Condensate drain

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ND = wet steam, WD = water vapor, W = water

Condensate drains (also called condensate or "stevedores") are control valves that automatically divert the condensate that forms in steam lines and forming processes into a mostly parallel pipeline without any significant amount of water vapor escaping from the line.

In most systems in the chemical, pharmaceutical and energy technology industries, steam is used as a heat transfer medium. This is usually made available centrally in different pressure levels, for example from a power plant. Due to conduction losses and the respective applications, the release of energy leads to the condensation of part of the steam. In order to prevent steam hammer and to ensure that energy is used effectively, condensate must be removed from the system at an early stage. Steam traps are also used to return the condensate to the system to ensure that there is only water in the return lines, which are still under overpressure.


To distinguish between the various states of aggregation and to separate them, the various steam traps make use of different physical properties of the gas / liquid of a substance:

  • Float steam traps use the higher specific gravity of water to separate it from the steam.
  • Capsule steam traps work with the boiling point of water, which is solely dependent on the pressure, and open at temperatures below this.
  • Thermodynamic steam traps make use of thermal and fluid dynamics phenomena in order to discharge condensate with low losses.
  • Venturi condensate drain In the venturi condensate separator, the opening uses the venturi effect. The performance range is influenced both by the size of the opening and by the back pressure generated in the opening.

The condensate in front of the opening is under pressure and heat, so it contains a lot of energy. When it moves through the opening, the condensate loses pressure, i.e. energy. Since this energy cannot simply disappear, it converts part of the condensate in the opening back into steam.

The greater the pressure difference on both sides of the condensate separator, the more steam is created in the venturi opening. This also creates a counterpressure there, because this steam takes up a thousand times as much volume as the condensate from which it was created. As a result of this sudden expansion, the steam produced in the opening is very strongly accelerated and generates pressure both forwards and backwards to the same extent. This limits the flow of fresh condensate through the condensate separator.

Other types are u. a. Bellows condensate drain, bimetal condensate drain .


Depending on the design, the different types of steam traps have different advantages and disadvantages, so that depending on the application, one type is either an option or not. When choosing an arrester, the requirements for the pressure and temperature range are decisive, but factors such as capacity, service life, efficiency, contamination levels, etc. also play a role in the selection.

Since condensate naturally tends to reach the deepest points of a pipeline system, it is generally installed there and in front of inclines. Since a particular amount of condensate accumulates in every steam conversion process ( heat exchanger , ...), condensate discharge must also be provided there.


  • Fritz Mayr: Handbook of boiler operating technology . Publishing house Dr. Ingo Resch, Graefelfing 2003, ISBN 3-930039-13-3

See also

Web links

Individual evidence

  1. ^ Herbert Wiemann, Ulrich Eberle, Alfred Soherr: Metallfachkunde 5: Heating and ventilation technology . Springer-Verlag, 2013, ISBN 3-322-96780-8 , pp. 275 ( online [accessed April 29, 2016]).