Peripheral discharge sludge collection centrifugal drum
US 3125516 A
Description (OCR text may contain errors)
March 17, 1964 F. KALDEWEY 3,125,516 CTION CENTRIF'UGAL DRUM PERIPHERAL DISCHARGE SLUDGE COLLE 2 Sheets-Sheet 1 Filed March 14, 1961 INVENI OR ERA/v2 KALDEWEV BYBMW ATTORNEYS I March 17, 1964 F. KALDEWEY PERIPHERAL DISCHARGE SLUDGE COLLECTION CENTRIFUGAL DRUM 2 Sheets-Sheet 2 Filed March 14, 1961 INVENTOR FRANZ KALDE WE Y United States Patent 3,125,516 PERIPHERAL DISCHARGE SLUDGE COLLECTION CENT RIFUGAL DRUM Franz Kaidewey, Oeide, Westphalia, Germany, assignor to Westfalia Separator Aktiengesellschaft, Oelde, Westphalia, Germany, a German corporation Filed Mar. 14, 1961, Ser. No. 95,755 Claims priority, application Germany Mar. 14, 1960 6 Claims. (Cl. 23339) The present invention relates to a centrifuge drum arrangement for centrifuging material to separate a lighter fraction from a heavier fraction of material being centrifuged, and more particularly to such a drum having at least two peripheral annular collection zones axially disposed one above the other for collecting outwardly centrifuged material, and nozzle means for discharging peripherally collected sludge or heavier fraction material.
Peripheral discharge drums are known, and such drums are used for separating a heavier fraction, such as a heavier liquid or a solid, from a lighter fraction, such as a lighter liquid. Normally, the drum is provided with a plurality of spaced apart axially positioned separator discs or cones for efiecting the separation of the lighter fraction from the heavier fraction of material being centrifuged. The lighter fraction is usually inwardly directed towards the axis of the drum whereby the same may be discharged from the drum from an axially positioned outlet. On the other hand, a sludge discharge chamber or zone is located radially outwardly out of the separator zone, containing the separator discs or cones. The top and bottom walls of the drum outwardly converge to form a nozzle-containing periphery. By the converging of the top and bottom walls of the drum an annular groove or sludge discharge collection chamber is defined along the interior of the drum radially outwardly of the separator discs. The nozzles communicate the sludge collection zone with the exterior of the drum so that, if desired, a sludge heavier fraction may be continually discharged from the drum during centrifugal action. It is a common expedient to employ a portion of the liquid in the material being centrifuged as conveying medium for the sludge solid particles in order to achieve the effective discharge of such sludge material through the nozzles peripherally disposed about the drum. However, it is necessary that the top wall downwardly and outwardly converge with the bottom wall which upwardly and outwardly extends to form an apex therewith. This is true since an angle of slope of the sludge discharge chamber must be present which will ensure the easy passage through the nozzles of the material to be discharged in this manner. Accordingly, the angle of inclination of the'top and bottom walls of the drum with respect to the drurn axis must be greater than the natural angle of slope of the solids being centrifuged, i.e. the angle necessary for permitting the solids to slide radially outwardly to the nozzle openings along the periphery of the drum.
Centrifugal operations of the foregoing type contemplate the recovery through the discharge nozzles of solids in as highly a concentrated form as possible, and the recovery of the carrier liquidor lighter liquid fraction through an axial discharge outlet in a form as clear and free from solids as possible. 'In order to achieve a high concentration of solid-s peripherally discharged from the drum, the total nozzle cross-sectional area must be comparatively small, while for attaining a clear lighter fraction of liquid through axial discharge outlets, the total cone or disc surface area of the separator discs in the separator zone must be comparatively large.
