8/16/2019 Marine Engine Troubleshooting Air Starting Systems_ Engine Will Not Start or Starts and Runs in the Wrong Direction

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Leave a commentStarting & Reversing Problems in Marine Engines

written by: Willie Scott • edited by: KennethSleight • updated: 11/14/2011

There are a number of reasons for starting and reversing problems in marine engines. This malfunction is one of the

most frightening and dangerous situations to encounter when maneuvering a ships main diesel engine, but it can be

avoided through regular maintenance of the air start components.

 A ship ’s main marine diese l en gine is started on co mpressed air tha t is co ntrolle d by variou s compo nents o f the a ir start

system. It is a well-tried and tested reliable system, but it can go wrong if not properly maintained.

The following sections examine a typical air start system, with the first section providing a n overview of the system.

Overview of System

The air start system looks rather complicated, but it is quite simple wh en you examine it without the safeguards. These

are put in place to prevent such occurrences as starting the engine without having a signal from the engine room

telegraph, trying to start the engi ne with the turning gear engag ed, or trying to start ahead when the telegraph asks for 

astern. There are also safety systems incorporated such as a bu rsting disk and numerous non-return valves in the event

of a leaking air start valve.

The next section lists some of the problems that can be encountered when maneuvering.

Problems in Air Start Systems

We shall look at two common problems encountered when maneuvering the main engine: not starting and starting in the

wrong direction (reversing instead of starting ahead).

Not Starting

 As we have seen, the re ar e vari ous i nterlocks in p lace to pre vent the engi ne bein g started until certain criteria are met. If 

the engine won’t turn over on air, the bridge should be informed then the following checks should be carried out.

1. Check air start supply valves from air receivers are open and that the pressure is 30 bar.

2. Check that the turning gear is disengaged

3. Check that the turning gear and telegraph solenoid valves have actuated. This will supply air to the automatic valve,

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8/16/2019 Marine Engine Troubleshooting Air Starting Systems_ Engine Will Not Start or Starts and Runs in the Wrong Direction

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air distributer, the air manifold, and air start valve.

These are the initial checks that can be quickly carried out. If these are all satisfactory, then the problem lie s in the

controls ahead/astern solenoids. The air distributer or the air start valve itself may be stuck in the closed po sition. The

ship will need to anchor or be towed alongside for these checks to be carried out.

Engine starts in wrong direction

If the engine starts in the astern instead of ahead direction, the following checks should be carried out.

1. Ensure the air start control moves to reverse mode at the control station. This is a visual check and can be observed

when the telegraph rings from ahead to stop then astern. If this does not happe n, the solenoid valve may be stuck.

2. The oil and air supply to and from the reversing valve should be checked. A blockage of either will stop the

reversing servo motor operating and allowing change over from the astern to ahead position.

This again will take further investigation, so the ship should anchor or remain tied up to the quay.

 As this a head /astern cha ngeo ver is controll ed by lu be oil and compresse d ai r an d is interlo cked w ith the fuel p umps.

These are the usual culprits and the starting point of a thorough investigation. I have experienced this situation only

once and fortunately we were leaving port and still tied to quay by stern spring. Once the bridge was informed, a rope

from the fo’c’sle was thrown ashore and made fast. This gave us the chance to check for the fault, which turned out to be

the oil supply from the crosshead oil supply pipe being blocked.

 As I have said before, the mainten ance of the air start system compo nents i s para mount to the opera tion o f the system.

Main Components of the System

Air supply system

Two air compressors

Two air start vessels

Numerous non-return valves

Numerous drain valves

Control system

Turning gear out sol v/vTelegraph signal sol v/v

 Automatic val ve

 Ahead and astern ch ange -over 

 Air di stributer 

 Air start val ve

Anti-explosion components

 Air sup ply to manifol d from air vessels n on-return valve- this pre vents ho t gasses from return ing to air receive rs.

 Air man ifold pressure relie f valve – this opera tes if pre ssure ri ses du e to heat from gasse s.

 Air sup ply to air start valve bursting disk – this di sk rupture s un der i ncreased pressure caused an a ir start va lve

leaking back.

Mandatory Safety Precautions

Before we get into the op eration of the system in the next section, this is an opportune moment to make a closer 

examination of the precaution against explosion, which is a very real threat even in today’s modern engines that

incorporate the latest in engine management systems.

Compressors

The compressor air inlet filters should be positioned in an oil-free zone, i.e. no oil fumes should be present.

The compressed air supply lin es to the air receivers must be p rotected by no n-return valves.

The air receivers

There are two air receivers, linked by a common d ischarge pipe to the system. The air from the compressors will contain

oil and water (there is no way around this). This mixture ends up in the air vessels as a mist, eventually settling to the

bottom of the vessel. It is imperative, and I cannot overstress this, that the mixture be drained from the vessels after every

charge, and regularly when maneuvering. The oil also coats the internal of the supply pipes; this too can be reduced by

draining the air vessels.

These actions, as well as checking by hand for heat in the air supply pipe between the air start valve and the air 

manifold, form part of the watch keeper’s duties. Any excess heat here, and the fuel an d air to that particular cylinder 

should be isolated, and the bridge made aware of the situation.

Before we leave the precautions there are many examples o f air start system explosions. One of worst ones occurred on

the MV Capetown Castle, killing seven engineers. Lloyd’s register recorded 11 such explosions between 1987 and

1998; all down to oil gathering in the receivers and piping and ignited by exhaust gasses. One a year speaks for itself:

drain the air vessels regularily and maintain the system.

 A sketch sh owin g an air start system whe re the air start valve is le aking is sho wn b elow. No te the pipe that shou ld b e

checked by hand for overheating;

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References

marinediesels: Air Start System

 Author's Experi ence

 All Dr awing s by Au thor 

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