US Patent 7506663 Magnetic check valve

A magnetic check valve includes a cage mountable in a fluid flow duct and supporting a plunger movable between a closed position blocking fluid flow past the valve, and an open position permitting fluid flow past the valve. One of the cage and the plunger includes a magnet, and the other of the cage and the plunger includes ferrous material magnetically attracted to the magnet to magnetically bias the plunger to the closed position.