Abstract:
The invention concerns a fluid pumping apparatus including a pump unit having an inlet housing, a plurality of pumping stages, and a discharge housing, surrounded by a continuous layer of waterproof material. The waterproof layer is further surrounded by a structural shell. Moreover, the pump unit is threadably engaged to a motor adapter, and no tools are required for the attachment of the pump unit to, or removal of the pump unit from, the motor adapter. The motor adapter is designed so that the mechanical seal is easily accessible.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     None. 
     BACKGROUND OF THE INVENTION 
     This invention relates to fluid pump construction and, in particular, to a multi-stage centrifugal pump. 
     Multi-stage fluid pumps are widely known and utilized in both commercial and residential applications. Such pumps use multiple pumping stages mounted to a rotating shaft to pump a fluid from one end of the pump to the other and to increase the fluid pressure. The pumping requirements determine the number and size of stages in the pump. 
     Fluid pumps involve a wide variety of design types, e.g., positive displacement, venturi and the like. One design type, a cylindrically-shaped centrifugal pump, is widely used to provide a pressurized water supply. Examples of such fluid pumps are described in U.S. Pat. No. 4,708,589 (Nielsen et al.) and U.S. Pat. No. 4,923,367 (Zimmer). 
     These fluid pumps comprise an inlet housing, a cartridge of stacked pump stages, and a discharge housing remote from the inlet. Each “stage” of such a pump has an impeller which “flings” water radially outward by centrifugal force; each stage also includes a diffuser assembly which encloses the impeller. The diffuser assembly may consist of one or more components. Typically, a plurality of such stages are “stacked” so that the discharge portion of one stage feeds liquid into the inlet portion of the next stage. For applications where the pump is not submerged in water, a pump casing, or shell, surrounds the cartridge of stacked stages, the inlet housing, and the discharge housing. An impeller or drive shaft, coupled to a motor shaft, extends axially through the cartridge and is fixed to the impeller within each of the stages. Rotation of the drive shaft thus turns each impeller to force fluid radially outward toward an adjacent, stationary diffuser. In turn, the cooperating diffuser directs the fluid radially inwardly and toward the next pump stage. At the inlet end of the cartridge is a motor adapter for receiving and mounting an electric motor. At the discharge end of the cartridge is an outlet from which pumped water flows. 
     For leakage prevention and pump efficiency, it is desirable to retain the inlet housing, the pump stages, and the discharge housing snugly compressed against one another. In one type of prior art pump, as shown by Nielsen in U.S. Pat. No. 4,708,589, compression is accomplished by a hollow, cylindrical metal shell sleeved over the stacked stages. One way compression is maintained is by crimping the shell to a motor adapter on one end and an output flange on the other. Another way is by having formed screw threads on the shell which are engageable with complementary threads on the discharge housing and the inlet housing. During assembly, the stages are slipped into the casing and the inlet and discharge housings are then threaded into the casing until they engage respective ends of the stage cartridge. Rotation may be prevented by a set screw or other fastener. The diffusers of such pumps are thus held stationary by the axial force exerted on the cartridge by the inlet and discharge housings once the latter are tightened. In another type of pump, as shown by Zimmer in U.S. Pat. No. 4,923.367, the shell is embodied as a pair of plastic half-cylinders joined together by fasteners. Compression of the stages is provided by an adjustment cone rather than by the shell. 
     In such prior art pumps, the axial force of the housings against the cartridge is sometimes insufficient to preclude lateral movement of the diffusers along the drive shaft because the compressive force holding the stages against each other can decrease over time. As a result, the stages (or parts of stages) may separate slightly, allowing leaks to develop. Moreover, as the axial compressive forces diminish, they may not provide sufficient frictional forces to preclude rotation of the diffuser plates and/or the diffusers (which are subjected to torsional forces by the moving water in the pulp). Both leakage and unwanted rotation of pump parts result in a decrease in pump performance. 
