Fuel tanks need to be vented to eliminate any pressure that might build up inside the tank and supply a constant flow of fuel to the engine. Venting lets air out, helping keep the pressure inside the tank down to a nice, safe number that the fuel pump can easily handle. Not releasing pressure can force it all on the pump, straining it and shortening the pump's life by as much as 20%. Since the pump sucks fuel from the tank, it would create a vacuum effect, and if it is not vented properly, then it could be a case of vapor lock, where the fuel vaporizes before reaching the engine, which means stalling and loss of power.
Today's venting systems are integrated with the OEs evaporative emissions control (EVAP) system, which keeps fuel vapors in the vehicle and out of the environment. The function of the EVAP system is to trap vapors, recycle them and send the vapors back to the engine to be burned—waste not, want not. This is where venting comes into play, if there is excessive pressure in the tank the fuel pump will not be able to achieve the necessary 40-60 PSI pressure range. Vent is even more critical in high-performance applications where pressures can > 100 PSI and is at extreme risk for pump damage and vapor lock in race conditions.
Finally, venting minimizes the chance of overheating the fuel pump. Because in-tank pumps are cooled by the surrounding fuel, lack of venting can create an excess amount of pressure, which drives the pump temperature up 10-15 degrees Fahrenheit. Excessive wear on components from high temperatures can lead to pump failure, sometimes before it reaches the end of its expected life. The automotive community generally advises that bromination systems (both for blowers and evaporators) be checked frequently, particularly in older vehicles; plugged vents or defective EVAP components can be expensive to fix and will require pumping replacement.
A fully functional venting system ensures optimal Fuel Pump performance, reduces the risk of vapor lock, and helps keep the fuel system balanced and efficient. Venting enables pump life extension and preserves the vehicle performance under all driving conditions by enabling pressure to stabilize.