Jacketed Kettles - Xylem Bell & Gossett Hoffman Speciality Series Engineering Data Manual

Jacketed
Kettles
Stationary type
jacketed kettle with
internal siphon
Tilting type
jacketed kettle with
external siphon
External and internal jacketed kettles
Figure 6
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Jacketed Kettles

Kettles are often of the tilting type. These
require the use of a siphon drain. Siphon
drains may either be internal or external. The
Fig. 6 shows both types.
As shown in the illustration, external siphons
are surrounded by ambient air, while the inter-
nal siphon is surrounded by steam.
Flash steam tends to form in siphons and the
trap must be able to operate properly with a
certain amount of it present in the conden-
sate. Figure 7 illustrates how this takes
place, and how a steam main is drained.
First, condensate drains into the water seal.
Steam in the siphon above the water seal
condenses, dropping the pressure.
Condensate rises in the siphon as this takes
place. The siphon may form and break several
times before it is established and condensate
enters the trap.
A check valve must be used to hold the
siphon while it is forming. This should be
installed after the strainer as shown. Once
the siphon is established, the drop in static
pressure as the elevation decreases causes
some of the hot condensate to "flash off."
The presence of steam in the condensate
decreases its density and actually assists the
flow. An external type siphon loses some heat
by radiation to the ambient air and the con-
densate within it tends to cool. As a result,
the amount of flash steam is less than in an
internal siphon, which absorbs heat from the
steam surrounding it.
STRAINER
CHECK VALVE
TRAP
STATIC PRESSURE
DROPS AND FLASH
STEAM FORMS
STRAINER
CHECK VALVE
MAXIMUM STATIC
PRESSURE
TRAP
Principle of condensate line siphon
Air Handling Capability
The excellent air handling capability of
Thermostatic Traps makes them suitable for
trapping applications where quick air removal
is required. For example, batch processes
resulting in on-off operation of steam heating
equipment are prone to air problems. The
steam space becomes filled with air in
between heating cycles. Unless this air is
quickly removed with the condensate, slow
heating of the batch results. Thermostatic
Traps must be fitted with a cooling leg, when
used for this purpose, to minimize back up of
condensate into the equipment.
Figure 8 shows a steam kettle serviced by a
Thermostatic Trap. A cooling leg with a mini-
mum length of 5 ft. is provided to insure
enough cooling of the condensate to open the
trap.
Notice the check valve provided at the trap
outlet. This prevents back drainage of the
condensate in the vertical line. A check valve
should always be provided at the trap outlet
where vertical lifts exists.
The safety factor for steam kettles is usually
3 times rated capacity. Siphon type kettles
may use either F & T or Bucket Traps.
Stationary kettles may use Thermostatic
Traps.
STRAINER
CHECK VALVE
TRAP
STEAM MAIN
WATER SEAL
Figure 7
OVERHEAD
RETURN MAIN
THERMOSTATIC
TRAP
STRAINER
COOLING LEG
5 FT. MINIMUM
CHECK VALVE
Steam kettle showing cooling leg
Figure 8