The interior space of the drum is determined in magnitude not only by the diameter of the drum but also by the aforementioned angle of inclination of the top and bottom walls of the drum. In this connection, the interior space of the drum must also be divided into a radially inward separator zone containing the axially disposed separator discs or cones, and a radially outward sludge discharge collection zone. The number of nozzles and the size and number of the spaced apart separator discs must be adjusted with respect to one another such that the diameter of the separator discs does not exceed a certain value so as to extend into the annular sludge discharge collection zone. This is true, since otherwise a back up of accumulated sludge will occur which may extend radially inwardly into the separator zone clogging the space between the various separator discs. It will be appreciated that where a small number of nozzles are provided, large portions of solids will collect in the collection chamber in the form of wedges with the base of the wedge extending between respective nozzles and the apex of the wedge extending radially inwardly toward the drum axis. In order to prevent the extending of the wedge apex into the separator zone, the separator discs or cones must be provided with a smaller diameter. On the other hand, where a larger number of nozzles are provided, smaller wedges of collected solids will form, such that the apex of the Wedges will not extend radially inwardly an undesired distance. Accordingly, the discs or cones in the separator zone may be provided with a larger diameter. It will be appreciated that the combination of a small number of nozzles along the drum periphery and a large diameter for the discs or cones of the separator zone may not be achieved in practical operations due to the foregoing drawbacks. As a consequence, it is not always possible to obtain, in addition to a sludge solids recovery in high concentration, a desirably clarified lighter liquid fraction containing little or no solids suspended therein. Usually, a small number of nozzles, having a small total cross section of nozzle flow area is used where the recovery of sludge is desired having a high concentration of solids, whereas discs or cones are used, in the separator zone, having a larger diameter in the event good clarification of the lighter or liquid portion is sought as opposed to the recovery of the heavier or solid fraction in high concentration.
It has been well recognized in the art that for each drum construction, the number of nozzles and the diameter size of the separator discs or cones may be quite specifically defined. in order to obtain as high as possible a concentration of the solids being centrifuged and as far as possible a clarification of the carrier liquid therefor, the nozzles must be provided with small cross sectional flow areas while the separator discs or cones must be stacked closely together in the normal manner yet have a maximum diameter allowing a clearance between the separator zone and the collection zone radially outwardly thereof. Maximum efliciency, however, cannot always be achieved in this manner since the magnitude of the solids particles being separated will, of course, influence the minimum crosssectional area of the nozzles and the minimum axial distance between the separator discs or cones as Well as the largest diameter which the discs or cones may assume. To prevent clogging of the nozzles and the space between respective discs or cones, a certain marginal excess of dimensions must be allowed for in the drum construction, whereby practical operational efiiciency may be obtained.
Nevertheless, the concentration of the solids does not depend upon the total nozzle cross-sectional flow area alone, but also depends upon the concentration or content of solids in the material being centrifuged as well as the throughput capacities of the particular drum. It may be said, therefore, that large total nozzle cross-sectional flow area, low solids content or concentration in the material being centrifuged and low throughput capacity result in a low concentration of recovered solids. On the other hand, small total nozzle cross-sectional area, high solids content or concentration of the material to be centrifuged as well as high throughput capacity result in the attaining of a sludge discharge product having high concentration of solids therein.
in contrast thereto, the clarifying or clearing capacity of the lighter or liquids fraction of the material being centrifuged in the drum depends not only upon the amount of total surface area of the cones or discs, but also upon the throughput capacity of the particular drum. Additionally, the difference in the specific weight between the carrier liquid or lighter fraction and the solids or heavier fraction will definitely influence the separation operation as is well known. Significantly, an increase in the throughput capacity of the drum influences favorably the concentration of the solids although at the same time it influences unfavorably the clarifying or clearing effect upon the carrier liquid or lighter fraction.
It will be understood that in a given drum for the centrifugal treatment of a specific suspension, if the nozzle total cross-sectional flow area is kept as small as possible, and the axial distance of the separator discs or cones have been kept as small as possible as well, then the total nozzle cross-sectional area may still be too great to obtain the desired concentration of peripherally discharged solids. This is true, for example, where the individual solids particles are comparatively large yet where the solids content of the suspension is small. Where the drum is operated at full separational load, i.e. just at the point where turbidity is noticed in the clear phase or lighter fraction, indicating the carrying over of solids with the lighter fraction, if the desired concentration of the solids has not yet been reached, then the capacity of the drum is at a maximum. Consequently, While a clear lighter fraction may be obtained, the solids fraction or sludge peripherally discharged from the drum must be further concentrated in another step such as by means of an after-connected second separator drum or by recycling a portion of the concentrate peripherally discharged from the drum back into the drum for further separation effect and concentration.
