressure on the discharge side of centrifugal pump at the time of startup. If we think differently,If there is a pressure on the pump’s discharge side,before starting it may flow back through the pump,causing a backward spin and can draw more current , resulting damage to the pump.Thus can be prevented by keeping the discharge valve of centrifugal pump closed when starting. |
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Hyper mist :-
Sprinkler System :-
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In this Article,we will learn What is the Angle of Contraflexure ?
This is the angle at which the curve goes / moves from concave to convex.
Or
It is the angle of heel up to which the rate of righting lever ( GZ ) With the heel is changes I.e Before this point rate of righting lever with heel is increasing but after this point rate of righting lever will decrease.
Must Read:- How does a ship move
The physical Significance of this point is that ,it is the point or angle at which Deck just touches the surface of sea.
The below figure is the Curve of Statical stability for a ship in Particular condition of loading.
How this Curve Obtained ?
This curve is obtained by plotting the Righting Lever against the angle of the heel.
The above curve is for Positive Metacentric Height
The above curve is for negative Metacentric Height.
From the above figure we can get following information:-
The above figure is for Negative Metacentric Height.
In the above figure,we can see that ,at an angle less than 18° the the righting arm / lever are negative and beyond 18° to 90° the righting lever is positive.
Hence, 18 degree is the angle of look or point of loll.
Note :- Initial GM of ship is plotted at 57.3°.
Now the Question come in mind that why we take Initial GM of ship at 57.3° ?
The answer of this Question is that 57.3 °= 180÷ 3.14 57.3°.
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In this Article ,I have mentioned How to convert purifier into clarifier ?
Beside it,you will also learn listed topic in this Article.
For better understanding watch video:-
https://youtu.be/bdCiOitnjGA
Must read:- Purifier
Answer is NoIt is because in clarifier there is no water outlet and sealing water line.
Purifier
Clarifier
Blind Disc means the disc is blind.It means there is no holes in the disc.It is used to convert the purifier into clarify. It is inserted at the bottom of the disk stack, because there are no holes.
A ring fitted at the top of disc stack from where water is passing out is called gravity disc.Oil maybe of different densities,so the interface changes.To create the correct line of interface between water and oil it is very important to select correct gravity disc size.
The function of gravity disc are as follows
gravity disc in the purifier is one which controls the output of the quantity of fuel. It is responsible for creating the interface between the oil and water.
Back pressure is maintained by gravity disc.
It is responsible for creating the interface between the oil and water.
Back pressure is maintained by gravity disc.
In a purifier, water sealing is established before introduction of the oil, so that oil filling does not flow through the heavy liquid outlet.
Purpose :-
To seal the water outlet & also to prevent the overflow of oil through the water outlet.
For better understanding ,How purifier change into clarifier and why not clarifier change into purifier, please read full Article .
I am 100 percent sure,After reading this 5 minute article you have no Doubt.
Basic principle of separation of water and impurities from fuel is gravity difference.
When a bowl containing impure fuel is rotated, the centrifugal forces throw any item with a density greater than the density of fuel oil (solids and free water) to the bowl ‘s periphery.
Centrifugal separators used to separate two liquids with different densities (fuel and water) are known as purifiers, and clarifiers are those used to remove solid impurities.
Note:- Purifiers will also remove some solids, and clarifiers will remove small amounts of water as well.
In above figure,the addition of an inlet and an outlet connection forms a simple clarifier.
The particle is pushed upwards by the oil stream to the centre, while the centrifugal force directs it to the periphery.
The residual force on the denser particles (impurities) will drive them towards the periphery, while the less dense particles (oil) will be directed towards the center of the bowl and will rise to the outlet connection.
When a centrifuge is configured as a purifier, the second outlet pipe is used for the discharge of water as shown in figure.
In the fuel oil purifier, the untreated fuel contains a mixture of oil, solids and water, which is separated into three layers by the centrifuge.
While in operation, a quantity of oil remains in the bowl to form a complete seal around the underside of the top disk and, due to the difference in density, the oil is confined to the outer diameter of the top disk.
