US2953993A - Pump construction - Google Patents

Description

Sept. 27,- 1960 c. STRICKLAND ETAL 2,953,993

PUMP CONSTRUCTION Filed Feb. 12, 1958 2 Sheets-Sheet 1 +1-1 ='w-\ w /"7J" 1.- J I h iV 19%] a Win INVENTOR. GERALD STRICKLAND FREDERICK L. HORN BY HOWARD T- WHITE Sept. 27, 1960 G. STRICKLAND EI'AL 9 2,953,993

PUMP CONSTRUCTION Filed Feb. 12, 1958 2 Sheets-Sheet 2 INVENTOR.

GERALD STRICKLAND FREDERICK 1.. HORN BY HOWARD T. WHITE flwfi W Patented Sept. 27, 1960 PUMP CONSTRUCTION Gerald Strickland, Blue Point, and Frederick L. Horn, Sayville, N.Y., and Howard T. White, Melrose Park, Pa., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Feb. 12, 1958, Ser. No. 714,934

3 Claims. (Cl. 103-87) This invention relates to an improved lubrication system and has particular reference to hearing lubrication in certain types of pumps to effect a reduction in, or the elimination of, thrust bearing wear and which also pro vides sufiicient lubrication between journal-bearing surfaces.

It is the primary object of this invention, in pumps of the kind in which the pumped fluid serves as the lubricat ing fluid, to provide a thrust balancing construction combined with lubricating means whereby the pump may be operated for long periods of time without excessive scoring of bearing surfaces.

Another object of this invention is the provision of a thrust balancing construction wherein the fluid flowing between confronting thrust surfaces establishes a pressure gradient responsive to the unbalancing forces exerted on said surfaces.

In order to achieve the above objects and advantages and others which will hereinafter appear, the invention includes an improved bearing construction and is illustrated in connection with a pump of the enclosed or canned rotor type. The thrust balancing construction of our invention lies between a body of pumped fluid at discharge pressure and a body of fluid to be pumped and operated in such a manner that the difference between the discharge pressure and the relatively low pressure of the fluid entering the pump is used to control the axial movement of the rotor. The invention further comprises means for lubricating the rotor journal bearing.

For a more complete understanding of the nature of the invention and the advantages derived from its use, reference may be had to the following description taken in conjunction with the accompanying drawings in which:

Figure 1 is a vertical elevation, mainly in section, and partly diagrammatic, of a pump of the canned rotor type embodying the improvements of our invention. Basically, the pump isan induction motor comprising anannular stator 16 and anannular rotor 14 canned in a suitable corrosion resistant metal with animpeller 24 attached to the rotor at the output end of the pump with the rotor adapted to revolve about a hollowstationary shaft 29 In Figure 1, the rotor is divided by a center line, along the axis of rotation; the relative position of the rotor at rest is shown at the left of the center line and the axially displaced position of the rotor during rotation is shown at the right of the center line.

Figure 2 is a cross section taken along the line 22 of Figure 1 showing the organization of part of the pump and particularly in the vicinity of the impeller.

Figure 3 is an end view taken along theline 33 of Figure 1 showing the pump intake and illustrating certain of the thrust-balancing elements of our invention.

Referring to the drawings and particularly to Figure l, numeral designates a pump of the canned rotor type comprising anannular casing 12 and anannular rotor 14. Thestator 16 is located in an annular compartment of thecasing 12, and therotor 14 consists of anarmature 18 sealed or canned within ametal jacket 19. Twoopenings 42 and 43 are provided in the casing compartment to permit circulation of a fluid therethrough to cool the field windings of the stator.

