Which of the following statements describes how the main propulsion turbine over speed relay initiates closing of the throttle valve?

Correct Answer: Option B — Excessive speed causes an oil pump to develop sufficient pressure to open a spring loaded relay valve which tends to close the steam control valve.

Marine main propulsion turbines frequently employ hydraulic overspeed relays where excessive rotor speed drives an auxiliary pump to develop hydraulic pressure. This pressure overcomes a spring-loaded relay valve, dumping control oil and rapidly shutting the main steam throttle.