Question 382General Subjects - Assistant Engineer

The correct answer is C) apparent net positive suction head. When the existing vapor pressure is subtracted from the indicated pressure at the pump suction, the remainder is the apparent net positive suction head. This is the pressure available at the pump suction to prevent the liquid from vaporizing and causing cavitation. The apparent net positive suction head is a critical parameter in pump selection and operation, as it needs to be greater than the net positive suction head required by the pump to ensure proper and efficient operation. The other options are incorrect because they represent different pump performance parameters: total suction head, pump head, and discharge head, which are not directly calculated by subtracting the vapor pressure from the indicated suction pressure.