What type of valve prevents backflow in a UST system?

The type of valve that prevents backflow in a UST (Underground Storage Tank) system is the check valve. A check valve allows fluid to flow in one direction while preventing it from flowing backward, thus avoiding any potential backflow issues that could contaminate the tank or lead to leaks. This is particularly important in UST systems where maintaining fuel integrity and preventing contamination are critical for environmental safety and compliance with regulations.

The anti-siphon valve, while it serves a similar purpose in preventing siphoning, is not the primary type of valve designed explicitly for backflow prevention in all UST systems. Its functionality is more specialized towards controlling fluid movement to ensure that fuel does not siphon out of the tank under certain conditions.

Flow control valves regulate the flow of the liquid but do not inherently prevent backflow. Pressure relief valves, on the other hand, are designed to release excess pressure to prevent tank rupture, rather than addressing backflow concerns. Selecting the check valve as the appropriate answer highlights its crucial role in maintaining the integrity of the UST system.