Apparatus for transferring pressurized fluid in a back-to-back multi-stage pump

A multi-stage pump includes a first set of pump stages directing fluid in a first direction from a first end of the multi-stage pump to a diffuser casing disposed at a central portion of the multi-stage pump. A second set of pump stages directs the fluid expelled from the diffuser casing in a second direction, opposite to the first direction, from a second end of the multi-stage pump to the diffuser casing. The diffuser casing receives the fluid from the first set of pump stages and directs the fluid toward the second end of the multi-stage pump and receives the fluid from the second set of pump stages and directs the fluid in a radial direction with respect to a longitudinal axis of the multi-stage pump.

FIELD OF THE INVENTION

This application relates generally to a multi-stage pump, and more particularly, to a method and apparatus for transferring pressurized fluid in a back-to-back multi-stage pump.

BACKGROUND OF THE INVENTION

Conventional means for directing pressurized fluid in a multi-stage pump typically include a plurality of impeller stages, wherein a first half of the plurality of impeller stages directs the fluid in a first direction and a second half of the plurality of impeller stages directs the fluid in a second direction, opposite to the first direction. This configuration successfully balances thrust concerns between the first and second halves of the plurality of impeller stages. However, with respect to known, conventional configurations, it is difficult to effectively direct the flow of fluid from the first half of the plurality of impeller stages to the second half, and to subsequently direct the flow from the second half of the plurality of impeller stages out of the pump (e.g., to a working environment).

One such conventional configuration employs additional tubing to externally route the fluid. For example, the fluid directed from the first half of the plurality of impeller stages is expelled outside of a housing of the multi-stage pump via an external tube. The external tube directs the fluid back into the housing at a location were the second half of the plurality of impeller stages resides. From there, the second half of the plurality of impeller stages directs the fluid to a downstream location where the fluid is expelled out of the multi-stage pump to a working environment. This known configuration requires additional parts (e.g., the external tube) and increases manufacturing complexity.

BRIEF SUMMARY OF THE INVENTION

In accordance with one aspect, there is provided a multi-stage pump having a first set of pump stages directing fluid in a first direction from a first end of the multi-stage pump to a diffuser casing disposed at a central portion of the multi-stage pump. A second set of pump stages directs the fluid expelled from the diffuser casing in a second direction, opposite to the first direction, from a second end of the multi-stage pump to the diffuser casing. The diffuser casing receives the fluid from the first set of pump stages and directs the fluid toward the second end of the multi-stage pump and receives the fluid from the second set of pump stages and directs the fluid in a radial direction with respect to a longitudinal axis of the multi-stage pump.

In accordance with another aspect, there is provided a multi-stage pump comprising an outer housing having an inlet and an outlet. A first set of pump stages is disposed at a first end of the outer housing for directing fluid in a first direction from the inlet of the outer housing to a central portion of the outer housing. A second set of pump stages is disposed at a second end of the outer housing, the second end being opposite to the first end of the outer housing. The second set of pump stages directs the fluid in a second direction, opposite to the first direction, from the second end of the multi-stage pump to the central portion of the outer housing.

The multi-stage pump further includes a diffuser disposed in the central portion of the outer housing at a location between the first set of pump stages and the second set of pump stages. The diffuser casing comprises an outer circumferential passage that extends in a longitudinal direction through the diffuser for directing fluid in the longitudinal direction from an outlet end of the first set of pump stages to an inlet end of the second set of pump stages. An inner passage extends in a radial direction through the diffuser for directing fluid exiting an outlet end of the second set of pump stages in a direction tangential to the direction fluid flows through the outer circumferential passage. The fluid flowing in the inner passage is directed radially away from the diffuser.

