US2464011A

US2464011A - Helical hollow rotor pump

Info

Publication number: US2464011A
Application number: US712918A
Authority: US
Inventors: John B Wade
Original assignee: FMC Corp
Current assignee: FMC Corp
Priority date: 1946-11-29
Filing date: 1946-11-29
Publication date: 1949-03-08
Anticipated expiration: 1966-03-08

Description

Mami: 8, 1949. J. B. WADE HELIGAL HoLLow no'ron Puur 3 Sheets-Sheet 1 Filed Nov. 29, 1946 a l l l l I l Il llllfrl I l l A l I I l Il l I r l l l l l l Il March 8,1949. J. E, WADE 2,464,011

HELICAL HOLLOW ROTOR PUMP Filed Nov. 29, 1946 3 Sheets-Sheet 2 -lnvenor :falen Wade ,amd/4M N Homey Mmh s, 1949. J, B, WADE 2,464,011

HELICAL HOLLOW RO'I'OR PUMP Filed Nov. 29, 1946 s sheets-Sheet :s

1 d Eu/entor f@ fahrplan/ade Patented Mar. 8, 1949 HELICAL HOLLOW ROTOR PUMP John B. wade, Arcadia, Calif., signor to Food Machinery and Chemical Corporation, a corporation of Delaware Application November 29, 1946. Serial No. 712,918

9 Claims. 1

'Ihis invention relates to improvements in Moineau type pumps.

In the Moineau type pump, shown in U. S. Letters Patent No. 2,028,407, a metal rotor provided with a wide, steeply-pitched helical thread is rotated within a central opening in a rubber stator. This opening has a double internal helical Jthread so that a series of pockets or closed duid-tight spaces is formed between the rotor and stator, which move axially from the inlet end of the pump toward the outlet end thereof as the rotor is rotated. Each of these pockets is generated While in communication with 'the inlet end of the pump and thus sucks uid therefrom and transports this fluid to and reverse direction to that in which the rotor is` rotated. The practice has been to make the rotor solid and turn .this out on a lathe to produce the necessary helical thread thereon.

Because of the revolution of the axis of mass of the rotor aforesaid, it has been found expedient to connect the rotor to the line shaft with a flexible coupling. This has served -to transmit power from the line shaft which rotates about a stationary axis to the rotor which rotates about a reversely revolving axis. At low speeds no difficulty results from this revolution ofthe rotor. It is the practice in well pumps, however, to turn the rotor 1500 R. P. M. or better. The vibration produced byvrotating a solid metal rotor at such speeds is excessive and tends to loosen up the connections oi the pump assembly and crystallize the metal parts thereof.

It is accordingly an object of my invention to provide a Moineau type pump in' which this excessive vibration is eliminated.

The manufacture of rotors for Moneau pumps individually on a lathe is a laborious, expensive process. Machinery has been provided for making these automatically but this has been so expensive to yproduce as not to greatly reduce the cost of the rotors.

It is another object of my invention to provide a rotor for a Moineau pump and a method for producing the same whereby said rotors may be made at a relatively low cost.

(Cl. 10S- 117) A considerable portion of any exible drive coupling used for driving the rotor o1 a Moineau pump revolves reversely with the rotor and the lower portion of this coupling revolves over substantially the same path. I-t is` therefore important in reducing the vibration caused by this revolution of. the rotor to reduce to a minimum the weight of the connection between the coupling and the rotor. Y

Yet another object of my invention is to pr vide a combination coupling and rotor in which the connecti-on between the coupling and the rotor is effected by means much lighter than originally employed for this purpose yet without sacrificing essential strength in the connection.

It has been recognized in the art to which this invention relates, and indeed is even pointed out in the aforementioned U. S. Letters Patent, that it is preferable for the rotor of a Moineau pump to have a density which is practically equal to the density of the fluid in which it operates in order to obtain a perfect equilibrium. Heretofore, however, no Way has been discovered of producing a practical Moineau type pump rotor which will have such a low density.

