Steam Traps

Posted by: Jeffrey Ahbe

A steam trap is an automatic valve that opens to expel air and condensation from steam lines and closes to prevent the flow of steam.  The main functions of steam traps are:

• Prevent steam fro leaving the system until all of its latent heat are removed.
• Removes (drain) the condensation from the system after the latent heat has been removed.
• Removes (vent) air from the system so that steam can enter. Air in the pipes will block the flow of steam into the radiators.

All steam traps operate on the fundamental principle that the pressure within the trap at the time of discharge will be slightly in excess of the pressure against which the trap must discharge. This will include the friction head, the static and velocity head on the discharge side of the trap. The steam trap will not be able to operate unless the excess discharge pressure is is greater than the total back pressure.

Each stream trap is designed for specific applications that its operating characteristics best suit in steam heating.  There really isn’t a universal steam trap but most traps can be classified into the following:

• Air Traps – generally operated by a float
• Separating Traps – designed to release condensation but close against steam. They operate with a float and thermostat
• Return Traps – operate to receive condensation under a vacuum and return it to atmosphere or higher pressure.

Another helpful HVAC Resource article: Tips for Storing your AC Unit