a. With suitable sketch & describe the operation of a large starting air v/v.
b. Explain main causes of starting air line explosion.
c. Discuss how explosion can be avoided.
d. During maneuvering if starting air line explosion occurs what action will you take?
e. What are some indication fire in starting air line?
f. How do you check the cylinder starting air valve for leak?
g. What are the reasons for an engine failing to turn on air although your air receivers are fully charged?
h. What are the reasons for an engine that can turn on air but fails to fire?

a. Starting air valve sketch:

Description:

• Fitted in each cylinder cover
• Timing of opening & closing is controlled by air distributor
• Balance piston & valve head are of same nominal dia to hold the valve in balance when main starting air is in the chamber
• Spring holds the valve closed
• Guide ensures correct alignment of valve
• pilot air comes from the distributor pushes the Operating piston downward to open according to the sequence

b. Causes of starting air line explosion:

• The ‘link’ between the starting air-line manifold and the cylinder combustion chamber is the cylinder starting air valve.
• The main causes are due to leaking or sticking/sluggish/erratic operation of the cylinder starting air valve.
• When the above occurs, the hot semi-burned fuel gets forced into the starting air manifold. This is because firing pressures are usually higher than 100 bars as compared to starting air pressures of 30 bar.
• As more of the hot semi-burned fuel accumulates in the air line, the fuel reaches the explosive limit and spontaneously ignites causing an explosion.

c. Prevention of starting air line explosion:

1. maintain air start valves
2. Ensure good working condition of flame trap
3. maintain starting air lines clean
4. drain air bottles regularly
5. open air line valves slowly
6. maintain proper compressor lubrication

d. Action in the event of starting air line explosion:

• Immediately inform bridge and slow down ME
• Stop engine when order received
• Cut off fuel of the affected cylinder
• Stop aux blowers.
• Start boundary cooling adjacent the affected cyl. in the starting air- line branch.
• Do not attempt to the start the M/E whilst the standing air-line branch is hot.

e. Indication of starting air line explosion:

1. The starting air-line manifold starts to
   1. Becomes ‘smoky’ due to paint burning
   1. ‘Blisters’ or ‘bubbles’ form on painted manifolds
   1. The manifold becomes glowing red hot
2. Due to loss of compression pressure, unit may experience high exhaust temperature and power developed will be lower

f. Starting air valve leak test

• Finished with engine
• Get propeller clearance from bridge
• Indicator cocks must be open
• Unit to be tested to be brought to TDC
• Turning gear must be disengaged for test
• Control air to starting air distributor must be SHUT
• Automatic starting air valve must be manually opened
• If start air valve leak, hissing sound is heard at indicator valve.

g. Engine fail to start even if air receiver full:

• Although Turning gear disengaged, limit switch stuck in engaged position
•  Engine not on ‘standby’ mode
• Aux blowers’ circuit breakers in ‘off’ position
•  leaks in the pneumatic control pipes
•  Automatic starting air v/v stuck / defective
•  Air distributor v/v and/or limit switch stuck in close position
•  Reversing mechanism faulty due to stuck pneumatic actuator/incorrect position of roller and proximity switch not activated
• No electrical power supply to remote control unit
  •  Solenoid operated valve problem
• Interlock / safety cut out device active / faulty or not reset

h. Engine start on air but fail to run on fuel:

• Minimum engine rpm not attained on starting air or the rpm not sensed by pick-up sensor to run on fuel. Check setting for engine start level
• Governor defective and/or regulating lever defective
• Fuel pressure in the engine manifold to the fuel pumps insufficient due to defective pressure regulating valve in the return line
• When change-over to LSFO (gas oil), due to worn fuel pump plunger/barrels, there will be insufficient fuel oil pressure build up
• Puncture valves stuck in open position
• Fuel rack maybe stuck due to high cat fines.