ORNL-1771 - Oak Ridge National Laboratory

sump in that it must be sufficiently high at all
times to provide the necessary flow into the seal.
To stop the unit, the sump tank would be vented
at the same time the pump was stopped, but the
gas pressure would be maintained until draining
had been completed. This would cause a flow of
gas along the shaft into the seal cavity and would
blow out any fluid that might enter along the shaft.
It would also maintain a seal cavity pressure
somewhat greater than the sump tank pressure and
would force the fluid out of the seai into the sump.
IC this procedure were not followed, the sealing
annulus of fluid would, upon collapsing when the
pump was stopped, momentar i I y f i I I the sea S cavity
above the shaft level and cause fluid to enter
along the shaft.
Vertical-Shaft Centrifugal Sump Pump
D. R. Ward
Aircraft Reactor Engineering Division
Developmental work has been continued on the
vertical-shaft centrifugal sump pump (Model LFB)
for use with forced-circulation loops, both in-pile
and out. This is a vertical-shaft centrifugal sump
pump with a side inlet and a bottom discharge
(Fig. 3.2). A Graphitar face seal prevents the
pressurizing gas from escaping along the shaft.
Circulating spindle oil serves to lubricate this
face seal and to carry away heat from the seal
region.
Typical performance curves for this pump with
water are shown in Fig, 3.3. In a recent test the
pump was run for 864 hr at 6000 rpm while pumping
140OOF sodium at about 3 gpm. Typical oil leakage
past the shaft face seal was under 0.1 cm3/hr.
Developmental work during the past eight months
has resulted in the following improvements in this
pump: the elimination of the tendency for the pump
to introduce gas into the liquid stream at flow
rates up to 6 gpm; an improved anti-flowback seal
to prevent recirculation of the liquid within the
pump; an improved means for cooling the face-seal
region of the pump; and a reduction of pump volume,
which is desirable when the pump is used for
in-pile loop tests.
The main difficulty, that of gas entrainment, was
primarily caused by vortexing and the passage of
gas downward along the rotating shaft. The ad-
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2 24
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II
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3
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46
8
0
PERIOD ENDING SEPTEMBER 70, 1954
UNCLDSSIFIED
ORNL -LR-OWG 3096
2 4 6 8
FLOW (gpm)
Fig. 3.3. Performance Curves for Vertical-
Shaft Centrifugal Sump Pump (Model LFB).
dition of vertical baffles adjacent to the shaft
merely broke up the large vortex into several
smaller ones, which were just as obiectionable.
The problem is solved in the present arrangement
by permitting liquid from the high-pressure region
of the pump to be bypassed up through a hole in
the shaft to an annular space surrounding the
shaft. This liquid, in turn, forms a seal and
prevents the gas from following its former path.
Acceptance tests for these pumps include oper-
ating each pump with water to check the pmping
Characteristics and freedom from gas entrainment
and pumping sodium at 1400OF for 72 hr at 6000
rpm with acceptable oil leakage past the face seal.
This hot test also serves to clean oxide film from
the wetted pump parts, as well as io reveal any
mechanical faults that might be present. Five of
these pumps are being built, and four similar
pumps (Model LFA) are now in use.
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