US 3637134 A
The rotor of a sludge centrifuge has an indicating channel extending inwardly from the sludge space to the rotor axis and provided with a throttled passage opening into the separating chamber. When the outer end of this channel is not clogged by accumulated sludge, liquid discharging through the throttled passage from the channel is replaced by liquid entering its outer end, so as to maintain a certain liquid level or pressure at the inner part of the channel; but when the above-mentioned replacement of liquid is arrested by the occurrence of such clogging, the resulting change in this liquid level or pressure is sensed by a suitable device communicating with the channel.
Description (OCR text may contain errors)
United States Patent Nelson 51 Jan. 25, 1972  APPARATUS FOR INDICATING THE SLUDGE LEVEL IN CENTRIFUGES  Inventor: Kurt Nelson, Wappingers Falls, NY.
 Assignee: The DeLaval Separator Company,
 Filed: Jan. 21, 1970  Appl. No.: 4,600
 11.8. CI. ..233/19A  ..B04b11/00  Field of Search ..233/14 R, 19 R, 20 R, 20 A,
233/19 A, 27, l R
 References Cited UNITED STATES PATENTS 2,917,230 12/1959 Kaldewey ..233/14 R 3,167,509 1/1965 Steinacker ..233/20 R 3,301 ,476 1/1967 Hemfort 233/20 3,408,000 T07i968 Nilson ..233 20 R 3,410,481 1l/l968 Dahlberg et al ..233/l9 R 3,445,062 5/1969 Loddenkemper et al. ..233 20 R Primary Examiner-Jordan Franklin Assistant Examiner-George H. Krizmanich Attorney-Davis, Hoxie, Faithfull & Hapgood  ABSTRACT The rotor of a sludge centrifuge has: an indicating channel extending inwardly from the sludge space to the rotor axis and provided with a throttled passage opening into the separating chamber. When the outer end of this channel is not clogged by accumulated sludge, liquid discharging through the throttled passage from the channel is replaced by liquid entering its outer end, so as to maintain a certain liquid level or pressure at the inner part of the channel; but when the above-mentioned replacement of liquid is arrested by the occurrence of such clogging, the resulting change in this liquid level or pressure is sensed by a suitable device communicating with the channel.
8 Claims, 2 Drawing Figures AlllPAllt/t'lllUS lFOlit INDIHCA'IING 'llllllE SlLlJlDGlE LEVEL IN CIENTMRWUGES The present invention relates to sludge centrifuges of the type having means for indicating the level of the sludge in the sludge space of the rotor.
Such indicating means usually comprise an indicating channel which extends from the sludge space of the rotor toward the center of the rotor and rotates with the rotor, and a member connected to this channel for sensing the clogging by sludge of the opening of the channel into the sludge space. In a known centrifuge of this type, the radially inner end of the channel discharges into a skimming chamber containing a skimming disc which senses the clogging with sludge of the opening of the channel into the sludge space. The skimming disc in one embodiment has a drainage hole through which indicating liquid removed by the skimming disc is returned to the separating space in order to make possible a signal which indicates clogging sludge. In order for the desired plug of sludge to form in the channel opening in such a manner that a sharp indicating signal is obtained, the flow of liquid into the channel through its radially outer opening must be maintained small so that the formation of the plug of sludge is not disturbed. This means that the skimming disc must operate with a small depth of immersion in the ring of indicating liquid. It is difficult, however, to establish such a small depth of immersion in this ring, since this requires an accurate adjustment of the depth of immersion of the skimming disc which removes the separated liquid. The latter adjustment requires a certain constriction of the skimming disc outlet and therefore is dependent upon the discretion of the operator of the centrifuge for accuracy.
In accordance with the present invention, this dependence upon the operator of the centrifuge is elimiated in that the indicating channel of the centrifuge is provided with a throttled communication with the separating space of the rotor, this communication being provided in the wall of the channel in a selected position between the axis of the rotor and the outer end of the channel. The position of the throttled communication determines the strength of the indicating signal and is independent of settings of liquid level or the action of the centrifuge. This is due to the fact that the pressure drop in the such communication is determined by the difference in specific gravity between the liquid in the indicating channel and the liquid in the separating space, as will become clear presently.
