The Vac-Alert Model VA-2000S is a Safety Vacuum Release System (SVRS) designed for submerged suction applications. Submerged suction in this case applies to all applications where the circulating pump suction is below the level of the pool water surface. This unit incorporates a 0.375â€Â diameter orifice opening installed below the surge tube section. This orifice opening is sized to provide a limited amount of pump start-up surge protection, while at the same time allowing enough air into the piping system to insure dissipation of the dynamic suction force caused by the circulating pump. The Model VA-2000S SVRS unit also utilizes a check valve assembly equipped with a 0.25 pound spring and a non-vented poppet (no poppet disc or hole through the poppet). This check valve assembly utilizes a light duty spring to minimize the sealing force of the check valve. The non-vented poppet insures that water from the circulating system, under a positive hydrostatic head condition, does not migrate up into the SVRS. For pumps operating 24/7 we recommend installation of the VA-2000S (even if it's a lift application situation).