Answer: B) When there is excessive blow-by gas pressure or high crankcase pressure
Explanation: Relief valves in diesel engine crankcases operate when there is excessive blow-by gas pressure or high crankcase pressure. These conditions can occur due to high engine load, worn piston rings, or inadequate ventilation, and the relief valves help to prevent damage by releasing excess pressure.
Answer: B) When there is excessive blow-by gas pressure or high crankcase pressure
Explanation: Relief valves in diesel engine crankcases operate when there is excessive blow-by gas pressure or high crankcase pressure. These conditions can occur due to high engine load, worn piston rings, or inadequate ventilation, and the relief valves help to prevent damage by releasing excess pressure.