Pelican cases are molded plastic containers that seal perfectly, with an airtight and watertight gasket. Pelican cases include a barometric relief valve to prevent barotrauma to the case, during transportation, or when the air pressure in the environment may change.

Water leakage through barometric relief valve

If the case falls into a river, generally, if there is not too much contents, there will be enough air in the case to keep it afloat. Since most rivers flow downstream, the case will go from a high altitute to a low altitude, with a likely increase in pressure. The barometric relief valve will therefore, most likely, result in an exit of air, such that the contents of the case remains dry, since water will not go into a valve that is exhaling air.