     Another disadvantage arises merely from the fact that many known pump shells are made of metal, such as stainless steel. Such shells are relatively thin walled and may dent if dropped. In a severe case, a diffuser or diffuser plate within the shell may be fractured. Fabricating stainless steel components is also a relatively expensive process. If ordinary steel, a less expensive material, is selected for the shell or for other components, rust and corrosion are inevitable. Further, for a shell of given dimensions, metal shells weigh more than those made with alternative materials such as plastic. Fabricating plastic and composites is typically a less expensive process than using materials such as stainless steel. 
     While most shelled pumps use metal shells, some have used glass-filled thermoplastic shells. Gay et al. teach, in U.S. Pat. No. 5,407,323, the construction of a multistage centrifugal pump with a polymeric composite (wound fiberglass) shell. An essential element of the &#39;323 invention is that the shell is bonded directly to the pump stage diffusers in an attempt to create a water tight seal. However, in practice, it has been found that fiberglass on its own is not waterproof; water may “weep” through the channels of the fibers, resulting in leakage through the shell. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages of the prior known pump constructions by providing a pump shell which eliminates fluid leakage and thus enhances pump performance while reducing manufacturing costs. 
     The present invention includes a stage containment system which encapsulates an inlet housing, one or more pump stages, and a discharge housing, resulting in a fully encapsulated disposable pump unit. Each pump stage consists of a diffuser plate and a diffuser which cooperate to house an impeller. Two or more pump stages are typically arranged to abut one another in “stacked” relationship to increase pump pressure output and form the cartridge of the pump. An impeller shaft is drivably connected to the motor, which is mounted by a motor adapter to the inlet end of the pump. The shaft extends axially through the pump to drive the individual impellers. 
     In one preferred embodiment, a shrink-wrap inner shell used with o-rings forms a leak-proof pump unit casing by providing compressive forces which hold the inlet housing, the discharge housing, and the pump stages in a fixed relationship to each other. Moreover, the compressive forces prevent rotation of the pump stages in response to torque forces. A composite outer shell lends structural integrity. 
     In another preferred embodiment, the inner shell is in the form of a waterproof coating. The coating layer provides a leak-proof casing, and also prevents diffuser rotation, by bonding with the inlet housing, the pump stages, and the discharge housing. Similarly, a composite outer shell provides structural strength. 
     In a preferred embodiment, the encapsulated pump unit is threadably engaged to the motor adapter. This “quick connect” feature allows the pump unit to be easily and quickly attached and removed from the motor without the use of tools. This modularity gives a user a convenient way to replace individual pump units as needed. Furthermore, the present invention provides for a motor adapter design that allows easy access to the mechanical seal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the exterior of a fluid pump unit and motor adapter embodying the present invention, attached to a motor. 
     FIG. 2 is a cross sectional view of a pump unit, motor adapter, and motor assembly of a first preferred embodiment. 
     FIG. 3 is an exploded view of the pump unit. 
     FIG. 4 is an exploded view of the motor adapter and motor assembly. 
     FIG. 5 is a cross sectional view of a pump unit, motor adapter, and motor assembly of another preferred embodiment. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a multi-stage centrifugal pump assembly  10  embodying the present invention. Assembly  10  includes motor  12 , motor adapter  18 , and pump unit  22 . Motor  12  includes electrical junction box  14  and mounting piece  16 . Motor adapter  18  includes water inlet  26  and bolt openings  20 . Pump unit  22  includes inlet port  25  and discharge port  29 . 
     Motor  12  contains electrical junction box  14  and mounting piece  16  for the attachment of motor  12  to other equipment as necessary for a particular operation. Motor adapter  18  is bolted onto motor  12  by four screws inserted into openings  20 . A shaft coupling connects the drive shaft of motor  12  to an impeller shaft which extends into pump unit  22 . Pump unit  22  slides over the impeller shaft, and inlet housing  24  of pump unit  22  threads onto a threaded nipple (to be explained with reference to FIG. 4) of motor adapter  18 . Motor adapter  18  contains water inlet  26 , which initiates water flow through pump unit  22 . The impeller shaft drives impellers within pump unit  22 , thereby pumping water from water inlet  26 , through inlet port  25 , through pump unit  22 , and out discharge housing  28  and discharge port  29 . The details of operation will be explained with reference to FIG.  2 . 