In accordance with yet another aspect, there is provided a multi-stage pump comprising a first set of pump stages directing fluid in a first direction from a first end of the multi-stage pump to a central portion of the multi-stage pump, wherein the first direction is parallel to a longitudinal axis of the multi-stage pump. The multi-stage pump further includes a second set of pump stages directing the fluid in a second direction, opposite to the first direction, from a second end of the multi-stage pump to the central portion. A diffuser casing is disposed at the central portion and includes a first inlet that receives the fluid directed from the first set of pump stages, a first outlet that expels the fluid received by the first inlet, a second inlet that receives the fluid directed from the second set of pump stages, and a second outlet that directs the fluid to a chamber within the diffuser casing. An outer housing encases the first set of pump stages, the second set of pump stages, and the diffuser casing.

The diffuser casing further includes a first casing and a second casing. The first casing has a first vane that defines a first internal passage from the first inlet to the first outlet. The second casing has a second vane that defines a second internal passage from the second inlet to the second outlet. A through-hole is formed in the first vane. The through-hole directs the fluid in a radial direction with respect to the longitudinal axis of the multi-stage pump and expels the received fluid to an outside chamber of the diffuser casing. A reservoir is defined as a space between an inner surface of the outer housing and an outer surface of the second set of pump stages, and wherein the reservoir directs the fluid expelled from the first outlet to the second end of the multi-stage pump.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Referring now to the drawings,FIG. 1depicts a perspective, cross-sectional view of a multi-stage pump100taken along a first longitudinal axis L1thereof. The multi-stage pump100includes an outer housing102defining an inner space configured to receive and encase a diffuser casing104disposed longitudinally between a first set of pump stages106and a second set of pump stages108. In the depicted embodiment, the outer housing102is formed in the shape of a hollow cylinder (half of the outer housing102is shown inFIG. 1). That is, an outer surface102aof the outer housing102has a generally circular shape in a cross-sectional view taken perpendicular to the first longitudinal axis L1. Similarly, an inner surface102bof the outer housing102(i.e., the inner surface102bthat delimits the inner space of the outer housing102) likewise has a generally circular shape in the cross-sectional view taken perpendicular to the first longitudinal axis L1. As can be appreciated, the inner surface102bmay be contoured to have features, e.g., recesses, cavities, steps, ledges, etc. for mating with components that are mounted in the inner space of the outer housing102.

It is to be understood that the geometric configuration of the outer housing102is not limited to a hollow cylinder. For example, the outer and inner surfaces102a,102bof the outer housing102can have a shape in the cross-sectional view taken perpendicular to the first longitudinal axis L1other than circular (e.g., square, rectangular, triangular, etc.). Further still, the outer and inner surfaces102a,102bof the outer housing can have different shapes, with respect to one another, in the cross-sectional view taken perpendicular to the first longitudinal axis L1. For example, the outer and inner surfaces102a,102bcan have rectangular and circular shapes, respectively, in the cross-sectional view taken perpendicular to the first longitudinal axis L1.

As further shown inFIG. 1, the outer housing102extends longitudinally (i.e., along the first longitudinal axis L1) from a first end110ato a second end110b. The diffuser casing104is disposed within the inner space of the outer housing102at a central portion thereof, with respect to the first and second ends110a,110b. As briefly mentioned above, the diffuser casing104is positioned between the first set of pump stages106and the second set of pump stages108. In this manner, the first set of pump stages106is disposed between the first end110aof the outer housing102and the diffuser casing104, and the second set of pump stages108is disposed between the diffuser casing104and the second end110bof the outer housing102, with respect to the first longitudinal axis L1. As such, the multi-stage pump100has a back-to-back configuration wherein each of the first and second sets of pump stages106,108includes multiple pump stages disposed directly adjacent to one another, and wherein the first and second sets of pump stages106,108are in fluid communication with one another.

As will be further detailed below, the multi-stage pump100is configured such that the first set of pump stages106directs a fluid in a first direction D1from the first end110aof the outer housing102to one end of the diffuser casing104and the second set of pump stages108directs fluid expelled from the diffuser casing104in a second direction D2from the second end110bof the outer housing102to an opposite end of the diffuser casing104. Specifically, the first and second directions D1, D2are parallel to the first longitudinal axis L1and are opposite to one another. For example, as shown, the first direction D1is the direction from the first end110ato the second end110bof the outer housing102, along the first longitudinal axis L1, and the second direction D2is the direction from the second end110bto the first end110aof the outer housing102, along the first longitudinal axis L1.