A bell-shaped re-entrant fitting 28 having a central bore is seated withincasing 12 at the inlet end of the pump. Fitting 28 and the proximate wall ofcasing 12 define a casing well 26. Thewell 26 is sealed at the outlet end of the pump by an outlet fitting 30 similar to inlet fitting 28 and having acentral bore 82. The central port of inlet fitting 28 receives a bushing 36. A hollowstationary shaft 29 is positioned centrally within thewell 26 of the casing. Theshaft 29 comprises a reduced portion which is seated in bushing 36 and an extendedportion 84 which, at its outer end, fits on abushing 33 which is sealed to outlet end fitting 30. The upper end of the extendedportion 84 ofshaft 29 is provided with aflange 39. Between theflange 39 and the outlet fitting 30 the shaft is slotted as at 37 to permit fluid to pass from the interior of theshaft 29 to casing well 26.

Surrounding the central bore ofinlet fitting 28 is a plurality of orifices 34 (Figure 3) to permit fluid communication between the pumped fluid in well 26 and the fluid to be pumped. A thrust collar 38 (Figure 1) in the form of an annular ring is mounted, as by welding, oninlet bell 28 and encircles the ring oforifices 34.

Theannular rotor 14 is mounted within the casing between the internal wall of thecasing 12 and the external surface of theshaft 29. The rotor is secured to a journal bearing sleeve 22 on its inside wall. The outer diameter of the rotor is less than the internal diameter of the casing so that there is an annular gap orpassage 31 between the rotor and the casing wall. Thepassage 31 connects the pump discharge with a chamber 35 between the inlet fitting 28 and therotor 14. As shown in Figure 1 to the left of the center line, the rotor at rest is in contact with thethrust collar 38 and encircles a portion of the bushing 36. The height of the thrust collar is such that, even when therotor 14 is at rest, the rotor bearing sleeve 22 never touches the bushing 36. The total axial movement of the rotor is limited by the clearance between end surface 74 of bearing sleeve 22 and the confronting surface 76 on theflange 39 ofshaft 29.

At the discharge end of therotor 14 animpeller 24 is secured to the rotor by means ofscrews 40. Theimpeller 24 has a series of four vanes 25 (Figure 2) for propelling the incoming fluid. Theslots 37 in the shaft are positioned to discharge into theimpeller 24.

As noted, the well 26 of the casing is sealed at its outlet end by the reentrant bell-shaped outlet fitting 30. Thecentral bore 82 of fitting 30 receives a bushing sealed thereto as by welding. Sealed intobushing 85 is asmall bore tube 52 which extends centrally through theshaft 29 to about its mid-section where it penetrates the shaft wall and terminates in aport 41 on the exterior surface of the shaft. The port communicates with a pair ofhelical grooves 54 on the exterior of the shaft to distribute lubricant between the shaft and bearing sleeve 22. The grooves terminate close to each end of bearing sleeve 22.

Outlet ports 46 are provided in fitting 30 for passing the pumped fluid to a conduit 60 (shown in dashed lines) of a fluid flow system connected to thepump 10.

In pumps of the canned rotor type as described above, the pumped fluid is usually used to lubricate any bearing surfaces in the pump. In cases where the fluid to be pumped is essentially non-lubricating in character an especially diflicult lubricating problem arises. Bromine trifiuoride is an example of a fluid which is essentially non-lubricating since, when hot, its viscosity is very low.

One of the advantages of our invention will be appreciated by setting forth the ditficulty which our bearing construction overcomes. In an ordinary thrust bearing in which the thrust is supported by two plane surfaces, the conditions are unfavorable for effective lubrication with a low viscosity non-lubricating fluid. Consider for example a canned rotor pump operating with its rotor and impeller vertical with the inlet end down, as shown in Figure 1. With this arrangement, and while pumping a fluid which is essentially non-lubricating in character, there will be little tendency for the fluid to form a sustaining lubricant film between the bearing surfaces and excessive wear of the thrust bearing surfaces would re sult. Also, although the pressure of the pumped fluid will cause separation of the bearing surfaces, our experience has shown that the rotor will oscillate between a position in which the bearing surfaces are separated and one in which they are in contact. The repeated contacts between the bearing surfaces cause excessive scoring of the surfaces and this, in turn, substantially reduces the operating life of the pump.