     FIG. 2 shows multi-stage centrifugal pump assembly  10  in cross section, illustrating the connections between motor  12 , motor adapter  18 , and pump unit  22 . Motor  12  includes motor shaft  42 . Motor adapter  18  includes water inlet  26 , o-ring groove  50 , o-ring  52 , mechanical seal stationary seat  114 , bore  116 , and seal holder  122 . Pump unit  22  includes inlet housing  24 , inlet port  25 , discharge housing  28 , discharge port  29 , inlet housing bore  32 , pump stages  36 , discharge housing bore  38 , o-ring groove  46 , o-ring  48 , o-ring grooves  53 , o-rings  54 , step  55 , discharge bearing  56 , bores  58 , discharge threads  60 , inlet threads  62 , shrink-wrap lining  66 , o-ring compression collars  68 , and structural shell  70 . 
     The water to be pumped flows from water inlet  26 , through threaded nipple  30 , through port  25  and bore  32  of inlet housing  24 , through pump stages  36 , and out bore  38  and port  29  of discharge housing  28 . Shaft coupling  40  within motor adapter  18  joins motor shaft  42  of motor  12  to impeller shaft  44 . The details of the connection between motor  12  and motor adapter  18  will be explained later in this description, with reference to FIG.  4 . Impeller shaft  44  extends axially through pump unit  22  to drive stages  36 . 
     Pump unit  22  slides over impeller shaft  44 ; inlet housing  24  of pump unit  22  threads onto threaded nipple  30  of motor adapter  18  and is tightened by hand. An improvement of the present invention over the prior art lies in its modularity and ease of assembly and disassembly. If pump unit  22  fails, the failed unit can be easily removed and replaced by a new encapsulated pump unit, quickly and without tools. This allows for a lower capital investment by a customer who desires to have backup pump units on hand. The customer can invest in extra pump units rather than complete assemblies of pump units, motor adapters, and motors. Inlet housing  24  has o-ring groove  46  to accommodate o-ring  48 . Motor adapter  18  has o-ring groove  50  to accommodate o-ring  52 . When pump unit  22  and motor adapter  18  are threaded together, o-rings  48  and  52  prevent leakage of water flowing through motor adapter  18  and inlet lousing  24 . While prior art pumps can be separated into a pump unit, a motor adapter, and a motor, the pump unit and motor adapter generally require tools for assembly and disassembly. 
     Inlet housing  24  and discharge housing  28  are preferably molded from a plastic material in order to reduce manufacturing costs while also reducing the overall weight of pump unit  22 . The inlet and discharge housings,  24  and  28  respectively, are preferably molded of the same materials using the same mold. O-ring groove  53  and step  55  are molded into the circumference of both inlet housing  24  and discharge housing  28 . Inlet housing  24  and discharge housing  28  both have central cylindrical bores, inlet bore  32  and outlet bore  38 , thorough which liquid passes. Referring to discharge housing  28 , a portion of it may be machined away to provide space for discharge bearing  56 . As contemplated, the primary difference between inlet housing  24  and discharge housing  28  is in the threads of each piece. For example, threads  60  on discharge housing  28  may be 1 inch standard pipe threads, and threads  62  on inlet housing  24  may be 1½ inch straight threads. Bore  58  and threads  60  and  62  may be either machined into pre-molded pieces or molded into the pieces initially. Each of inlet housing  24  and discharge housing  28  have grooves  53  to accommodate o-rings  54 . 
     Between inlet housing  24  and outlet housing  28  lie a plurality of identical pump stages  36 . Pump stages  36  are stacked in contiguous relation to each other concentric with impeller shaft  44 . This stack of pump stages  36  may be referred to as cartridge  64 . A detailed description of the internal mechanics of pump unit  22  will be recited later, with reference to FIG.  3 . 
