At the bottom of the deepest section of concrete swimming pools sits the main drain assembly. Screwed into the floor of the drain sump is a small, spring-loaded brass or plastic valve called the hydrostatic relief valve.
The Purpose and Failure Mode of Hydrostatic Valves
When high groundwater tables threaten to lift or "float" an empty concrete pool out of the earth, this valve opens to allow underground water into the pool. However, fine desert sand, plaster dust, or worn spring gaskets can jam the valve partially open, allowing pool water to continuously drain out into the subterranean soil.
Underwater Dye Testing and SCUBA Replacement
Our certified diving technicians test the valve using heavy fluoroscein dye at the bottom of the pool. If leaking, we replace the valve underwater using specialized tools without draining the pool.