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Steam Trap in Piping

Posted by Antony Thomas at Thursday, February 14, 2013



What is a Steam Trap?

ANSI’s definition for Steam trap - Self contained valve which automatically drains the condensate from a steam containing enclosure while remaining tight to live steam, or if necessary, allowing steam to flow at a controlled or adjusted rate. Most steam traps will also pass non-condensable gases while remaining tight to live steam.
ANSI/FCI 69-1-1989

Steam traps are a type of automatic valve that filters out condensate (i.e. condensed steam) and non-condensable gases such as air without letting steam escape.


Steam traps to discharge air and condensate while not permitting the escape of live steam
Steam Trap’s goal is to ‘purify’ the steam of excess air and water (condensate) to :
Improve efficiency (Excess water or air in the system prevents it from reaching operating temperature quickly during start-up)
Protect system (Inadequate steam trapping can lead to waterhammer, corrosion, leakage, and high maintenance costs)
Provide maximum heat transfer (‘dry’ steam has best heat transfer properties in equipment like a heat exchanger)

Types of Steam Taps:

1. Mechanical steam traps -

Have a float that rises and falls in relation to condensate level and this usually has a mechanical linkage attached that opens and closes the valve. Operate in direct relationship to condensate levels present in the body of the steam trap.

2. Temperature steam traps - Have a valve that moves in/out of position by either expansion/contraction caused by temperature change. Some condensate builds up as it cools sufficiently to allow the valve to open. In most circumstances this is not desirable as condensate needs to be removed as soon as it is formed.

3. Thermostatic steam traps - Work on the difference in response to velocity change in flow of compressible and incompressible fluids. As steam enters, static 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. As the steam starts to condense, the pressure against the disk lessens and the trap opens to allow condensate out.




2.Temperature steam traps -

Have a valve that moves in/out of position by either expansion/contraction caused by temperature change. Some condensate builds up as it cools sufficiently to allow the valve to open. In most circumstances this is not desirable as condensate needs to be removed as soon as it is formed. 






3.Thermodynamic steam traps -

Work on the difference in response to velocity change in flow of compressible and incompressible fluids. As steam enters, static 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. As the steam starts to condense, the pressure against the disk lessens and the trap opens to allow condensate out. 

Animation Courtesy from tlv.com

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