TECHNICAL FIELD

[0001] The present subject matter relates in general to impellers, and in particular, to enhancement of volumetric efficiency of an impeller.

BACKGROUND

[0002] Pumps are mechanical devices which use suction to raise or move fluid. Typically, centrifugal submersible pumps are used to pump water from bore wells for agriculture, residential or commercial purposes. Generally, pumps comprise an impeller and a volute casing placed on a shaft. The volute casing is flush with a stuffing box to prevent leakage of fluid, such as water or steam, between sliding or turning parts of the pump. The fluid to be pumped is transferred from the impeller to a discharge outlet through the volute casing. However, some fluid enters and is retained in the clearance space between impeller, volute casing, and the stuffing box. Fluid retained in the clearance space remains unused and causes unbalanced pressure distribution between a front-shroud plate and a back-shroud plate of the impeller. This further results in an axial thrust in a direction of the shaft, volumetric losses, and, thereby, decreased performance efficiency of the pump.

BRIEF DESCRIPTION OF DRAWINGS

[0003] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.

[0004] Fig. 1(a) depicts an isometric view of an impeller, in accordance with an implementation of the present subject matter. [0005] Fig. 1(b) depicts a cross-sectional view of the impeller enclosed in a volute casing, in accordance with an implementation of the present subject matter.

[0006] Fig. 2(a) depicts a plan view of the impeller with curved vanes, in accordance with an implementation of the present subject matter.

[0007] Fig. 2(b) depicts a sectional view of a back-shroud plate of the impeller, in accordance with an implementation of the present subject matter.

[0008] Fig. 2(c) depicts an example section of back vane of the impeller with curved vanes, in accordance with an implementation of the present subject matter.

[0009] Fig. 2(d) depicts yet another example section of back vane of the impeller with curved vanes, in accordance with an implementation of the present subject matter.

[00010] Fig. 2(e) depicts a sectional view of the impeller, in accordance with an implementation of the present subject matter.

[00011] Fig. 3(a) depicts a plan view of yet another impeller, in accordance with an implementation of the present subject matter.

[00012] Fig. 3(b) depicts a first side of a back-shroud plate of the impeller, in accordance with an implementation of the present subject matter.

[00013] Fig. 3(c) depicts cross-section of back vane of the impeller with straight vanes, in accordance with an implementation of the present subject matter.

DETAILED DESCRIPTION

[00014] The present subject matter provides an impeller for reducing volumetric losses and axial thrust caused due to accumulation of fluid in a clearance gap between the impeller, a volute casing, and a stuffing box of a centrifugal pump.

[00015] Centrifugal pumps are typically used in domestic, agricultural, industrial, and residential purposes to pump water, chemicals, and the like. In a semi-open and closed- type impeller, the impeller is closed by a shroud on one and both sides of the impeller, respectively. The impeller and volute casing are arranged on a rotary shaft that is coupled to a motor. The volute casing is flush with a stuffing box which prevents leakage from the volute casing due to the movement of the pump parts.

[00016] Typically, for pumping the fluid, the fluid from the impeller is transferred through the volute casing. During pumping, some fluid enters and is retained in the clearance gap between the impeller, the volute casing, and the stuffing box. Fluid retained in the clearance gap remains unused and can cause unbalanced pressure distribution between the front-shroud plate at a front portion and a back-shroud plate at a back portion of the impeller. Further, the fluid retained in the clearance gap causes an axial thrust in a direction of the rotary shaft. Therefore, the fluid retained causes volumetric losses and performance losses in the pump.

[00017] Thrust balancing techniques have been used to balance the axial thrust. A popular form of thrust balancing is to drill balance holes through a back-shroud plate of the impeller. This allows retained fluid at a back portion of the impeller, behind the back-shroud plate, to bleed through the balance holes back into the suction side. However, these balance holes do not completely eliminate axial thrust.

[00018] The present subject matter provides an impeller for a centrifugal pump having mechanism to remove fluid retained in the clearance gap from a pressure side of the impeller and, thereby, reduces the volumetric losses and axial thrust. The impeller comprises a front-shroud plate provided on a suction side of the impeller and a back- shroud plate arranged co-axial to the front-shroud plate. A first side of the back-shroud plate is on a pressure side of the impeller and a second side of the back-shroud plate is opposite to the first side. A plurality of impeller vanes is provided between the front- shroud plate and the back-shroud plate. The plurality of impeller vanes is in contact with the second side of the back-shroud plate.

[00019] A plurality of back vanes is provided on the first side of the back-shroud plate. Each of the plurality of back vanes comprises a flow passage to transfer fluids from the first side to the second side of the back-shroud plate. An inlet of the flow passage is provided on the first side of the back-shroud plate and an outlet of the flow passage is provided on the second side of the back-shroud plate.

[00020] The flow passage in the back vanes reduces volumetric losses and axial thrust on the rotary shaft by removing the retained fluid from behind the impeller. This further helps in improving the efficiency of the pump. By removing and introducing the retained fluid into the discharge gap, impeller head is improved, thereby, increasing the overall performance of the pump.

