Where must the pressure relief valve of all containers be positioned?

The pressure relief valve must be positioned in the vapor space of all containers to ensure optimal safety and effective functioning. The vapor space is the area in the container where the gas phase exists above the liquid propane. This positioning allows the relief valve to release excess pressure that could accumulate in the container.

When pressure inside the container exceeds the design limits, the relief valve opens to release gas, which helps prevent potential overpressure situations that could lead to catastrophic failures such as explosions or ruptures. Additionally, by being located in the vapor space, the relief valve can efficiently vent excess pressure without being influenced by the liquid propane, which would not only be inappropriate but could also hinder the valve’s operation.

It's important to note that positioning the pressure relief valve in the liquid space, gas space, or atmospheric space would not provide the same level of safety and efficiency. For example, placing it in the liquid space could result in liquid propane being released instead of gas, creating a much greater risk due to the flammability of propane. Thus, the vapor space is the safest and most effective location for the pressure relief valve.