Steam and condensate glossary

Back pressure

Back pressure – pressure acting to oppose operational pressure, which can result from friction or an ascending pipe section, from valves, from hydrostatic pressure or from any other resistance to the flow of the fluid.


Blowdown, blow-down – elimination of liquids or solids from a tank (for example, a boiler) or a piping section, by the use of pressure.


Boiler – a cast iron or steel vessel designed to supply hot water or steam for use in building heating or in industrial processes.

Carbon dioxide

Carbon dioxide – non-condensable gas, colorless and non-combustible which enters a steam system via the boiler feed water. Symbol : CO2.


Condensate – water formed by the condensation of steam.

Condensate drain valve

Condensate drain valve – valve that automatically evacuates, at system shut down, the condensate that fills the piping on the steam side (i.e. before the steam trap).


Deaeration – partial or total elimination of air and other non-condensable gases, usually with the help of a deaerator.


Deaerator – device used to eliminate air and other non-condensable gases from the boiler feed water.


Desuperheater – device designed to cool superheated steam in order to bring its temperature down to that of saturated steam.

Differential pressure

Differential pressure – pressure difference between two locations of a single system. In a SCCS®, this expression usually refers to the difference between the pressure before the steam trap and the pressure after the steam trap.


Downstream – part of a steam system located after a specified location.


Downtime – period during which a steam system is not under operation, usually because of a failure.

Drip leg

Drip leg – short section of vertical piping in an horizontal steam line, used to collect condensate and dirt. The drip leg is usually equipped with a steam trap, a valve and a screwed cap.

Dry steam

Dry steam, dry saturated steam – saturated steam which contains no liquid phase. Just like the expression “wet saturated steam”, the expression “dry saturated steam” doesn’t describe a physical state of steam, but rather a special case of saturated steam.