The liquid which flows through the separating space toward the separated liquid outlet will, at least in the outer parts of the separating space, be richer in sludge and therefore heavier than the liquid which is located in the indicating channel. This means that of the columns of the two liquids which balance each other, the column of liquid in the indicating channel will be the higher. Consequently, with equal entrainment of the two liquids in rotation, the liquid in the indicating channel will have a higher pressure than the liquid in the separating space, measured at the same distance from the axis of rotation. In a centrifuge with an open-to-atmosphere outlet for separated liquid, therefore, the liquid level in the indicating channel will lie closer to the axis of rotation than the level of separated liquid; and in a centrifuge with an hermetically connected discharge line for separated liquid, the liquid in the indicating channel will have a higher pressure than the separated liquid in the center of the rotor. With substantially less rotational entrainment of the liquid in the indicating channel than the liquid in the separating space, this pressure relationship can be reversed, but this modification is less desirable. With the firstmentioned pressure relationship, therefore, there will be a certain flow of liquid through the aforesaid communication from the indicating channel into the separating space. At the same time, a replacement flow of liquid will take place inwardly through the radially outer opening of the channel.
The present invention has been found applicable not only to centrifuges with an open-to-atmosphere outlet for separated liquid, but also to centrifuges with a discharge line for separated liquid connected hermetically to the rotor. In the case of the latter embodiment, the clogging by sludge can be sensed by means of a pressure meter inserted in a line extending from the rotor and hermetically connected to the indicating channel.
Air which has entered the pressure meter line increases the indicated pressure and can thus counteract the signal which the clogging of sludge produces. In order that the result of the pressure measurement will not be distorted by this air, the lastmentioned line may be provided with an air vent. This vent in its simplest form consists of a small hole through which air entering the pressure meter line discharges. When all the air has disappeared, a small negligible flow of liquid continuously discharges through the hole.
In a centrifuge with a level-maintaining outlet for separated liquid, there is preferably provided in the rotor a central space into which the indicating channel opens, and in this space there is again a level-sensing member. It may be of known type, such as a pressure meter inserted in a liquid-filled line connected to a skimming disc. The measurement of the level can also be effected by blowing compressed air below the liquid level in the central space and measuring the blowing pressure required.
Optimum signal strength is obtained, in the case of a centrifuge with a level-maintaining outlet for separated liquid, if the communication hole arranged in the channel wall is placed at substantially the same radial distance from the axis of rotation as the level of the separated liquid.
In a centrifuge with the conventional set of conical discs which increase the effectiveness of the separation, it is advisable that the communication hole in the channel wall be arranged outside (as viewed radially) the inner edge of the set of discs and even outside the outer edge of the set, if the signal strength continues being satisfactory, since the liquid flowing from the indicating channel into the separating space can to a certain extent contaminate the separated liquid with sludge.
In order to obtain a desired signal intensity, the indicating channel is provided with members for placing the liquid in rotation in order to prevent slippage of rotating liquid in the indicating channel from counteracting the formation of pressure in the channel and thereby lowering the intensity of the signal.
The invention will be described in further detail below with reference to the accompanying drawings showing two different embodiments of the present centrifuge in axial section. More particularly, the centrifuge is shown in FIG. 1 with a skimming disc outlet for separated liquid, and in FIG. 2 with a discharge line for separated liquid connected hermetically to the rotor.
In FIG. 1, the centrifuge rotor ll has a cover 2 which is held fast to the part l by means of a locking ring 3. The rotor is supported and driven by a shaft t provided with a central channel 5 for supplying a sludge-containing liquid to be separated. The latter is conducted by a distributor 7, provided with entrainment wings 6, into the separating space 8. In the separating space there is a set of conical discs 9. Sludge separated from the liquid is collected at the periphery of the separating space and is removed intermittently through openings ill in the rotor body I. These openings are exposed and closed by a piston valve 12, the movements of which are produced in a known manner by liquid from a cylindrical supply member 13 surrounding the shaft 4. The piston 12 is held pressed up against the cover 2 when liquid is fed to a space 14 below the piston, a certain efflux of liquid simultaneously taking place through drainage hole 15. The piston is pressed down by the liquid pressure in the separating space 8 when the supply of liquid through the member 113 is interrupted, since liquid in the space 14 is then drained out through the hole 15.
