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
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
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
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.