US2954739A - Pumps - Google Patents

Description

K. R. LUNG Oct. 4, 1960 PUMPS 2 Sheets-Sheet 1 Filed Jan. 3, 1956 FIG-'l FIG-5 INVENTOR.

KENNETH R. LUNG ATTORNEYS Oct. 4, 1960 K. R. LUNG 2,954,739

PUMPS Filed Jan. 3, 1956 2 Sheets-Sheet 2 FIG -6 41 5s \7 3 30 QZZ 4 52 4a 44 45 61 FIG-1O 61 v, zz e1 57 6'1 57 5o l l 4 56 5 56 62 FIG-11 IN V EN TOR.

KENNETH R. LUNG ATTORNEYS 2,5 as Fatented Get. 4, 1960 PUMPS This invention relates to centrifugal pumps.

The invention has special relation to multistage centrifugal pumps, including such pumps of the type adapted to be entirely submerged in the water or other liquid to be pumped, and the invention is particularly concerned with problems frequentlyencountered in such pump installations as a result of the presence of abrasive materials in the water, and which for convenience may be generally referred to as sand. The major trouble with sandy water is that when the pump is temporarily shut off, some of the sand may settle between complementary bearing surfaces, and ,such sand may and often does create sufficien-t friction to make it difiicult or even impossible to restart the pump. Furthermore, even if the pump can start again, the sand in metal bearings is capable of doing sufiicient damage by scoring and the like as ultimately to interfere with proper operation of the pump.. 1

' It is accordingly a primary object of the invention to provide a multistage centrifugal pump which is capable of efficient operation in spite of the presence of sand in the water, and which not only can pump water containin-g sand but also is capable of efficient intermittent operation irrespective of the presence of sand in the water.

In general the most difficult operations from the standpoint of sand in the water are usually encountered when a new Well is first put into use, since the concentration of sand is then highest but is likely to be reduced after the first few hours or days of use of the well. This means that the greatest potential damage to the pump by sandy water occurs when the pump is first installed in the water, and it is therefore an important object of the present invention to provide a multistage centrifugal pump which has its maximum capacity for handling sandy water when it is first put into use.

An additional object of the invention is to provide a multistage centrifugal pump wherein the component parts are individually of simple construction and cooperate in use to offer high resistance to the entry of sand at points where harmful frictional effects could be produced while making it readily possible for sand to be carried through the pump with the water and without creating undesirable friction.

Another object of the invention is toprovide a multistage centrifugal pump wherein the pumping unit forming each stage is composed of only three parts, namely a casing and an impeller and diffuser mounted within the casing, and wherein each component part is individually of a construction facilitating economical production and assembly.

A further object of the invention is to provide a multistage centrifugal pump in which the component parts of each stage or pumping unit cooperate to minimize undesirable thrust loads in any direction in operation but at the same time to establish a control thrust force which maintains proper sealing conditions against the entry of sand at points where harmful frictional effects could otherwise develop.

structed of a material such as a plastic which has the a property of relatively slow and limited swelling in the presence of water, and wherein this impeller is initially made of proportions establishing suflicient clearances for sand at locations where it is desirable to prevent trapping of sand during initial use of the pump with these clearances being gradually reduced for increased smoothness of operation after the pump has been in use for sufficient time to eliminate the major proportion of the sand initiaily present in the well.

Still further objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

In the drawings- Fig. 1 is a partial view generally in axial section and showing a submersible multistage centrifugal pump constructed in accordance with the invention;

Fig. 2 is a detail sectional view of one of the impellers in the pump in Fig. 1, the View being taken on the line 2-2 of Fig. 3;

Fig. 3 is a detail view showing the front or inlet side of the impeller of Fig. 2 with a portion of the front shroud broken away;

Fig. 4 is an enlarged fragmentary section on the line 4-4 of Fig. 3;

Fig. 5 is a detail view in radial section through the casing of one of the pumping units of Fig. 1;

Fig. 6 is a greatly enlarged view of a fragment of Fig. 1 taken in radial section;

Fig. 7 is a projection of a fragment of the outer periphery of the dififuser plate in one of the pumping units of Fig. l;

Fig. 8 is a detail elevational view showing the back side of the diffuser plate;

Fig. 9 is a section through the diffuser plate taken on the line 9-9 of Fig. 8; and

Figs. 10 and 11 are fragmentary sections taken on the lines 10-10 and 11-11, respectively, of Fig. 8.

