Also Known As:
In a gravity-feed system, the pump draws water from a second tank, called a collector or surge tank. Atmospheric pressure on the pool surface forces water from the pool to replenish the water in the tank. If an outlet is blocked, air is pushed into the pump suction line, releasing the entrapping suction. There are no submerged drains. Instead, an overflow or gutter system circulates the pool water, while water returns ensure that chemicals are properly circulated.
The collection tank must be vented to the atmosphere, and if it is accessible by swimmers, it must also meet entrapment standards, depending on water depth. If there is only one accessible main drain for the system, the system may not have a modulating float valve that allows direct suction.
A gravity feed system and collector tank comply with the Virginia Graeme Baker Pool and Spa Safety Act, a federal law enacted in 2007 that is designed to prevent suction entrapment.