Steam passes from the boiler into the steam mains. Initially the pipe work is cold and heat is transferred from the steam. When steam from the boiler to steam mains and to the distribution system, it will again give up energy by warming up the equipment and by continuing to transfer heat to the process. As steam loses heat, it turns back into water. The condensate, which tends to run to the bottom of the pipe, is carried along with the steam flow. This must be removed from the lowest points in the distribution pipe work as the Condensate does not transmit heat effectively, accumulated condensate can cause noisy and water hammer. A device known as a steam trap is used to release condensate from the pipe work without discharging steam.

There are several types of steam traps. The general identification for Steam trap:  “TD” for Thermodynamic, “TS” for Thermostatic, “FT” for Float + Thermostatic and “IB” for Inverted Bucket.

Thermodynamic Steam Traps-TD

Thermodynamic traps have a disk situated on a central orifice.  As condensate pressure builds, it lifts the disk, passes through the orifice at the center of the disk and exits through smaller orifices surrounding the disk.  Flash steam builds up pressure on top of the disk and closes the orifice. Condensate is discharged intermittently. 

Thermostatic Steam Traps-TS

Thermostatic traps operate on the difference in temperature between steam and condensate.  As condensate cools, the volume of an enclosed bellows decreases and the discharge valve opens.  Thermostatic traps always cause some condensate to remain in the system. Condensate is discharged continuously.

Float and Thermostatic Steam Traps-FT

In Float and Thermostatic traps, condensate is discharged when the rising level of condensate lifts a float attached to a level.  A thermostatically operated vent discharges air from the top of the trap.  Float and Thermostatic Traps have superior gas removal characteristics. Condensate is discharged continuously.

Inverted Bucket Steam Traps-IB

In inverted bucket traps, steam is contained within an inverted bucket floating in condensate.  As the level of condensate rises, it is discharged.  Inverted bucket traps require water within the bucket, called the prime, to operate.  This trap is good for distribution systems. Condensate is discharged intermittently.

Testing Steam Traps

It is recommended that all traps be tested at least once per year. The most common accurate method of testing steam traps is with an ultrasonic sensor. 

Inverted bucket and thermodynamic traps (TD & IB) have a cyclic discharge when functioning properly.  A steady discharge on the condensate side of the trap indicates that the trap has failed open.

Thermostatic and Float + Thermostatic Steam Traps (TS & FT) have a continuous discharge and it is difficult to assess whether these types of traps are functioning properly merely by listening to the discharge.  The best field method available to test (TS & FT) is to measure the temperature on both sides of the trap. Properly functioning traps (TS & FT) are generally hotter on the steam side than the condensate side.

SIGHT GLASS                      FLAME / DETONATION ARRESTOR                   RUPTURE DISC                  STRAINERS