Referring to the drawings, which illustrate a preferred embodiment of the invention, the cylindricalv shell 13 which forms the main pump housing has an upper end cap 14 threaded at its upper end for connection to the lower end of the usual down pipe 15 by which the entire apparatus is suspended in a well. At the lower end of the shell 13 is an intake end cap 16 which is shown fragmentarily and supports the drive motor (not shown) in the usual way. The drive shaft 17 of the motor is connected by a coupling 18 with the pump drive shaft 20 which extends through substantially the entire length of the shell 13 to drive the plurality of pumping units or stages therein.

These several pumping units are of identical construction, and the component parts of each unit are an impeller 21, a diffuser plate 22, and a casing 23 which encloses its associated impeller and diffuser. These multiple pumping units are clamped between the end caps 14 and 16 in stacked relation along shaft 29 with the inlet of each unit arranged as described hereinafter to receive the output of the next lower unit. The main inlet of the pump is through the intake end cap 15 as indicated at 25, and the discharge from the uppermost unit reaches the downpipe 15 through a port 26 controlled by a check valve 27 and sealing washer 28.

As stated, all of the impellers 21 are of identical structure, and one is shown in detail in Figs. 2-4. It includes a hub 30 having internal spines 31 for driving engagement in a corresponding keyway 32 in shaft 20, and the back shroud 33 of the impeller extends radially outwardly from the hub 30. A cylindrical sleeve 34- projects rearwardly from the hub beyond the back shroud 33, and the front shroud 35 of the impeller is connected with the back shroud 33 by a plurality of impeller vanes 36. The inner diameter of the back shroud is substantially smaller than that of the front shroud, and the outer diameter of the back shroud is therefore substantially reduced with respect to that of the front shroud in order to provide the outer surfaces of both shrouds with more nearly the same effective areas as described in detail hereinafter.

A convenient manner of constructing this impeller is to cast it initially as two pieces, one including the hub and back shrould and the other including the front shroud and vanes. Lugs 37 are included on each vane and are received through complementary holes 38 in the back shrould and then riveted over to secure the assembled parts together. This arrangement is shown in detail in Fig. 4, which also shows how the holes 38 are initially countersunk to assure riveting of the lugs 37 into flush relation with the outer surface of the back shroud 33.

The front shroud 35 of the impeller includes an annular boss 40 which cooperates with the front end portion of the hub 30 to define an annular inlet 41 to the interior of the impeller. The interior of the boss 40 is provided with a counterbore 42 which receives a complementary cylindrical flange 44 extending inwardly from the periphery of the corresponding inlet opening in the center of each casing 23. These respective parts are so proportioned that the front end face of boss 40 normally engages the inner surface portion 45 of the casing which surrounds flange 44, and which is recessed as shown to form a bearing surface for boss 40. The remainder of each casing 23 is generally cup-shaped, with its outer wall being cylindrical to fit within the cylindrical shell 13, and each casing is provided at the outer edge of the front thereof with a circumferential notch or shoulder 46 which forms a seat for the rear! ward edge for the adjacent casing upstream thereof.

In addition, the rearward edge of each casing 23 is provided with a plurality of notches 47 for interlocking engagement with the associated diffuser 22 as described in more detail hereinafter.

Each diffuser plate 22 is a single piece which is illustrated in detail in Figs. 7-1l as cast from a plastic material. The main portion of the diffuser plate is an annular web 50 radiating from a central hub 51 which forms a bearing for the sleeve portion 34 of the associated impeller and is preferably provided with a liner bushing 52 of stainless. steel or other suitable material. As shown in Fig. 9, this bushing 52 is provided with a circumferential groove 53 which assists in holding it in assembled relation in the hub 51.

The web 50 of the diffuser 22 is of greater diamfiter than the back shroud 33 of the associated impeller, and it approaches the diameter of the front shroud 35. The web 50 is provided at its peripherywith a cylindrical rim 55 which overhangs the periphery of the shroud 33 and thus in effect forms a continuation of the back shroud for cooperation with the front shroud to guide the liquid flow outwardly: from the impeller. This rim 55 is of sufficiently smaller outer diameter than the inner diameter of the associated casing 23 to provide a space therebetween, and in this space lie a plurality of generally helical fins 56 which project outwardly from rim 55 as best seen in Figs. 7 and 9. Each of these fins in turn terminates in a shoulder 57 proportioned to engage within one of the notches 47 in the back edge of the associated casing 23 in order to lock the diffuser and casing together.

