This is a “check” valve that is installed in the main drain of most pools. It is held in the “closed” position by the weight of water in the pool. (Think of your 9-ft. deep, empty swimming pool as being a big boat sitting in the ground. Now, imagine that the water table in your area is only 6 ft below the surface. Your empty pool could actually lift up out of the ground or float to the top of the water table.) If the water level in the pool is reduced to a level lower than the depth of ground water around the pool, the hydrostatic relief valve should open, allowing the ground water to enter the pool, relieving pressure on the pool structure.
PLEASE SEEK PROFESSIONAL ADVICE BEFORE EMPTYING YOUR POOL.
Posted in: NEW POOL OWNER