Master Air Starting Valve Exploredwritten by: Ricky • edited by: Lamar Stonecypher • updated: 7/11/2009

Let us find out what is the function of the air starting valve in the starting air line of a ship.

IntroductionWe have learnt how compressed air is used for various purposes on board ships, and its use in

solving starting problems related to main and auxiliary engines. We have seen the full layout of the

compressed air starting system. Now it is time to take an individual look at the various components

of this system and we will study the master air starting valve of a marine engine in this article.

Master Air Admittance ValveIf you remember the air starting system from our previous article, you will notice that a main valve

is fitted at the entrance to the main air starting line from the air bottles. This valve has to fulfill the

following functions

To supply pressurized air from the bottles to the engine cylinder via individual cylinder valves

To ensure that once the engine has started it cuts off the air supply

To ensure that no products of combustion pass over to the bottle side

The last point is very important since once the engine starts firing, the cylinders are full of hot

gases and if these gases find their way across to the main air storage tanks or bottles, the result

could be anybody’s guess. It could cause a huge explosion and could lead to damage of life and

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In order to ensure this sort of safety, a non-return valve is incorporated inside the starting air valve

so that there is only one way passage for the air from the bottle to the engine cylinders but not the

other way round. This is all explained in the next section in more detail.

Construction & WorkingThe construction of the master air starting stop valve is shown clearly in the diagram below which

shows the cut section of the valve and all the internal parts and passages are clearly shown and

legibly marked for the benefit of the readers.

The inlet and outlet for the starting air are shown in the diagram as well as the drain and the

control air path. It must be understood that there is a difference between the control air and the

starting air. The starting air actually goes inside the cylinders and makes the engine start, while

the control air is used to control the timing of the main starting air and cutting it off at an

appropriate time.

The arrangement consists of a spring loaded non-return valve which is used for safety purpose and

to prevent blow back of the gases to the engine aided with the flame trap which is also provided

there.

There is also an arrangement to operate this valve manually in case it does not open or close

automatically due to some problem. Now suppose the control air line suddenly gets faulty so the

starting air pressure could keep the valve open, but because of the stop valve it gets shut when

blow back gases try to escape to the other side.

It is important to note that the main starting air line is kept in vented position when not in use. This

is important to prevent any build up of pressure due and also to remove any condensate in the line

which could cause knocking in the line when the compressed air at high pressure whizzes past it.

Next to the starting air master valve are the individual cylinder valves which deal with different

cylinders, as well shall see in our next article.

Preferential trip

The non-essential circuits or loads on ships are air conditioning, exhaust and

ventilation fans, and galley equipments which can be disconnected momentarily and

can be connected again after fault finding. The main advantage of preferential trip is

that it helps in preventing the operation of main circuit breaker trip and loss of power

on essential services and thus prevents blackout and overloading of  generator.

Construction and Working

The preferential trip circuit consists of an electromagnetic coil and a dashpot

arrangement to provide some delay to disconnect the non-essential circuits. Along

with this, there is also an alarm system provided, which functions as soon as an

overload is detected and trips start operating. There are some mechanical linkages

also in the circuit which instantaneously operates the circuit and completes the circuit

for preferential trips.

The dashpot arrangement consists of a small piston with a small orifice and which is

placed inside a small cylinder assembly. This piston moves up against the fluid

silicon and the time delay is governed by the orifice in the piston.

Working of Preferential Trip

The current passes through the electromagnetic coil and the linkages are kept from

contacting using a spring arrangement. As soon as the current value increases the

limit, the electromagnetic coil pulls the linkage up against the spring force and

operates the instantaneous circuit and the alarm system. The lower linkage

completes the circuit for the preferential trip circuit.

The current passes through the coil in the preferential trip circuit  which pulls the

piston in the dashpot arrangement. The movement of this piston is governed by the

diameter of the orifice and the time delay made by the same. The preferential trip

operates at 5, 10 and 15 seconds and the load is removed accordingly. If the

overload still persists, then an audible and visual alarm is sounded.

The preferential trip is one of those important electrical circuit diagrams which help in

removing the excessive load from the main bus bar, thus preventing situation like

blackout which is a dangerous incident to ship, especially when the ship is sailing in

restricted or congested waters.

What is Lambda Control in Ships?

MARCH 25, 2011 BY ANISH1 COMMENT

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With new stringent regulations against pollution being introduced, it is important for

the manufacturers to build marine engine that satisfy these norms and do not

hamper the normal operation of the engine. To achieve this, engines are provided

with several automation systems, which not only reduce the pollution level but also

increase the efficiency of the engine and reduce other operational cost.

One such introduced automation is lambda control which controls the fuel injection

system of themarine engine according to the variation in the load on the same.

