What device is installed in the fill pipe of underground tanks to stop the flow of product during delivery?

The device designed to stop the flow of product during delivery in the fill pipe of underground tanks is a flow shut-off device. This type of device plays a critical role in ensuring that the delivery process is safe and prevents overfilling, which could lead to hazardous spills and environmental contamination. Flow shut-off devices are typically equipped with sensors that detect when the tank is nearing its maximum capacity and automatically halt the inflow of product to prevent overflow.

In the context of underground storage tank systems, having a flow shut-off device is essential for adhering to safety regulations and protecting the surrounding environment. Other systems, while important in their respective functions, do not serve the purpose of stopping or controlling the flow of liquid during tank filling. Therefore, the effectiveness and necessity of flow shut-off devices make them the correct choice for this question.