Obviously, not every material being centrifuged may be recycled for further centrifugal treatment without damage occurring to the particular material. This is true whether a continuous or only an intermittent or partial recirculation of the collected solids material is contemplated. As will be appreciated, suspensions which contain flocculated albumin, for example, may not be repeatedly centrifuged in the drum without damage to the material. Thus, the albumin particles are broken up to such an extent during the first passage through the drum separator, especially by impact with the sludge collection chamber or zone outlying walls, that a recycling of the sludge material will no longer result in sludge separation but rather Will lead to a colloidal or finely distributed particle suspension of the albumin in the carrier liquid. Besides this, various other materials centrifuged in a drum will frequently lead to a deterioration of the clarifying or clearing capacity of the drum in consequence of the recycling of concentrate in the foregoing manner.
It is an object of the present invention to overcome the foregoing drawbacks and to provide a centrifuge drum arrangement for centrifuging material including a heavier or solids fraction and a liquid or lighter fraction, and for eihciently recovering the sludge material in a plurality of axially disposed collection zones within the drum whereby a desired peripheral discharge of collected sludge may take place.
Other and further objects of the invention will become apparent from a study of the within specification and accompanying drawings in which,
FIGURE 1 is a cross-sectional view of a centrifugal d drum arrangement in accordance with the present invention, illustrating details of construction,
FIGURE 2 is a partial schematic sectional view taken along the lines IIII of FIGURE 1,
FIGURE 3 is a sectional view of a further embodiment of the invention, and
FIGURE 4 is a partial schematic view of portions of collection zones axially disposed one above the other in the manner indicated in FIGURE 3.
It has been found in accordance with the present invention that an efiicient centrifuge drum arrangement for centrifuging material may be provided including a rotatable drum having at least two peripheral annular collection zones axially disposed one above the other for collecting outwardly centrifuged material, a plurality of spaced apart outlet nozzle means disposed along the drum periphery for peripherally discharging collected material, and a corresponding plurality of spaced apart separate conduit means for each of the zones, a separate conduit means for one of the zones and a separate, corresponding conduit means for the other of the zones jointly radially outwardly communicating with a common outlet nozzle means therefor.
Preferably, the spaced apart outlet nozzle means are defined in a carrier ring peripherally disposed on the rotatable drum. Each of the annular collection zones is defined by a pair of radially outwardly directed walls converging at their radially outermost portions so as to form a common apex. The conduit means advantageously pass to the nozzles in the carrier ring from the common apex.
Specifically, the rotatable drum is provided with a radially inward separation zone containing a plurality of separator discs axially disposed in spaced relation one above the other for separating a lighter fraction from a heavier fraction of material centrifuged in the drum. Radially outwardly disposed with respect to the separation zone are at least two peripheral annular collection zones axially positioned one above the other for collecting the outwardly centrifuged heavier fraction material. Each of the collection zones is constructed to define a groove of V-shaped cross section wherein the apex of the V of each groove is radially outwardly directed while the free ends of the V are radially inwardly directed. The free end of one groove and the corresponding free end of the next adjacent groove together form a radially inwardly directed common apex. The plurality of spaced apart outlet nozzles are disposed along the drum periphery and communicate with the drum interior by means of a corresponding plurality of spaced apart conduit means passing to the respective collection zones along the apex of the V of the groove in each particular collection zone. Notably, a separate conduit means for one zone and a separate conduit means for another zone adjacent thereto in axial direction together jointly communicate with a common outlet nozzle therefor.
Suitably, each separate conduit means which jointly communicates with a corresponding nozzle includes a pair of spaced apart separate passages converging from the apex of the V of the groove in the particular collection zone to a common channel jointly communicating with the nozzle therefor. It will be appreciated, therefore, that in accordance with the construction of the drum in the foregoing manner, solids may be continually discharged with a portion of the carrier liquid through the nozzles along the periphery of the drum in the desired high concentration while the remainder of the carrier liquid or lighter fraction will be discharged from the drum through axially positioned outlet means.
In accordance with the present invention, a drum construction may be provided which permits, for a given drum diameter and a given number of nozzles or a given flow cross-sectional area of the nozzles, an increase in the total separator disc surface area as 'well as an increase in the throughput capacity of the drum. By subdividing the collection zone into a plurality of annular collection zones axially positioned one above the other and assigning a joint nozzle means for each collection zone, an increased capacity of the drum may be achieved. Significantly, at various spaced apart points along the drum periphery, corresponding outlet means are provided in each of the collection zones which jointly communicate with a common nozzle means. These outlet means may comprise in each instance one or more separate passages which converge to the common joint connection with the nozzle therefor.
