Thank you, that answered the questions I had.To control the direction of the engine and set the cutoff point, the engineer at the controls would have to move a “reversing” lever that would cause the expansion linkage to move to an ahead or astern position. For large engines such as on the Titanic, a hydraulic cylinder called a Brown’s engine would be used to actually move the linkage. The movement of the linkage would be adjusted to control the desired cutoff point that steam is admitted to the cylinders and thereby set the desired degree of steam expansion within the cylinders. At full ahead speeds, a cutoff point of about 40 to 45% of the piston stroke might be used.
See: Titanic’s Propulsion Plant