It is another object of fthis invention, therefore, to provide a rotor for a Moineau type pump which will meet the exacting structural requirements of accuracy in helical contour and resistance to damage under operating conditions but which, nevertheless, will have substantial-ly the same specific gravity as the liquid in which the rotor operates.

Yet another object is to provide such a rotor which will be comparable in serviceability to the lightest rotors lpreviously available, which were turned from solid -bar stock and fthen provided with an axial cylindrical bore, and which have a specific gravity greatly in excess of that of water.

The manner of accomplishing ythe foregoing objects as well as further objects and advantages will be made manifest in the following description taken in connection with the accompanying drawings in which:

Fig. 1 is a diagrammatic longitudinal sectional view of a Moineau pump. incorporating a preferred embodiment of my invention.

Fig. 2 is an enlarged view of the novel rotor of my invention and illustrates the connection between this rotor and the flexible coupling associate dtherewith.

Fig. 3 is a vertical elevational view on the same scale as Fig, 2 and partly broken away to illustrate the means for connecting the upper end of the flexible coupling with the line shaft.

Fig. 4A is a View similar to Fig. 4 illustrating' another modified means for connecting the rotor and coupling.

Fig. 5 is a plan view of a novel mold of my invention opened as when commencing operations.

Fig. 6 is a perspective view of said mold when so opened.

Fig. 'I is a perspective view of one of the clamping rings employed in connection with said mold.

Fig. 8 is a rotor lapping machine employed in performing the method of my invention.

Fig. 9 is a fragmentary detail view taken on the line 9-9 of Fig. 8.

Fig. 10 is a front elevational view of the aforesaid mold with the latter opened and illustrating the insertion into said mold of a section of tub'- ing when starting to perform the method `of my invention.

Fig. 11 is a vertical sectional view of said mold Aillustrating the manner of applying the clamp- Fig. 13 is an enlarged fragmentary sectional' view of the base of the mold of my invention.

Referring specifically to the drawings, my in- 'vention is shown therein as embodied in a Moineau pump I0 which is suspended from the lower end of a string of pump tubing II in a well I2 having an outer casing I3. The tubing II is made up of sections between which are mounted bearing spiders I4 having bearings I5 in which is journaled a rotary line shaft I6.

Ihe pump Ill includes a housing I9 which is threadedly connected with the lower end of the pump tubing II and is provided at its lower end with a grating to strain water entering the pump I0. Provided within the housing I9 is a rubber Moineau stator 2l having an opening 22 through which a Moineau rotor 23 extends. The stator 2| and the rotor 23 have the characteristic congurations respectively of the stator and the rotor of the Moineau type pump, in which the opening 22 has a double helical female thread and the rotor 23 has a single male thread of the same pitch length.

The rotor 23 is driven by the shaft I6 through aA flexible coupling 25 which connects the lower end of this shaft with the upper end of the rotor.

The outer conformation of the rotor 23 of my invention has a single male thread 26 of exactly that form and pitch as will cause it to produce a pumping action when rotated in the stator 2 I. This conformation must be mathematically exact within a very small tolerance.

To cause the rotor 23 to be of exceptionally light weight as compared with the Moineau pump rotor formerly in common use I form this of relatively thin sheet material which is preferably a ductile metal. While various methods may be used in producingthe rotor 23, I have found it preferable to forml this by expanding aA ductile annealed steel tube into conformity with a mold, the cavity of which has a shape corresponding to the desired shape ofthe rotor 23, although slightly larger in radial dimensions so that when pressure is relaxed from the interior of the tube the latter will contract to approximately exactly 4 the desired shape of the rotor 23. This tubular shell 30 comprises the main body of the rotor 23 and is produced in the following manner:

The apparatus for manufacturing the shell 30 includes a mold and a lapping machine 36, these being illustrated in Figs. 6 and 8 respectively. The mold 35 is for forming the shell 30 into approximately its desired shape and the lapping machine is for the purpose of perfecting the outer contour of the shell 30.

of rails 42 so that a central boss 43 of the base extends downwardly between the rails 42. TheseA rails are connected by shafts 44 on which are pivoted eye bolts 45.

