Steam Traps Explained

Ahern Project
What is a Steam Trap

Steam traps are a type of automatic valve that filter out condensate and non-condensable gases (such as air) without letting steam escape. They open, close or modulate automatically, discharging condensate as soon as it is formed in an energy efficient manner. There are several different types of traps each best for a specific application.

Steam traps are used in piping and process equipment, space heating equipment, tracer lines, and power-generating equipment, such as turbines.

How a Steam Trap Works

The vast majority of steam traps in current operation are mechanical or thermostatically operated. These types of steam traps open when condensate and inert gases need to be removed and close when all the condensate is removed. The process repeats when new steam is condensed and ready to be drained.

Types of Steam Traps

Mechanical traps (Inverted bucket, Float) have a float that rises and falls in relation to condensate level. Through the use of internal mechanisms, the float or bucket floats on the condensate present in the trap when the level is high enough this opens an orifice to allow condensate removal. Mechanical traps operate in direct relationship to condensate levels present in the trap and have a typical service of life of three years.

Temperature traps (such as Thermostatic traps, Bi-Thermostatic traps, and bimetallic traps) have a valve that is driven on or off the seat by expansion and contraction caused by temperature fluctuations. They differ from mechanical traps in that they hold back some condensate until it has cooled sufficiently for the valve to open.

Thermodynamic (TD) traps work by relying on the properties of compressible and incompressible fluids. As steam enters, pressure above the disk forces the disk against the valve seat. The static pressure over a large area overcomes the high inlet pressure of the steam. Then, as the steam starts to condense, the pressure against the disk is reduced and the trap cycles.

Venturi Nozzle traps work by using the physics of fluid flow for the removal of condensate from steam systems. These types of steam trap must be expert engineered for precise sizing in steam systems which make them less common.

While differing in operation all types of traps essentially keep Steam on one side and condensate on the other. In order to get maximum efficiency from the system, traps need to be tested properly and regularly. For more information, contact us today!

Industrial Steam trapping handbook, What are Steam traps and why must they be monitored,