Abstract:
A fluid pump ( 10 ) has a body housing ( 14 ) a fluid pumping chamber having a rotatable pumping member ( 16 ), a drive shaft ( 12 ) which passes through an aperture in the body into the pumping chamber to effect rotation of the pumping member in use, a seal ( 18 ) between the pump body and drive shaft to inhibit fluid moving along the shaft out of the pumping chamber, and a dividing shroud ( 32 ) operably located between the seal and the rotatable pumping member to divide the fluid pumping chamber ( 30 ) between the seal and the rotatable pumping member.

Description:
FIELD OF THE INVENTION 
     This invention relates to improvements in pumps and in particular but not exclusively to improved performance and reliability of shaft fluid seals as used in impeller pumps. 
     BACKGROUND OF THE INVENTION 
     In the field of impeller pumps which incorporate a single impeller on an overhung shaft, the shaft seal is often provided with a suitably shaped annular space around it commonly referred to as a seal chamber or balance chamber. One purpose of the seal chamber is to assist in conducting away heat generated by the shaft seal. The seal chamber must be of adequate capacity and of suitable shape to promote a sufficient degree of swirling to enable a necessary proportion of the heat generated by the shaft seal to be transferred into the pumped media during the passage of that pumped media from wearing ring to impeller balance holes. 
     Sometimes the swirling action in the seal chamber is assisted by a duct or multiplicity of duets which permit a portion of the outlet pumped media to be directed into the seal chamber in a manner conducive to the cooling of the shaft seal. Typically the ducts may be drillings or pairs of drillings each of which also may need to be tapped or plugged, or one or more external tubes or pipes to pipe connectors which require drilling and tapping and may be also plugging. The ducted pumped media is typically circulated back to the main pumped flow through conventional impeller balance holes. 
     However, many impeller pumps are called upon to be axially compact. As such there may be insufficient space for an effectively proportioned seal chamber. Also there may be insufficient space for wearing rings or, alternatively, no wearing rings may be fitted as a cost saving. 
     In such arrangements it is thought that fluid circulation is impeded because the whole mass of fluid between the impeller and pump head tends to rotate as a whole in the manner associated with a liquid annular seal. The resulting pressure differential available across each of the impeller balance holes is insufficient to promote the flow rate which is required for adequate shaft seal cooling. 
     Accordingly, the present invention seeks to avoid or at least mitigate certain problems in the prior art including the lack of cooling of the shaft seal in, for example, an axially reduced pump arrangement. One object of the invention is to increase fluid recirculation back into the main flow path of the pump thereby to effect cooling and/or recirculation of fluid in the region of the shaft seal. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a fluid pump comprising a body housing a fluid pumping chamber having a rotatable pumping member, a drive shaft which passes through an aperture in the body into the pumping chamber to effect rotation of the pumping member in use, and a seal between the pump body and rotary shaft to inhibit fluid moving along the shaft out of the pumping chamber, characterised by a dividing shroud operably located between the seal and the rotatable pumping member to divide the seal chamber between the seal and the rotary pumping member. Preferably, the dividing shroud is stationary in use. 
     Beneficially, the dividing shroud is found to increase circulation of the pump fluid, especially around the seal. 
     Preferably, fluid inlet into the first portion of the divided seal chamber, which first portion is adjacent the seal, is provided. Beneficially, a pressure gradient exists across the fluid inlet, and indeed across the whole first portion of the divided seal chamber, thereby to effect fluid flow into the first portion of the seal chamber. 
     Preferably, the dividing shroud comprises a central aperture which operably surrounds the rotatable shaft in use. Preferably, the radius of the aperture is slightly greater than the radius of the shaft thereby to provide a fluid passageway between the first and second divided portions of the seal chamber. Preferably, the circular rim of the central aperture can comprise a lip. The lip can extend axially along the rotatable shaft. Preferably, the lip extends away from the seal. 
     Preferably, means for attaching the dividing shroud to the pump body are provided. For example, the shroud can comprise one or more apertures to enable co-operating locking means such as a threaded bolt and threaded sockets in the pump body to be used to attach the shroud to the pump body. Of course, threaded bolts can protrude from the pump body and nuts can be used to fasten the shroud onto the pump body in this reverse configuration. 
     The dividing shroud can comprise an attachment or retaining device for co-operating with part of the pump body. For example, the shroud can comprise an annular resilient clip which engages a lip on the pump body thereby to provide a mechanical/frictional attachment. 
     The fluid inlet to the first portion can comprise a series of fluid passageways in the pump body around the dividing shroud. For example, a series of passageways can be provided between a series of bosses, castellations, or crenallations in the pump body itself. 