The operation of our improved thrust balancing construction is as follows:

Referring to the portion of Figure l to the left of the center line, the rotor in its rest position is axially supported by thethrust collar 33 which presents a narrow annular bearing surface 79 confronting the lowerthrust bearing surface 72 of the rotor 1d. Thus the external wall of the bushing 56, the interior surface ofthrust collar 38 and the portion ofsurface 44 between thethrust collar 38 and the bushing 36 define anannular chamber 50 communicating throughorifices 34 with the fluid entering the pump through inlet fitting 28.

When the roto-impeller assembly revolves, the incoming fluid passes through the interior ofhollow shaft 29, through theslots 37 near the end of the shaft whence the fluid is pumped byvanes 25 of the rotatingimpeller 24 to thereby increase the pressure of the fluid. The main body of fluid passes throughoutlet ports 46 to conduit 60. In addition, a small portion of the fluid at discharge pressure flows back toward the inlet end through theannular passage 31 into chamber 35. The pressure of the fluid is then exerted axially onsurface 44 of therotor 14 thus imposing a balancing force to overcome the unbalancing thrust (i.e., the thrust toward the inlet end). This is so because the product of the average pressure in chamber 35 and the area ofsurface 44 is greater than the unbalanced thrust.

The position of the rotor when the axial thrust exerted toward the inlet end is balanced by the hydraulic pressure provided by the pumped fluid is shown in Figure 1 to the right of the center line. The fluid pressure exerted onsurface 44 of the rotor results in movement of the rotor axially along the stationary shaft toward the outlet end of the pump and this opens a narrow space between the confronting surfaces 72 (on the rotor) and 70 (on the thrust collar 38). Consequently a variable orifice is developed between the chamber 35 and the chamber 59. This orifice permits the fluid at substantially discharge pressure to pass frompassage 31 through chamber 35 intoannular chamber 50 and thence throughorifices 34 into the low pressure fluid entering the pump. Any unbalance in the opposing thrusts results in slight axial movement of the rotor on the shaft and consequently changes the width of the annular orifice between hearingsurface 70 onthrust collar 38 and confrontingbearing surface 72 of the rotor in direct response to the change in thrust.

When the distance between the two confronting hearing surfaces 70 and 72 respectively is relatively large, the pressure of the fluid in chamber 35 will be reduced relative to the discharge pressure of the pumped fluid. Hence a reduced balancing thrust will be applied to surface 44- of the rotor. The rotor will then move toward the inlet end to reduce the width of the orifice, and this will result in an increase in pressure in chamber 35 and hence an increase in the thrust balancing force. Conversely when the width of the orifice defined by the two confronting bearing surfaces 70 and 72 is relatively small, or when the two confronting bearing surfaces are in contact with each other, the pressure in chamber 35 will be increased relatively to the discharge pressure although never exceeding the discharge pressure. Under these conditions the rotor will move toward the outlet end thereby increasing the width of the orifice and resulting in a lower pressure in chamber 35.

With this thrust balancing construction, the rotor revolves at its normal operating speed without contact between the thrust bearing surfaces, i.e., a continuous clearance will be maintained between the confronting bearing surfaces 7tl72 and 7d76, respectively. While the thrust balancing means as here described has been 0perated with the pump in the position as shown in Figure 1, it is a feature of this thrust balancing construction that the pump is similarly operable when mounted at other than a vertical axis. That is, the pump may be vertical- 1y 180 from the position shown in Figure 1 or at any intermediate position. In each case a sufficient pressure will be developed in chamber 55 to balance any existing unbalanced thrust so that the rotor revolves free.

The radial load developed by the rotor is supported by diverting a portion of the pumped fluid between the rotor bearing sleeve 22 and the external surface ofshaft 29.