The fins 56 cooperate with the outer periphery of the diffuser plate and: the inner surface of; the associated casing 23 to o m a p r ity. pass eways. .0 le din rearwardly from the outer periphery of the associated mp ller. lone h y nne ulfa fi e; a i 3. towar the back of the diffuser. Accordingly, the diffuser inlude a so p u a ty f: en ra y pi al. v nes. 61.;

on the back surface of the web 50 which extend from a position near the hub 51 to the outer periphery of web 50 and include outer wall portions 62 which are cylindrically curved and annularly spaced with respect to each other and which merge with the rim 55. These vanes 61 thus cooperate with the inner surface of the casing 23 to define diffuser passageways which form continuations of passageways 60 and are of increasing flow area with respect to the passageways 60 for slowing down the velocity of theliquid with respect to its velocity through the passageways 60 before this liquid is conducted inwardly from the diffuser passageways for delivery to the inlet of the next casing and impeller.

As clearly shown in Fig. 6, the front surface of such adjacent casing 23 cooperates with the diffuser and the vanes 61 to form a back wall for these passages and thus to assure proper directional flow of the water from stage to stage. As also most clearly shown in Fig. 6, the outer diameter of the impeller front shroud 35 is only slightly less than the inner diameter of the casing 23, which assures clearance in operation, while the outer diameter of the rim 55 is less than the outer diameter of the shroud 35, and therefore the discharge from the impeller is forced to flow primarily axially and then inwardly of the casing 23 as its velocity is converted to pressure by flow through the diffuser passageways. In this process, the liquid flows first axially and circumferentially through the relatively restricted passageways 60 which extend between adjacent fins 56 and are bounded circumferentially by the inner wall of the casing and by the outer surface'of the rim 55 and the wall portions 62, and it then enters the rapidly widening diffuser passageways bounded on the inside by the spiraling vanes 61; and extending between the back surface of the diffuser and the front surface of the next adjacent casing 23. The velocity conversion therefore takes place behind the impeller and within its outer diameter and thus makes possible use of an impeller of the maximum size and capacity for the overall diameter of the pump.

The relative proportions of these parts and the materials of which they are composed are important in achieving the advantages of the invention to the maximum extent. Thus the front and back shrouds of each impeller are proportioned as previously described to have closely comparable respective areas, and thereby to approach a balancing of the axial thrusts thereon. At the same time, it is desirable to maintain a small excess thrust downwardly i.e., towards the motor, in order to assure maintained pressure engagement between the boss 40 and the bearing surface 45 which will seal the junction between these surfaces against possible entry of sand. Satisfactory results from this standpoint have been obtained with the back shroud having inner and outer diameters of approximately .658 inch and 2.437 inches respectively, as compared with inner and outer diameters for the front shroud of 1.00 inch and 2.938 inches.

The importance ofmaintaining the seal between boss 40 and its bearing surface 45 derives from a variety of factors. In the first place, the velocity of flow of liquid is at a minimum through the inlets of the impellers, and the pressure is therefore at a maximum in these locations, the forces tending to encourage entry of sand between each impeller and its casing are accordingly substantially at a maximum adjacent the bosses 40. In addition, the average radius of the bearing surface on boss 40 is approximately twice that of the other bearing surface of the impeller, namely, the outer surface of the sleeve 34, so that frictional resistance to turning of the impeller resulting from sand between boss 40 and surface 45 will be correspondingly greater than it would be for the same conditions between the sleeve 34 and the metal bushing 52. For the same reasons, a substantial clearance is provided between the counterbore 42 and the outer surface 44 on the casing, namely, approximately .01 in r a c earance.

so that the impeller will be free to slide with respect both to shaft 20 and to its associating casing 23. In addition, the impeller is constructed of a material having the property of swelling in water toa limited extent over a substantial period of time, and preferred results have been obtained with the impeller molded from a resin of the nylon type which not only has such properties of water absorption but also is an excellent bearing material. For example, if the sleeve 34 has an outer diameter of .658 inch, a recommended material for the impeller is a nylon resin having the property of swelling approximately .030 inch for each inch of diameter, and particularly such a resin which will swell to approximately one-half its total extent in a matter of about ten days but will then not complete its swelling for another ninety days. For similar resins which swell to a different extent in water, the initial proportions for the impeller should be computed to provide the preferred final relative dimensions indicated above.