Purpose of Lambda Controller

The main function of any engine is to supply enough power so that it can handle the

load put on it. The load may increase or reduce during the operation and to

accompany this, some excess fuel may be given to keep up the performance.

Lambda controller is used to control the excess fuel injection in the combustion

chamber of a marine engine when there is a change in the engine load i.e. during a

momentary increase in the engine load.

This is done by controlling the two main elements which are responsible for

combustion- fuel and air. This controller senses the relation between the charge air

pressure and fuel index of the engine at that load.

Principle of Working

The working of Lambda controller can be understood with the help of the following

diagram:

When there is a sudden momentary increase in the engine load, the lambda control

will regulate the fuel through injection pump using the regulator arm. For this, (1) is

turned on which in-turn commands the switch (2) to touch the Piston arm (3) and be

pushed downward, where in the electric circuit will be closed.

Hence, solenoid valve (4) will open which will then actuate the jet system to

accelerate the turbocharger resulting in increase in charged air pressure. This will

result in pressing the piston (3) back in the lambda cylinder (5). When the lambda

value or lambda ratio is satisfactory, then the solenoid valve will get closed,

deactivating the jet system.

When the system is activated for more than 10 seconds, then the solenoid valve is

signaled to shut off and there is an alarm for system failure

Fuel oil limiting during start

During the start procedure, the lambda controller is used as an index limiter.

Hereby heavy smoke formation is prevented during start procedure and the

regulating device cannot over-react.

Advantages

It reduces the emission of excess visible smoke when there is a sudden increase in

engine load.

The overall load efficiency of engine increases.

The exhaust side of the engine .i.e. exhaust valve, exhaust gas way, exhaust uptake

etc are less fouled due to carbon deposits.

The maintenance work reduces due to less fouling of parts.

"Normal" lifting of the relief valve can occur in the following situation, and should give no cause for

concern;

When too much fuel is supplied by the engineer when on starting the engine; I have done this

a few times!

If air is being used to stop engine in “emergency stop” situation.

Running engine full astern for a prolonged period, in this case the bridge should be informed

that astern running is at its limit.

However, there are situations that could lead to a relief valve lifting while engine is operating

under normal load and conditions and warrant a full inspection.

Faulty fuel pump or incorrectly set fuel injector delivering excessive fuel.

Badly leaking fuel injector; through loose nozzle or enlarged injection holes.

Water leaking into the combustion chamber.

Scavenge fire.

Slow turning

A slow turning valve is fitted. This will open instead of the main automatic valve if the engine has been stopped for more than 30 minutes during manoeuvering. It will only supply enough air to turn the engine over very slowly; This is a precaution in case a cylinder has had oil or water leak into it which would cause damage to the engine when starting. If the engine completes a full revolution on the slow turn, then the main automatic valve opens and the engine will start. (note: The operating system for the slow turning has been omitted for simplicity).

Boiler Starting Failure – Troubleshooting

NOVEMBER 12, 2010 BY ANISH1 COMMENT

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Failure in boiler starting is a common phenomenon on ship. There can be several

reasons for the failure in staring of a boiler. In this article we will learn about the most

common reasons for not starting of boiler.

1)     Fuel inlet valve to the burner is in close position:

The fuel line for boiler’s burner consists of several valves located at fuel tank, pumps

suction, discharge valve, or valve before the boiler burner. Any of these can be in

closed position resulting in starvation of fuel.

2) Line filter at the inlet of the fuel line for burner is choked:

If the system runs in heavy oil then there are chances of filters in the line getting

choke. To avoid this, boiler system are normally built for changeover from diesel to

heavy oil during starting and heavy to diesel during stopping. This keeps the filter

and the fuel line clean.

3)     Boiler fuel supply pump is not running:

There are two main reasons for fuel pump not running. Normally when the pumps

are in pairs, the change over auto system is kept in manual position, and if the

operating pump trips, the stand by pump will not start automatically. Another reason

is tripping of pump due to short circuit in the system etc.

4)     Solenoid valve in the fuel supply line is malfunctioning

Nowadays most of the system adopts advance automation, but their can be a

possibility wherein the solenoid in the fuel supply line is malfunctioning and not

opening.

5)     Flame eye is malfunctioning:

A Flame eye is a photocell operated flame sensor fitted directly on the refractory to

detect weather the burner is firing or not. If the flame eye unit is malfunctioning, then

it will give a trip signal even before the burner starts firing.

6)     Air or Steam ratio setting is not proper

For proper and efficient combustion, air fuel ration is very important, if the supply of

air is excess then there will be excess of smoke, and if it exceeds more than normal

level the combustion will burn off causing flame failure.