     In one preferred embodiment, O-rings  54  are placed in each of the o-ring grooves  53 . Then, an external, temporary, axial compressive force is applied to align and compress together inlet housing  24 , stages  36 , and discharge housing  28 . A one-piece resilient polymeric shrink-wrap sleeve  66 , made of a material such as polyolefin, is slipped over cartridge  64 , inlet housing  24 , and discharge housing  28 . The thickness of shrink-wrap sleeve  66  may vary greatly, but in this example, a thickness of about 40 thousandths of an inch to about 60 thousandths of an inch has been found to work well. The entire pump unit  22  is then heated to shrink sleeve  66  so that it conforms to the shape of inlet housing  24 , cartridge  64 . and discharge housing  28 . O-ring compression collars  68  are placed over each o-ring  54 , in the space provided by step  55 , to provide even compression on o-rings  54 . FIG. 2 shows shrink-wrap sleeve  66  after heating, in cross-section. Then, composite shell  70 , preferably made of a material such as a long fiber composite (e.g., e-glass/epoxy fiberglass), is formed around the outside of shrink-wrap sleeve  66  and o-ring compression collars  68  to provide structural integrity. The thickness of composite shell  70  may vary greatly, but in this example, a thickness of about 40 thousandths of an inch has been found to work well. Preferably, composite shell  70  has circumferential as well as bias layers of fiberglass for strength. Once shell  70  is cured, the temporary external axial force is removed, and the result is a fully encapsulated disposable pump unit. FIG. 3 shows an exploded view of pump unit  22 . Pump unit  22  includes structural shell  70 , shrink-wrap lining  66 , o-ring compression collars  68 , o-rings  48  and  54 , inlet housing  24 , discharge housing  28 , impeller shaft  44 , discharge bearing  56 , diffuser  78 , impeller  76 , diffuser plate  74 , and diffuser plate adapter ring  72 . Inlet housing  24  further includes inlet housing port  25 , o-ring grooves  46  and  53 , and step  54 . Diffuser plate  74  further includes central opening  92 , circular offset  94 , and outer cylindrical edge  96 . Impeller  76  further includes hub  80  and vanes  90 . Diffuser  78  further includes cylindrical wall surface  82 . vanes  84 , openings  86 , and central circular opening  88 . Discharge bearing  56  further includes disk  98  and bearing  100 . Discharge housing  28  further includes discharge housing port  29 , o-ring groove  53 , and step  54 . Impeller shaft  44  includes ends  102  and  110 . 
     Between inlet housing  24  and the first of the pump stages  36 , a diffuser plate adapter ring  72  may be used to fill the “step” between diffuser plate  74  and inlet housin,  94 . Adapter  72  may be necessary due to the geometry of inlet housing  24  and diffuser plate  74 . Adjacent to diffuser plate adapter ring  74  lie one or more pump stages  36 . 
     While FIG. 3 shows the components of only one stage  36  in detail, it is to be understood that a typical pump unit  22  uses a plurality of identical stages  36  stacked on impeller shaft  44 . Fach pump stage  36  includes a centrifugal impeller  76 , a diffuser plate  74 , and a diffuser  78 . Impeller  76  is confined within the diffuser plate and diffuser assembly. Impeller shaft  44  is inserted through keyhub  80  of each impeller  76  and thereby drives such impellers  76 . Pump stages  36  are preferably formed of plastic materials in order to reduce the weight of pump unit  22  while ensuring smooth, efficient operation. Noryl, a thermoplastic manufactured by General Electric, is preferably used for pump stages  36 , diffuser plate adapter ring  72 , and discharge bearing  56 . A filled variety of Noryl may also be used. 
     Diffuser  78  has a cylindrical wall surface  82  on its periphery and radial vanes  84  on one side. Radial vanes  84  define fluid passageways which terminate in a plurality of circumferentially spaced openings  86  at the perimeter of diffuser  78 . A central circular opening  88  fitted with a metal bushing (not shown) is sized to provide a running fit with hub  80  of impeller  76 . 
     Impeller  76  includes a plurality of vanes  90  for directing fluid flow centrifugally outwardly as impeller shaft  44  rotates impeller  76 . Impeller  76  has an eye, or water inlet opening, on its opposite side (not shown) of larger diameter than, and coaxial with, hub  80 . 