Major advantages of the invention derive from this impeller construction. In particular, with a substantial clearance as described between the sleeve 34 and bushing 52 when the pump is first put into operation, whatever sand may be present will tend to flow through such clearances rather than to be caught therein, and at the same time the boss 40 will seal against entry of sand between itself and the bearing surface 45 as previously described. The majority of the sand in a new well will ordinarily be eliminated from the water being drawn therefrom in not more than about two days, and during this time the impeller sleeve 34 will be slowly swelling to reduce its clearance in the bushing 52 after the danger of entry of sand is also reduced, thus increasing the efi'iciency of the pump as a whole.

This process continues until the impeller has reached its maximum absorption for water, but even if thereafter sand should enter between any of the bearing surfaces of the impeller, it will still not be too severe a problem. Thus if both the complementary bearing surfaces were metal, sand entering therebetween would tend to scratch at least one metal surface before it could be crushed or otherwise eliminated. With one bearing surface of nylon, however, the sand would tend to imbed itself therein without too great an increase in friction until it had been gradually worn away, and the overall results of all of these individual advantages are increased efiiciency and reduced maintenance as well as low initial cost of the pump as a whole.

While the form of apparatus herein described constitutes preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

l. A multistage centrifugal pump comprising a plurality of individual casings each forming a part of one of said pump stages, each said casing being of generally cup shape including an outer portion of circular section and a central inlet opening in the front thereof, meansmaintaining said casings in axially stacked relation with ing said shrouds together, an annular boss at the center of said front shroud defining the inlet to said impeller, a bearing surface within said casing for running engagement by the forward end of said boss, said back shroud of each said impeller being of substantially less diameter than said front shroud and having a total effective area slightly greater than said front shroud to establish a correspondingly small thrust force maintaining said boss in running engagement with said bearing surface in operation, a diffuser secured within each said casing and including a web of greater diameter than said back shroud having thereon a cylindrical rim projecting into radially overhanging relation with said back shroud for cooperation with said front shroud to guide the liquid flow outwardly from said impeller, said rim being of less outer diameter than said front shroud for cooperation with said casing to define an annular space of re stricted flow area axially overlying said front shroud for receiving the liquid flow from said impeller, and cooperating means on said diffuser and casing defining a plurality of diffuser passageways of increasing flow area leading from said annular space inwardly to the inlet of .the adjacent said impeller.

2. A multistage centrifugal pump comprising a plurality of individual casings each forming a part of one of said pump stages, each said casing being of generally cup shape including an outer portion of circular section and a central inlet opening in the front thereof, means maintaining said casings in axially stacked relation with said outer portion of each casing seated on the front of the adjacent casing upstream therefrom, a drive shaft extending axially through said stacked casings, an impeller in each said casing including a hub splined on said shaft for movement axially thereof and a back shroud extending generally radially from said hub, each said impeller also including a front shroud and vanes securing said shrouds together, an annular boss at the center of said front shroud defining the inlet to said impeller and registering with said casing inlet opening, said back shroud of each said impeller being of substantially less diameter than said front shroud, a diffuser secured within each said casing and including a Web of greater diameter than said back shroud having thereon a cylindrical rim pro jecting into radially overhanging relation with said back shroud for cooperation with said front shroud to guide the liquid fiow outwardly from said impeller, generally helical fins projecting radially from said rim in axially overlying relation with said front shroud and cooperating with said casing and said rim to define a plurality of restricted passageways for conducting the liquid flow from said impeller rearwardly and circumferentially along the inner wall of said outer casing portion, and cooperating means on each said difluser and the adjacent said casing downstream thereof defining a plurality of diffuser passageways of increasing flow area leading from said restricted passageways inwardly to the inlet of the adjacent said impeller.

