Xylem Bell & Gossett Hoffman Speciality Series Engineering Data Manual page 24

modulate over a wide range of conditions, pro-
viding a drainage rate equal to the system
load. The Float and Thermostatic Trap also
has a separate thermostatic vent to provide
quick passage of air during start-up or during
a change of condition. The bucket trap will
completely drain the condensate but operates
in cycles between full open and close. The
bucket trap has a slower air venting rate
unless fitted with a separate thermostatic ele-
ment. Return line sizing can be minimized
using the Float and Thermostatic Trap due to
its modulating feature which provides a con-
tinual flow equal to the condensing rate.
General practice in sizing traps is to allow a
safety factor in the selection. During start-up
when the heat exchanger shell is cold, the
steam piping is cold and the fluid to be heat-
ed may be at less than design temperature.
All these conditions will cause a higher steam
condensing rate. Float and Thermostatic Trap
safety factors are normally 1.5 to 2.5 times
rated load. Bucket Trap safety factors are nor-
mally 2 to 4 times rated load .
Typical Heat Exchanger Installation
Float & Thermostatic Traps assure complete condensate drainage
at saturation temperature. They also modulate to handle varying
condensate loads associated with temperature regulators. The
thermostatic element provides rapid air venting during start-up.
FLOAT AND
THERMOSTATIC
TRAP
GATE
VALVE
CONDENSATE
RETURN
Guidelines for selecting traps for heat
exchangers using modulating steam tempera-
ture regulators are as follows:
—Select capacity based on maximum con-
densing load at minimum differential pressure
that can occur. The heat exchanger manufac-
turer can provide this information.
—No lifts should be installed in the return line
piping. The trap must drain into an atmo-
spheric gravity return line.
—Install a vacuum breaker to prevent induced
vacuum in the heat exchanger from causing a
reverse in differential pressure across the
trap.
—Install the trap as far below the heat
exchanger as possible to develop a static
pressure to the trap inlet. The minimum
should be 15 inches.
—Select a trap that provides complete
drainage of condensate. Avoid use of temper-
ature controlled traps.
—Allow an adequate safety factor for start-up
conditions.
PRESSURE
GAUGE
Y STRAINER
GATE
VALVE
VACUUM
BREAKER
FLOAT AND
THERMOSTATIC
TRAP
Y STRAINER
GLOBE
VALVE
Y STRAINER
GATE
VALVE
TEMPERATURE
REGULATING VALVE
CONNECTION TO
HEAT EXCHANGER
HEAT EXCHANGER
15" MINUMUM
RECOMMENDED
GATE
VALVE
PRESSURE
GAUGE
HOT
WATER
THERMOMETER
COLD
WATER
CONDENSATE
RETURN
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