Deaerators are used to remove dissolved, corrosive gases from boiler feedwater. They heat incoming makeup water for injection into the boiler, and return the condensate to a temperature which minimizes the solubility of gases such as oxygen, carbon dioxide, and ammonia. Typically, deaerators are located inside boiler rooms, where they are elevated to increase head pressure and heat water for injection. Because boiler water contains significant amounts of dissolved oxygen, pitting and iron deposition can occur. Pitting produces failures when only small amounts of metal are lost, and the rate of corrosion is still low. The high temperatures of boiler feedwater increases the corrosivity of dissolved oxygen so that even small amounts of this dissolved gas can cause significant corrosion. There are two basic types of deaerators: tray and spray. Both use cold makeup water and a high-temperature steam environment to remove dissolved gases. Tray deaerators reduce incoming makeup water to a fine spray as it falls over rows of trays. By heating this water to within several degrees of its steam-saturation temperature, tray-style deaerators can remove most of the dissolved oxygen from the makeup water. The remaining deaerated water then falls below the trays, and a steam blanket prevents recontamination. Spray- deaerators operate on the same principle as tray deaerating heaters, but differ in terms of method. Nozzles spray makeup water into a steam environment while a vent valve remains open to maintain a continuous plume of vented vapors. Tray deaerators and spray deaerators can be either vertical or horizontal. They may feature a one- or two-tank configuration and offer an optional pump package. Tray-type deaerators have a water inlet, heating trays, air separating trays, overflow area, drain inlet, and steam inlet. Spray-style deaerators have many more components. In two-tank systems, the top tank includes deaerating trays, distributing pans, spray valves, atmosphere vanes, and relief valves. Spray deaerators also have a tray door, hood enclosure, water box, condensate inlet, steam baffle, steam inlet and high-pressure heater drain relief. The bottom tank has a deaerated water outlet, thermometer, flush preventer, outlet to service, manhole and level gauge. Both the top and bottom tanks have equalizers.