Vac-Alert Anti-Entrapment Pool Safety Vacuum Release System - VA200L Vac-Alert reacts in milliseconds, stopping accidents before they happen Designed for suction lift applications only Vac-Alert easily plumbs in line on the suction side of existing filtration equipment Triggers valve pistons to lock, allowing air to enter system and releases the vacuum on main drain Utilizes a check valve assembly, 3.5 pound spring, poppet disc and a one-way vented poppet