The construction in accordance with the present invention may be achieved only by increasing the axial height of the drum so that a larger number of discs or cones may be provided in the separator zone whereby at equal speeds of drum rotation, the throughput capacity may be increased. Naturally, depending upon the number of passages which lead from the respective collection zones to the nozzles, the separator discs or cones may have even larger diameters. 'It will be appreciated, that one cannot merely extend the diameter of the drum outwardly so as to accommodate a larger capacity since diminishing effects occur and greater stresses are placed upon the rotating parts than would be desirable. To avoid this, the number of revolutions per unit time would have to be decreased, but this measure will also adversely influence the quality of separation with the drum.
While drum constructions are already known having a plurality of axially disposed separate collection zones, in the past each said zone has been provided with separate nozzle means for discharging the sludge collected in the particular zone. Generally, each zone is provided with a peripherally disposed carrier ring containing spaced apart nozzle means therein. Therefore, while the separator disc or cone area might be increased with the use of a plurality of spaced apart axially positioned separate collection zones, as has been done heretofore, the total nozzle flow cross-sectional area correspondingly increased therewith, such that the problem of attaining highly concentrated solids was still beset with the known difliculties.
Referring to the drawing, FIGURE 1 shows a centrifugal drum having a bottom wall 1 extending from the drum axis outwardly and downwardly at la and then outwardly and upwardly at lb to the peripheral portion of the drum whereupon said wall inwardly and upwardly extends back towards the drum axis at 1c. On the other hand, the top wall 2 extends outwardly and downwardly, the same being connected to the inwardly and upwardly directed portion is of bottom wall 1 by means of connecting ring 3. It will be appreciated, however, that top wall 2 may extend, if desired, directly outwardly to the peripheral portion of the drum whereby the same will connect with the bottom wall portion thereat. Within the drum interior, a plurality of axially disposed spaced apart separator discs or cones 4 are provided defining a radially inwardly disposed separation zone. Radially outwardly thereof are a pair of peripheral sludge collection and discharge zones 6a and 6b, said zones being axially adjacent one another. Zone 6b is defined by the top interior wall lc of the drum and the top portion of the annular projection 5 while the zone 6a is formed by the lower interior drum wall lb and the lower portion of projection 5. Each chamber or collection zone 6:: and 6b assumes the cross sectional shape of a V-groove having its apex peripherally directed and the free ends of the V directed radially inwardly. Of course, the lower free end of the V of zone 61) and the upper free end of the V of zone 6a, together converge so as to form an inwardly directed apex. A carrier ring 11 is provided along the eriphery of the drum outwardly enclosing the side wall thereat. The carrier ring contains a plurality of spaced apart nozzles ill. The collection zone 61) is provided with passages 8 while the collection zone 6a is provided with passages 7. A passage 7 and a passage b is disposed within projection 5 adjacent each nozzle 10, said passages 7 and 8 jointly communicating with nozzle ill) at one end and separately communicating with their respective collection zones at the other end. Carrier ring ll is suitably provided with packing rings 13 and 14 to prevent the seepage of carrier liquid or sludge material therepast along the surface connections between carrier ring ll and the peripheral side wall of the drum defined by the rearward face of projection portion 5.
Thus, it will be appreciated that While a material may be centrifuged within the drum, whereupon a lighter liquid fraction may be separated from a solid or heavier fraction, the lighter fraction will be axially discharged through an outlet 4a while the sludge or solids material will collect in highly concentrated form within the collection zones 6a and 6b and in turn be continuously discharged from the drum periphery through the passages 7 and 3 and the common nozzle 10 situated adjacent corresponding passages 7 and 8.
In FiGURE l the normal upward limit of the drum in accordance with conventional constructions is indicated by the dotted line N. The portion of the drum above this point would be absent from a conventional drum since such drum could not attain the axial height which is possible to attain in accordance with the instant construction. Specifically, the broken line N illustrates the maximum size of the drum interior space, at the same diameter and angle of inclination of the top and bottom walls defining the collection zone, which may be achieved without the projection 5 serving to axially increase the collection zone of the drum. It will be seen that the axial height of the drum interior, and in turn of the stacked separator discs in the separator zone, is increased by about 35% due to the presence of the projection 5.