     Each of the stages  36  also includes a generally flat diffuser plate  74  having a central opening  92  for passage of fluid from the central areas of the preceding diffuser  78  toward the impeller eye of the next adjacent stage  36 . The periphery of each of the diffuser plates  74  is provided with a circular offset  94  which complementally fits within the adjacent diffuser  78  to provide locating shoulders to properly position plate  74  in the stacked assembly. Diffuser plate  74  has a relatively narrow outer cylindrical edge  96  of a diameter that is substantially equivalent to a relatively wide, cylindrical wall surface  82  forming the periphery of diffuser  78 . 
     Discharge bearing  56  is disposed between the last pump stage and discharge housing  28 . Discharge bearing  56  typically includes a disk  98  and a cylindrical rubber bearing  100  inserted in the center of disk  98 . The diameter of disk  98  is substantially equivalent to that of the diffuser plates  74  and diffusers  78 . Discharge bearing  56  rides on the end  102  of impeller shaft  44  to support shaft  44 , keeping it centered and straight within pump unit  22 . 
     O-rings  54  are placed in o-ring grooves  53  of inlet housing  24  and discharge housing  28 . Then sleeve  66  is slipped over inlet housing  24 , pump stages  36 , and discharge housing  28 , and heated so that it shrinks to conform to the shape of inlet housing  24 , pump stages  36 , and discharge housing  28 . o-ring compression collars  68  are placed over shrink-wrap sleeve  66  and positioned over each o-ring  54 , in the space provided by step  55 . Then, composite shell  70  is formed around the outside of shrink-wrap sleeve  66  and o-ring compression collars  68  to provide structural integrity. FIG. 3 shows one-half of shrink-wrap sleeve  66  and one-half of composite shell  70 , in perspective. This view is for illustrative purposes only; in practice, sleeve  66  and composite shell  70  are each preferably composed of one continuous piece of material, not two halves joined together. 
     O-ring  48  is placed into o-ring groove  46  of inlet housing  24 , and o-ring  52  is placed into o-ring groove  50  of motor adapter  18 . When pump unit  22  is threaded onto threaded nipple  30 , o-rings  48  and  52  help seal the juncture between pump unit  22  and motor adapter  18 . 
     This pump stage containment system, consisting of o-rings  54 , shrink-wrap sleeve  66 , o-ring compression collars  68 , and composite shell  70 , uses mechanical forces, rather than chemical bonding, to accomplish a watertight seal and prevent diffuser rotation. It can be appreciated that the fluid forces of the swirling water stream created by operation of impellers  76  exert a substantial rotative force on vanes  84  of diffusers  78 . However, it has been found that compression of the shrink-wrap casing  66  on the walls  82  of the diffusers  78  and the complete circumferential contact between casing  66  and diffusers  78  provide sufficient frictional forces for retaining diffusers  78  in a stationary position as impellers  76  are rotated. The fit of cartridge  64  within casing  66  enables the latter to exert a plurality of equal, radially inwardly directed forces toward cartridge  64  such that each of the diffusers  78  and diffuser plates  74  are retained in substantial alignment relative to each other. 
     FIG. 4 illustrates the manner in which motor adapter  18  connects motor  12  and pump unit  22 . FIG. 4 shows motor  12  with electrical junction box  14  and motor mounting piece  16 ; motor shaft  42  with shoulder  106  and end  108 ; washer  104 ; mechanical seal  112 ; shaft coupling  40 ; mechanical seal holder  122  with relief area  120  and flats  124 ; o-ring  118 ; mechanical seal stationary seat  114 ; motor adapter  18  with water inlet  26  and openings  20 ; threaded nipple  30 ; o-ring  52 ; o-ring groove  50 ; and impeller shaft  44  with end  110 . 
