When installed between the fixture waste outlet and the plumbing drainage system, SMITH Fixed Air Gaps provide protection of fixtures such as food processing equipment, kitchen fixtures, storage tanks, etc., from contamination due to back flow in the drain line. (Air Gap fittings in plumbing waste lines are installed on the house side of the fixture trap.) SMITH Fixed Air Gaps when installed in the water supply to a fixture or appliance, such as evaporative coolers, sterilizers, etc., will prevent contamination from cross connection between the potable water supply and the fixture that handles a contaminating liquid or one that is connected to a plumbing waste line. Local codes should be checked.