Because marine fuel oil usually contains a small amount of water , it is important to prime the bowl each time it runs, or otherwise,all the oil would passes over the side of the water outlet to waste.
The radius of the water outlet is greater than the fuel’s. There is a gravity disc within the water outlet, which did the work of controlling the radial position of the fuel- water interface.
As the fuel centrifuge operates, particulate matter accumulates on the bowl walls.
Notes:- In older machines it is important to stop the centrifuge to manually clean the bowl and the disc stack, but today most devices will discharge the contents of the bowl while the centrifuge operates.
Electrical Safety Devices
Dead front type switchboard, Fuses, Relays, Circuit breakers, Earth fault indicators, Under voltage relay, Reverse power trip, Preferential trip, Over current trip, Short circuit trip, Arc chute, Ebonite Rod ( to remove static charge).
Main Engine Safety Devices
General Safety Devices :-
Insulated hand gloves, dry boiler suits, shoes without metallic part, Rubber pad in front of switchboard, 0.6m gap behind switchboard, Panel doors to be earthed, interlocked handles for opening doors.
No water, oil, or steam pipeline in its vicinity.
Overhead crane safeties
1) The most important safety feature of the crane is the electromagnetic fail safe brakes which do notallow the crane to fall with the load even when there is failure of power. For this:·
Normally centrifugal brakes are used which are fitted inside the rotating drum.·
The brake pads are always in applied state and pushed by magnetic springs when not in operation or when there is a power failure.·
As the crane is operated or the power is supplied, the spring gets pulled inward or compressed due to the electromagnetic effect of the current. This allows the crane to be operated normally.
2) Emergency stop is provided in the remote so that the operator can stop the crane at any time.
3) The motor is fitted with distance limit switch in both transverse and longitudinal direction.
4) Mechanical stoppers are provided for both directions in case the electrical distance limit trips fail.
5) The up and down travel of the hook is also attaches with automatic stopper to avoid overloading of the motor.
6) The motor is fitted with thermal protection trip. When the motor windings get overheated, trip will activate saving the motor winding from burning.
7) Load limit switch is also fitted which will trip the motor if the load to be lifted is above the crane capacity.
8) It’s the responsibility of senior officers to operate the crane and to make sure all the personnel involve in any lifting operation are at a safe distance during operation of the crane.
9) Additional tools like i-bolts, shackle, wire sling, belts etc. used for lifting must be checked before use.
10) It should be noted that no one walks or stand below the crane when it is in the loaded condition.
Motor protection and safeties:
1. Overcurrent and single phasing protection relays
2. under voltage relay
3. Short circuit relay (Trigger fuses for HV systems)
4. Temperature sensor for motor insulation
Safety device on life boat
Mechanical brake (to prevent accident falling)
Centrifugal brake (to control life boat falling speed between 20 to 40 m/min)
Limit switch (to prevent over tightening of rope) (it is fitted arm of davit just before in limit)
Harbour safety pin (for davit)
Safety devices for steering system
@Hunting gear
@Buffer spring
@ Angle adjusting stop (Hand over position limit switch)
@ Double shock valve
@Relief valve
@ Tank level alarm (oil)
@ Over load alarm
STEERING GEAR SAFETIES
Hydraulic safeties:
Level switch, low level, low low level alarm for hydraulic oil tank.·
Relief valve.·
Manual bypass valve.·
Low pressure valve.·
High lub oil temp. Cut out
Low level cut out
Electrical safeties:
Electrical and mechanical stopper for rudder.
Electrical motor overload alarm.·
Power failure alarm.·
High temp. Alarm.·
Self starting after power failure.·
Short-circuit trip.·
Phase failure alarm.·
200% insulation in motor
Windless safety device·
Cable stopper (chain stopper, bow stopper)·
Overload trip·
Overspeed trip·
Hand brake·
Slipping clutch for overload prevents any undesirable damage such hull damage due to anchor and rope broke out.