Moreover, as will be further detailed below, the diffuser casing104is configured to receive the fluid from the first set of pump stages106and direct the fluid toward the second end110bof the outer housing102. Specifically, the fluid is directed from the diffuser casing104to the second end110bof the outer housing102via a reservoir112. The reservoir112is defined as a space between the inner surface102bof the outer housing102and an outer surface108aof the second set of pump stages108. More specifically, the reservoir112extends longitudinally between the diffuser casing104and the second end110bof the outer housing102. In this manner, the reservoir112receives fluid expelled from the diffuser casing104and directs the expelled fluid toward the second end110bof the outer housing102.

When the fluid reaches the second end110bof the outer housing102, the fluid is received by the second set of pump stages108, which directs the fluid (in the second direction D2) back to the diffuser casing104. The diffuser casing104is further configured to receive the fluid from the second set of pump stages108. The fluid received from the second set of pump stages108is then directed via the diffuser casing104in a radially outward direction R (i.e., a radial direction with respect to the first longitudinal axis L1of the outer housing102) away from the multi-stage pump100.

Individual components of the multi-stage pump100will now be structurally discussed in detail. Thereafter, the overall assembly and functionality of the multi-stage pump100will be explained with reference to a method of transferring pressurized fluid in the multi-stage pump100.

As shown inFIG. 6, which is an enlarged view of the central portion of the multi-stage pump100(encircled in dashed line “A” inFIG. 1), the diffuser casing104includes a first casing114and a second casing116. The first casing114of the diffuser casing104is configured to at least partially, peripherally surround an outlet impeller115of the first set of pump stages106(shown inFIG. 1) and the second casing116of the diffuser casing104is configured to at least partially, peripherally surround an outlet impeller117of the second set of pump stages108(shown inFIG. 1).

As best shown inFIG. 2, the outlet impeller115has a second longitudinal axis L2extending through a central opening of the outlet impeller115. When the outlet impeller115is positioned in the outer housing102, the second longitudinal axis L2of the outlet impeller115is positioned to coaxially align with the first longitudinal axis L1(as shown inFIG. 1). The outlet impeller115of the first set of pump stages106includes a first wall115aand a separate second wall115b. The first and second walls115a,115bare spaced apart from each other to define a channel119therebetween. A plurality of blades121are disposed within the channel119and are dimensioned and positioned to draw fluid in an axial direction (i.e., along the second longitudinal axis L2) from the outlet impeller115and exhaust the fluid in a direction perpendicular to the second longitudinal axis L2via an outlet of the channel119, i.e., in a direction radially outward from the second longitudinal axis L2.

The overall number of blades121of the outlet impeller115of the first set of pump stages106may be any number. Further, it is to be understood that the outlet impeller115may be formed as a single piece-part or formed from separate and distinct parts that are subsequently secured thereto.

As illustrated inFIG. 6, the first casing114is positioned adjacent to the outlet impeller115of the first set of pump stages106. Moving now toFIGS. 3A-3C, the first casing114is depicted as taking the form of a hollow cylinder (only a half section of the first casing114is illustrated inFIGS. 3A and 3B). It is to be understood that the geometric form of the first casing114is not limited thereto, and that the first casing114may be shaped in any geometric configuration. As shown, the first casing114includes a circumferential wall118extending longitudinally along a third longitudinal axis L3from a first end114ato a second end114bthereof. When the first casing114is positioned in the outer housing102, the third longitudinal axis L3of the first casing114is positioned to coaxially align with the first longitudinal axis L1(as shown inFIG. 1). Towards, the second end114bof the first casing114, the circumferential wall118includes an inner wall118aseparated and spaced apart from an outer wall118bsuch that a gap118cis formed therebetween.

