Page 276 - Boiler plant and distribution system optimization manual
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Steam Traps 261
the trap as the thermostatic element allows air
and gases to be dispelled from the top.
The liquid level rises above the open bucket
filling it and causing it to sink, opening the valve.
Condensate is discharged until steam enters the
trap body and the water is forced from the open
bucket, making it light enough to float up closing
the discharge valve.
Without the thermostatic element or some
other means to clear the trap body of air, the trap
will air bind and fail closed.
Float Traps and Float and
Thermostatic Traps
Float traps (Figure 14.11) are one of the old-
est trap designs still in use and are not considered
obsolete.
Figure 14.10—Inverted bucket trap with inverted
bucket lowered and the valve open and discharging
condensate.
fore, in order to maintain the proper relationships
between the closing force of the pressure on the
valve and the opening force of the weight of the
bucket, orifice sizes must be designed to match
steam system pressure. Figure 14.11—Float type steam trap.
Since the orifice must be sized to match the
maximum steam system pressure, care must be A float trap consists of a closed float attached
taken to ensure adequate capacity is still avail- to a valve by mechanical linkage. During start up,
able. the float rests on the bottom of the trap, closing
the valve. Air and gases must be removed from
Open Bucket Traps the system, which is usually done by a thermo-
The open bucket trap is an older and pos- static element or air vent in the top of the hous-
sibly obsolete type of mechanical trap. It is sim- ing.
ply a bucket arrangement that pivots around one As condensate enters the trap, the liquid lev-
end when it fills with water, opening a discharge el rises lifting the float and opening the valve. As
valve. Most open bucket traps have a separate this type of trap is self regulating it will operate
thermostatic air vent at the top. in the modulation mode. As the condensate level
During start up the bucket rests on the bot- rises, the outlet valve opens further handling the
tom of the trap body and the valve is fully open. greater quantity of condensate. If the condensate
The thermostatic element is also open, allowing load diminishes, the ball lowers, partially closing
the discharge of air and gases. When condensate the valve reducing the discharge.
enters the trap the enclosed trap body is filled The valve is located below the water level,
with condensate causing the bucket to rise shut- providing a water seal preventing the loss of live
ting off the valve. Condensate continues to enter steam.
