Hi PD's
Ok...so I think you've got the telegraph bit sussed out pretty well...but the notched ARC ..... and SPEED control.....NO.
The, so called, notched arc originated in the early railways, and it's sole purpose is to control and position the engine valve gear for either FORWARDS or REVERSE, with a Neutral position in the centre.
Which end of the arc was Forward or Reverse was dictated largely by the particular valve gear layout.
A considerable number of steam operated vehicles used such a REVERSING QUADRANT, including locomotives, traction engines, steam lorries and of course, ships; or at least the smaller versions of the later.
Its application was applied only where the size and weight of the valve gear permitted it's use....on larger machines, such as very large locomotives or large marine steam engines, where the physical weight of the valve gear was quite large, to say the least, then alternative means were used...eg. screw reversing or hydraulic or even steam, however, in most of these cases the notched quadrant was ommited, since it became redundant.
Take a look at the pictures of the TITANIC'S engines I posted a short while back......the BL***Y great wheel in the centre of the engines is the reversing gear control....took three men to work it.....but then the valve gear did weigh in at around 600 tons.
For those engines that did have notched quadrants, the valve gear was connected , via a pushrod (known as a reach rod), to a latching control lever (hand operated) which worked over the quadrant and could be locked into any of the notches.
When in the central position, the engine was said to be in Neutral Gear, and if the engine could be turned over manually, you would see that the slide valve, or piston valve, would only move a very small amount (in a well designed valve gear system this movement would only be sufficient to accomodate the LAP and LEAD (if used) of the slide/piston valve).
In this position the valve gear would only permit the smallest amount of steam to enter the cylinder (and then only if LEAD was used) and it would certainly not be sufficient to start the engine under normal load conditions.
When the control lever was in either of the outer ARC (quadrant) notches, either Forward or Reverse, then the valve gear was said to be in FULL GEAR. IN these positions the engine could produce MAXIMUM power.
The intermediate notches were there to provide a means of locking the gear at differing CUT-OFF points. (but with reduced power output)
EG. if FULL GEAR = 80% cut-off, then it would be reasonable to have say 3 other positions, each one a little closer to the centre, for say 70%, 60% and 50%.
The purpose of reducing cut-off is to reduce the amount of steam the engine uses for a given load state, and thus improve the overall efficiency of the vehicle/vessel.
Typically, this would occur once the vehicle/vessel had attained its desired speed and, since kinetic energy could now play a part in continued movement, the valve gear could be altered to say 60% cut-off, which would allow the vehicle/vessel to continue on its way, with no speed loss, but using far less steam.
THIS IS KNOWN AS 'NOTCHING UP', for obvious reasons.
:wink:
THE NOTCHED ARC(quadrant) is NOT USED to control the SPEED of the engines.
This task is performed by the REGULATOR (or THROTTLE) and this is a completely separate control.
When STARTING any steam engine, the valve gear is placed into FULL GEAR (for the chosen direction) and the Steam is allowed in via the REGULATOR.
When a ship (like Waverley) is being manouvered then the valve gear is moved between both FULL GEAR POSITIONS...never any intermediate one, OTHER THAN NEUTRAL, and this would only be when either STANDBY or FINISHED WITH ENGINES was selected on the telegraph.
STOP ENGINE can occur at any position of the quadrant, since this just means...SHUT OFF THE BL***Y steam.
The difference between STANDBY and FINISHED WITH ENGINES, is that in the latter case the engineer/s would close off all steam valves from the boilers, and possibly also turn off the boiler burners.
OK chaps, I hope that helps a bit more.
I will be going in to valve cut-off , LAP, LEAD etc in the next part of the SAGA....So don't panic, if you are not familiar with these terms.
Best Regards.
Sandy

:vacat