A plurality of first vanes120are positioned within the gap118cand extend along the third longitudinal axis L3for drawing fluid into an annular first inlet124and exhausting the fluid through a peripheral first outlet126defined by the gap118c. Specifically, the plurality of first vanes120extend in a curved manner about the third longitudinal axis L3. The plurality of first vanes120are disposed within the gap118cand are spaced apart from each other to define a plurality of first internal passages122through which fluid flows from the annular first inlet124to the peripheral first outlet126. Specifically, the plurality of first internal passages122are defined between a pair of adjacent first vanes120. In this manner, the plurality of first internal passages122are positioned within the circumferential wall118of the first casing114and are spaced circumferentially, one from the other, therein via the plurality of first vanes120.FIG. 3Cis a simplified illustration of the first casing114with exterior walls around the plurality of first vanes120removed (e.g., the outer wall118b) to allow the plurality of first vanes120to be visible.

As described above, the first casing114is configured to intake fluid in the radial direction R and direct the fluid in the axial direction (i.e., along the third longitudinal axis L3) via the first internal passage122. It is to be understood that any number of first vanes120can be disposed with the gap118cof the first casing114so long as at least one first internal passage122is defined therein. Moreover, it is to be understood that the first vanes120have a specific configuration that permits a pressure of fluid flowing through the first internal passages122to increase. Specifically, as will be further discussed below, the first vanes120are configured to convert the dynamic pressure, imparted to the fluid by the first set of pump stages106, into static pressure.

As best shown inFIGS. 3A and 3C, a through-hole128extends through the circumferential wall118of the first casing114. Specifically, a single through-hole128is dimensioned and positioned to extend through a single first vane120. That is, the through-hole128extends through the inner wall118aand the outer wall118bof the circumferential wall118of the first casing114in the radial direction R of the multi-stage pump100and is dimensioned and positioned such that through-hole128is within the area bounded by the walls of the respective first vane120. It is to be understood that the through-hole128extends through the first vane120such that the through-hole128is not in fluid communication with the gap118cdefined between the inner and outer walls118a,118bof the circumferential wall118. Further, as shown, a single through-hole128extends through each of the first vanes120disposed within the gap118c. However, it is to be understood that a single through-hole128need not extend through each of the first vanes120. For example, the through-holes128may be disposed in half of the first vanes120, or any other fraction of the first vanes120. It is also contemplated that only a single through-hole128may extend through a single first vane120. It is also contemplated that a plurality of through-holes128(not shown) may extend through a single first vane120. It is to be understood that an entirety of the first casing114may be formed integrally, as a single piece-part or formed from a plurality of parts that are joined together.

As illustrated inFIGS. 3A and 3B, an inner flange131may extend from the circumferential wall118and include a plurality of mounting holes133. The mounting holes133may be positioned and dimensioned to secure the first casing114to the second casing116. An outer surface of the circumferential wall118may include a plurality of annular grooves135, each dimensioned to receive a seal element, e.g., an O-ring (not shown). In this respect, when the first casing114is disposed in the outer housing102the first casing114sealingly engages the inner surface102of the outer housing102.

As mentioned above, the diffuser casing104includes the first casing114and the second casing116. As illustrated inFIG. 6, the second casing116is positioned to mate with the first casing114. Moving now toFIGS. 4A and 4B, the second casing116takes the form of a generally hollow cylinder (only a half section of the second casing116is illustrated inFIGS. 4A and 4B). However, it is to be understood that the geometric form of the second casing116is not limited thereto, and that the second casing116may be shaped in any geometric configuration. The second casing116includes a circumferential wall136extending longitudinally along a fourth longitudinal axis L4from a first end116ato a second end116bthereof. When the second casing116is positioned in the outer housing102, the fourth longitudinal axis L4is positioned to coaxially align with the first longitudinal axis L1(as shown inFIG. 1). As further shown, the circumferential wall136includes an inner wall136aseparated and spaced apart from an outer wall136bsuch that a gap136cis formed therebetween. That is, the outer wall136bis spaced radially outwards from the inner wall136a.

