US2736825A - Electric motor - Google Patents

Description

Feb. 28, 1956 R, HILL 2,736,825

ELECTRIC MOTOR Filed June 12, 1951 ll j a 3 IN V EN TOR.

4Q fgyeri H H United States Patent ELECTRIC MOTOR Robert H. Hill, Fort Wayne, Ind., assignor, by mesne assignments, to Perfect Circle Corporation, Hagerstown, Ind., a corporation of Indiana Application June 12, 1951, Serial No. 231,192

6 Claims. (Cl. 31087) to remove the oil by pumping the same out of the well through suitable tubing, that the sand strata or other producing formations at the bottom of the well eventually become clogged or obstructed to such an extent that the yield from the well becomes too low to warrant further operation of the well. In some cases the well is abandoned, but in many instances an attempt is made to clean the well by forcing water, acid, or other suitable purging material into the producing formation whereby to remove the obstructions in the formation and restore the flow of oil to a profitable level. In some cases the purging fluid may even contain added solid material for the purpose of further expanding and enlarging the producing formation. Heretofore, in cleaning an oil well it has been necessary to remove the production tubing from the well together with the usual reciprocating pump and sucker rod in order to permit the insertion of a temporary pipe into the well casing for injecting the cleaning fluid into the well. Upon completion of the cleaning operation, the temporary pipe had to be removed and the reciprocating pump with its sucker rod and tubing reinstalled before the production of oil could be resumed. Obviously, this manner of cleaning an oil well is cumbersome and time consuming and involves substantial expense. In fact, in many cases where the production of the well at best is small, it is questionable whether the expense of cleaning the well is warranted.

However, it has been found that by means of a novel reversible pumping arrangement, hereinafter described in detail, it is possible to effect alternate or intermittent periods of production and pressurizing or purging of the well in a very convenient and reliable manner and at relatively low cost. In general, this apparatus comprises the combination of a reversible rotary pump and a reversible electric motor connected closely adjacent the pump so that the entire apparatus may be positioned adjacent the bottom of the well. When the production of the well diminishes to an undesirably low level, the operation of the apparatus can be reversed to pump oil or other suitable purging fluid downwardly and under pressure through the production tubing into the well whereby to purge or otherwise remove obstructions from the production strata and the fluid intake of the apparatus. A suitable packer is provided in the well casing for confining the fluid pressure to the lower portion of the well during the pressurizing periods. A pumping apparatus of this character offers a number of important advantages over the previous oil well cleaning techniques. Perhaps the most important advantage is the fact that the apparatus is adapted for more or less permanent installation in an oil well in the sense that it is unnecessary to remove the apparatus or the production tubing in order to effect pressurizing or cleaning of the well.

The present invention is concerned with a reversible electric motor structure comprising several novel features which render the motor particularly well suited for use in a reversible oil well pumping apparatus of the character described above. As will appear hereinafter, a motor of this type requires special provision for the passage of oil out of the well and for the passage of oil or other purging fluid into the well. In addition, adequate cooling arrangements for the motor must also be made. Furthermore, proper precautions must be taken to prevent undesirable leakage between the dielectric and lubricating oil system within the motor and the crude oil or other fluid being pumped into or out of the well.

Accordingly, a primary object of my invention is to provide a novel electric motor construction which is especially adapted for the uses hereinbefore described.

A further object of the invention is to provide a submersible electric motor adapted for use with an oil well pumping apparatus or the like comprising novel means for permitting the passage of oil or other fluid into or out of the well.

Another object of the invention is to provide a novel electric motor construction of the type adapted for installation in an oil well or the like including novel cooling means for the motor.

Still another object of the invention is to provide a novel electric motor construction of the character described having novel pressure balancing means for preventing leakage between the dielectric and lubricating oil system of the motor and the external fluid being pumped out of or into the well.

