Operation and Control of a Steam Ships Engine

[Captain Jerry]

Bob

No electric motors on Monitor but the big hand wheel does drive a screw that  shifts the eccentrics. 

There has been some discussion of the correct angle with a good contribution by Tim (Tvought)  as what is needed to achieve a symetric  forward/reverse valve position as a function of "the angle of advance" which depends on the length of the connecting rod and the crank throw. It is never exactly 180 deg just as adjusting the eccentric/crank lead is never actually 90 degrees, but it is a good starting point. 

After making my post last night, I went back to the videos of Ericsson's gear and see that I was slightly mistaken.  The gear only rotates the two outer eccentrics which control the slide valves and not the two inner eccentrics which control the cut off valves.  This would seem to put the cut off valves out of sync with the main valves.  There is a very convenient lever that by-passes the cut off valves and seems likely that cut off would not be needed in reverse.  You have to remember that the valve rods work through crank/levers where the outer eccentric rod motion is translated to the inner valve rod motion.

If you haven't seen this, here is a YouTube link to Carlstadt's model.
[youtube1]https://www.youtube.com/watch?v=VWn8gQ9Ykpk[/youtube1]

[Dan Rowe]

Shell and tube vaps are blowndown to descale. you were had!!

Bob,
That was my first ship as an engineer fresh out of school....

Wow what a slow burn

I never saw another one of those in my sailing days so I never gave it another thought or obviously read the book.

Cheers Dan

[Maryak]

After making my post last night, I went back to the videos of Ericsson's gear and see that I was slightly mistaken.  The gear only rotates the two outer eccentrics which control the slide valves and not the two inner eccentrics which control the cut off valves.  This would seem to put the cut off valves out of sync with the main valves.  There is a very convenient lever that by-passes the cut off valves and seems likely that cut off would not be needed in reverse.  You have to remember that the valve rods work through crank/levers where the outer eccentric rod motion is translated to the inner valve rod motion.

Hi Jerry,

In a "normal" triple expansion marine engine with Stevensons link and two eccentrics per cylinder the ability to vary cut off is only available for the ahead eccentric and is a part of the weigh shaft which moves the links via the reversing engine. The cut off adjustment is arranged on the weigh shaft such that it is somewhat below being horizontal in the ahead position and can be screwed in or out for each cylinder thus varying the valve travel from full out to line-in-line to full in. When the engine is reversed the screw mechanism adopts a vertical position and can in no way affect the valve travel via the astern eccentric. Cut off varies between cylinders so that the cylinders are balanced in the amount of horsepower each is providing with the aim being to make them each produce the same fraction of the total. For most economical operation, the HP is linked full in providing maximum cut off. The engine is now out of balance but is using the minimum amount of steam as less in the HP results in less into the IP and LP. Lastly it is a long and involved procedure to balance an engine, many indicator diagrams are taken of the cylinders before the Chief is satisfied. Like most things to do with these engines the work is hot heavy and dangerous.

Thanks for the link to the engine.

Regards
Bob