A plurality of second vanes138are positioned within the gap136cand are spaced apart from each other to define a plurality of second internal passages140through which fluid flows from an annular second inlet142to a peripheral second outlet144. Specifically, the second vanes138extend in a curved manner about the fourth longitudinal axis L4. The second vanes138extend between the inner wall136aand the outer wall136bof the circumferential wall136. As shown, the plurality of second vanes138are spaced apart, one from the other, to define the plurality of second internal passages140within the gap136c. Specifically, the second internal passage140is defined between a pair of adjacent second vanes138. In this manner, the plurality of second internal passages140are positioned within the circumferential wall136of the second casing116and are spaced circumferentially, one from the other, therein via the plurality of second vanes138. The second casing116is configured to intake fluid (via the annular second inlet142) in the radial direction R and direct the fluid in the axial direction (i.e., along the fourth longitudinal axis L4) via the second internal passage140to the peripheral second outlet144.

The inner wall136amay include a plurality of mounting holes137that are positioned and dimensioned to align with the mounting holes133of the first casing114. In this respect, the first casing114and the second casing116may be secured together using fastening elements (e.g., bolts141, shown inFIG. 6). The outer wall136bof the second casing116may include one or more annular grooves139on an outer cylindrical surface of the outer wall136b. The annular grooves139may be dimensioned to receive seal elements, e.g., O-rings (not shown), for allowing the second casing116to sealingly engage an inner surface of the inner wall118aof the first casing114.

It is to be understood that any number of second vanes138can be disposed within the gap136cof the second casing116so long as at least one second internal passage140is defined therein. It is further to be understood that an entirety of the second casing116may be formed integrally, as a single piece-part or manufactured from a plurality of discrete parts. Moreover, it is to be understood that the second vanes138may have a specific configuration that reduces the dynamic pressure of the fluid while increasing the static pressure of fluid flowing through the second internal passages140.

Moving now toFIG. 6, the outlet impeller117of the second set of pump stages108is disposed adjacent the first end116aof the second casing116. As shown inFIG. 5, the outlet impeller117of the second set of pump stages108is similar in most respects to the outlet impeller115of the first set of pump stages106. The outlet impeller117includes a first wall117aand a separate second wall117b. The first and second walls117a,117bare spaced apart from each other to define a channel148therebetween. A plurality of blades150are disposed within the channel148and extend in a curved manner about a fifth longitudinal axis L5. When the outlet impeller117is positioned in the outer housing102, the fifth longitudinal axis L5of the outlet impeller117coaxially aligns with the first longitudinal axis L1(as shown inFIG. 1). As will be further detailed below, the plurality of blades150of the outlet impeller117of the second set of pump stages108is configured to intake fluid in an axial direction (i.e., along the fifth longitudinal axis L5) and exhaust the fluid in the radial direction R via the channel148.

As further shown, the plurality of blades150are disposed within the channel148. The overall number of blades150of the outlet impeller117of the second set of pump stages108may be any number. It is to be understood that the entirety of the outlet impeller117of the second set of pump stages108may be formed integrally, as a single piece-part or manufactured from a plurality of components that are joined together.

Moving back toFIG. 1, the first set of pump stages106includes an inlet pump stage106aand an outlet pump stage106bwith at least one intermediate pump stage106cdisposed therebetween. The inlet pump stage106ais disposed at the first end110aof the outer housing102and the outlet pump stage106bis disposed adjacent the first casing114of the diffuser casing104(e.g., directly adjacent to the first end114aof the first casing114). Each of the inlet pump stage106aand the at least one intermediate pump stage106cincludes an impeller that is peripherally surrounded by a pump stage housing. For example, the inlet pump stage106aincludes an inlet impeller107aperipherally surrounded by an inlet pump stage housing109aand the at least one intermediate pump stage106cincludes an intermediate impeller107bperipherally surrounded by an intermediate pump stage housing109b. The outlet pump stage106bincludes the outlet impeller115which is peripherally surrounded by the first casing114of the diffuser casing104.