FIGURE 2 illustrates the point more clearly. In the normal drum construction indicated by the dotted line N, in FIGURE 1, a solids wedge A extending radially inwardly to the tip B of the cones or discs 4, occupies the collection zone along the periphery between respective nozzles it) which are disposed radially outwardly thereof in carrier ring il. This is true, for instance, where eight equidistantly spaced nozzles 10 are provided in carrier ring 11 along the periphery of the drum for communicating with the collection zone through conical passages 8 in the drum wall. Assuming that such drum construction is replaced by that of the instant invention, wherein an increased axial height of the drum is provided as well as an increase in the number of axially disposed adjacent collection chambers along the drum periphery, the radially outermost limit of these collection zones 6a and 611 (see FIGURE 1) would be situated closer to the axis of the drum than the nozzles lit Hence, communication with the nozzles ltl would be effected via outwardly converging corresponding passages iic from each collection zone, such that the solids wedges A in each instance would extend beyond the periphery of the separator discs or cones d as indicated by the circle 13 to the circle C. Were this to occur during centrifugal operations, the collected solids extending radially inwardly past the outer edges B of the separator cones or discs 4 to circle C would clog the spaces between the axially disposed discs and lead to disturbances in the over-all operation and the degree of effective separation of the fractions being treated in the drum. In order to prevent such disturbances and interruptions in centrifugal operations, the separator cones or discs 4 would have to be provided with a correspondingly decreased diameter, although this would be compensated for by an increase in the number of discs in axial direction by reason of the increase in axial height of the drum. Nevertheless, by providing the collection zones 6a and 6b with double the number of passages, i.e. 7a, 7b, and 8a, 8b, then a narrower base is possible for the solids wedges A Accordingly, the apex of the wedge will no longer extend past the outer edges of the separator discs 4 but instead will inwardly terminate at the circle D, leaving a suitable marginal distance between the collection zone sludge material and the separator zone discs. However, if desired, the diameter of the cones or discs 4 may be increased to some extent so long as they remain at a distance preventing the clogging of the separator zone by collected sludge wedges A It is seen that in accordance with the present construction, as opposed to the conventional construction, an increase in the number of separator discs or cones 4- may be achieved in axial direction as well as an increase in the diameter of such discs or cones, whereby the total separator surface of the discs or cones is increased markedly with a given or constant total nozzle cross sectional flow area. FIGURE 3 illustrates an alternate embodiment of drum construction in accordance with the invention wherein three axially disposed collection zones or chambers 6a, 6b, and 6c are provided, positioned one above the other, in adjacent spaced relationship. The provision for increased axial height of the drum interior is clearly seen in this embodiment. Like parts have like reference numerals with respect to the embodiment of FIGURES 1 and 2, although in this instance the central channel 9 is provided for an intermediate collection zone 60 positioned between a pair of projection members 5a and 51), each of which, in turn, defines a further collection zone 6a or til; with the adjacent portion of the drum wall suitably sloped for this purpose.
In FlGURE 4 is seen more clearly the axial and peripheral relationship between the plurality of separate collection zones 6a, 6b, and 60 as well as of the pair of passages 8a and 811 for the top chamber or zone 6b, the pair of passages 9a and 9b for the intermediate chamber or zone 6c, and the pair of passages 7a and 7b for the bottom chamber or zone 6a. A set of these passages, including a pair from each collection zone, communicates the respective zones with a common nozzle 10 located in the immediately adjacent carrier ring 11, peripherally disposed along the outer surface of the drum side wall defined by the base portions of projections 5a and 5b.
It will be appreciated that the nozzles 16, in accordance with the preferred embodiment of the invention, are provided in a removable carrier ring 11 for ease in mounting, inspection, and cleaning of the same. The carrier ring 11 may be mounted upon the shoulder 12 (see FIGURES l and 3) provided in the drum outer wall to prevent displacement of the ring. Moreover, the ring 11 is also provided with pins or set screws (not shown). The pins or set screws will prevent not only axial displacement but also rotational displacement of the ring 11 along the periphery of the drum. Of course, the sealing rings 13 and 14 serve to seal the gap be tween the drum side wall and the carrier ring 11 during centrifugal operations.
By enlarging the total disc or cone separator surface while yet maintaining a given or total constant nozzle cross-sectional flow area, the throughput capacity of the drum will be considerably increased thereby permitting a higher concentration of separated solids or sludge to be achieved as well as a considerable increase in the clarification capacity of the drum with respect to the carrier liquid or lighter liquids fraction treated therewithin. Therefore, with the drum construction in accordance with the invention, it is possible to centrifugally separate from suspension having low solids content, a sludge or solids material having a markedly higher concentration of solids therein as well as a carrier liquid in a form practically free from solids material. Moreover, in suspensions having a higher solids content, the drum construction in accordance with the invention renders possible a considerable increase in the throughput capacity wherein the individual nozzles are provided with a larger cross-sectional flow area than heretofore.