     Another aspect of the invention provides a dividing shroud for a seal chamber of pump. Another aspect provides a flow or recirculation enhancer for increasing recirculation of the fluid or pumped medium past a shaft seal in a pump back into the main flow path between pump inlet and outlet. A further aspect provides a pressure enhancer for increasing fluid pressure in the vicinity of the seal, preferably taking it close to the fluid outlet pressure for the pump. 
     A yet further aspect of the invention provides a fluid pump comprising a body housing a fluid pumping chamber having a rotatable pumping member, a drive shaft which passes through an aperture in the body into the pumping chamber to effect rotation of the pumping member in use, and a seal between the pump body and rotary shaft to inhibit fluid moving along the shaft out of the pumping chamber, wherein the fluid pumping chamber comprises a seal chamber defined at least in part by the seal and the rotatable pumping member and wherein the pump further comprises means locatable within the seal chamber for effecting circulation of fluid over the seal and back into the main fluid pumping chamber in use. 
    
    
     DESCRIPTION 
     Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic sectional side elevation view of a first embodiment of part of a pump according to the invention; 
     FIG. 2 is a schematic side elevation view of part of a second embodiment of a pump according to the invention; 
     FIG. 3 is a schematic perspective view of part of the pump shown in FIG. 2 viewed from the right hand side of FIG. 2; 
     FIG. 4 is a schematic sectional side elevation view of part of a pump according to a third embodiment of the invention; 
     FIG. 5 is a schematic side elevation view of a fourth embodiment; and 
     FIG. 6 is a schematic side elevation view of part of a fifth embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1 there is shown part of a pump  10  according to the invention comprising a rotatable shaft  12 , a pump body  14  and an impeller  16 . Impeller  16  comprises a series of blades for effecting fluid flow along the axial direction indicated by arrow I through to a radial outlet direction indicated by arrow  0 . 
     Pump  10  comprises a seal  18  comprising an annular stepped clip  20  for engaging part of the pump body  14  adjacent the central aperture for shaft  12 . Clip  20  carries an annulus  22  having a seat portion  24  for engaging and co-operating with a second seat portion  26  which in turn is attached to a sleeve  28  which is located to effect abutment between seats  24  and  26  in a rotationally fast position on shaft  12 . 
     Pump  10  further comprises a dividing shroud  32  which is substantially disk shaped, having a radially outer cup portion  34  for gripping part of pump body  14  and a central aperture through shaft  12 , which aperture is defined by a lip  38  which extends axially along shaft  12  away from seal  18 . Shroud  32  further comprises a series of apertures  36  in a radial outer position. 
     Shroud  32  divides the seal chamber  30 O forming part of the pumping chamber within pump  10 , which seal chamber  30  is defined by seal  18  and part of the pump body  14  as well as the face of impeller  16 . Shroud  32  acts to divide the seal chamber  30  into a first portion  31  a adjacent seal  18  and a second portion  31   b  which in this embodiment is between shroud  32  and impeller  16 . 
     In use, shaft  12  is caused to rotate thereby to effect rotation of impeller  16  thereby causing fluid flow along the direction of arrow I into pump  10  and out along the direction of arrow  0 . Shaft  12  further effects rotation of sleeve  28  and annular rotational seat  26 . The frictional contact between seats  24  and  26  causes heating of the seal. The pumped media between the impeller  16  and stationary stepped annular disc or shroud  32  typically will rotate at approximately half the impeller speed thereby effecting a radial pressure imbalance between the impeller periphery and the shaft seal. No such pressure imbalance is generated between the stationary pump head  14  and shroud  32 . A circulation of fluid consisting of a substantially radial inward flow between the stationary pump head  14  and shroud  32  and a radially outwardly spiralling fluid movement between shroud  32  and the rotating impeller  16  is thus promoted by the impeller thereby enhancing the cooling of the shaft seal  18 . 
     Hence, in accordance with the present invention, impeller  16  increases fluid flows past seal  18  along a path through apertures  36  in shroud  32  down to shaft  12  via the portion  31   a  of chamber  30  between shroud  32  and seal  18  thereby to effect some cooling of seal  18 . The fluid is further recirculated back into the second portion of the seal chamber between shroud  32  and impeller  16  via the annulus between lip  38  on shroud  32  and shaft  12 . The fluid is then drawn up towards outlet arrow  0  between shroud  32  and impeller.  16  and or drawn through the axial bores or balance holes  17  in impeller  16 . Accordingly, shroud  32  acts to divide chamber  30  and disrupts the otherwise isolated movement of fluid within chamber  30 , and effects recirculation of fluid about seal  18  thereby to provide better cooling of the seal. 
     Moreover, in impeller pumps where the fluid pressure at the pump inlet is close to the vapour pressure of the pumped medium, it is preferable that the pressure in the seal chamber should be maintained at a level sufficiently remote from the vapour pressure to prevent the pumped medium from boiling and, in the case of coolant pumps in the I.C. engine field, to prevent the well-known phenomenon of filming of the shaft seal surfaces from occurring which leads to coolant leakage. 