3. A multistage centrifugal pump comprising a plurality of individual casings each forming a part of one of said pump stages, each said casing being of generally cup shape including an outer portion of circular section and a central inlet opening in the front thereof, means maintaining said casings in axially stacked relation with said outer portion of each casing seated on the front of the adjacent casing'upstream therefrom, a drive shaft extending axially through said stacked casings, an impeller in each said casing including a hub splined on said shaft for movement axially thereof and a back shroud extending generally radially from said hub, each said impeller also including a front shroud and vanes securing saidshrouds together, an annular boss at the center of said front shroud defining the inlet to said impeller and registering with said casing inlet opening, said back shroud of each said impeller being of substantially less diameter than said front shroud, a diffuser within each said casing and including a web of greater diameter than said back shroud having thereon a cylindrical rim projecting into radially overhanging relation with said back shroud for cooperation with said front shroud to guide the liquid flow outwardly from said impeller, generally helical fins projecting radially from said rim in axially overlying relation with said front shroud and cooperating with said casing and said rim to define a plurality of restricted passageways for conducting the liquid fiow from said impeller rearwardly and circumferentially along the inner wall of said outer casing portion, cooperating notch means on the rearward edge ofeach said casing and radially projecting shoulders on said helical fins for locking said casings and diffusers together, and generally spiral vanes on the back of each said diffuser cooperating therewith and with the front of the adjacent said casing to define a plurality of diffuser passageways of increasing flow area leading from said re-' stricted passageways inwardly to the inlet of the adjacent said impeller.

4. A multistage centrifugal pump of the character described comprising a plurality of individual casings each forming a part of one of said pumping stages, an impeller in each said casing, means on each said impeller defining the inlet thereto, each said casing being of generally cup-shape including an outer portion of circular section relatively slightly greater in diameter than the associated said impeller and having a central opening in the front thereof adapted to register with said inlet of said associated impeller, means maintaining said casings in axially stacked relation with said outer portion of each said casing seated on the front of the adjacent casing downstream therefrom, a unitary diffuser in each said casing including a web of lesser diameter than said impeller cooperating with said casing to define an annular space immediately behind said impeller, generally helical fins on the periphery of said web axially overlying said impeller and cooperating with said casing to define a plurality of restricted passageways within said annular space for conducting the liquid flow from said impeller rearw-ardly and circumferentially along the inner wall of said casing, and means including generally spiral vanes on the back of each said diffuser web forming a diffuser passageway of increasing flow area leading from each said restricted passageway inwardly to the space between said diffuser web and the next adjacent said casing for delivery to said impeller within said adjacent casing.

5. A multistage centrifugal pump comprising a plurality of individual casings each forming a part of one of said pump stages, each said casing being of generally cup shape including an outer portion of circular section and a central inlet opening in the front thereof, means maintaining said casings in axially stacked relation with said outer portion of each casing seated on the front of the adjacent casing upstream therefrom, a drive shaft extending axially through said stacked casings, an impeller in each said casing including a hub splined on said shaft for movement axially thereof and a back shroud extending generally radially from said hub, each said impeller also including a front shroud and vanes securing said shrouds together, an annular boss at the center of said front shroud defining the inlet to said impeller, a bearing surface within said casing for running engagement by the forward end of said boss, said back shroud of each said impeller being of substantially less diameter than said front shroud and having a total effective area slightly greater than said front shroud to establish a correspondingly small thrust force maintaining said boss in running engagement with said bearing surface in operation, a diffuser secured within each said casing and including a web of greater diameter than said back shroud having a cylindrical central portion forming a bearing, each said impeller being formed of a resin having the property of swelling in. water over an extended period of time to a predetermined appreciable limited extent proportional to the diameter thereof and including a sleeve projecting from said hub rearwardly of said back shroud within said bearing, each said sleeve being of predetermined cross sectional dimensions in proportion to said property thereof of swelling in water and to the inner diameter of the associated said bearing such that when said pump is first placed in service, the outer diameter of said sleeve issufliciently less than the inner diameter of said bearing to provide substantial running clearance for the passage of sand therebetwcen and upon comple tion of said limited swelling of said impeller, the outer diameter of said sleeve is less than the inner diameter of said bearing by a sufliciently small amount for proper bearing relation therebetween, said web having thereon a cylindrical rim projecting into radially overhanging relation with said back shroud for cooperation with said front shroud to guide theliquid flow outwardly from said impeller, said rim being of less outer diameter than said front shroud for cooperation with said casing to define an annular space of restricted flow area axially overlying said front shroud for receiving the liquid flow from said impeller, and cooperating means on said diffuser and casing defining a plurality of diffuser passageways of increasing flow area leading from said annular space inwardly to the inlet of the adjacent said impeller.

