Which component is essential if a fuel tank outlet is above the fuel distribution line level?

An anti-siphon device or electric valve is essential when the fuel tank outlet is positioned above the fuel distribution line level because this setup creates a risk of fuel siphoning due to gravity. If a breach in the fuel distribution system occurs, gravity can cause the fuel to flow from the fuel tank into the distribution line uncontrollably, potentially leading to fuel spills, hazardous situations, or fire risks.

The anti-siphon device is designed to prevent backflow by creating a physical barrier that stops siphoning action. This component effectively maintains fuel integrity and safety within the system by ensuring that fuel only flows in the intended direction and does not leak due to gravitational forces. Electrical valves can also be used to control fuel flow electronically, adding an additional safety feature that can be activated during emergency situations.

Having only a pump would not suffice in preventing siphoning on its own, as the pump typically only moves fuel when actively powered; without additional measures, siphoning could still occur when the pump is off. Similarly, a valve cap and an emergency shut-off serve different purposes in the fuel system and do not directly address the risk of siphoning in the scenario presented. Consequently, the correct answer emphasizes the necessity of components that specifically counteract the gravitational siphoning risk