The Pressure Relief Valve was designed to counter the effects of hydrostatic pressure in larger ponds with a minimum depth of five feet. The Pressure Relief Valve is a spring-loaded device (rated at 90 PSI) that opens when enough hydrostatic pressure is present, allowing the ground water to enter the system. Once the pressure is released, the valve will close on its own and the spring gasket will re-seal the system. A 2″ bulkhead fitting is required to thread the valve into.