The base has a shallow upward boss 43 which has the -same outside diameter as a mold body 49 mounted thereon. The base 40 has a. hole 50 extending upwardly therein, this hole having a counter-bore 5I with an enlargement 52 at its upper end adapted to form part of'a mold cavity 53 provided in the mold body 49.

Extending upwardly through the hole 50 is a hydraulic injection pipe 54 having a cap 55 screwed onto its upper end. The cap 55 has a squared end 56 and is centrally apertured to a1- low hydraulic fluid to be delivered from the pipe 54I into the interior of the mold. Surrounding the pipe 54 within the counter-bore 5I beneath the cap 51 is a washer 5B and a rubber packer 59. It might be noted here that the diameter of the counter-bore 5I is such as to snuggly receive the lower end of a tube 65 employed in the process and the washer 58 and the packer 59 snuggly fuit the interior of Ithis tube when so received. d 1

The mold body 49 is formed of a low temperature casting metal and it originally kis cast as a unit about a turned master rotor having exactly the configuration which it is desired to produce in the rotor 23. The master rotor is then screwed out of the casting and the latter is sawed into three

segments

66, 61 and 68. These lsegments are then provided with

radial plates

69, 10 and 1I, the inner edges of which are ground to accurately complement the surfaces of the mold cavity 53 formed in the segments 66, 61 and 6B of the mold body 49 when the latter was originally molded.

The

plates

69, 10 and 1l are slightly thicker than the kerf formed by the saw when dividing the mold body into these segments so that the mold cavity 53 is slightly larger, as measured from the axis thereof, than the rotor shell 30 which it is desired to produce therein. This, as previously explained, is due to the fact that in forming the shell 30 in the mold 35, tube 65 is expanded hydraulically and allowance must be made in the sizel of the mold cavity 53 for the inevitable contraction of the tube 65 away from `the surfaces of the mold cavity 53 when the hydraulic pressure inside the tube is relaxed.

The segment 66 is fixed on the boss 48 and the segments 61 and768 are connected by hinges 12 to the segment 66`.` Annular ring seats 18, 19 and are provided with the same inside diameter as the external diameter of the mold body 49 when the

segments

66,61 and 68 thereof are swung together. These ring seats are divided as clearly shown in Figs. 5 and 6 and the respective sections thereof secured to the mold segments 66, 61 and 6B so that when these segments are swung together the ring seats 18. 1.9 and 80 will surs round the mold body 49 and provide tapered surfaces adapted to be engaged by the tapered inside Vsurfaces 8| of a series of clamping rings 82,

To complete the assembly of the mold 35 a mold head 90 is applied to the top of the mold body 49, this mold head having a flange 9| which snugly receives the upper end of the mold body. The mold head 90 has an upwardly extending boss 92 which carries opposite pairs of clamp arms 93 between which the eye bolts 45 extend to clamp down on these arms and thus hold the head 90, the .mold-body 49 and the base 40 from being separated vertically during the molding operation.

The mold head 90 has a hole` 94 in which is formed a counter-bore 95, the latter having an enlargement 96 at its\lower end Which complements and unites with the upper end of the mold cavity 53.

Extending through the hole 94and the head 90 is an air relief pipe 91 having a lower head 98 which traps a washer 99 and a packer 00 in the counter-bore 95. ',Ihe counter-bore is of the same diameter as the counter-bore and the washer 99 and packer |00 are of the same diameter as the washer 58 and packer 59. Thus when the mold 35 is assembledwith the annealed steel tube 65 disposed therein, as shown in Fig. 11, and the head 90 applied as shown in Fig. 12, the upper end of the tube 65 extends snugly into the counter-bore 95 and about the washer 99 and packer |00. The pipe 91 is provided with a nut |0| and comprising a pair of -rigidly spaced channels ||0 on which are mounted a motor a lathe head ated to cause the reversal of the motor thereby reversing the 'direction of the movement of the nut |30 0n the shell 30. This continues until the arm |3| engages arm |26 which actuates the switch |2| to again reverse the motor to cause the nut |30 to return in the opposite direction. Thus the nut |30 is caused to ride back and forth on the shell 30 so that by placing `a grinding compound between the nut and. the

shell and keeping the nut snugly tightened up on the shell, the latter willbe lapped into conformity with the nut |30.

