The mechanical deaeration process is one of the most economical methods for removing corrosive gases such as dissolved oxygen from boiler feed water. Dissolved oxygen in feed water is the major cause of boiler corrosion. A standard .03 deaerator design removes dissolved oxygen to a maximum level of .03 cubic centimeters per liter of feed water; rating can also be expressed as 44 parts per billion of oxygen in the feed water by weight. A standard .005 deaerator design removes dissolved oxygen to a maximum level of .005 cubic centimeters per liter of feed water; rating can be expressed as 7 parts per billion of oxygen per liter of feed water.