Other objects and advantages of the invention will become apparent from the subsequent detailed description taken in conjunction with the accompanying drawing wherein;

Fig. 1 is an elevational view on a reduced scale of a complete oil well pumping apparatus including one embodiment of the novel electric motor of my invention and showing the apparatus in position in a well casing;

Figs. 2 and 2A comprise a fragmentary vertical sectional view on an enlarged scale of the electric motor portion of the apparatus seen in Fig. l; and

Fig. 3 is a fragmentary transverse sectional view taken along the line 3-3 of Fig. 2.

Referring first to Fig. 1, the fragmentary lower portion of an oil well casing 6 is shown and'the surrounding earth formation is indicated diagrammatically at 7. It will be understood that the casing 6 extends in the usual manner from the ground level to the bottom of the well although neither of the extreme ends of the casing are illustrated in the drawing. A pumping apparatus is shown in position in the well casing and comprises generally a reversible motor section A comprising the present invention, a reversible pump section B, and a valve section C connected in end-to-end relation for fluid flow therebetween. An intake 8 comprising a length of perforated or slotted pipe is provided at the bottom of the pumping apparatus, and an outlet pipe 9 extends upwardly from the top of the pumping apparatus through the well casing to the ground level. Suitable electrical conductors comprising a cable 11 extend from the ground level downwardly through the casing 6 to the motor section A for operating the latter.

During production, the reversible motor section A is operated so that the reversible pump section B draws oil from the bottom of the well casing through the inlet 8 and the valve section C and discharges the oil through suitable passageways in the motor section A, hereinafter described in detail, to the outletpipe 9 which is connected into the reservoir space.

to a tank or other storage facilities at the ground level. When the producing formation and/or the intake 8 become clogged or obstructed to an objectionable degree, as indicated by a low volume of oil issuing from the well, the motor is reversed and the pump is thereby operated in reverse fashion so that oil or other suitable purging material is pumped downwardly through the pipe 9 and is discharged from the intake 8 under pressure. In order to insure that the oil or other material is forcibly iniected into the adjacent producing formation at the bottom of the well, a portion of the pump section B is fitted with an expansible packer 12 of a type adapted to resist upward pressure.

In the embodiment shown in the drawing, the packer 12 is of a conventional type comprising an axially compressible rubber sleeve. The rubber sleeve is secured around the upper portion of the pump casing, and as the apparatus is initially installed in the well casing the rubber sleeve is retracted as seen in dotted lines in Fig. 1. However, by means of a telescoping action, well known in the packer art, slidable sections of the pump casing are shifted after the apparatus is in place in the well and the rubber sleeve is compressed and bulged outwardly into tight fitting sealed relation with the inside of the well casing 6, as shown in full lines in Fig. 1. In this manner, it will be understood that the packer 12 effectively segregates the lower portion of the well so as to define a reservoir space between the packer and the bottom of the well. The rubber sleeve comprising the packer 12 is disposed only around the upper portion of the pump so that the lower end of the pump extends below the packer Thus, when oil or other purging material is pumped downwardly into the well under pressure, the reservoir space is sealed at its upper end by the packer 12 and the oil is therefore readily forced under high pressure into the obstructed producing formation or strata for purging and cleaning the same. At the same time, the perforated or slotted intake 8 is also cleaned and flushed out.

When an oil well is equipped with a pumping apparatus as described above in connection with Fig. 1, the desired free flowing conditions in the well may, if desired, be maintained by periodically reversing the flow of oil on a predetermined cycle so that the intake and the producing strata of the well are subjected to frequent back flow of oil for cleaning and flushing purposes. Such intermittent operation may obviously be effected manually, but it is possible to utilize an automatic means such as a time controller device in the electrical circuit for the motor section A so that the well is automatically cleaned on. a predetermined time schedule. Other control schemes may also be employed, for example, reversal of the motor for pressurizing of the well may be arranged to occur in response to a decrease in the pressure or flow rate of the effluent oil below a predetermined level.