Scavenge Space Protection Devices
1) Electrical temperature sensing device
fitted within the trunking, which will automatically sound an alarm the event of an excessive rise in local temperature (above 200°C)
2) Pressure relief valves
consisting of self-closing spring loaded valves are fitted and should be examined and tested periodically.
3) Fixed fire extinguishing system may be CO2, Dry Powder or Steam.
crankcase safety devices
1. Breather pipe with flame trap
2. Crankcase exhaust fan
3. Oil mist detector
4. Crankcase relief doors
5. Bearing temperature sensor
6. L.O return temperature sensor
Battery room safety arrangement
Safety is provided by
1) Proper ventilation
2) Prevention of heat source for ignition
Ventilation
Independent exhaust fan provided·
Inlet duct should be below battery level, and outlet at top of the compartment
Prevention of heat source for ignition
No naked light and no smoking·
Uses of externally fitted light or flameproof light·
Cables of adequate size and they are well connected·
Never placed Emergency Switchboard in this room·
Use insulated spanner and plastic jug for distilled water, to prevent short circuit·
Room temperature, maintained at 15 ~ 25°C
Generator safety devices ·
Over speed trip·
L.O low pressure trip
@ alarm·
Low level sump trip·
F.O low pressure alarm·
Jacket water high temperature alarm·
Thermometer·
Pressure gauge·
L.O high temperature alarm·
Dip stick·
Crankcase relief valve
ALTERNATOR SAFETIES
The three main type alternator protection are:
a. Over current protection.
b. Reverse power tripc.
c.Under voltage trip
Safety devices on starting air line
Î Spring loaded safety valve or bursting cap.(if bursting cap fitted, no need relief valve)
Î Flame trap.(At Joint where manifold to each cylinder startingline)
Î Starting air line drain valve (Inlet of automatic valve)
Î Turning gear interlock
Safety device on O.W.S
Pressure relief valve on discharge pipeO.D.M system with high ppm alarm and automatic pump stopping device.Test cock (level), drain valve
Incinerator Safety System
1) The safety devices shut down the unit and give out alarms:a. When the pilot and main burner fail to operateb. When the flue gas temperature reaches above 400’Cc. When the cooling fan fails to operate
2) Emergency fuel shutdown valve
3) Micro switch, fitted to hinged furnace door (Interlock)
AUTOMATIC MOISTURE DRAIN VALVE(Unloader)this reduced the starting torque for the machine and clear out any accumulated moisture and oil in the system
Safety devices on refrigeration system.
1)L. P cut-out on compressor suction side: Set at a pressure corresponding to 5°C below the lowest expected evaporating gauge reading
2)H.P cut-out on compressor discharge side:Set at a pressure corresponding to 5°C above thehighest expected evaporating gauge reading
3) Lube oil low pressure cut-out: Oil pressure usually set at 2 bar above crankcase pressure
4) Cooling water L .P cut-out in condenser side
5) Safety spring loaded liquid shock valve on compressor cylinder head
6) Bursting disc on cylinder head, between inlet and discharge manifold
7) Bursting disc on Condenser, [if fitted]
8) Relief valve on Condenser; air purging valve on condenser
9) Master solenoid valve: to prevent liquid being entered into Compressor, when theplant is standstill, especially in Large Plant
COMPRESSOR
Relief valve:
Fitted after every stage to release excess pressure developed inside it. The setting of the lifting pressure increases after every ascending stage. Normally fitted between 1st stage and intercooler and 2nd stage – aftercooler.
Bursting disc:
A bursting disc is a copper disc provided at the air cooler of the compressor. It is a safety disc which bursts when the pressure exceeds over the pre-determined value due to leaky air tubes of the cooler (intercooler or aftercooler).
Fusible plug:
Generally located on the discharge side of the compressor, it fuses if the air temperature is higher than the operational temperature. The fusible plug is made up of material which melts at high temperature.
