Main propulsion engine reversing systems. 1

[turbo65]

Back in 1995 when I was studing for my first class M.O.T , I came accross some questions for which not precise answers were avialables in marine books. One of that was about Reversing system. Tyopicaly there atre two types of tis system one is Lost Motion( B&W GBE, GFC sieries)For which details are given in the books. Another is gain motion for which i couldnot find any theory. If some one can give me references for this system. Also i need definate differnce between safey valve and relief valve.

Turbo65

 

[2081940]

There are Reversing engines and non reversing engines coupled with reversing systems e.g.Reversing Gears, Controllable Pitch Propellers e.t.c
Can you give us an example of a Lost Motion Revercing System?

 

[turbo65]

hi 2081940

example for lost motion reversing system is like in GBE B&W engines where after receiving reversing order came shaft moves few degree against the new direction of rotation of the engine. This backward movement of came alter the timing of fuel pump. Axial shiting of starting came alter the start air timing and consequently engine starts rotating in reverse direction compare to its previous rotation. cam in this typy of reversing is specially designed like an apple .long up circle and very short base circle. in some engines change of follower also alter the fuel pump timing. like in rta seiries of Sulzer engines. Need any more information i m here.

bye

turbo65

 

[bvenkat]

Hi turbo,
As far as I remember, the earlier sulzer engines (RD, RND, and also RTA) had lost motion for reversing, and the earlier B&W engines have gained motion (LGFCA, etc). Difference being in the direction in which the camshaft would have to be turned to achieve the difference in timings, which was because sulzers had positive fuel cams, B&W had negative fuel cams.
About safety and relief valves - safety valves, due to the seat geometry, construction, etc., go to the maximum lift (D/24 to D/4, depending upon the type) the moment the set pressure is exceeded. Lift of relief valve is proportional to the excess pressure. Also, relief valves resit at same pressure, safety valves have reseat pressures lower than popping pressure.

Hope this helps,
Venkat

 

[turbo65]

hi bevnkt,

Thanks for ur valued information regarding my thread. I am fully agreed with ur defination for safety and relief valve. For reversing system of marine engines i need some more detail. U are right about negative and positive cam in sulzer and B&w engines but I need some litrature about these systems. Hoping to continue sharing information

Bye