Operation While the tube 65, of which the rotor 23 is formed, may be made of any of a variety of materials, it has -been found preferable to use a metal which is resistant 'to corrosion by the liquid to be handled in the pump in which the rotor is to be employed and then coating the rotor with a layer of chromium applied electrolytically, Among the metals suitable for this use, Chromium-nickel 18-18 stainless steel has been found preferable. seamless is preferred, although it is practical to use a welded tube from vwhich the ash has been removed. l

The tube 65 is cut to the proper length so that its lower and upper ends extend into the counterbores 5| and 95 and against the bottom shoulders respectively thereof, when the mold 35 is stock ||2 and a lathe tail stock ||3, the motor being connected by any suitable means such as a belt ||4 -to the head stock H2. The head stock hasel chuck ||5 and the tail stock a collar H8, the latter being adapted to center one end of a shell 30 when the opposite end is gripped in the chuck I 5.

The motor has a hand switch |20 and an automatic reversing switch |2|, the latter being actuated by the longitudinal shifting of a rod |22 which slides in blocks |23 and |24 provided on one of the channels ||0. The rod |22 has two arms |25 and |26 which extend horizontally over the space between the two channel arms 0. Adapted to be screwed onto a shell and remain thereon while the latter is being operated on by the machine 36 is a split lapping nut |30 having an arm |3| extending downwardly therefrom with a roller |32 on its lower end which is adapted to ride against one or the other of the channels ||0. The nut |30 has a clamping bolt |35 by which the nut can be tightened or relaxed as desired. The nut |30 has internal threads formed by casting the same around the same master rotor which the mold body 49 was formed from so that the nut |30 is adapted to threadedly receive a shell 30 asshown in Fig. 8.

Afterthe tube 65 has been inserted as shown in Fig. 11, and before the mold head is applied, a Wrench is inserted through the tube 65 and the squared end 56 of the cap 55 turned to screw this onto the pipe 54 and expand the packer 59 within the lower end of the tube 65. After the head 90 has been applied, this is clamped down as shown in Fig. 12 by swinging the eye bolts 45 into vertical position and screwing the nuts thereof downwardly against the clamp arms 93. The nut |0| is then rotated to lift the pipe head 98 and thus expand the packer |00 in the f upper end of the tube 65.

Before the tube 65 is inserted into the mold and the latter assembled thereabout, as just described, the tube is subjected to a thorough annealing by heating this to a cherry redand then quenching it in water.

With the tube thus annealed and assembled with the mold and with the' air bleedervalve |0| open, the pipe 56 is connected to a high pressure hydraulic pump and the latter operated to inject liquid through the pipe 56 and cap 5l into the interior of the tube 65. The valve |0| is left open until the liquid rises, fills 'the tube 65, and starts to discharge from the valve, whereupon the latter is closed.

As the hydraulic pressure in the tube increases beyond the capacity of the tube 65 to resist distortion, the latter is expandedoutwardly to partial conformity with the mold cavity 53.

Owing to the tendency of a tube 65 of this particular material to burst when attempting to expand it into complete conformity with the mold cavity 53 in one stage, I have found it preferable to employ several stages in expanding the tube before finally reaching the desired shape, and removing the tube from the mold and annealing the same between successive stages in the ex. pansion thereof.

When returning tube 65 to the mold after it has been thus partially expanded and removed for annealing, it must be returned in exactly the Tubing of this material which is rotor known as No. Moineaurotor which has l0 a diameter of 2.008" after plating, a tube 65 which is of 16 gauge material with a 11A" outside diameter is quite suitable. g

Escape of liquid from Opposite ends of the tube 65 during one of the expanding operations is pre- 15 vented by the expansion of the packers 59 and |00 in the lower and upper ends of the tube 65 where these are disposed in the counter-bores 5|' and 95 respectively.- The higher the pressure'of the liquid in the tube 65 the tighter the seal 20 formed by the packers 59 andv |00 to prevent-the escape of liquid from the tube.