Lube Oil low pressure alarm and trip:
If the lube oil pressure goes lower than the normal, the alarm is sounded followed by a cut out trip signal to avoid damage to bearings and crank shaft.
Water high temperature trip:
If the intercoolers are choked or the flow of water is less, then the air compressor will get over heated. To avoid this situation high water temperature trip is activated which cut offs the compressor.
Water no-flow trip:
If the attached pump is not working or the flow of water inside the intercooler is not enough to cool the compressor then moving part inside the compressor will get seized due to overheating. A no flow trip is provided which continuously monitor the flow of water and trips the compressor when there is none.
Motor Overload trip:
If the current taken by motor during running or starting is very high then there is a possibility of damage to the motor. An overload trip is thus fitted to avoid such situation.
Boiler safety devices
1) Safety valve
2) Low / high water level alarm
3) Too low water level alarm and shut down
4) Water level indicators
5) Pressure gauge
6) Low fuel oil pressure alarm
7) Low / high fuel oil temperature alarm
8) Flame failure alarm
9) Smoke density alarm
10) Easy gear arrangement
11) Air vent
12) Force draught fan stop alarm
13) Low / high steam pressure alarm
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How to do Salvaging of motor ?
● First of all,take out the motor from the sea water by Isolating it from the connections and take it to the electrical workshop.
● Now,measure the insulation resistance which will be very low hoti 200 ohm so,the main problem is to restore the insulation resistance and this can be restored by three ways.
1.cleaning
2.Drying
3.Re-varnishing
●Dismantle it and wash the windings with fresh water and clean the grease or oil on the windings with the help of using a degreasant liquid such as Armaclean.
●Now, dry the stator windings with the help of heaters or cargo clusters with plenty of ventilation to allow the dampness to escape
●Same thing fir rotors and bearings cleaning can be done with high speed diesel oil.
● Now, Assemble the motor and turn the motor for some revolutions for checking tightness and all.
●Go for insulation resistance test (IR Test ) ,as if it remains high over a few hours .Apply a couple of coats of good quality air -drying Insulating varnish.
●Now load the motor with the pump by taking proper alignment.
Main engine safety devices are critical components in marine and industrial engines designed to protect both the engine and the surrounding systems from various operational hazards. These devices serve multiple purposes, including preventing catastrophic failures, ensuring safe operation, and protecting personnel.
The main engine safety devices are provided in the system to safe guard the main engine
in case of any damage in the system Mainly are fitted in engine when all the alarm and trips fails to work then the last means for safe guarding the engine and components is these safety devices fitted in the main engine.
These are mainly of the type of pressure relief valve which release the excess pressure built in case of malfunctioning of the engine and no action is well in
advance to rectify or to avoid the situations.
| Main Engine Safety Devices | Main Engine Alarms and Trips | Main Engine Shut Down Trips | Main Engine Interlocks |
| 1. Crankcase Relief Door | 1. Over Speed Trip | 1. Low Lube Oil Pressure | 1. Turning Gear Engage Interlock |
| 2. Scavenge Space Relief Door | 2. Lube Oil Low Pressure Trips | 2. JCW High Temp. | 2. Running Direction Interlock |
| 3. Cylinder Head Relief Valve | 3. Camshaft Lube Oil Low Pressure Trip | 3. JCW Low Pressure | 3. Auxiliary Blower Off Interlock |
| 4. Starting Air Relief Valve | 4. JCW low pressure trip | 4. Thrust Bearing High Temp. | 4. Starting Air Distributor In end Position |
| 5. Starting Airline Flame Trap | 5. Piston Cooling Low Pressure Trip | 5. Over speed | 5. Air Spring Pressure Interlock |
| 6. Oil Mist Detector | 6. Thrust Bearing High Temperature trip | ||
| 7. Rotation Direction Interlock | 7. Main Bearing High Temperature Trip | ||
| 8. Turning Gear Interlock | 8. Oil Mist Detector Alarm | ||
| 9. Spring Air Low Pressure Trip | |||
| 10. Manual Emergency Trip |
Here We have provided Description of Main Engine Safety Device and for others Main Engine Alarms and Trips, Shut Down Trips, and Interlocks.