The inlet impeller107ais configured to intake fluid in an axial direction (i.e., along the first longitudinal axis L1) and exhaust the fluid in the radial direction R to the inlet pump stage housing109a. The inlet pump stage housing109athen directs the fluid in the axial direction (i.e., along the first longitudinal axis L1) to the intermediate impeller107b. The intermediate impeller107bintakes the fluid and exhausts the fluid in the radial direction R to the intermediate pump stage housing109b. The fluid continues to be directed in this manner to any subsequent pump stages until the fluid is received by the outlet pump stage106b, which will be further discussed below.

Similar to the first set of pump stages106, the second set of pump stages108includes an inlet pump stage108aand an outlet pump stage108bwith at least one intermediate pump stage108cdisposed therebetween. The inlet pump stage108ais disposed at the second end110bof the outer housing102and the outlet pump stage108bis disposed adjacent the second casing116of the diffuser casing104(e.g., directly adjacent to the first end116aof the second casing116). Each of the inlet pump stage108aand the at least one intermediate pump stage108cincludes an impeller that is peripherally surrounded by a pump stage housing. For example, the inlet pump stage108aincludes an inlet impeller111aperipherally surrounded by an inlet pump stage housing113aand the at least one intermediate pump stage108cincludes an intermediate impeller111bperipherally surrounded by an intermediate pump stage housing113b. The outlet pump stage108bincludes the outlet impeller117which is peripherally surrounded by the second casing116of the diffuser casing104.

The inlet impeller111ais configured to intake fluid in an axial direction (i.e., along the first longitudinal axis L1) and exhaust the fluid in the radial direction R to the inlet pump stage housing113a. The inlet pump stage housing113athen directs the fluid in the axial direction (i.e., along the first longitudinal axis L1) to the intermediate impeller111b. The intermediate impeller111bintakes the fluid and exhausts the fluid in the radial direction R to the intermediate pump stage housing113b. The fluid continues to be directed in this manner to any subsequent pump stages until the fluid is received by the outlet pump stage108c, which will be further discussed below.

The total number of pump stages in each of the first and second sets of pump stages106,108is not limited to a specific number. That is, the first and second sets of pump stages106,108may each include any number of pump stages so long as the first set of pump stages106includes the outlet pump stage106band the second set of pump stages108includes the outlet pump stage108b.

The multi-stage pump100further includes a shaft152disposed within the inner space of the outer housing102and extending longitudinally therein. The shaft152is configured to rotate about the first longitudinal axis L1. Specifically, the shaft152may be operatively connected to a motor (not shown) that rotatably drives the shaft152. Moreover, the outlet impellers115,117of the first and second sets of pump stages106,108, respectively, are connected (e.g., secured) to the shaft152such that as the shaft152rotates, the outlet impellers115,117likewise rotate therewith. Moreover, the diffuser casing104is shaped and configured to house a bearing support151therein. Specifically, as shown inFIG. 6, the second casing116of the diffuser casing104peripherally surrounds the bearing support151. However, it is to be understood that other configurations are contemplated. That is, the bearing support151need not be peripherally surrounded by the second casing116of the diffuser casing104. The bearing support151supports bearings that promote smooth rotational movement of the shaft152.

Further still, the multi-stage pump100is configured such that the first casing114is separate and distinct with respect to the second casing116. That is, the first casing114is an individual piece-part that is manufactured separately from the second casing116. In this manner, if one of the first and second casings114,116is damaged, then only the damaged casing needs to be replaced (as opposed to the entire diffuser casing104). However, in alternative embodiments, the first and second casings114,116of the diffuser casing104may be formed integrally together as a single-piece part. Moreover, the multi-stage pump100is configured such that the first and second casings114,116of the diffuser casing104are stationary with respect to the outlet impellers115,117. That is, as the outlet impellers115,117rotate about the first longitudinal axis L1(via the shaft152), the first and second casings114,116remain stationary (i.e., not moving in a rotational direction or in a translation direction with respect to the first longitudinal axis L1).

