What function does an OPD serve in relation to propane cylinders?

An Overfill Prevention Device (OPD) serves a critical function as a secondary means of preventing overfilling of propane cylinders. This device is designed to restrict the filling of a tank beyond the specified safe capacity, thereby reducing the risk of potential overpressure situations and ensuring safe operation during use.

When a propane tank is filled, the OPD automatically stops the filling process once the liquid propane reaches a certain level, which helps to prevent overfilling that can lead to leaks or explosions. This is particularly important because excessive propane can expand and create pressure that exceeds the cylinder’s designed limits, posing a danger if not properly managed.

Other options mentioned do not accurately reflect the primary function of the OPD. For instance, while a primary fill indicator or visual weight reference may assist in determining how much propane is in the tank, they do not actively prevent overfilling. Additionally, while a pressure relief mechanism plays a role in safety, it functions differently by releasing pressure in case of an emergency rather than actively preventing overfilling during the filling process.