Question 648Steam Plants - Assistant Engineer

The correct answer is D) Steam pressure. In a turbo-generator's nozzle control speed regulator, the poppet valves are held closed by the steam pressure. The steam pressure acts on the poppet valves, providing the necessary force to keep them closed and maintain the desired speed of the turbo-generator. This is the primary mechanism used to regulate the speed of the turbo-generator. The other options, such as oil pressure (A), springs (B), and a lifting beam (C), are not typically used to hold the poppet valves closed in this type of speed regulator. The steam pressure is the key factor that controls the poppet valves and, consequently, the speed of the turbo-generator.