To remove the tube 65 from the moldv 35 after it has been partially or fully expanded to form a rotor shell 30, the process of assembling the v l sockets |12 and |16.

tube 65 with the mold and above described is merely reversed. JNhen the shell has been formed as completely as it is possible to do this in the mold 35,

there still remainimperfections in the outer-sur- 30 face of the shell 30 whihgnust be eliminated andr this surface then providedwlth va protective coating of chromium.

The perfecting of the contour of ththread 26I on the rotor shell 30 is accomplished in tire-1151.152:`A 35 ping machine 3B. Being formed-directly from ai; r`

master rotor of the exact shape which i-s'desired to be given to the rotor shell 30, the lapping nut |30, when supplied with a grinding compound and put to work on the shell 30 in the machine 4u 36, as already described, will smooth the outer surface of the shell 30 and bring this into very close approximation of the conformation of the master rotor.

The lapping operation is also preferably car- 45 ried-on in three stages with coarse, medium and fine grinding compounds, the iinal stages being a polishing operation.

The lapping and polishing of the rotor shell 30 is carried out with a view t0 finishing with 50 the rotor being at least .004" less in diameter than the desired final size of the rotor shell. A coating of chromium is then applied electrolytically to the outer surface of the rotor shell which may be anywhere from .002" to .004" in thickness depending upon what it is necessary to add to the diameter of the shell 30 to give it the out side diameter it should have in order to cause it to function properly in the stator 2|.

This chromium is applied to the shell 30 in the 60 same manner as it is now customary to apply chromium to shafts where these rotate in water lubricated rubber bearings.

Theupper and lower tubular ends |45 and |46 of the shelll 30 remain cylindrical without chang- 65 ing diameter throughout the expansion of the tube 65. 'I'he bottom tubular end |46 may be shortened as shown in Fig.v 2 and closedv by a Aplug |48 welded therein'. The upper tubular end |45 .is preferably utilized to form a connection 70 Three modes of performing this connection are illustrated herein, one of these being shown in Fig. 2, another in Fig. 4, and still an-` other in Fig. 4A. p

The coupling 25 is` of the general type disclosed Vin U. s. Letters Patent of James M. Hau, No. 2,346,426, issued April 11, 1944, on Flexible rotary drive coupling. AThis 'type of coupling comprises a steel cablev |1|, the upper end of which extends into and is securely held in a cable socket |12 of a coupling head |13 having a screw receptacle |14 which screws onto the threaded lower end |15 of the shaft I6.

This is` made readily possible by the construction.

shown in Fig. 4. In this construction the upper tubular end |45 of the shell 30 is cut off rather short and receives a nipple formed on the lower end of a short internally threaded socket |9| having the same outside diameter as,the tubular shell end |45. The two are then welded together so as to permanently unite the socket |9| with the rotor shell 30. When this construction is used the lower end of the flexible coupling 25 has a socket |94 which 'receives and is swedged about the lower end of the cable |1| vand in turn is provided with threaded male member |95,l which screws into the threaded socket |9|.

As shown in Fig. 4 the flexible coupling 25 and member |94 have the same outside diameter as the socket |9| and upper tubular end |45 of the shell 30. Thus there is a of interference with the flow of water from the pump I0 upwardly through the pump tubing The rotor 23 of my invention weighs approximately one pound, whereas the solid rotor made 'of stainless steel, which has preceded it in common use, weighs seven pounds. Moreover, since the solid rotor must be'turned from a solid piece of stainless steel which weighs ten pounds, it is readily seen that the method of my inventionl oiers an opportunity to produce a Moineau pump rotor with a saving of about 90% in the amount of the critical materials required. It is further evident that by my method Moineau pump rotors may be produced at a great saving in expense over the cost of producing rotors by turning these from a solid piece of stainless steel.

