Water seal deaerator DA 5-25 is designed to operate as a device of protection against dangerous build up of pressure and water level in the atmospheric deaerator. The safety device consists of two valves and the expansion tank. One water seal protect the deaerator from excessive pressure, and the other from a dangerous increase of a water level; they are United in a common hydraulic system. Expansion tank water seal is required for the accumulation of the water volume once the water seal has worked. ie makes the device smazlivaya. The hydraulic lock DA 5-25 is connected to the deaerator tank through the overflow fitting. Also, to reduce the construction height and the installation of de-aerators in the rooms, instead of valves install relief valves that protect against excess pressure and steam traps to the overflow fitting.