     In prior art pump arrangements, the pressure of the pumped medium in the seal chamber  30  can be close to the low pump inlet pressure and if the inlet pressure is close to the vapour pressure of the pumped medium then the additional heat generated by the shaft seal  18  may cause the pumped medium to boil at the seal and/or advance the rate of filming at the shaft seal mating surfaces as just described. 
     In the arrangement of the present invention, the fluid pressure in portion  31   a  of seal chamber  30  is raised to be closer to the higher outlet pressure and hence shroud  32  helps to mitigate the problems in the prior art arrangement by reducing the possibility of boiling and/or filming at the seal  18 . This effect is enhanced by ensuring a small running clearance between the internal diameter of lip  38  and shaft  12 , and by arranging a series of apertures or slots  36  in the shroud  32  near to the outlet of the pump. Accordingly, the seal chamber pressure self adjusts to a value appreciably closer to the pressure at the impeller periphery than to the pump inlet pressure thereby reducing the possibility of the shaft seal to film over and leak. 
     In another embodiment of the invention, a pump  110  is provided as shown in part in FIGS. 2 and 3. In this embodiment, components having identical or like functions to those shown in the first embodiment are given the same two digit reference number prefixed with the number  1 . Accordingly, pump  110  comprises a shaft  112 , pump body  114  and seal  118 . Shroud  132  comprises a inner stepped annulus  142  which extends down to rim  138 . The shroud  132  further comprises a series of apertures  140  for receiving bolts  147 . Referring in particular to FIG. 3, it can be seen that the pump body  114  in this embodiment comprises fluid communication passageways which lead into seal chamber  130  and in particular portion  131   a . In this embodiment, the fluid communication passageways comprise slots  148  between the series of bosses, castellations or crenallations  144 . The castellations  144  each comprise a threaded bore  146  for co-operating with bolts  147  thereby to locate shroud  132  in plate. 
     It should be noted that shroud  132  shown in FIG. 3 differs slightly from that shown in FIG. 2 in that stepped inner annular portion  142  is not shown. Beneficially, stepped portion  142  increases the size of the first portion of cavity  130  adjacent seal  118  thereby enabling greater fluid movement in the vicinity of the seal. 
     Of course, the nature and number of fluid passageways, in this embodiment slots  148  can be varied. Similarly, the number of castellations  144  can be varied such that any number can be provided and not just the four shown in the present embodiment. 
     Referring to FIG. 4, there is shown part of a third embodiment of a pump  210  according to the invention. Here, like components with the earlier embodiments are given the same two digit reference number prefixed with the number  2 . Accordingly, pump  210  comprises a shaft  212 , pump body  214 , seal  218  and seal chamber  230 . A dividing shroud  232  is provided which engages a series of castellations  244  at an intermediate radial position. In this embodiment, shroud  232  comprises a radially outer curved portion  250  for guiding fluid down towards castellations  244 . Shroud  232  further comprises an annular stepped portion  252  which grips the radially outer surfaces of castellations  244  thereby to fix the shroud  232  in position. Of course, further mechanical attachment devices can be used such as a nut and bolt arrangement as shown in the previous embodiment. Shroud  232  further comprises an inner stepped annulus  254  and finally a lip  238 . Accordingly, stepped annulus  252  acts to secure the shroud  232  in position whilst stepped annulus  254  acts to increase the area around seal  218 . 
     A yet further embodiment of the invention is shown in part in FIG. 5 wherein a shroud  332  comprises a radially outer portion  350  for guiding fluid between shroud  332  and pump body  314  down towards apertures  336  in the shroud. Here, like components with earlier embodiments are given the same two digit reference number prefixed with the number  3 . Shroud  332  comprises a stepped portion  354  which engages part of pump body  314  thereby to locate the shroud in position. In this embodiment, shroud  332  further carries annulus  320  which forms part of the seal  318  (not shown). Accordingly, annulus carries a further annulus  322  (not shown) and stationary circular seat  324  (not shown). Beneficially, shroud  332  acts, in particular through outer portion  350 , to increase fluid flow down towards shaft  312  through apertures  336  thereby to effect cooling of the seal. 
     In a further embodiment of the invention shown in FIG. 6, a shroud  432  comprises a stepped radially outer portion  460  for engaging crenallations in the pump body  414 . The S-shaped central portion of shroud  432  extends from stepped portion  460  to apertures  436  which can be provided in a circular series around the shroud  432 . Accordingly, the central portion of shroud  436  acts to guide fluid between slots located between the series of bosses or castellations  444  in the pump and the apertures  436 . Shroud  432  further comprises an inner annular clip  420  for engaging part of pump body  414 . Annulus  420  forms part of a seal  418  (not shown), and therefore carries a further annulus and seat for engaging the rotatable part of the seal as shown in earlier embodiments.