The total length of stroke in a reciprocating steam pump can be adjusted by __________.

Correct Answer: Option D — changing the setting of the tappet collars on the pilot valve operating rod

The stroke length of a steam reciprocating pump is governed by the timing of the pilot valve. By adjusting the tappet collars on the operating rod, the engineer controls when the steam valve shifts, thereby determining the point of reversal for the piston and the total length of the stroke.