CENTRIFUGAL PUMP LUBRICANT STRAINER SYSTEM

Abstract: A centrifugal pump (1) of the "sealless" type including an impeller (12) mounted on a shaft (11) supported by an independent bearing system. The impeller shaft is driven by a motor (19) located outside of the casing through a set of magnets (58). The bearing system includes a lubricating system using the pumped fluid as a lubricant and coolant. A pocket (63) located behind and in close proximity to the rear face of the impeller receives the lubricating fluid and a passage (64) in the casing of the pump carries the lubricating fluid to the bearings. A strainer (70) covers the pocket to prevent the entry of fluid-carried particulate matter into the pocket (63), and the rotation of the fluid, in the chamber, continuously washes any particulate matter from the face of the strainer for discharge thereof through the fluid outlet.

Description: CENTRIFUGAL PUMP LUBRICANT STRAINER SYSTEM BACKGROUND OF THE INVENTION This invention relates generally to centrifugal pumps of the type having bearings using the pumped fluid as a lubricant. One example of this type σf pump is a sealless pump using a set of concentric rotors carrying magnets separated by a pump housing wall sealing the pumped fluid from leaking from the pump housing. This type of pump requires a clean fluid for the lubrication of the internal bearings because the bearings may have a high mortality rate if the lubricating fluid has particulate matter suspended therein. An externally-supplied fluid can be used for the purpose, but such an expedient can dilute the fluid being pumped, and requires a separate fluid source and appropriate conduits. Similar arrangements in the prior art tap off a portion of the fluid being pumped, pass it through a strainer, and conduct it on to the bearings. Such strainers require frequent cleaning causing the need for stopping the pump to remove and clean or replace the strainer. To avoid this difficulty, some prior art pumps employ a so-called wash-flow strainer or filter located in the discharge outlet to tap off and filter the fluid before conducting it to the bearings. Although this arrangement has the advantage of the pump discharge fluid continuously washing the strainer, it also has the disadvantage of the strainer being continuously eroded by the discharge fluid causing the need for frequent replacement of the strainer. Another disadvantage of the aforesaid prior art is that the removal of a portion of the high pressure fluid from the discharge stream of the pump reduces the efficiency of the pump. The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter. SUMMARY OF THE INVENTION It is an object of this invention to provide a centrifugal pump which taps off a portion of the pumped fluid for service as bearing lubrication, clarifies the same by means of a strainer, and overcomes the problems caused by the prior art. It is particularly an object of this invention to provide a pump comprising a casing including a body and a cover coupled together defining a pumping chamber there between and having an inlet and outlet for the flow of pumped fluid into and out of the pumping chamber; an impeller located in said pumping chamber for pumping fluid through the chamber and discharging fluid from the outlet at a higher pressure than the fluid entering the chamber through said inlet; a shaft supporting said impeller and journalled in bearing means located outside of said chamber; a conduit for tapping a portion of the fluid from the chamber and conducting it to the bearing means for lubrication; and a strainer covering the mouth of said conduit where it opens into said chamber for filtering the fluid as it is enters said conduit, said strainer being located adjacent a face of the impeller and inwardly of the outlet in the casing for the pumped fluid where the rotating face of the impeller causes the fluid in the chamber adjacent said impeller fact to flow across the stainer and to wash any particulate matter from the strainer during the operation of the pump. It is also an object of this invention to disclose a pump comprising a casing; and a shroud; wherein said casing and shroud (1) are coupled together, and (2) have mutually confronting surfaces which define, therebetween, a chamber and a compartment; an impeller journalled in said casing; said impeller having a bladed body rotatably confined within said chamber; and wherein shroud has a single means for admitting fluid into said chamber, and a single means for discharging fluid from said chamber; said confronting surfaces cooperatively define an open, unobstructed fluid pathway between said chamber and said fluid discharging means; said compartment opens onto said bladed body of said impeller; and further including means formed in said casing for conducting fluid from said compartment into said casing and to said chamber, serially. The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures. It is to be expressly understood, however, that the drawing figures are not intended as a definition of the invention but are for the purpose of illustration only. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a cross-sectional view of a sealless type of centrifugal pump taken along the rotary axis of the pump impeller and illustrating an embodiment of the invention; Figure 2 is an enlarged view of a portion of Fig. 1 showing the impeller, casing cover interface and associated elements including the strainer covering the mouth of the conduit for conducting pumped fluid to the pump bearings; and Figure 3 is a perspective view of the strainer and casing cover illustrating the swirling of the pumped fluid across the face of the strainer. DESCRIPTION OF PREFERRED EMBODIMENTS The sealless centrifugal pump shown in the drawings includes a pump casing 1 containing an axial inlet 2, a pumping chamber 3 and an outlet 4, all of which are interconnected by passages extending through the casing. The casing 1 also contains a mounting foot 5 and an annular flange 6 surrounding the pumping chamber 3. The annular flange 6 is adapted to receive a casing cover 7 circling a pump cartridge 10 containing a number of components including an axially extending shaft 11 carrying a semi-open pump impeller 12 rotating in the pump chamber 6 during pump operation. The cartridge 10 will be specifically described later. The semi-open impeller 12 includes a shroud 13 and a series of vanes 14 having one edge integral with the shroud 13. A power frame 16 fits over the cartridge 10 and is attached to the casing 1 and casing cover 7 by a series of bolts 17 circling the outside of the flange 6. The power frame 16 further includes a mounting foot 18 adapted to support the pump in conjunction with the mounting foot 5 on the casing 1. A drive shaft 19 is rotatively mounted in the power frame 16 by a pair of axially spaced bearings 20 and 21 fixed in the frame 16 on the opposite sides of a bearing chamber 22 adapted to contain lubricant for the bearings 20 and 21. The outer end of the shaft 19 is adapted to be coupled to a driving motor (not shown) using a conventional coupling means. The casing cover 7 is an annular member that slides into a recess in the casing 1 circling the pumping chamber 3 and has a lip 25 overlying the flange 6 with holes receiving the bolts 17. The annular lip 25 is sandwiched between the flange 6 and an annular flange 26 on the open end of the power frame 16 with the bolts 17 serving to hold both the casing cover 7 and the power frame 16 to the casing 1. The cartridge 10 includes a cartridge body 30 which fits into the casing cover 7 and has an annular step 31 seating against the outer face of the casing cover 7 controlling the distance that the cartridge body 30 extends into the casing cover 7. The cartridge body 30 contains recesses at both ends surrounding respective front and rear journal bearing bushings 33 and 34. The impeller shaft 11 extends through the bushings 33 and 34 and carries respective bearing sleeves 36 and 37 rotating in the bushings 33 and 34. The bearing sleeves 36 and 37 are slipped on the shaft 11 with a spacing sleeve 39 located therebetween. The front end of the shaft 11 carries an outwardly extending flange 41 with a thrust collar 42 seating against the flange 41 and the forward end of the front bushing 33. The collar 42 controls the rearward axial movement of the shaft 11. The impeller 12 carries a threaded member 44 that threads into a threaded hole in the front end of the shaft 11 and seats against the shaft flange 41. The rear end of the shaft 11 carries a thrust bearing 47, an inner magnet holder 50 keyed on the shaft 11 and a nut 52 threaded on the rear end of the shaft 11. The nut 52 locks all of the rotating components of the cartridge 10 in place on the shaft 11 in the cartridge body 30 extending through the bearing bushings 33 and 34. The periphery of the inner magnet holder 50 carries a series of magnets 58 which rotate closely about the interior of a relatively thin can-shaped shell 59 which fits over the magnet holder 50 and the other parts of the cartridge 10. The power frame 16 contains an outer magnet holder 61 attached to and rotating with the drive shaft 19 around the can-shaped shell 59 in close proximity thereto. The outer magnet holder 61 carries a series of magnets 62 spaced around its interior which are magnetically linked to the magnets 58 on the inner magnet holder 50 for transmitting torque from the outer magnet holder 61 to the pump impeller shaft 11. Driving a pump impeller using magnets in this manner is well known in the art of sealless pumps. The casing cover 7 contains an annular pocket 63 formed in the front face 66 of the casing cover 7, circling the shaft 11 and located adjacent the rear face 68 of the impeller 12, and a fluid passage 64 extending from the pocket 63 for conducting the pumped fluid from the pumping chamber 3 into the cavity 60, surrounded by the can-shaped shell 59, containing the magnet holder 50. This fluid flows from the cavity 60 to the thrust bearing 47, passing through such thrust bearing and then forwardly along the shaft 11 through the journal bearings including the bearing bushings 7 33 and 34 and exits from the thrust bearing 42 on the shaft 11 adjacent the impeller 12. Such fluid serves to lubricate and cool such bearings. Using the pumped fluid as a lubricant is possible when the nature of the pumped fluid enables it to serve as a lubricant. It is essential for the lubricating fluid to be free of particulate matter to provide the bearings with a long life; hence it is desirable that particulate matter not pass into the fluid passage 64 and the cavity 60 from the pumping chamber 3. Otherwise, particulate matter could lodge in the cavity 60, including the space between the bearing bushings 33 and 34, causing a buildup of particulate matter interfering with the operation of the " pump and, possibly, damaging the bearings of the pump. A strainer or screen 70, of annular shape, corresponding to the outline of the pocket 63, is placed over the top of the pocket 63, formed in the front face 66 of the casing cover 7, to capture particulate matter before it enters the pocket 63. Such strainer 70 can be attached in place over the pocket 63 in any suitable manner and no attempt is made to describe the details of such mounting. For example, the strainer 70 could be attached by adhesive or by threaded fasteners. It is important to see that such particulate matter does not either remain on or erode the strainer 70. The invention accounts for this, in that the strainer 70 is in close proximity to the rear face 68 of the impeller 12. The