The purpose of the valve section C is to maintain the head of oil in the pumping apparatus and the outlet tubing 9 during a period in which the direction of oil flow is being reversed or in which the motor is stopped for any reason. However, the details of the pump section B and the valve section C do not constitute a part of the present invention and accordingly these portions of the apparatus need not be described further, reference being made to my copending application Serial No. 227,845, filed May 23, 1951, and also to my copending application Serial No. 247,437, filed September 20, 1951, for certain of the details of sections B and C.

Referring now to Figs. 2, 2A and 3, the electric motor section A is enclosed in an outermost tubular housing 13 which is connected at its lower end to a threaded coupling member 14 (Fig. l), the latter being provided for the purpose of interconnecting the housings or casings of the motor section A and the pump section B. The upper end of the housing 13 is secured by means of a retaining ring 16 to a head or cap member 1-7.

Mounted in close fitting concentric engagement in the lower portion of the housing 13 is an elongated motor sleeve 18 containing the operating parts of the motor and being formed at its outer periphery with a plurality of circumferentially spaced axial grooves 19. The sleeve 18' is supported by means of a cylindrical spacer member 21 (Fig. 2A) having a plurality of endwise slots 22 at its upper end and positioned in supporting engagement between the upper end (not shown) of the coupling member 14 and the lower end of the sleeve 18. A transverse divider or partition 23 (Fig. 2) is disposed more or less centrally of the housing 13 and is provided with a peripheral flange portion 24 which seats against the upper end edge of the sleeve 18. A set screw 26 extends through the sleeve 18 adjacent the upper end thereof into the partition 23 for retaining the sleeve 18 and the partition 23 in proper relation. As will be seen more clearly hereinafter, the partition 23 serves to divide the motor housing into a lower portion containing the working parts of the motor and an upper chamber which houses a pressure balancing mechanism in the form of an expansible bellows means indicated generally at 27. A tubular spacer 28 (Fig. 2) is disposed longitudinally between the upper surface of the partition structure 23 and the lower end of the cap 17 thereby surrounding the bellows means 27 and defining a chamber therefor. The spacer 28 is also formed at its outer periphery with a plurality of circumferentially spaced axial grooves 29 which are aligned with the correspondingly spaced grooves 19 in the motor sleeve 18 in order to provide for free fluid flow therebetween.

The operating parts of the electric motor contained Within the sleeve 18 comprise a field coil or annular stator 31 having the usual windings 32 and a rotor or armature 33 rotatably disposed within the stator in the usual manner. The stator 31 is retained in close fitting concentric relation within the sleeve 18. The rotor 33 is afiixed by means of a key 34 to a rotor shaft 36 which is journalled at its upper end in a radial bearing 37 (Fig. 2) mounted at the lower portion of the partition structure 23. The lower end of the rotor shaft 36 extends below the stator windings 32 into an inverted cupshaped bearing retainer 38 (Fig. 2A) disposed adjacent the lower end of the sleeve 18. For journalling the lower end of the rotor shaft 36, a double thrust bearing assembly consisting of an upper bearing unit 39 and a lower bearing unit 41 is mounted in the bearing re tainer 38, the two bearing units thereby being held in side to side relation.

As described more fully in my aforementioned copending application Serial No. 227,845 a double thrust bearing arrangement of this type is required in order to receive the oppositely acting thrust reactions of the retor shaft 36 when the pumping apparatus operates in either a clockwise or counter-clockwise direction. To this end, each of the bearing units 39 and 41 comprises a pair of inner and outer annular races between which are mounted a plurality of balls 42 and 43, respectively. The inner races of each bearing unit are formed with suitable annular grooves 44 in which the balls 42 and 43 are seated. The outer races of each of the bearing units are formed withnon-symmctrical shoulder portions for resisting axial thrust or reaction in a single direction, either upwardly or downwardly. Thus, the upper bearing unit 39 has a lower shoulder portion 46 which coacts with the balls 42 to resist the downward thrust of the rotor shaft 36 during the period when the pumping apparatus is pumping oil upwardly out of the well. Similarly, the lower bearing unit 41 is formed with an upper shoulder portion 47 which coacts with the bails 43 whereby to resist the upward thrust on the rotor shaft 36 during the time when oil or other purging fluid is being pumped downwardly into the well under pressure.

