AIR-ONLYVENTILATORS.COM

Air-Only ventilator, which is a core device for all models, let air in and keep water out via the use of spherical floats... Operating principle: soft PVC balls float within the vent as soon as there is water on deck, along vertical guides, and form a watertight seal. As soon as the water subsides, the balls descend, letting air in again. Illustrated on pictures below.