Feed seal for bottom feed centrifuge

A nozzle type centrifuge having a bottom feed inlet to a main pumping chamber at the base of the machine for injecting the feed slurry to a rotor bowl having separator discs for effecting a two-fraction separation comprising an overflow at the top and an underflow at the peripheral mid portion of the bowl with a portion of the underflow delivered to a return pumping chamber beneath the main pumping chamber and seal means between said chambers to prevent dilution of the underflow fraction.

BACKGROUND OF THE INVENTION 
The present invention is directed to new and useful improvements in 
centrifugal machines and in particular to a nozzle type centrifuge having 
vertically spaced pumping chambers and a bottom feed pipe for introducing 
a feed slurry upwardly into the centrifuge. 
In one nozzle type centrifuge of the type mentioned, a double cone-shaped 
rotor bowl is provided having a separating chamber comprised of a stack of 
rotatable separating discs for effecting a two fraction separation of the 
bottom feed slurry into a heavy nozzle discharge for an underflow fraction 
at the periphery of the bowl and a light fraction discharge as an overflow 
at the top of the machine. 
Centrifuges of this type are well known and are disclosed in prior art 
patents such as U.S. Pat. No. 4,005,817 which issued Feb. l, 1977 and U.S. 
Pat. No. 4,067,494 which issued Jan. 10 1978. In the centrifuge embodying 
the present invention such as disclosed in the latter patent a portion of 
the underflow fraction is returned to the separating discs from an annular 
return pumping chamber at the base of the rotor bowl. The feed slurry is 
introduced by injection from the bottom of the centrifuge upwardly into 
the rotor bowl via a second annular main pumping chamber which is spaced 
vertically from the return pumping chamber. These pumping chambers propel 
their respective slurries upwardly to the separating discs in the rotor 
bowl. The mentioned portion of the underflow which is recycled or returned 
back to the return pumping chamber enters the return impeller therein and 
it is pumped to the periphery of the rotor to be discharged again by 
discharge nozzles. In these centrifuges the rotor arrangement requires 
that the feed and return impellers be located respectively in spaced 
vertically adjacent pumping chambers arranged in superimposed 
relationship. Due to mechanical requirements a passageway is provided 
between the two chambers adjacent the main feed slurry pipe. 
In use problems have been encountered in that a portion of the feed slurry 
can spill from the main pumping chamber through the passageway to the 
return pumping chamber. As a result the feed can enter the peripheral 
underflow discharge zone of the rotor bowl via the return chamber and 
dilute the underflow product. It is also possible that the diluted return 
can create buoyancy currents in the peripheral zone of the rotor. These 
factors can adversely affect the efficiency of the centrifuge in certain 
applications of use such as starch gluten thickening processes by 
upsetting the density gradients in the thickening zone of the centrifuge. 
It is the object of the present invention to provide a bottom feed 
centrifuge having novel sealing means between the feed and return pumping 
chambers. 
Another object is to provide a novel sealing means for reducing spillage 
between the feed and return pumping chambers at the passageway between the 
two chambers. 
Another object is to provide a seal having means for adjusting the position 
of the seal to vary the gap between the return and feed pumping chambers. 
BRIEF SUMMARY OF THE INVENTION 
The present invention contemplates a centrifuge wherein the slurry feed 
pipe is located at the bottom of the machine for delivering the slurry to 
pumping impellers of the feed pumping chamber for discharge to the 
separating discs of a double cone-shaped rotor bowl. A novel deflector or 
seal means is provided on the exterior of the feed pipe and is provided 
with a sealing lip to seal the passageway between the feed pumping chamber 
and the return pumping chamber located beneath the feed chamber. Means are 
adjustably mounted on the feed pipe for adjusting the gap clearance 
between the pumping chambers. 
The above and other objects and advantages of the present invention will 
appear more fully hereinafter from a consideration of the detailed 
description which follows taken together with the accompanying drawings 
wherein one embodiment of the present invention is illustrated.