The double thrust bearing assembly described above is retained in position by means of a lock nut 48 threaded to the rotor shaft 36, and the lower extremity of the rotor shaft 36 is fitted with a mechanical seal 49 of a conventional type. The seal 49 is mounted in a seal housing in the form of an end plate member 51 having an upright skirt portion 52 which extends into endwise abutment with the lower thrust bearing unit 41 for supporting the latter. The seal housing 51 is secured to the lower end of the bearing retainer 38 by means of a plurality of screws 52 and is supported on the motor sleeve 18 by means of a retainer ring 53. A pair of upper and lower spacers 54 (Fig. 2) and 56 (Fig. 2A) are disposed between the respective ends of the stator structure and the partition 23 and the bearing retainer 38, respectively, the inner most ends of the spacers being slotted or notched for the purpose hereinafter described.

The lower end of the rotor shaft 36 projecting beyond the seal 49 is connected by means of a shaft adaptor 54 to a universal connection (not shown) which is in turn connected to the pump shaft of the pump section B, the details of this latter structure being explained more fully in my aforementioned copending application Serial No. 227,845.

The electrical conductors enter the motor through the armored cable 11 mentioned above which extends through a packing gland 57 (Fig. 2) into a junction box 58 having a detachable cover 59. A plurality of individual electric wires or conductors, indicated at 61, extend downwardly through aligned apertures in the bottom of the junction box 58 andthe cap structure 17.and thence through an elongated conduit 62 fitted at its upper end into the cap 17 and at its lower end into the partition structure 23. A terminal bushing 63 extends upwardly through the partition structure 23 and is threaded into the lower end of the conduit 62. A plurality of suitable terminal inserts 64 are contained in the bushing 63 for permitting electrical connection of the wires 61 with the stator windings 32.

In the operation of the pumping apparatus comprising the electric motor section A described above, oil is pumped upwardly during the production period by the pump section B and passes radially through the slots 22 in the spacer member 21 into the elongated fluid passages formed by the grooves 19 in the motor sleeve 18, as indicated by the double-headed arrow in Fig. 2A of the drawing. The oil thence passes upwardly through the grooves 19 into the aligned grooves 29 in the bellows chamber spacer 28 and thence into a plurality of radially directed bores 66 formed in the cap structure 17, as clearly shown by the double-headed arrow in Fig. 2 of the drawing. The plurality of streams of eifluent oil are then combined in a central pocket portion 67 in the cap 17 and the combined stream is discharged through the outlet conduit 9 which is threadedly connected at its lower end to the cap structure 17. It will be understood that the outlet 9 extends upwardly through the casing 6 to the ground level. During a pres'surizing or reverse flow period, oil or other suitable purging fluid is drawn downwardly from the ground level through the fluid passageways in the motor section just described and into the pump section B for ultimate discharge under pressure through the intake 8. Thus, it will be seen that my invention provides a convenient and highly effective means of permitting oil or other fluid to be passed through the motor section of the apparatus without actually contacting the operating parts of the electric motor.

In addition, as hereinbefore mentioned, the arrangement above described has very advantageous cooling features which are particularly important in the case of a motor of the present type which is intended to operate at great underground depths. The present structure comprises a highly elfective cooling arrangement because of the passage of oil or other fluid through the numerous peripheral grooves 19 in the motor sleeve 18 which houses the operative parts of the motor. As will be quite clear from Fig. 3, the oil passageways 19 are disposed closely adjacent the outer periphery of the stator 31 so that the maximum cooling effect is obtained. For example, I have found that a three horsepower motor of the type illustrated having a motor sleeve with twelve circumferentially spaced grooves can be readily operated so that the passage of fluid through the grooves causes the temperature of the motor to decrease from about 130 F. to about F. over a distance of only six inches of the motor length.

