7/30/2019 API-23
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This flush plan is most commonly seen in boiler feed water
service. It is essentially a closed loop
system; virtually the same product is repeatedly circulated
between the seal and the heat exchanger. Thisarrangement is a much
more efficient cooling system than API PLAN 21 and the exchanger
itself will
have longer life since it will operate at cooler temperatures.
Plan 21 is still recommended for viscous
applications that may plug at low temperatures.
A close clearance throat bushing is recommended to prevent the
mixing of hot product behind the impeller
and the cool product in the seal chamber. A water jacket is also
used to further reduce the seal chamber
temperature. The piping and installation of this system is
critical to its success.
Guidelines for API PLAN 23:
1) The heat exchanger should be located as close to the seal as
possible with a maximum
distance of 3 feet.
2) The bottom of the heat exchanger should be approximately 12
inches above the shaftcenterline.
3) Avoid sharp elbows or bends in the tubing. Use as gentle a
sweep in the turns and
always have an upward slope from the seal to the exchanger to
avoid vapor locking.
4) There must be sufficient shaft surface speed for the pumping
ring to be effective.
5) If possible, use .500" to .750", stainless steel tubing from
the exchanger supplying cooledfluid to the seal. Tubing from the
seal back to the exchanger can be .375" for 2" shafts and
smaller. Use .500" for shaft sizes above 2".
6) Make sure the tubing is vented before pump start up. You want
to insure a fluid
packed system.
7) Always slope horizontal runs of tubing slightly upward (1 to
5 degrees) from the seal to
the exchanger to prevent low spots in the line where air can be
trapped and vapor lock the
system preventing flow.
8) Any valves used in the closed loop should be of the free
flowing type.
9) Whenever possible, locate the pumping ring in the gland where
tangential port
approaches can be utilized and clearances can be more clearly
controlled.
POTENTIAL PROBLEMS:
1) Air should be vented from the tubing and seal chamber before
starting the pump. Ifnot, a vapor locked system can cause the seal
to overheat and shorten life dramatically.
2) Products that become viscous when cooled will prevent the
pumping ring from circulatingthe fluid. Lines can become plugged.
The pumping ring (plan 23) does not have sufficient
head capacity to drive the viscous plug from the cooler. For
these viscous applications that
