5 Brilliant starting air line safeties to avoid an Explosion

Safeties in air starting line:

In ancient times, when people refuse to listen to their storyteller at night, guess what happens?
They become lunch for the lioness.

It's important. to pay attention to the "air starting line safety" in preparatory classes. Since this could potentially turn into a serious hazard- if left unattended.

Like what happened in 1960.
Capetown Castle took the lives of 7 men as a result of starting air line explosion

Have this short post on a way to become a reliable engineer.!

How Can the Air starting Line Explode?

Before we dive into the essential safeties, let's fire up your air starting line neurons in case if it's inactive for the last 230 days. Or if it's overwritten by your favorite song.

air starting line explotion and safety diagram
A simple air starting diagram for easy understanding.

Understanding this simple air start line diagram can help you at the time of manoeuvering. Or when you look up to the actual manoeuvering diagram in the future.

Now, From our fire triangle

Fuel, air, oxygen are needed for a fire.

1. Oil carried from air compressor air acts as fuel
2. And we have plenty of oxygen from incoming air 
3. And the third side is completed if the air start valve on the cylinder is leaky.

Understanding this simple air start line diagram with fire triangle

And yes. If all the ratios are correct, then there is a chance of fire or air starting line explosion.

Causes of starting airline explosion on ships

1.  Leaking start air valve or air start valve stuck in an open condition.

2. Oil particles carried along with the air compressor stick to the internal surface of the pipe which has the potential for combustion.

3. If starting air valve leaks, flame or hot gases vapourize the oil and sets the oil mist on fire.

Air start valve on the air start line
Air start valve on the cylinder

Prevention of starting air line explosion.

Here are the little things you need to do for avoiding air starting line explosions.

1. Maintenance and overhaul of air start valve.

2. Air starting valve leakage test before manoeuvering.

3. Regular draining of air bottle and air starting system.

4. Minimum cylinder lubrication to air compressor if there is a setting.

5. Regular maintenance of air compressors especially air compressor valves.

Essential air starting line safeties

1. Flame arrester in air starting line

Difference between flame arrester and a flame trap?

Flame trap: It traps flame.

Flame arrester: It traps and quenches. ie; dissipates heat by absorbing. With its high specific heat material which is copper

 A typical flame arrester and dissipation of heat.

2. A safety relief valve in air starting manifold

Okay. I understand. A relief valve doesn't need an intro.
Anyway, this relief valve in air starting manifold vents to the atmosphere. Check the Diagram Below

A diagram showing internal parts of a relief valve on the air start manifold as safety
A diagram showing internal parts of a relief valve on the air start manifold.

3. Bursting disk (Material - copper) in the air start valve

If the valve leaks, the pressure increases, and the bursting valve bursts.

ie; if the cylinder head valve is leaky, the firing pressure acts on the branch pipe. and depending upon the class. each bursting disk is located at the branch pipes. See the diagram down for better understanding

Bursting disk in the air start valve as safety

For example, let's say, for Japanese class, 1 bursting disk on the manifold and 6 flame arresters on each branch pipe. for a 6 cylinder engine

and in the case of Lloyd's, there are each bursting disks and one flame arrestor on the manifold.

Actions to be taken when bursting disk burst while running:

We could hear a sound of the leaking air coming out if the bursting disk bursts. 

And we can identify in every upward and downward stroke of the piston. We can hear the sound through the burst out bursting disk which comes from the leaky cylinder head valve. Gotcha.!

Some might say that by checking at the air bottle pressure we could know, but the automatic air starting valve will close -  while the engine is running. 

PS: Not to confuse with Automatic air start valve and air start valve on the cylinder.

What action will you take if Bursting disk Bursts? 

Lock the bursting disk

1. Slacken the butterfly nut.
2. Turn the perforated cover.
3. A perforated cylinder Inside the perforated cover so that holes get covered.

If you are in the middle of the manoeuvering, replacing the air start valve is not possible. so, cut-off fuel pump to that specific unit.

Slacken the wing nut. There are holes in the cylinder as well. so when you turn, there is a mismatch between holes and the cover. so that the air will not come out. ( ie, Turn the perforated cover on the perforated cylinder) 

You still can continue manoeuvering but reduced load.

4. Non return valve in air starting line

Non return valve is incorporated in the Automatic air start valve.

All 4 safety devices shown in the air starting diagram.
All 4 safety devices shown in the air starting diagram.

5. Thermal patch in air starting line

It's just a sticker on the branch pipe to the cylinder head valve line. 

When starting air valve becomes leaky, the branch pipe becomes hot hot hot and colour of thermal patch changes. so that you don't have to touch and feel it. Just by looking itself, one can understand that the air starting valve is leaky.
PS: Turning gear interlock and reversing interlock aren't safeties for the air starting line. these are safeties for the engine.

How do you test air starting valve for leakage?

1. While running - Air leakage test

By touching the nearer pipe or by the thermal path that we discussed earlier. 

2. While stopped condition - Air leakage test

Shut the valve to the air distributor (valve shown near to the relief valve in the above diagram)
if you do this, no pilot air opens the air start valve. and all the air start valve remain closed position.

 At this point, I highly recommend you to watch this video by Sriram sir. As he beautifully explains air starting valve working.
Video explaining how air starting valve works
Now, as we were discussing, 

1. Shut the valve to the air distributor so that all the air start valves on the cylinder head remain closed.

2. Open all the indicator cocks.

3. Disengage the turning gear.

4. Give an air kick.

5. If air leaks through the indicator cock, it is leaky. Change the air starting valve.

Air starting valve is a great friend. It helps in starting the main engine and crash stopping.

I'm working on a detailed Man B&W Manoeuvering diagram for you.

Comment down if you still got any doubts. And as always, We are happy to help you.
I hope you got a complete understanding of the starting air line and its safeties. 

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Thank you and have a nice day.!

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