If a sight gauge is used on a diesel fuel tank, what must accompany the gauge?

When a sight gauge is installed on a diesel fuel tank, it is crucial to have shut-off valves both above and below the sight gauge. This requirement ensures that the fuel flow can be halted on either side of the gauge, allowing for safe maintenance or replacement of the gauge without releasing fuel into the environment or compromising system safety.

The presence of these shut-off valves enables a safe and controlled way to isolate the sight gauge, preventing spills and minimizing risks associated with handling diesel fuel. Moreover, since sight gauges can be susceptible to breakage or malfunction, having the ability to quickly shut off the fuel supply is essential for safe operations.

While other components or systems like pressure relief valves, filters, or bleed valves may serve important roles in fuel management and safety, they do not directly relate to the operational requirement and maintenance considerations specific to sight gauges. The primary focus here is on maintaining control over the fuel system during maintenance or repair, which is why the option of shut-off valves is the correct answer.