     Washer  104  slides onto motor shaft  42  and abuts against shoulder  106  of motor shaft  42 . Then, shaft coupling  40  is attached onto end  108  of motor shaft  42 . End  110  of impeller shaft  44  is attached onto the other end of shaft coupling  40 . Substantially cylindrical mechanical seal  112  slides onto coupling  40  and abuts washer  104 . Mechanical seal stationary seat  114  presses into bore  116  (more easily seen in FIG. 2) of motor adapter  18 . O-ring  118  is placed in relief area  120  of seal holder  122 . Substantially cylindrical seal holder  122  is threaded onto motor adapter  18  to hold mechanical seal stationary seat  114  in place. Motor adapter  18  then slides over impeller shaft  44  and abuts motor  12 . Motor adapter  18  is then attached onto motor  12  using four screws (as dictated by the type of motor) (not shown), through openings  20 . When motor adapter  18  and motor  12  are connected, seal holder  122  concentrically surrounds mechanical seal  112  and imparts correct compression on the mechanical seal components. Mechanical seal  112  contains a spring which allows it to retain the correct amount of compression, even as the seal material wears down over time. This feature allows the seal to have a much longer useful life. 
     Another novel feature of the motor adapter of the present invention is the easy accessibility of mechanical seal  112  and mechanical seal stationary seat  114 . Mechanical seal  112  and mechanical seal stationary seat  114  are designed to be easily serviceable by requiring only two disassembly steps that use common tools. Motor adapter  18  is removed from motor  12  by removing four screws (not shown). This allows access to seal holder  122  and mechanical seal  112 . Seal  112  may be slid off coupling  40  and replaced. Seal holder  122  has flats  124  on the outside diameter that may be gripped by a pair of pliers to unscrew seal holder  122  and remove it from motor adapter  18 , thereby exposing seat  114 . Seat  114  may be removed from bore  116  and replaced. Once a new seal  112  and seat  114  are installed and motor adapter  18  bolted onto motor  12 , mechanical seal  112  has the correct compression. Since mechanical seals and seats are major wear items, and inexpensive to replace, having easy access provides great utility to the user. 
     As shown in FIG. 5, another embodiment of the invention substitutes a waterproof coating  126  for shrink-wrap shell  66 , collars  68 , and o-rings  54 . This embodiment is similar to the first embodiment, except that the material of the waterproof inner layer is different, the method of applying the waterproof layer is different, and no o-rings or o-ring compression collars are necessary. FIG. 5 shows inlet housing  24 A, discharge housing  28 A, and waterproof layer  126 . With respect to the other parts, similar numbers are used to identify similar parts, which were explained with reference to FIG.  2 . 
     As with the previous example, an external, temporary, axial compressive force is applied to align and compress together inlet housing  24 A, stages  36 , and discharge housing  28 A. Then, a waterproof material such as a rubber elastomer is applied over cartridge  64 , inlet housing  24 A, and discharge housing  28 A to form waterproof layer  126  and to prevent rotation of diffusers  78  in cartridge  64 . Because the material itself bonds to cartridge  64 , inlet housing  24 A and discharge housing  28 A, o-rings and o-ring compression collars are not needed to create a watertight barrier. Thus, step  55  in inlet housing  24 A and discharge housing  28 A may be omitted. Additionally, the complete circumferential bonding between layer  126  and cartridge  64 , inlet housing  24 A. and discharge housing  28 A prevents rotation of pump stages  36  of cartridge  64 . One material that has been found to work well for layer  126  is a polysulfide-based rubber which comes in a thick liquid form. It is ideally applied to cartridge  64 , inlet housing  24 A, and discharge housing  28 A as they are rotated slowly on a lathe. The application may be accomplished with a brush or stick, or by any other known method. One advantage of this material is that it is self-leveling; the surface evens out as it cures, resulting in a smooth surface on which composite shell  70  may be formed. The thickness of layer  126  may vary greatly, but in this example, a thickness of about 40 thousandths of an inch to about 80 thousandths of an inch has been found to work well. While layer  126  provides for waterproofing and rotation prevention, outer shell  70  lends structural integrity to the completed pump unit. 
     In conclusion, the present invention provides for an inexpensive, lightweight, efficient, and non-corrosive pump unit design and a convenient motor adapter configuration. While the principles of this invention have been described in connection with specific embodiments, it should be understood clearly that these descriptions are made only by way of example and are not intended to limit the scope of the invention. Workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.