Referring to Figure 1conduit 60 connected to the output end conducts the pumped fluid away from the pump. A portion of the pumped fluid in conduit 6% is diverted to a by-pass conduit 58. Afilter 63 is connected inbypass conduit 58 to remove any entrained solids from the fluid.

Under certain operating conditions we have found it necessary to pump bromine trifluoride at temperatures of the order of C. At these temperatures the viscosity of the fluid is very low. Consequently, a portion ofconduit 58 is jacketed with a coolingcoil 62 to cool the fluid and thereby increase its viscosity. The cooled fluid continues throughconduit 58 intotube 52 and thence intospiral grooves 54, whence it is distributed, under pressure, between the rotor bearing sleeve 22 and theshaft 29. Thetube 52 may be lined internally with a layer of insulating material to insure against reheating the cooled fluid. A suitable material for this purpose is KelF (monochlorotrifluoroethylene polymer). This fluid is permitted to rejoin the incoming fluid stream by flowing to each end of the bearing sleeve 22 and around bushing 36 andflange 39. The pressurized cooled fluid produces a lubricating film between the rotor bearing sleeve and the shaft, thus preventing scoring of these two surfaces.

The combination of the thrust balancing construction and the lubricant distributing means permits the operation of the rotor substantially free of any metal to metal contact even with fluids of very low viscosity. The thrust balancing action for the axial bearing surfaces and the lubrication system for the radial bearing surfaces together give floating support to the rotor unit which remains essentially wear-free except for slight initial wear between the bearing surface iii of thethrust collar 38 and thelower bearing surface 72 of therotor 14 at startup.

The embodiment of the invention disclosed herein is representative of a preferred form and it is to be understood that various modifications and changes may be made in the invention by those skilled in the art. All such variations and equivalents are intended to come within the scope of the claims attached hereto.

We claim:

1. A pump comprising, in combination, an inlet and an outlet, an annular casing having a continuous passage for the purpose of cooling, a stator in said passage, a hollow rotor provided with an impeller in said casing, said rotor being radially spaced from the inner wall of said casing and mounted for rotation concentrically about a hollow shaft in said casing, said shaft being in fluid communication with said inlet and said impeller, an axially disposed thrust collar having a plane bearing surface confronting an end surface of said rotor, said confronting surfaces defining a variable orifice through which fluid at discharge pressure flows from the passage defined by the inner wall of said casing and the periphery of said rotor to thereby create a differential pressure responsive to the axial thrust of said rotor and duct means between the said inlet and said variable orifice for preventing an abrupt change in differential pressure.

2. A pump comprising, in combination, a stator and a rotor, a casing for said stator having a wall separating said rotor from said stator, said pump having an inlet and an outlet, an impeller at one end of said rotor discharging into said outlet, a hollow shaft within said rotor about which said rotor is rotatable within the stator, said shaft being in fluid communication with said inlet and the impeller, a by-pass through which a portion of the pump fluid passes from the impeller discharge to said inlet, thrust means disposed in said by-pass, said thrust means including a bearing surface confronting one end surface of and supporting thereby said rotor when not in motion and defining therewith a variable orifice when said rotor is in motion due to pressure of said fluid exerted on said surface of said rotor, and a fixed orifice in fluid communication between said variable orifice and said inlet whereby fluid passing through said by-pass sup ports said rotor in rotation.

3. The pump ofclaim 2 including a second by-pass comprising a plurality of fluid distributing grooves in the surface of said shaft, a passageway extending axially into and through said shaft terminating in said grooves, and means for cooling a portion of said pump fluid prior to conveying the latter successively into said passageway means and fluid distributing grooves.

References Cited in the file of this patent UNITED STATES PATENTS 2,485,408 PeZzillo Oct. 18, 1949 20 2,537,310 Lapp Jan. 9, 1952 FOREIGN PATENTS 319,020 Great Britain Feb. 27, 1930

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