Another important feature of my invention comprises the arrangement for preventing leakage between the internal dielectric and lubricating oil system of the motor and the fluid being pumped into or out of the well. As described above, the partition structure 23 secured to the upper end of the motor sleeve 18 and the seal housing structure 51 secured adjacent the lower end of the motor sleeve 18 define a motor chamber which houses the operating parts of the motor. As is common in motors of this type, this chamber is filled with a sealing or protective fluid which preferably comprises a so-called transformer oil having suitable dielectric properties for surrounding the stator windings and also having suitable lubricating properties for lubricating the radial and thrust bearings of the motor. Keyed to the lower portion of the rotor shaft 36 below the stator windings 32 is an impeller 68 (Fig. 2A) for effecting internal circulation of the transformer oil within the motor chamber. Although the motor chamber is initially filled with a supply of transformer oil or the like, it will be understood that as the motor heats up and cools down with repeated operation thereof, the volume of the transformer oil in the system will necessarily increase and decrease with changes in temperature. Consequently, an expansible oil reservoir is provided comprising the bellows structure 27 which is in fluid communication with the motor chamber and the supply of transformer oil contained therein.

The bellows means 27 comprises a bottom member 69 threadedly secured in a bore 71 in the partition structure 23. An expansible metal bellows 72 is secured to the bottom member 69 and is provided with a top member or flange 73 secured thereto. A cap 74 is fitted in the flange 73 and is retained in place by means of a retainer ring 76. Rigidly secured to the underside of the cap 74 is a depending guide stem 77 having a square or other polygonal section which is slidably received in a matching upstanding tubular portion 78 of the bottom member 69 for guiding the movement of the bellows 72 during longitudinal expansion and contraction thereof. A vent tube 79 extends upwardly from an aperture in the bellows cap 74 through an enlarged aperture 81 in the cap structure 17. A removable vent tube plug 82 is aflixed in the upper end of the tube 79, and a cover 83 having a threaded connection with aperture 81 in the cap structure 17 is detachably disposed over the upper end of the tube 79 for closing the upper end of the system.

In filling the system with transformer oil, a filler plug 84 (Fig. 2A) is first removed from the seal housing 51 at the bottom of the motor and, with the cover 83 and the plug 32 removed, the system is filled with transformer oil through the filler hole in the seal housing 51, air being displaced upwardly through the vent tube 79 until the system is filled to the desired extent. Upon completion of the filling operation, the filler plug 84, the vent plug 82, and the cap 83 are replaced and the system is ready for use. During operation of the motor, rotation of the impeller 68 causes a continuous circulation of the transformer oil throughout a closed system, the oil passing downwardly through an axial bore 36 in the rotor shaft 36 and thence through a connecting radial bore 87 (Fig. 2A) into the space surrounding the thrust bearing units 39 and 41 and then being forced upwardly by the impeller 68, as indicated by the arrows in the drawing. To permit upward circulation of the transformer oil, the

outer periphery of the laminations comprising the stator 31 is provided with a plurality of axially extending grooves 88, and the transformer oil is forced upwardly by the impeller 68 through the notched portions of the spacer 56 (Fig. 2A) into the grooves 88 and thence through similar notched portions in the spacer 54 (Fig. 2) into the space surrounding the upper end of the stator windings. An angularly extending bore 89 (Fig. 2) in the partition 23 provides fluid communication between the latter space and the interior of the bellows 72, the transformer oil being permitted to pass through an inner bore, indicated at 91, in the member 69 and thence through a radial aperture 92 into the interior of the bellows 72. it will be understood that upon repeated expansion and contraction of the bellows '72 in response to heating and cooling of the supply of transformer oil, the bellows 72 will thereby function as a reservoir for receiving excess oil or providing additional oil to the motor as required. In addition, by the above-described structure it will be seen that the transformer oil has access to the upper bearing 37 and also to the lower bearings 39 and 41 for lubricating purposes.