Moving again toFIG. 6, as depicted, the first and second casings114,116are disposed directly adjacent to one another in order to form the diffuser casing104. In particular, the third longitudinal axis L3of the first casing114is coaxially aligned with the fourth longitudinal axis L4of the second casing116. Fasteners141may be provided for securing the first casing114to the second casing116through the mounting holes133,137of the first and second casings114,116, respectively. The diffuser casing104is configured such that the first casing114extends radially (i.e., in the radial direction R) beyond the second casing116. That is, the first casing114is dimensioned such that the circumferential wall118thereof has a larger radius (from the first longitudinal axis L1) than that of the circumferential wall136of the second casing116. Specifically, the inner wall118aof the first casing114has substantially the same radius as that of the outer wall136bof the second casing116, and the outer wall118bof the first casing114has a larger radius (from the first longitudinal axis L1) than that of the inner wall118aof the first casing114. In this manner, as will be detailed further below, the first outlet126of the first casing114exhausts fluid radially outside of the second casing116.

The fluid exhausted from the first casing114is directed (downstream) to the reservoir112via a bridge member154. The bridge member154is shown in the form of a cylinder and is positioned such that the bridge member154is disposed on and peripherally surrounds the second casing116. Specifically, the bridge member154is disposed on the outer wall136bof the second casing116. The bridge member154may be formed in any geometric shape permitted by the dimensions of the outer housing102. Further, the bridge member154includes vanes155configured to direct the fluid to the reservoir112. The vanes155further provide structural support for the bridge member154, thereby ensuring a proper seal between the diffuser casing104and the inner surface102bof the outer housing102(e.g., provided via an O-ring, not shown). Moreover, the bridge member154is shown as being a separate and distinct element with respect to the diffuser casing104. However, the bridge member154may be formed integral with the first casing114and/or the second casing116.

As further shown, the first casing114and the second casing116define a chamber156therebetween. For example, in the depicted embodiment, the inner wall136aof the second casing116is peripherally surrounded by inner wall118aof the first casing114. In this manner, the first and second casings114,116define the chamber156therebetween. It is to be understood that the chamber156is not limited to being defined in the aforementioned manner. That is, the chamber156may be defined entirely in the first casing114or the second casing116. The chamber156is in direct fluid communication with the second internal passage140of the second casing116and the through-holes128in the first casing114. In this manner, as will be further detailed below, fluid is directed from the second internal passage140of the second casing116to a downstream location (i.e., outside of the diffuser casing104) in the radial direction R via the chamber156and the through-holes128.

The functionality of the multi-stage pump100will now be discussed in detail with reference to a method for transferring pressurized fluid within the multi-stage pump100. With respect toFIG. 1, a fluid enters the multi-stage pump100from the first end110aof the outer housing102. The fluid is directed to the first set of pump stages106wherein the fluid enters the inlet pump stage106a. The fluid is directed from the inlet pump stage106ato the outlet pump stage106b, as detailed and described above. As understood by those skilled in the art, the impellers of each stage of the first set of pump stages106are configured to successively increase the pressure of the fluid as it flows from the inlet pump stage106ato the outlet pump stage106b. With respect toFIG. 6, when the fluid reaches the outlet pump stage106b, the fluid is directed along a first flow path P1wherein the fluid enters the channel119of the outlet impeller115(as shown inFIG. 2) and is directed (in the radial direction R) to the first internal passage122formed in the first casing114. Specifically, as the outlet impeller115rotates (via the shaft152) the blades121(shown inFIG. 2) forcefully direct the fluid to the first internal passage122of the first casing114.

