Deaeration in a Spray & Tray-type Deaerator occurs in two distinct stages.

The first stage occurs in the spray section, where the feed water passes through the Spray Valve, forms a water film, and comes into contact with the steam for heating. At this stage, the feed water is heated to within approximately 2–3°C of the Deaerator's operating temperature, and more than 90% of the non-condensable gases in the feed water are removed.
The second stage takes place in the tray section, which consists of multiple layers of a Tray Assembly. As the feed water passes through this section, it continues to contact the heating steam and is heated to saturation temperature, and the remaining dissolved gases are fully deaerated.
Although the temperature rise and quantity of gas removed in the tray section are proportionally smaller than in the spray section, this stage has a direct bearing on the final deaeration performance. Therefore, it is an indispensable feature of any high-efficiency deaerator.