In a system of the above type comprising a sealed supply of internal transformer oil, it is important to prevent loss of the transformer oil by leakage or, vice versa, contamination of the transformer oil by reverse leakage. This protection is particularly necessary in the region adjacent the mechanical seal 49 which is normally designed for effective operation within a relatively narrow range of pressure differential between the fluids at the opposite sides of the seal. Accordingly, it is another important feature of my invention that the bellows means 27 constitutes not only an expansible reservoir for transformer oil but also a pressure balancing mechanism whereby to maintain the internal pressure of the transformer oil substantially the same as the pressure of the crude oil or other fluid being pumped. For this purpose, the upper and lower ends of the bellows chamber spacer 23 are notched, as at 93 (Fig. 2), whereby to permit the fluid passing upwardly through the grooved passageways 18 and 29 to enter the bellows chamber defined by the spacer 28 and thereby surround the outside of the bellows 72. The transformer oil system being substantially filled with liquid oil, it will readily be seen that even the slightest increase or decrease in the pressure of the oil or other fluid outside the bellows 72 will he reflected immediately by a corresponding change in the pressure of the internal transformer oil due to expansion or contraction of the bellows 72 in response to the change in pressure of the fluid surrounding the same. In

other words, by providing a closed transformer oil systern including an expansible bellows which is subjected interiorly to the transformer oii pressure and which is subjected exteriorly to the pressure of the fluid being pumped, i am able to achieve the desired balancing of pressures so that there is no undesirable leakage into or out of the transformer oil system, particularly at the mechanical seal 49.

A very significant advantage of the arrangement above described resides in the cooperating relationship between the crude oil passageways 19 in the motor sleeve 18 and the adjacent transformer oil passageways 88 in the stator structure 31. By reference to Fig. 3, it will readily be seen that these passageways are disposed in relatively close proximity adjacent the opposite sides of the motor sleeve 18. Consequently, it will be understood that an effective heat exchange relationship exists between the two fluids passing through the grooves 19 and 38 with the result that the heat of the motor which is picked up by the transformer oil circulating through the passages 83 and the bore 86 in the shaft 36 is readily transmitted to and carried away by the fluid being pumped through the passageways 19. Thus, the heat evolved during opera tion of the motor is removed both by direct transmission to the fluid passing through the grooves 19 and also by the transformer oil circulating through the grooves 88, the latter heat being in turn transmitted to the fluid being pumped through the grooves 19. As a result, the transformer oil in the motor section is readily maintained at a suitable operating temperature.

From the foregoing description, it will be evident that my invention provides a novel electric motor construction having features which render it particularly suitable for use in oil well pumping apparatus of the character referred to. The structure makes special provision for passage of the fluid being pumped exteriorly of the operating portions of the motor while at the same time providing for eflective cooling of the motor and prevention of loss or contamination of the transformer oil system of the motor.

Although the invention has been described in connection with a particular structural embodiment thereof, it will be understood that various modifications and equivalent structures may be resorted to without departing from the scope of the invention as defined in the appended claims.

I claim:

1. An electric motor structure adapted for use with a reversible rotary pump comprising an elongated tubular housing structure having a sealed motor chamber at the lower portion thereof, said motor chamber containing a stator and a rotor and being filled with a supply of a protective fluid, partition means across said housing structure defining the upper end of said motor cham ber, closure means at the upper end of said housing structure spaced above said partition means to define a second chamber therebetween, and pressure balancing means comprising an expansible bellows disposed in said second chamber with its interior in fluid communication through said partition means with the protective fluid in said motor chamber, said housing structure being provided adjacent said motor chamber with a plurality of circumferentially spaced axially extending fluid passages whereby to permit the passage of pumped fluid through the housing structure without contacting the operating parts of the motor contained in said motor chamber, and said passages being in fluid communication with said second chamber whereby. to subject the exterior of said bellows to the pressure of the pumped fluid.

