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manoeuvring system MAN B&W diagram

main engine start stop control
main engine start stop control

As seen in above manoeuvring diagram the starting handle is at the stop position. The starting handle control three micro switches that convey the following signals

  1. Stop signal (instantaneous signal)
  2. start signal (instantaneous signal)
  3. Run signal (varying signal)

Stop Signal

As long as stop signal has been pressed ,it shall allow the 7 bar control air to pass through and depress the puncture valve and their by not allow the fuel to be admitted to the fuel pump.

Start signal

As soon as the starting handle is moved,the start micro switch will be pressed and stop signal will be over which allows the passage of 7 bar control air through it.If no interlock has operated then it shall allow further passage of the air .Now if the reversing is completed then it shall allow the air to pass through to the air cylinder which shall operate and open the auto start valve on the main air manifold,now the starting air (30 bar) shall go to the distributor and shall convey the 30 bar pilot air to the unit which is in the starting position to start the engine.

Run Signal

Once the engine has started we shall further press the starting handle to the run position and the start signal finishes.The run micro switch being of varying type ,more the handle is turned ,more the switch would be compressed and the output of it shall vary accordingly . The varying signal control the 7 bar control air output that is fed to the governor to increase the fuel proportionately.

Reversing

The engine has stopped in the Astern position and we shall want to move in ahead position, so we will put the AHD/AST Lever to the ahead position , allowing the 7 bar control air to pass through (the pressed AHD micro switch ) and go to

  1. the fuel pump to reverse the cam position via the reversing cylinder
  2. to the starting air distributor reversing cylinder to reverse the distributor

Reversing Completed Interlock

As the reversing has completed ,the shaft of the start air distributor reversing cylinder shall move outwards to press the AHD micro switch ,allowing a part of (7 bar) control air to pass through it and a block valve is released and fulfill the reversing completed interlock.This is provided so that in the event of the reversing cylinder being stuck between AHD/AST micro switch ,then in that condition the interlock shall not allow the auto start valve to open.

man & bmw maneuvering diagram

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The A Frames

Otherwise known as the A Frames. These carry the crosshead guides and support the engine entablature (the cylinder block). On older engines, the A frames were individually erected on the bedplate directly above the transverse girders. When boxed in with plating they formed the crankcase. The trend nowadays is to build the frame box as a separate fabricated construction and then, after stress relieving and machining the mating surfaces, to mount it on the bedplate. This has the advantage of saving weigh.  a frame

engine a frame

Lowering the A frame onto the bedplate. A small amount of jointing compound is used to ensure an oil tight joint

 a frame

 

 

 

 

 

 

 

When the frames are aligned on the bed plate they are secured together by drilling and reaming and using fitted bolts.

Cracking in A frames can occur leading to misalignment and excessive wear of the running gear. Cracks can start from welds, sharp changes in section and where strengthening stringers are terminated sharply. Repairs can involve cutting the crack out, grinding and rewelding. The danger is that after repair there may still be misalignment.