6. In a multistage centrifugal pump of the character described incorporating a drive shaft and a plurality of pumping units stacked axially of said shaft and each including an impeller and a casing therefor, the combination of a hub on each said impeller splined on said shaft and a back shroud extending generally radially therefrom, an integral sleeve projecting rearwardly along said shaft from said hub beyond said back shroud, diffuser means mounted in fixed relation with each said casing and including an annular web having a cylindrical central portion forming a bearing receiving the associated said sleeve therethrough, each said impeller being formed of a resin having the property of swelling in water over an extended period of time to a predetermined appreciable limited extent proportional to the diameter thereof, and each said sleeve being of predetermined cross sectional dimensions in proportion to said property thereof of swelling in water and to the inner diameter of the associated said bearing such that when said pump is first placed in service, the outer diameter of said sleeve is sufficiently less than the inner diameter of said bearing to provide substantial running clearance for the passage of sand therebetween and upon completion of said limited swelling of said impeller, the outer diameter of said sleeve is less than the inner diameter of said bearing by a sufiiciently small amount for, proper bear-ing relation therebetween.

7. In a multi-s-tage centrifugal pump of the character described incorporating a plurality of pumping units stacked in axial relation and each including an impeller and a casing therefor, the combination of a hub on each said impeller and a back shroud extending generally radially therefrom, an integral cylindrical sleeve projecting rearwardly from said hub beyond said shroud, a diffuser mounted in fixed relation with each said casing, a drive shaft extending through all said impellers in splined driving and supported relation with said hub sleeves thereon, each said diffuser including a cylindrical central portion forming a bearing enclosing said sleeve on the associated said impeller in bearing relation and cooperating therewith to form the sole bearing supports for said shaft, each of said impellers being formed of a material having the property of swelling in water over an extended period of time to a predetermined appreciable limited extent proportional to the diameter thereof, and each of said impeller sleeves being of predetermined initial crosssectional dimensions in proportion to-said property thereof of swelling in water and to the inner diameter of said hearing such that when said pump is first placed in service, the outer diameter of said sleeve is sufficiently less than the inner diameter of said bearing to provide substantial running clearance for the passage of sand therebetween and upon completion of said limited swelling of said impeller, the outer diameter of said sleeve is less than the inner diameter of said bearing by a sufiiciently small amount for proper bearing relation therebetween.

8. A multistage centrifugal pump as defined in claim 4 comprising a drive shaft extending axially through said pumping stages, a hub on each said impeller splined on said shaft and including an integral sleeve projecting rearwardly along said shaft, each said diffuser web including a cylindrical central portion forming a bearing receiving the associated said sleeve therethrough, each said impeller being formed of a resin having the property of swelling in water over an extended period of time to a predetermined appreciable limited extent proportional to the diameter thereof, and each said sleeve being of predetermined cross sectional dimensions in proportion to said property of swelling in water and to the inner diameter of the associated said bearing such that when said pump is first placed in service, the outer diameter of said sleeve is sufficiently less than the inner diameter of said bearing to provide substantial running clearance for the passage of sand therebetween and upon completion of said limited swelling of said impeller, the outer diameter of said sleeve is less than the inner diameter of said hearing by a sufficiently small amount for proper beating relation therebetween.

10 References Cited in the file of this patent UNITED STATES PATENTS 966,428 Cornstock Aug. 9, 1910 1,267,180 Bur-ress May 21, 1918 1,495,167 Dixon May 27, 1924 1,837,873 Macrneeken Dec. 22, 1931 1,974,107 Hait Sept. 18, 1934 2,252,554 Carothers Aug. 12, 1941 2,270,666 Arutunofi Jan. 20, 1942 2,271,961 Walceman Feb. 3, 1942 2,515,956 Greenberg July 18, 1950 2,652,271 Gaubatz Sept. 15, 1953 2,753,807 Lung July 10, 1956 2,764,099 Werner-t Sept. 25, 1956 2,775,945 Arutunofl Jan. 1, 1957 2,784,673 Namur Mar. 12, 1957 FOREIGN PATENTS 62,273 Austria Nov. 25, 1913 117,558 Great Britain July 25, 1918 342,065 Great Britain Jan. 29, 1931 786,795 France June 17, 1935 OTHER REFERENCES E. I. du Pont de Nemours & Co. (Pub.) Zytel, copyright 1954 (first 20 pages).

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