Final answer:
The engine should be stopped when the desired delivery has been completed or when maintenance is needed.
Step-by-step explanation:
In engineering, the engine used to operate a pump during a delivery should be stopped when the desired delivery has been completed or when there is a need to perform maintenance on the pump or engine. Stopping the engine ensures that the pump is not running unnecessarily, conserving energy and reducing wear and tear on the system. For example, in a water distribution system, the engine may be stopped once adequate water pressure has been achieved and the desired amount of water has been delivered.