Where must fuel lines have a shut-off valve?

The correct answer identifies that shut-off valves must be located at the tank and the engine for safety and operational reasons. Having a shut-off valve at these two points allows for immediate control of the fuel supply in case of emergencies, maintenance, or fuel system issues.

The valve at the tank provides a means to stop the fuel flow to the engine, ensuring that leaks or issues can be addressed without the risk of fuel spilling into the boat, which could lead to fire hazards. Additionally, the valve at the engine allows for shutting off fuel during maintenance, reducing the risk of accidental fuel discharge while servicing the engine.

Shut-off valves placed elsewhere, such as at the pump or filter, do not offer the same level of control for immediate fuel supply interruption right before it enters the engine or from the tank, potentially leading to unsafe situations. Thus, the combination of having shut-off valves at both the tank and engine is the best practice for both safety and functionality in a marine fuel system.