Once in the first internal passage122, the fluid is conveyed along a second flow path P2from the first internal passage122(via the first outlet126, shown inFIG. 3A) of the first casing114and is directed to the reservoir112via the bridge member154. The fluid enters the reservoir112and continues to be directed in the first direction D1until the fluid reaches the second end110bof the outer housing102where the fluid enters the second set of pump stages108(seeFIG. 1).

When the fluid reaches the second set of pump stages108, the fluid enters the inlet pump stage108aand is directed therefrom to the outlet pump stage108b, as detailed and described above. As understood by those skilled in the art, the impellers of each stage of the second set of pump stages108are configured to successively increase the pressure of the fluid as it flows from the inlet pump stage108ato the outlet pump stage108b. When the fluid reaches the outlet pump stage108b, the fluid is directed along a third flow path P3wherein the fluid enters the channel148of the outlet impeller117(as shown inFIG. 5) and is directed (in the radial direction R) to the second internal passage140formed in the second casing116. Specifically, as the outlet impeller117rotates (via the shaft152) the blades150forcefully direct the fluid back to the diffuser casing104, and more specifically, into the second internal passage140.

The fluid exhausted from the outlet impeller117enters the second internal passage140of the second casing116(via the second inlet142, shown inFIG. 4A). The fluid is directed along a fourth flow path P4through the second internal passage140and is exhausted therefrom into the chamber156(via the second outlet144of the second casing116, shown inFIG. 4A). From the chamber156the fluid is expelled from the diffuser casing104in the radially outward direction R. Specifically, the fluid received in the chamber156is directed along a fifth flow path P5to a downstream location (i.e., outside of the diffuser casing104) via the through-hole128in the first vane120. As briefly mentioned above, the through-hole128extends through the first vane120in a manner such that the through-hole128is not in fluid communication with the gap118cdefined between the inner and outer walls118a,118bof the first casing114. In this manner, the first casing114of the diffuser casing104provides two separate fluid paths (i.e., the first flow path P1and the fifth flow path P5) wherein flow along the first flow path P1is in an axial direction to convey fluid from an outlet of a first set of pump stages to an inlet of a second set of pump stages, and the fifth flow path P5conveys fluid exiting the second set of pump stages in a radial direction so that the fluid may exit the multi-stage pump100.

More specifically, the aforementioned multi-stage pump100permits a fluid to enter the outer housing102and be directed (in the first direction D1) from the first end110athereof to the diffuser casing104(located at the central portion of the outer housing102) via the first set of pump stages106. The fluid then exits the diffuser casing104and is directed to the second set of pump stages108(via the reservoir112). The fluid is then directed (in the second direction D2) back to the diffuser casing104where the fluid enters the chamber156. The fluid is then subsequently gathered in a cavity outside of the diffuser casing to be exhausted from the multi-stage pump100. In this manner, a downstream path of the fluid (i.e., the fifth flow path P5) essentially crosses over an upstream path of the fluid (i.e., the first flow path P1) via the through-hole128. As such, the fluid is efficiently directed through the multi-stage pump100in a manner entirely internal thereto. That is, no additional parts are required to externally route the fluid from one location to another (e.g., from the first set of pump stages106to the second set of pump stages108).

Furthermore, the configuration of the diffuser casing104permits an efficient collection and transmission of fluid from the first set of pump stages106to the second set of pump stages108and from the second set of pump stages108to a downstream location disposed outside of the diffuser casing104. Specifically, the geometric configuration and number of first vanes120of the first casing114collects the fluid being exhausted from the first set of pump stages106such that the pressure of the fluid builds (i.e., increases) therein. That is, the first vanes120and the reservoir112are configured to convert the dynamic pressure imparted to the fluid by the first set of pump stages106into static pressure.

Moreover, the geometric configuration and number of second vanes138of the second casing116and the chamber156are configured to convert the dynamic pressure imparted to the fluid by the second set of pump stages108into static pressure. In this manner, the configuration of the second casing116provides the technical advantage of fluid pressure not being lost as the fluid is directed from the second set of pump stages108to a downstream location (i.e., outside of the diffuser casing104).