2. An electric motor structure adapted for use with a reversible rotary pump comprising an elongated'tubular housing member, a cylindrical casing member disposed in close fitting concentric relation in the lower portion of said housing member and defining a motor chamber, said motor chamber containing a stator and rotor and being filled with a supply of a protective fluid, closure means at the upper end of said housing member spaced above said motor chamber to define a second chamber therebetween, and pressure balancing means for equalizing the pressure of said protective fluid with the pressure of the fluid being pumped, said pressure balancing means including an expansible enclosure disposed in said second chamber and having its interior in fluid communication with the interior of said motor chamber whereby to permit expansion and contraction of the supply of protective fluid, one of said members having a plurality of confined axial passages spaced circumferentially around said motor chamber for permitting the passage of pumped fluid therethrough without contacting the operating parts of the motor contained in said motor chamber, and said passages being in fluid communication with said second chamber for contacting pumped fluid with the exterior of said expansible enclosure whereby changes in pressure of the pumped fluid are transmitted through said expansible enclosure to the supply of protective fluid.

3. An electric motor structure adapted for use with a reversible rotary pump comprising an elongated tubular housing, a sleeve of lesser length than said housing disposed in close fitting concentric engagement at the lower portion thereof, a stator and rotor assembly disposed within said sleeve, means at the opposite ends of said sleeve, including partition means at the upper end thereof, for journalling said rotor and for closing the ends of said sleeve whereby to define a sealed motor chamber below said partition means, closure means at the upper end of said housing spaced above said partition means, a tubular spacer disposed longitudinally between said partition means and said closure means whereby to define a second chamber above said motor chamber, freely expansible means in said second chamber communicating through said partition means with said motor chamber, and fluid conduit means extending from and connected to said closure means, said sleeve and said spacer being provided at their outer peripheries with a plurality of aligned circumferentially spaced axially extending grooves for permitting the passage of pumped fluid therethrough without contacting the operating parts of the motor contained in said motor chamber, and said closure means having a passage communicating with said conduit means and the grooves in said spacer.

4. An electric motor structure adapted for use with a rotary pump comprising an elongated tubular housing structure adapted to be connected at its lower end to a pump structure and having a motor chamber in the lower portion thereof, said motor chamber containing a stator and rotor and being filled with a supply of a protective fluid, closure means at the upper end of said housing structure spaced above said motor chamber to define a second chamber therebetween, a fluid conduit connected to said closure means and in fluid communication through the latter with said second chamber, an expansible enclosure disposed in said second chamber and having its interior in fluid communication with the interior of said motor chamber whereby to permit expansion and contraction of the supply of protective fluid, means for permitting the passage of pumped fluid through said housing structure between the pur' p structure and said fluid conduit Without contacting the operating parts of the motor contained in said motor chamber, vent tube means extending upwardly from said expansible enclosure through said closure means for use in filling the system with protective fluid, and a removable cap detachably connected over the upper end of said vent tube means.

5. The structure of claim 3 further characterized in that said spacer has aperture means providing fluid communication between said groves and said second chamber for subjecting the exterior of said expansible means to the pressure of the pumped fluid.

6. The structure of claim 2 further characterized in that said closure means is adapted to have a discharge conduit connected thereto for discharging eifluent pumped fluid, said closure means being formed with an internal passageway providing fluid communication between said axial passages and the discharge conduit.

References Cited in the file of this patent UNITED STATES PATENTS 771,468 Falk Oct. 4, 1904 1,842,457 Mendenhall J an. 26, 1932 1,974,183 Gunderson Sept. 18, 1934 2,285,436 Hoover June 9, 1942 2,309,707 Myers Feb. 2, 1943 2,311,805 Yost Feb. 23, 1943 2,325,930 Avigdor Aug. 3, 1943 2,423,436 Blom July 8, 1947 FOREIGN PATENTS 697,797 France Nov. 5, 1930

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