The Model 3K00 Pressure / Vacuum Vent is designed for use on atmospheric and low-pressure storage tanks where pressure and vacuum relief are required. Weight-loaded pallets in the vent housing allow the intake of air and the escape of vapors as the tank breathes due to thermal changes and product movement in and out of the tank. The pallets open and close to permit in-breathing and out-breathing necessary to maintain the tank pressure within permissible limits to avoid damage to the tank.