Note: Descriptions are shown in the official language in which they were submitted.
~S7062
COAL SLURRY PUMP SEAL ASSEMBLY
Fritz C. Catterfeld
Background of the Invention
l. Field of the Invention
This invention relates to seals for rotating machinery and is
particularly directed to seals for centrifugal coal slurry pumps and the like.
2. Description of the Prior Art
Almost as long as there have been rotatlng pumps, the need has been
recognized for seals to prevent leakage of the fluids about the drive shaft,
etc. In coal slurry pumps and the like, where the mater~al being pumped is
gritty and abrasiYe, such seals are needed to prevent jamming and/or erosion of
the components. To overcome these problems, the prior art has proposed to
inject a clean purge fluid into the seal cavity under high pressure to exclude
the slurry therefrom, The need for high-pressure purge fluid greatly compllcatesthe structure of the seal. Moreover, the purge fluid often reverses the process
and leaks into the pump chamber, thereby contam1natlng the materlal being pumped.
Thus, none of the prlor art pumps have been entirely satisfactory.
Summary of the Invention
These disadvantages of the prior are overcome with the present invention
and a pump seal is provided which greatly reduces the pressure requirements of
the seal and which includes means for preventlng the purge fluid from leaking
into the pump chamber.
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The advantages of the present invention are preferably attained by providing
a seal mechanism comprising a plurality of seal elements separated from each
other by a series of chambers: a first chamber being interposed between the
innermost seal element and the second inner seal element, pressure relief means
venting fluid from said first chamber to a low-pressure area to maintain the
fluid pressure in said first chamber below a first predetermined value; a secondchamber interposed between the outermost seal element and the second outer seal
element, means for introducing purge fluid into said second chamberi a third
chamber interposed between said second inner seal element and said second outer
seal element, and drain means connected to said thlrd chamber, said purge fluid
being 1ntroduced into said second chamber at a pressure greater than the fluid
pressure ln said third chamber but less thàn the pressure in said first chamber.Objects of the Invention
Accordingly, it is an object of the present Invention to provide improved
seal means for rotating meachinery.
Another object of the present invention is to provide imFroved seal means
for centrifugal coal slurry pumps and the llke.
A further object of the present invention is to provide seal means having
a plurality of chambers separated from each other by seal elements, a f1rst one
of sald chambers receivlng fluld leaked from the main pump chamber at a first
predetermined pressure, a second of said chambers recelving purge fluid at a
second predetermined pressure, and a third of said chambers interposed between
said first and second chambers to receive fluid leaked from said first and
second chambers.
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An additional object of the present invention is to provlde a method of
sealing rotating machinery, said method comprising the steps of providing a
sealing means having a plurality of sealing elements with a plurality of
chambers interposed between said sealing elements, permitting fluid leaked from
said rotating machinery to accumulate in a first of said chambers, maintaining
the fluid pressure in said first chamber below a first predetermined value,
introducing purge fluid into a second of said chambers at a pressure below said
first predetermined value, permitting fluid leaked from said first and second
chambers to accumulate in a th~rd chamber interposed between said first and
second chambers, and draining said third chamber to a suitable relatively low
pressure area.
These and other objects and features of the present invention will be
apparent from the following detailed description taken with reference to the
accompanying drawing.
Brief Description of the Drawing
The F~gure is a vertical section through a seal mechanism embodying the
present inventlon.
Des _iption of the Preferred Embodiments
In that form of the present invention chosen for purposes of illustration,
the figure shows a seal mechanlsm indicated generally at 2, for a centrifugal
coal slurry pump having an impeller 4 rotatable by a drive shaft 6 within the
working chamber 8 of a housing 10. The seal mechanism 2 comprises three
labyrinth seals 12, 14 and 16, and a face-type seal 18. The pressure of the
slurry in the working chamber 8 may be well in excess of 1000 psi and will forcesome of the slurry through the impeller labyrinth seal 12. To accommodate this
leakage, a reservair 20 is provided between the impeller labyrinth seal 12 and
the prtmary labyrinth seal 14,and vent means 2~ serves to connect the reservoir
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20 with a low-pressure location in the pump to limit the
pressure within the reservoir 20 to about 500-600 psi.
Additional reservoirs 22 and 24 are provided and are located,
respectively, between the primary labyrinth seal 14 and
the secondary labyrinth seal 16, and between the secondary
labyrinth seal 16 and the face seal 18. Some of the slurry
from reservoir 20 will leak through the primary labyrinth
seal 14 into reservoir 22. It has been found that the
fluid pressure in reservoir 22 will be about 200 psi. To
counteract this r purge fluid which is compatible with the
slurry, such as kerosene, is supplied to reservoir 24 via
inlet conduit 26 from a suitable source (not shown), and is
delivered at a pressure greater than that of the slurry in
reservoir 22. For example, the purge fluid may be supplied
to reservoir 24 at a pressure of about 250 psi. In addition,
an outlet conduit 28 serves to drain fluid from reservoir
22 to suitable disposal means (not shown) exterior to the pump.
In use, slurry from the pump's working chamber 8
leaks through the impeller labyrinth seal 14 into reservoir 20
at reduced pressure and some of this slurry leaks past primary
labyrinth seal 16 into reservoir 22 where it meets the
counterflow of purge fluid which has been introduced into
reservoir 24 and has leaked through secondary labyrinth seal 16.
: This arrangement prevents further outward leakage of the slurry
and also prevents contamination of the slurry in the working
chamber 8 by the purge fluid, since fluid pressure in any of
the chambers will.urge the face seal 18 to a more tightly
closed position
Obviously, numerous variations and modifications
may be made without departing from the present invention.
Accordingly, it should be clearly understood that the form of
the invention described above and shown in the accompanying
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drawing is illustrative only and is not intended to limit the
scope of the invention.
What is claimed and desired to be secured by
Letters Patent of the United States is:
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