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desirable level to be tested.) Check upstream and reduce the sensitivity so that the meter reads about
50% or lower, then touch the trap body downstream and compare readings.
General steam/condensate/flash steam confirmation
In instances where it may be difficult to determine the sound of steam, flash steam or condensate,
1. Touch at the immediate downstream side of the trap and reduce the sensitivity to get a mid-
line reading on the meter (about 50%).
2. Move 15-30 cm downstream and listen. Flashing steam will show a large drop off in intensity
while leaking steam will show little drop off in intensity.
INVERTED BUCKET TRAPS
Bucket trap drawing
Inverted Bucket Traps normally fail in the open position because the trap loses its prime. This
condition means a complete blow-through, not a partial loss. The trap will no longer operate intermittent-
ly. Aside from a continuous rushing sound, another clue for steam blow-through is the sound of the
bucket clanging against the side of the trap.
FLOAT AND THERMOSTATIC
A Float and Thermostatic trap normally fails in the "closed" position. A pinhole leak produced in the ball
float will cause the float to be weighted down or water hammer will collapse the ball float. Since the trap
is totally closed no sound will be heard. In addition, check the thermostatic element in the float and ther-
mostatic trap. If the trap is operating correctly, this element is usually quiet; if a rushing sound is heard,
this will indicate either steam or gas is blowing through the air vent. This indicates that the vent has failed
in the open position and is wasting energy.
THERMODYNAMIC (DISC)
Thermodynamic traps work on the difference in dynamic response to velocity change in the flow of
compressible and incompressible fluids. As steam enters, static pressure above the disc forces the disc
against the valve seat. The static pressure over a large area overcomes the high inlet pressure of the
steam. As the steam starts to condense, the pressure against the disc lessens and the trap cycles. A
good disc trap should cycle (hold-discharge-hold) 4-10 times per minute. When it fails, it usually fails in
the open position, allowing continuous blow-through of steam.
THERMOSTATIC TRAPS
Thermostatic (bellows & bimetallic) operate on a difference in temperature between condensate and
steam. They build up condensate so that the temperature of condensate drops down to a certain level
below saturation temperature in order for the trap to open. By backing up condensate, the trap will tend
to modulate open or closed depending on load. In a bellows trap, should the bellows become com-
pressed by water hammer, it will not function properly. The occurrence of a leak will prevent the bal-
anced pressure action of these traps. When either condition occurs, the trap will fail in its natural position
either opened or closed. If the trap fails closed, condensate will back up and no sound will be heard. If
the trap fails open, a continous rushing of live steam will be heard. With bimetallic traps, as the bimetallic
plates set due to the heat they sense and the cooling effect on the plates, they may not set properly
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