What is the purpose of a vent restriction device in USTs?

The purpose of a vent restriction device in underground storage tanks (USTs) is primarily to prevent overfilling. This device plays a crucial role in regulating the flow of vapors and liquid during the filling process. By limiting the amount of air that can escape from the tank during fill operations, the vent restriction device ensures that any expansion of vapors is managed effectively, thus preventing the risk of overpressurization or releases into the environment. If a tank were to be filled too rapidly or without appropriate venting, it could lead to spillage or overflow, which presents safety risks as well as potential environmental hazards.

This mechanism is essential in maintaining the integrity and safety of the UST system. It helps to ensure compliance with regulations regarding safe tank operation and prevents hazardous situations that could arise from improperly managed fill operations.