Figure 3-18. - A bimetallic-element steam trap.

of the trap. Prime the trap before starting operation by removing the test plug on top of the trap and filling the trap with water. If no test plug is available, the trap can be primed by closing the discharge valve and opening the steam supply valve slowly until the steam is condensed and the trap is filled with condensate.

Blow down steam traps periodically to rid them of dirt and sediment. Blow down and clean strainers as required.

When overhauling traps, do not remove thermostatic elements while hot. This practice may result in expansion beyond the stroke range of the bellows or diaphragm.

Periodically, open the air vents of float traps not provided with thermostatic air vents to vent out accumulated air.

Steam Trap Tests

Methods for testing traps without breaking the installation are stated below:

TEST VALVE METHOD. - Close the discharge valve and open the test valve. Observe discharge characteristics. Intermittent discharge, dribble, or semicontinuous discharge indicates correct operation. A continuous steam blow indicates loss of prime, defective valve operation, or foreign matter embedded in the valve seat. A continuous condensate flow may indicate that the trap is too small, the amount of condensate abnormally high, or a pressure differential that is too low.

GLOVE TEST METHOD. - Grab inlet and out- let pipes simultaneously, using a canvas glove on each hand for protection. A slight temperature difference indicates that no condensate is passing.

PYROMETER TEST METHOD. - This method is more accurate than the previous one, as it uses a surface contact pyrometer to check inlet- and outlet temperatures. File a clean spot on both pipes before taking readings.

PYROMETRIC CRAYON TEST METHOD. - Temperature-indicating crayons can be used when no pyrometer is available. Select crayons of proper temperature ratings and mark the required pipe spots. When the crayon marks melt, the temperature of the test spots corresponds to those of the crayon ratings.