Simply put, a steam trap is an automatic valve which opens to pass condensate and closes to prevent the flow of steam.  Its function in a steam system is to drain away condensate as it is formed.  Condensate must be removed from steam distribution piping to prevent erosion and water hammer.  Condensate formed in steam driven process heat exchangers must be drained away to make roomfor new steam.  A steam trap should also have other characteristics depending on the particular application.  These include:

	The ability to pass non-condensable gases.  Steam systems are typically full of air at the time of start-up.  This air has to be displaced by the steam before the system can reach its operating temperature.
	Ruggedness is an important feature.  Many steam systems operate under harsh conditions.  Traps are needed which can stand up to the abuse and still function properly.
	Responsiveness, or the ability to quickly react to changing loads, is critical in many applications which cannot tolerate condensate collecting upstream of the trap.
	Freeze-proof traps are typically required in outside installations.
	The ability to operate on superheated steam, commonly found on high pressure steam distributions systems, may be required.

Watson McDaniel manufactures a broad range of steam traps.  Their products are used across a variety of applications ranging from steam main drip service to product steam tracing applications to drainage of large process reactors.  One of their traps will suit your needs.