The oxygen-removal water tank level adjustment is achieved by the differential pressure balance container sending high and low level signals, which then controls the oxygen-removal valve's opening through the DCS to alter the incoming water flow. Should the water flow to the feedwater and other drainages be abnormal and exceed the control range of the regulating valve, causing the tank level to continuously rise to the overflow level (high-high level), the interlock will open the overflow electric valve to discharge the excess water from the tank into the condenser.

If the water level reaches a dangerous high level, close the steam backflow check valve to prevent the main engine from flooding when it's full; simultaneously, open the emergency drain valve to prevent the water level in the deaerator from rising further. When the water level drops slightly below the normal level, the overflow electric valve will close automatically. When the water level falls below the set value, the feedwater pump will trip in an interlock. The level of the deaerator can be observed locally through a magnetic float level indicator or monitored in the control room via a level indicator. When the water level reaches high level, overflow level, high level, and drops to low level, the indicator will send out an alarm signal with sound and light to the operating personnel.