rotation of the impeller 12 causes the pumped fluid adjacent the face 68 of the impeller to attempt to rotate with the impeller resulting in a body of rotating fluid passing across the strainer 70. The dynamically energized and swirling fluid across the strainer 70, as represented in Figure 3 by the flow arrows, vacuums or wipes the captured particulate matter from the entry face of the strainer 70 and carries it off to the remaining pumped fluid without eroding the strainer 70. As will be readily appreciated, heavier particulate matter, which might not be subject to the aforesaid vacuuming of the strainer 70, does not become lodged in the strainer 70; instead, such particulate matter is thrown outwardly by centrifugal force and evacuated with the pumped fluid. In fact, such heavier particulate matter probably never reaches the strainer 70 because of the location of the strainer 70 away from the main flow of the pumped fluid. It is the lighter particulate matter, which would otherwise find its way to the fluid passage 64, which is halted by the strainer 70 and swept therefrom by the energized and vortexing fluid flowing across the strainer 70. It is particularly to be noted that, in this novel pump, nothing obstructs the fluid pathway between the pumping chamber 3 and the discharge outlet 4. All pumped fluid is discharged to the outlet 4. The fluid behind the impeller 12 is at a relatively low pressure, as compared to the fluid adjacent the outlet 4; such fluid is not first pumped to discharge pressure and then reduced in pressure before being used as lubricating fluid, thereby eliminating a loss that occurs in the prior art using discharge pressure fluid for lubrication. No discharge fluid is recirculated as a lubricant, and no external piping for such, or for an externally-supplied lubricant, is required. The velocities of the fluid which pass across the strainer 70 are significantly lower than such velocities would be in the discharge fluid, flowing through the outlet 4, resulting in the effects of erosion on the strainer 70 being minimal. Providing an annular pocket 63, in which to tap off lubricating fluid, presents a far greater collecting area than a collector and strainer in the outlet of the pump could offer. While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.

Claims: WHAT IS CLAIMED IS: 1. A centrifugal pump comprising: a housing containing a pumping chamber, a pump inlet passage extending from an inlet in the housing and opening into the pumping chamber and a pump outlet passage running from the pumping chamber to an outlet in the housing; a shaft mounted in bearing means in said housing for rotation; a pump impeller attached to the forward end of the shaft for rotation with the shaft in the pumping chamber, said housing containing a passage for conducting pumped fluid from the pumping chamber to the bearing means; said passage having a mouth opening into said pumping chamber adjacent the non-pumping face of said impeller to receive fluid from the portion of the pumping chamber adjacent said face; and a strainer mounted on said housing over the mouth of said passage whereby the fluid entering said passage flows through and is filtered by said strainer, the fluid flowing through said strainer being at a lower pressure than the pressure of the fluid discharged through said outlet of said pump, and any particulate matter deposited on the face of said strainer is flushed from the face of said strainer by the fluid carried across said face by said impeller. 2. A centrifugal pump, according to claim 1, wherein: said housing has an annular pocket formed therein which confronts said non-pumping face of said impeller and surrounds said shaft carrying said impeller; and said strainer comprises an annular screen covering said annular pocket. 3. A centrifugal pump, according to claim 1, wherein: said strainer has a substantially planar surface which is in close proximity to said impeller body. 4. A centrifugal pump, according to claim 3, wherein: said pocket confronts, and is open to, said pumping chamber. 5. A centrifugal pump comprising: a housing containing a pumping chamber, a pump inlet passage extending from an inlet in the housing and opening into the pumping chamber and a pump outlet passage running from the pumping chamber to an outlet in the housing; a shaft mounted in bearing means in said housing for rotation; a pump impeller attached to the forward end of the shaft for rotation with the shaft in the pumping chamber, said housing containing a passage for conducting pumped fluid from the pumping chamber to the bearing means; said passage having a mouth opening into said pumping chamber adjacent the non-pumping face of said impeller to receive fluid from the portion of the pumping chamber adjacent said face, said mouth including an enlarged pocket formed in the wall of said housing; and a strainer mounted on said housing over the open face of said pocket whereby the fluid entering said passage flows through and is filtered by said strainer, the fluid flowing through said strainer being at a lower pressure than the pressure of the fluid discharged through said outlet of said pump, and any particulate matter deposited on the face of said strainer is flushed from the face of said strainer by the fluid carried across said face by said impeller. 6. A centrifugal pump, according to claim 5, wherein: said strainer has a substantially planar surface which is in close proximity to the non-pumping face of said impeller. 7. A centrifugal pump, according to claim 6, wherein: said pocket is annular shaped and concentric with said impeller.

Inventors: BUSE FREDERIC W, COOPER PAUL, BUSE, FREDERIC, W., COOPER, PAUL
Applicants: INGERSOLL RAND CO, INGERSOLL-RAND COMPANY
Application year: 1991
Main classification: F01D11
IPC codes: F04D13, F04D29