DETAILED DESCRIPTION 
Referring now to the drawings and more particularly to FIG. l wherein one 
embodiment of the present invention is clearly illustrated a nozzle type 
centrifuge is generally indicated by the reference numeral 10. Centrifuge 
10 comprises a double cone-shaped rotor bowl 11 having an upright 
frustro-conical top end section 12 having an overflow opening 13 and an 
inverted trunco-conical section 14 having a wide bottom opening 15. An 
intermediate peripheral section 16 of bowl 11 is provided with underflow 
discharge nozzles 17 (one of which is shown in FIG. 1) for discharging a 
separated heavy or underflow fraction at the periphery of bowl 11 in a 
usual manner. 
Top end section 12 comprises an upper conical part 18 and a lower 
complementary section 19 detachably secured together by means of a 
conventional threaded locking ring (not shown). This two part construction 
of the rotor bowl provides access in a known manner to a stack of 
separator discs 20 confined between upper conical part 18 and a hub member 
21 which closes wide bottom opening 15 of bowl 11. Hub member 21 is also 
of a frustro-conical configuration and is formed with a downward facing 
hollow 22. The stack of separating discs 20 represent an inner annular 
separating zone Z-1 which is surrounded by a second or outer separating 
zone Z-2. 
A rotatable rotor shaft 24 for rotating bowl 11 is fixed to hub member 21 
in a known manner and extends upwardly through the top overflow opening 
13. Shaft 24 is surrounded by a customary spider member 25 and is held in 
place by part of the bowl secured against rotation relative to the hub 
member. 
Outwardly divergent pipes 26 (one of which is shown in FIG. 1) for 
returning an underflow material from nozzles 17 are equally spaced about 
rotor and extend from the peripheral portion 27 of hub member 21 into zone 
Z-2. Also extending upwardly from peripheral portion 27 of hub member 21 
is a set of vertical slurry feed pipes 28 (one of which is shown in FIG. 
1). Vertical feed pipes 28 and return pipes 26 are more fully disclosed in 
the U.S. Pat. No. 4,067,494 which is being incorporated by reference 
herein. 
As seen in FIGS. 1 and 4, a main slurry feed pipe 29 extends upwardly into 
centrifuge 10 and discharges into an upper pumping chamber 30 formed by 
hollow 22. Pumping chamber 30 communicates with vertical feed slurry pipes 
28. An annular plate 31 carries a set of upright pumping vanes 32-33. A 
lower pumping chamber 34 is formed between plate 31 and a bottom annular 
closure plate 35. The closure plate 35 has a central opening 36 and with 
feed pipe 29 forms an annular passageway 37 between the chambers 30 and 
34. Bottom closure plate 35 of lower pumping chamber 34 carries a 
combination of pumping vanes 39 which register with the discharge nozzles 
17. 
As mentioned it is a feature of the present invention to prevent spillage 
of feed slurry material from upper pumping chamber 30 to lower return 
pumping chamber 34 via annular passageway 37 to avoid dilution of the 
underflow product. To this end sealing means is provided about the 
discharge end of central feed pipe 29. Sealing means comprises a circular 
deflector 40 member slidably fitted over the discharge end of pipe 29. 
Deflector 40 has a peripheral lip portion 41 in close adjacency with the 
edges of central opening 42 in plate 31 of upper pumping chamber 30 to 
prevent spillage of feed from chamber 30 into lower chamber 34. A second 
sleeve member 43 is provided at the bottom of pipe 29 and is fixed 
thereto. 
Means are provided for varying the gap between opposing edge surfaces of 
lip 41 and opening 42 in plate 31. These latter means comprise a bushing 
member 44 intermediate deflector 40 and base sleeve 43. As will be 
appreciated the vertical dimension of bushing member 44 predetermines the 
gap and may be of a preselected dimension in accordance with the designs 
of the centrifuge. 
In operation of centrifuge 10 and upon rotation of rotor shaft 24 and rotor 
bowl 11 the annular plate 31 of pumping chamber 30 is also rotated. It has 
been found desirable that deflector 40 be preformed from a plastic 
material such as an ultra high molecular weight polyethylene in order that 
lip surface 41 may initially engage the surface of plate 31. Upon the said 
rotation of plate 31 lips 41 will be abraded to set a gap therebetween of 
approximately 0.10" to prevent spillage between chambers 30 and 34. 
As will be appreciated from the foregoing description the novel sealing 
means described has many advantages in use. In addition to substantially 
eliminating spillage between the pumping chambers, means are provided to 
selectively adjust the gap between the chambers which does not interfere 
with the operation of the centrifuge and comprises a minimum number of 
parts. 
Although one embodiment of the present invention has been disclosed in 
detail, it is to be expressly understood that the invention is not limited 
thereto. Various changes can be made in the design and arrangement of 
parts without departing from the spirit and scope thereof as the same will 
now be understood by those skilled in the art.