A still moresignicant advantage of the rotor 23, however, is its extremely low weight and the marked decrease in the amount of vibration produced by my rotor over the vibration produced with solid rotors. The extreme low weight of the rotor 23 results, of course, from its being fromed of a shell of substantially uniform thickness, and its being closed at its lower end by the plug |48 and at its upper end by its connection with the coupling 25 so that the rotor remains hollow or empty, although during its operation it is continuously submerged in a liquid.

closing of the upper end of the rotor 23 so as toeiectively prevent the admission of liquid to the hollow interior thereof, (in the form of the rotor shown in Fig. 2) is accomplished by completely enclosing the coupling cable, exposed portions of the socket |16, and theupper tubular end |45 of the shell 30 within the rubber sheath |85 and vulcanizing this sheath to these metal parts as shown in Fig. 2.

The welding of the nipple |90 into the upper tubular end .|45 of the sneu so of the rotor' 23 also makes a liquid tight conection between the upper end ofthe rotor 23 and the threaded socket I9 I. When the latter is screwed into the threaded male member |95, a suitable sealing compound.,

such as paint, is used onthe threads to make the connection between the coupling socket |94 and the threaded socket l9| on the rotor, thereby forming a liquid tight closure for the upperend n of the rotor. .l q

The closing of the lower end of the rotor 23 by Welding the plug |48 therein hermetically seals the lower end of the rotor against the admission of liquid and it has been found preferable to also hermetically seal the upper end of the rotor in a similar manner as shown in Fig. 4A. In this,

view the rotor 23 is showniitted with a threaded socket |96 having a plug |9Tflwhich ts into and is welded to the upper tubular en dilfipf the shell 3U of the rotor 23 so as'to hermeticallysal the upper end of the rotor against the'admissionof liquid into the hollow interior thereof.

This application is a continuation in part of my co-pending U.v S. Letters Patent application, Serial No. 553,626, iled September 11, 1944, for Moineau pump coupling-rotor and method of making same," now abandoned.

The rotor 23 of my invention of the type shown in Fig. 4A and which is made in accordance with the foregoing data is substantially of the saine specific gravity as water, Iwhich is the liquid that Moineau pumps are ordinarily employed for handling.

The claims are:

1. A gear mechanism adapted for use as a pump and comprising: a stator having a femalethreaded chamber, the latter having an inlet and an outlet communicating therewith at axially spaced points; and a thin-walled, male-threaded rotor comprising a tube which, throughout substantially its entire llength, is 'hollow and has walls of substantially uniform thickness, said tube being plugged at opposite ends so as to seal the hollow interior thereof against the admission of liquid thereto and being revolubly disposed in said chamber and always in contact therewith in any cross section, the number of female threads of the stator exceeding by one unit the corresponding number'of male threads on the rotor, a closed fluid-tight axial space being comprised between said stator and rotor wherein the fluid is contained, rotation of said rotor generating a continuous series of said spaces, each such space being in communication with said .inlet while being generated, said rotation causing each such space to then travel in an axial direction until coming into communication with said outlet and then causing said space to be contracted until dissipated, iluid thus being transferred from said inlet to said outlet, said rotor, because of its lightness; producing a radically less amount of vibration than is produced by a like rotor of solid construction when so rotated in said stator.

2. A gear mechanism adapted for use as -a pump and comprising: a stator having a. femalei threaded chamber, the latter having an inlet and an outlet .communicating 'therewith at axially spaced points;A a thin-walled male-threaded rotor comprising a tube which, throughout sub-v stantially its entire length, is hollow and has walls of substantially uniform thickness, said tube being plugged at opposite ends so as to seal the hollow interior thereof against the admission of liquid thereto, said rotor being revolubly disposed in said chamber and always in contact therewith in any cross section, the number of female threads of the stator exceeding by onev unit the corresponding number of male threads on the rotor, a closed iiuid-tight axial space being comprised between said stator and rotor wherein the fluid is contained, rotation of said rotor generating a continuous vseries of saidspaces, each such space being in communication with said inlet while being generated, said rotation causing each such space to then travel in an axial direction until coming into communication with said outlet and then causing said lspace to be contracted until dissipated, iluid thus being transferredfrom said inlet to said outlet, the plugging means at one end of said rotor constituting a detachable connection between the rotor and a driving means therefore, said rotor, because of its lightness, producing a radically less amount of vibration than is produced by a like rotor of solid. construction when so rotated ginsaid stator. l

