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Test Your Knowledge: Flash Steam

The quantity of flash steam available depends upon ________?

  1.      Condensate temperature/pressure and flash steam pressure
  2.      Pressure of steam generated in the boiler
  3.      Steam enthalpy at atmospheric pressure
  4.      Total heat of flash steam

And the answer is…

1.Condensate temperature/pressure and flash steam pressure

‘Flash steam’ is released from hot condensate when its pressure is reduced. Even water at an ambient room temperature of 68°F would boil if its pressure were lowered far enough. It may be worth noting that water at 338°F will boil at any pressure below 100 psig. The steam released by the flashing process is as useful as steam released from a steam boiler.


As an example, when steam is taken from a boiler and the boiler pressure drops, some of the water content of the boiler will flash off to supplement the ‘live’ steam produced by the heat from the boiler fuel. Because both types of steam are produced in the boiler, it is impossible to differentiate between them. Only when flashing takes place at relatively low pressure, such as at the discharge side of steam traps, is the term flash steam widely used. Unfortunately, this usage has led to the erroneous conclusion that flash steam is in some way less valuable than so-called live steam.

In any steam system seeking to maximise efficiency, flash steam will be separated from the condensate, and used to supplement any low pressure heating application. Every pound of flash steam used in this way is a pound of steam that does not need to be supplied by the boiler. It is also a pound of steam not vented to atmosphere, from where it would otherwise be lost.

The reasons for the recovery of flash steam are just as compelling, both economically and environmentally, as the reasons for recovering condensate.

How much flash steam is available?

If use is to be made of flash steam, it is helpful to know how much of it will be available. The quantity is readily determined by calculation, or can be read from simple tables or charts like the one below.

Answer details exurpted from For more in-depth description read the full article.

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