7)     Forced draft fan flaps malfunctioning

For removing excess gases trapped inside the combustion chamber forced draft fan

(FDF) are used for pre purging and post purging operation and are connected with a

timer to shut the fan flaps. If the flaps are malfunctioning then continuous forced air

will go inside the chamber, preventing the burner to produce flame causing flame

failure of the boiler.

8) Any contactor switch inside Control panel is malfunctioning

Boiler control panel consist of several contactors and PLC cards. Even one contactor

malfunctioning may result in trouble for boiler starting.

9)     Trip not reset

If any previous trips like low water level, flame failure, emergency stop etc. has not

been reset than boiler will not start.

10)  Main Burner atomiser is clogged

Main burners consist of atomizer for efficient burning of fuel. If the atomizer is

clogged by sludge and fuel deposits then burner may not produce flame and trip the

boiler..

11)   Pilot Burner nozzle is choked :

A Pilot burner nozzle is very small and can be blocked by carbon deposits and

sludge resulting in flame failure. Some pilot burner consists of small filter which can

be clogged after continuous operation resulting in flame failure because of carbon

accumulation.

12)  Electrodes are not generating spark

Initial spark for generating a flame is produced by electrode which may be due to

carbon deposits on them or fault in the circuit of electrodes etc.

The fuel pump cam on the MAN B&W MC series engine is designed to raise the plunger on the injection stroke and then keep the plunger at the top of its stroke while the follower stays on the peak of the cam until just before the next delivery stroke when the follower returns to the base circle of the cam, and the fuel pump plunger moves down on its suction stroke.

The animation on the left shows the cam follower just beginning to move up the slope of the cam with the camshaft rotating in anticlockwise direction. (i.e. start of injection)

If the engine direction is reversed at this point, then air will enter the pneumatic cylinder as shown and will move the piston to the right. The cam follower will be moved across and would finish in the position shown which would be at the correct fuel pump timing for running astern.

It should be noted that the reversal of the follower only takes place while the engine is rotating. If the engine had been stopped from running ahead, and then started astern, the fuel pump followers would move across as the engine starts to rotate, and before the fuel is admitted by venting the fuel pump puncture valves.

A micro switch shown on the LHS detects whether the follower has moved across. If not, an indicator light is lit in the control room, However the engine will still start if a follower fails to move, perhaps due to corrosion in the servo cylinder. A high exhaust temperature deviation alarm would operate within a short time. Allowing the engine to start in this situation could be useful during manoeuvring in confined waters.

 

The video clip opposite shows a cam follower moving from astern to

ahead on a MAN B&W MC engine.

 

Reversing Servomotor on MAN B&W 2 Stroke Engine

Indicator Lights for Camshaft

 

On a two stroke engine, the fuel pumps must be retimed when the engine is required to reverse direction (i.e. run astern). This is done by moving the fuel pump cams or fuel pump cam follower positions relative to the crankshaft.

If one cylinder of the engine is considered (left), the piston is just before TDC with the engine running ahead and the crankshaft rotating clockwise. The piston is moving up towards TDC. The picture on the right shows the fuel cam at this point; where the cam follower is rising up the lift of the cam as it rotates clockwise. This point can be considered as the start of injection.

 The fuel pump cam follower is moving up the rise of the cam on the delivery

stroke. The cam is correctly in time with the engine

 

If, at this point the engine is stopped, and is started in the reverse direction (astern), the crankshaft now moves in an anticlockwise direction. Then the piston in this particular unit is now moving down the cylinder and is just after TDC. At this point fuel injection should have just finished. However, by studying the picture of the cam (right) it can be seen that the camshaft has reversed direction (because it is directly driven from the crankshaft), and is also rotating anticlockwise.

 In the picture the follower is moving down the cam which means the fuel pump plunger is just finishing the suction stroke;  i.e completely out of time with the engine.

 

Here the fuel pump cam is in the wrong position. When the piston is just after

TDC, fuel delivery should have finished and the follower should be approaching

the peak of the cam.

 

So that the Fuel Pump cam is timed correctly with the crankshaft when the engine is reversed, the fuel pump cams are rotated by a hydraulic servomotor which changes the position of the cams relative to the crankshaft. The angle through which the cams are turned is known as the Lost Motion angle.

Although this can be made to happen when the engine is still rotating, it is probably easier to think of the engine stopped as shown left and the camshaft moving as shown on the animation below. Once the fuel cams have moved, the engine can then start running in the reverse direction (anticlockwise).

Because the engine is started using compressed air admitted through the air start valves, the operating mechanism for these must also be retimed.

More details on the operation of the reversing servomotor as used on the Sulzer RTA engine can be found in themembers section

The angle that the cams move through is the lost motion angle.

This is not the only method of reversing a two stroke engine. Other methods include moving the whole camshaft axially so that a different set of cams are

used, and a rather clever method used by MAN-B&W which alters the position of the cam followers.