,3. A hollow male threaded pump rotor of relativelylight weight adapted to rotate at high speeds in a female threaded stator whereby said rotor is caused to revolve about an axis eccentric to the center of mass of said rotor and in the opposite direction to said rotation, said r0- tor comprising a tubular shell which, throughout substantially its entire length, is hollow and has walls of substantially uniform thickness, said shell being sealed at its opposite ends .against the admission of liquid thereto, the means for sealing one end of said rotor having means thereon for connecting said rotor with a driving means therefor, said rotor, because of its lightness, producing a radically less amount of vibration than is produced by a like rotor of solid construction when so rotated in said stator.

4. A combination as in claim 3 in which one end of said rotor has an axially disposed integral tubular neck, the sealing means 'connecting said rotor with a driving means therefor being housed within and bonded to said neck.

5. A combination as in claim 4 in which said sealing means housed within and bonded to said tubular neck comprises a cup which provides a detachable connection between said hollow rotor and said driving means.

6. A hollow pump rotor as dened in claim 3 in which said connecting means comprises a exible cable having a head permanently united therewith, said head being also permanently bonded with one end of said rotor whereby rotation of said cable is transmitted to said rotor and said'head forms the sealing means for said end of said rotor.

7. A hollow pump rotor as defined in claim 3 in which said connecting means comprises a ilexible cable having a head permanently united therewith and with one end of said rotor to form the sealing means therefor and to connect said A l l cable to said rotor,v said end of said rotor and said head and said cable being covered by a sheath of soft rubber molded thereon and bond- Aed thereto.l

8. Ahollow pump rotor as deiined in claim 3 in which the means for sealing one end of said rotor and connecting the rotor with a driving cup which fits within said rotor end and is bonded thereto; a male-threaded drive coupling head adapted to screw into said cup; and a Vflexible drive coupling element united with said head.

9. A gear mechanism adapted for use as a pump and comprising: a stator having a femalethreaded chamber, the latter having an inlet and an.- outlet communicating therewith at axiallyspaced points; a hollow, thin-walled ma1e. threaded, tubular rotor revolubly disposed in said chamber and always in contact therewith in any cross section, the number of female threads of the stator exceeding by one unit, the corresponding number of male threads on the rotor; a plug closing one end of said rotor; bearing means disposed concentrically with said stator; a shaft journalling in said bearing means and spaced axially from said rotor; a iiexible coupling comprising two heads connected by a fiexible cable, one of said heads being xed upon means therefor includes an internally threaded said shaft and the other of said heads extending into the other end of said hollow rotor and being bonded thereto to seal the same against the admission of liquid thereto and to transmit torque from said coupling to said rotor; and a rubber coupling sheath which covers and seals the connection between said hollow rotor and said coupling.

JOHN B. WADE.4 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 21,374 Moineau Feb. 27, 1940 736,039 Wainwright Aug. 11, 1903 1,702,047 Fulton Feb. 12, 1929 2,028,407 Moineau Jan. 21, 1936 2,212,417 George Aug. 20, 1940 2,267,459 Halt Dec. 23, 1941 2,346,426 Hait Apr. 11,-1944 FOREIGN PATENTS Number Country Date 780,791 France Feb. 11, 1935 Certiicateof Correction Patent No. 2,464,011. March 8, 1949.

JOHN B. IWADE It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 14, for the Word originally read ordinarily;

lines

50 and 51, for associate dtherewth read associated therewith; column 6, line 23, for IS-18 read 18-8; column 8, line 70, for fromed read formed; column 9, line 32, for en c1145 read end 145;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oce.

Signed and sealed this 9th day of August, A. D. 1949.

THOMAS F. MURPHY,

Assistant Gommasoner of Patents.