It will be appreciated that while the angle of inclination of the passages 7, 8, and 9, as well as the passages 7a, 7b, 8a, 8b, 9a, and 9b is less than the natural angle 8 of slope of the solids, i.e. that angle at which the sludge may be effectively peripherally discharged from the collection zone, a deposition or clogging of the solids within these passages is prevented due to the high flow velocity which occurs in the passages during centrifugal operations.
It will be appreciated that while the drum construction in accordance with the invention may be advantageously utilized for separating a solids fraction from a liquid fraction or carrier liquid for the solids, the drum construction may also be employed for effecting the separation of a liquid mixture into two components, i.e. a lighter liquids fraction and a heavier liquids fraction. Of course, the lighter liquids fraction will be inwardly urged during centrifuging so as to be discharged through an axially disposed outlet while the heavier liquids fraction will be outwardly urged toward the peripheral collection zone whereupon such heavier liquids fraction will be peripherally discharged through the passages and nozzles disposed along the drum peripherally thereat.
What is claimed is:
1. Centrifuge drum arrangement for centrifuging material including a rotatable drum having a top wall, a bottom wall, a constant outside diameter axially elongated intermediate wall axially separating said top and bottom walls and a radially inward separation zone containing a plurality of separator discs axially disposed in spaced relation one above the other for separating a lighter fraction from a heavier fraction of material centrifuged in the drum, at least two peripheral annular collection zones radially outwardly disposed with respect to said separation zone and axially positioned one above the other for collecting outwardly centrifuged heavier fraction material, each said collection zone defining a groove of V-shaped cross section, the apex of the V of each said groove being radially outwardly directed and the free ends of the V being radially inwardly directed, the free end of one groove and the corresponding free end of the next adjacent groove forming a radially inwardly directed common apex, all of the sides of the V-shaped grooves having a corresponding constant angle of slope with respect to the axis of the drum, a plurality of spaced apart outlet nozzles disposed along the drum periphery for peripherally discharging collected material, a corresponding plurality of spaced apart tubular conduit means being provided along the apex of the V of the groove in each said collection zone, a separate one of said tubular conduit means for one of said zones and a separate one of said tubular conduit means for the other of said zones jointly communicating with a common one of said outlet nozzles therefor, said annular collection zones being outwardly peripherally imperforate save for said tubular conduit means.
2. Arrangement according to claim 1 wherein said spaced apart outlet nozzles are defined in a carrier ring peripherally disposed on the rotatable drum intermediate wall at one axial level thereof and said separate tubular conduit means for each of said zones pass radially outwardly to said ring for communicating with said outlet nozzles.
3. Arrangement according to claim 2 wherein each said separate tubular conduit means jointly communieating with a corresponding nozzle includes a pair of spaced apart separate passages converging from the apex of the V of the groove in each said collection zone to a common channel jointly communicating with the nozzle therefor.
4. Arrangement according to claim 3 wherein said drum is provided with more than two axially positioned collection zones, all the separate passages of all of the separate conduit means of said zones, which jointly communicate with a corresponding common nozze therefor, radially outwardly converging from said axially positioned collection zones to said common nozzle.
5. Arrangement according to claim 1 wherein said drum is provided with eight nozzles equidistantly spaced around the drum periphery at one axial level of the drum intermediate Wall and each said collection zone is provided with eight tubular conduit means correspondingly equidistantly spaced around the drum periphery, a corresponding one of said conduit means from each said collection zone communicating the respective collection zone thereat with the corresponding nozzle therefor.
6. Arrangement according to claim 5 wherein each said tubular conduit means includes a pair of peripherally spaced apart passages leading from the corresponding collection zone to the nozzle means therefor, all of the passages for a corresponding nozzle jointly communicating with said nozzle through a common channel.
References Cited in the file of this patent UNITED STATES PATENTS Fawcett Dec. 10, Fawcett Sept. 19, Ortenblad Nov. 8, Komline Jan. 16, Eckers June 10, Aspegren Apr. 28, Monnet Sept. 7, Steinacker Mar. 12,
FOREIGN PATENTS France Feb. 8,