What is one purpose of a fuel tank vent?

A fuel tank vent serves multiple important functions, one of which is to maintain atmospheric pressure within the tank. As fuel is consumed or expands and contracts due to temperature changes, the air pressure inside the tank must be balanced with the outside atmospheric pressure. If this pressure becomes unbalanced (for example, if fuel is drawn from the tank without a vent allowing air in), a vacuum can form, making it difficult for fuel to flow. This would lead to operational inefficiencies or even damage to the fuel system. Proper venting ensures that air can enter the tank to fill the space left by the departing fuel, thereby facilitating smooth fuel flow and maintaining the integrity of the fuel system overall.

The other potential purposes listed have relevance, but they do not represent the primary function of the vent. For instance, while a vent may help with fuel expansion, its critical role is to ensure atmospheric pressure balance.