Separated liquid flows from the inner edge of the set of discs d to a skimming chamber 16 containing a stationary skimming disc ll7 which discharges separated liquid through an outlet 18. The indicating channel 19 may consist of one or more radially extending pipes or of spaced plates divided into subchannels by radially extending strips. In the left-hand part of FIG. I, there is shown a section passing through such a strip. The radially inner end of the indicating channel opens intoa skimming chamber 20 in which there is a stationary skimming disc 21. To the latter is connected a pipeline 22 in which there is inserted a pressure meter 23. The channel wall has a hole 24. If a higher signal intensity is desired, the hole is placed further inward radially, for instance at the location of hole 25, that is, in approximately the same position as the level 26 for separated liquid. The level of the indicating liquid is indicated at 27.
In the operation of the FIG. 1 embodiment, after emptying of sludge through the openings 11, the separating space 8 is filled again with the liquid to be separated. It also fills the channel 19. Due to the fact that the flow of liquid through the channel is slight in the part thereof located radially outside the hole 24, and not in the part thereof located radially inside the hole, the sludge contained in the indicating liquid is rapidly separated out. This means that the indicating liquid will become practically free of sludge and therefore lighter than the liquid in the separating space. As a result, the level 27 will establish itself closer to the axis of rotation than the level 26. At the outer opening of the channel 19, the indicating liquid and the separating liquid (liquid to be separated) have the same pressure; but at the level of the hole 24, the indicating liquid has a higher pressure than the separating liquid. The indicating liquid therefore flows out into the separating space 8 through the hole 24 while a corresponding quantity of separating liquid flows into the channel through its outer opening. When a plug of sludge has been formed in this opening, the last-mentioned liquid flow is interrupted, so that the indicating liquid and the separating liquid will assume the same pressure on both sides of the hole 24 due to the fact that a certain amount of indicating liquid from the radially inner part of the channel will flow out into the separating space through the hole 24. The level 27, in other words, will move somewhat radially outward. This shift in level is indicated by the meter 23.
In FIG. 2, the line 18 is hermetically connected to the rotor by a seal 28, and the line 22 is hermetically connected to the inner end of the indicating channel by a seal 29. The channel end above mentioned has the shape of a central space 30 into which the line 22 opens. This line has a vent hole 31, the purpose of which has already been indicated. Maximum intensity of the indicating signal is obtained if the hole is placed in the wall of the channel at the place indicated by a hole 32, that is, at the axis of rotation. An alternative possibility for the location of the hole is designated at 2511.
The arrangement in accordance with FIG. 2 operates, in principle, in the same manner as the arrangement of FIG. 1.
The difference is merely that in the embodiment in accordance with FIG. 2, a decrease of pressure in the space 30 is sensed when a sludge plug has been formed in the outer end of the channel.
In experiments, it has been found that placing of the hole 24 level with the outer edge of the set of plates in itself will give a signal intensity of about 0.5 kg./cm., which was sufficient for its purpose, of course, provided that the indicating channel extends a substantial distance outside the set of plates.
1. In a sludge centrifuge comprising a centrifugal rotor having a rotation axis and also having a separating chamber and a sludge space for collecting sludge separated from a sludgecontaining liquid in said chamber, the combination of means forming an indicating channel having an outer end opening into said space, said channel extending radially inwardly from said space to approximately said rotation axis, said means also forming a throttled communication spaced from said outer end opening and leading directly from said channel to said chamber, said communication being located between said axis and the radially outer end of said channel, and a device connected to said channel for sensing clogging of said outer end of the channel b sludge collected in said space.
2. A centn uge according to claim 1, compnsrng also a stationary outlet pipe for separated liquid, said pipe being hermetically connected to the rotor, said sensing device including a stationary pipeline hermetically connected to said channel and extending from the rotor, and a pressure-indicating meter inserted in said pipeline.
3. A centrifuge according to claim 2, comprising also an air vent in said pipeline.
4. A centrifuge according to claim 1, in which said rotor has a level-maintaining outlet for separated liquid, the rotor also having a central chamber into which said channel opens, said device including a level-sensing means communicating with said central chamber.
5. A centrifuge according to claim 4, in which said throttled communication is located essentially at the same radial distance from the rotation axis as the level-maintaining outlet for the separated liquid.
6. A centrifuge according to claim 1, comprising also a set of conical discs in said separating chamber for increasing the separation efficiency, said throttled communication being located radially outward from the inner edge of the disc set.
7. A centrifuge according to claim 6, in which said throttled communication is located radially outward from the outer edge of the disc set.
8. A centrifuge according to claim 1, in which said channel has means for entraining the liquid into rotation.