Suggested Read : Safety devices of all marine Equipment
The diesel engine is a type of internal combustion engine which ignites the fuel by injecting it into hot, high-pressure air in a combustion chamber.
In common with
all internal combustion engines the diesel engine operates with a fixed sequence of events, which may be achieved either in four strokes or two, a stroke being the
travel of the piston between its extreme points.
Each stroke is accomplished in half a revolution of the crankshaft.
As a practical safeguard against explosions which occur in a crankcase, explosion relief valves or doors are fitted. These valves serve to relieve excessive crankcase pressures and stop flames being emitted from the crankcase.
They must also be self closing to stop the return of atmospheric air to the crankcase.
Various designs and arrangements of these valves exist where, on large slow-speed
diesels, two door type valves may be fitted to each crankcase or, on a medium-speed diesel, one valve may be used.
One design of explosion relief valve is shown in Figure. A light spring holds the valve closed against its seat and a seal ring completes the joint.
A deflector is fitted on the outside of the engine to safeguard personnel from the
out flowing gases, and inside the engine, over the valve opening, an oil wetted gauze acts as a flame trap to stop any flames leaving the crankcase. After operation the valve will close automatically under the action of the spring.
The cylinder relief valve is designed to relieve pressures in excess of 10% to 20% above normal.
A spring holds the valve closed and its lifting pressure is set by an appropriate thickness of packing piece .
Only a small amount of lift is permitted and the escaping gases are directed to a safe outlet. The valve and spindle are separate to enable the valve to correctly seat itself after opening.
The operation of this device indicates a fault in the engine which should be discovered and corrected. The valve itself should then be examined at the earliest
opportunity.
Its purpose is to relieve excess pressure in the air start
manifold.
It consists of a spring loaded valve disk which locates on a mating seat which is bolted to the end of the air start manifold.
When the force exerted on the disk due to excessive pressure is
greater than the spring force holding the valve closed, the valve will open and release the excessive pressure.
The flame trap is manufactured from brass or aluminium alloy which both have a high specific heat capacity. A number of holes are bored through the thick circular form to allow the air to pass through.
They are fitted in the main air line immediately before the air start valve to restrict the risk of a flame in the cylinder propagating back to the main air start manifold, by dissipating the heat energy in the flame.
The presence of an oil mist in the crankcase is the result of oil vaporisation caused by a hot spot. Explosive conditions can result if a buildup of oil mist is allowed.
The oil mist detector uses photoelectric cells to measure small increases in oil mist
density.
A motor driven fan continuously draws samples of crankcase oil mist through a measuring tube. An increased meter reading and alarm will result if any
crankcase sample contains excessive mist when compared to either clean air or the
other crankcase compartments.
The rotary valve which draws the sample then stops to indicate the suspect crankcase. The comparator model tests one crankcase mist sample against all the others and once a cycle against clean air.
The level model tests each crankcase in turn against a reference tube sealed with clean air. The comparator model is used for cross head type engines and the level model for trunk piston engines.
The turning gear interlock is a valve which will not allow starting air to operate the system when the turning gear is engaged.
Running direction interlock prevents engine to be started in reverse direction until all cam rollers of fuel pump have shifted.
Telegraph position interlock allows engine to be started only in the direction intended by bridge.
Distributor position interlock.
checks whether distributor is
whether in start or stop direction.
It has to be in either in one direction to commence starting.
Main engine safety devices are essential for the safe and efficient operation of marine engines. They play a vital role in preventing accidents, protecting equipment, and ensuring the safety of personnel on board. Regular maintenance and testing of these safety systems are crucial to their effectiveness, as failure to operate correctly can lead to severe consequences, including equipment damage, environmental hazards, and threats to human life. By prioritising the functionality and reliability of these safety devices, operators can significantly enhance operational safety and performance, ensuring the longevity and reliability of the engine.