[00021] The above and other features, aspects, and advantages of the subject matter will be better explained with regard to the following description and accompanying figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter along with examples described herein and, should not be construed as a limitation to the present subject matter. It is thus understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and examples thereof, are intended to encompass equivalents thereof. Further, for the sake of simplicity, and without limitation, the same numbers are used throughout the drawings to reference like features and components.

[00022] Fig. 1(a) depicts an isometric view of an impeller 100, in accordance with an implementation of the present subject matter. The impeller 100 can have a pressure side 102a and a suction side 102b. The pressure side 102a can be proximate to a stuffing box and the suction side 102b can be proximate to a suction nozzle when assembled in a pump, as will explained with reference to Fig. 1(b).

[00023] The impeller 100 can comprise a front- shroud plate 104a on the suction side 102b of the impeller 100 and a back-shroud plate 104b on the pressure side 102a of the impeller 100. The front-shroud plate 104a and the back-shroud plate 104b can be arranged co-axial to each other. The front-shroud plate 104a and the back-shroud plate 104b can be fabricated from metals, such as, stainless steel. In one example, the thicknesses of the front-shroud plate 104a and the back- shroud plate 104b may be equal. In another example, the back-shroud plate 104b can be thicker than the front- shroud plate 104a to withstand pressure. The front-shroud plate 104a and the back- shroud plate 104b can be fabricated with multiple layers of metals as will be understood.

[00024] The back-shroud plate 104b can have a first side 106a and a second side 106b. The first side 106a can be on the pressure side 102a and the second side 106b can be opposite to the first side 106a. The second side 106b can be proximate to the front- shroud plate 104a. The back-shroud plate 104b can comprise a plurality of balance holes 107a, 107b, hereinafter referred to as the plurality of balance holes 107, provided around a central annular opening 103 of the back-shroud plate 104b to remove retained fluids from the pressure side 102a. As will be understood, distance of the plurality of balance holes 107 from the central annular opening 103 can be based on design considerations. In one example, the plurality of balance holes 107 transfer retained fluid from the pressure side 102a to the suction side 102b.

[00025] A plurality of impeller vanes 108 can be provided between the front-shroud plate 104a and the back-shroud plate 104b. The plurality of impeller vanes 108 may be in contact with the second side 106b of the back-shroud plate 104b. As will be understood, the plurality of impeller vanes 108 are radially disposed between the front shroud plate 104a and the back-shroud plate 104b. The plurality of impeller vanes 108 may be one of an axial, mixed flow, helical, and radial vane forms.

[00026] In addition to the plurality of impeller vanes 108, the impeller 100 can comprise a plurality of back vanes 110. The plurality of back vanes 110 can be provided on the first side 106a of the back-shroud plate 104b. As shown in Fig. 1(a), the plurality of back vanes 110 can be curved vanes. In another example, the plurality of back vanes 110 may be straight vanes as will be explained later with reference to Fig. 3(a). In one example, the plurality of back vanes 110 can be formed from the back-shroud plate 104b, for example, by machining. In another example, the plurality of back vanes 110 may be fitted on the first side 106a. In an example, a thickness of each impeller vane 108 is same a thickness of each back vane 110. In another example, the thickness of each of the back vane 110 is more than that of the impeller vane 108.

[00027] Each of the plurality of back vanes 110 can comprise a flow passage internally (not shown). In one example, an inlet 112 of the flow passage may be provided on a rim 105 provided around the central annular opening 103 of the back-shroud plate 104b. In an example, the rim 105 is a ring-like structure which is provided co-axially with the front-shroud plate 104a and the back-shroud plate 104b. The flow passage is for transferring fluids from the first side 106a to the second side 106b of the back- shroud plate 104b. The flow passage can comprise the inlet 112 on the first side 106a of the back-shroud plate 104b. The flow passage can also comprise an outlet (not shown) on the second side 106b of the back-shroud plate 104b. In an example, the thickness of each of the plurality of back vanes 110 is fabricated based on dimensions of the flow passage to be incorporated in the back vane 110. The thickness of back vanes 110 is considered an incremental thickness which may increase power required by the pump to deliver the desired flow.

[00028] The impeller 100 comprising the front-shroud plate 104a, the plurality of impeller vanes 108, and the back- shroud plate 104b with back vanes 100 is mounted axially on a rotary shaft and enclosed within a volute casing, as will be explained with reference to Fig. 1(b), to form a pump. As will be understood, the rotary shaft can be mounted at the central annular opening 103. Therefore, the pump comprises the volute casing and the impeller mounted on the rotary shaft where the volute casing encloses the impeller.

[00029] Fig. 1(b) depicts cross-sectional view of a pump comprising the impeller 100 placed within a volute casing 116 and mounted on a rotary shaft 118, in accordance with an implementation of the present subject matter. Fig. 1(b) depicts the cross- sectional view of the pump along with the impeller 100 along line A - A as shown in Fig. 1(a). The volute casing 116 with the impeller 100 is mounted on the rotary shaft 118. The rotary shaft 118 can be coupled to a motor (not shown) which causes the impeller 100 to pump fluid to an external environment through the volute casing 116. The volute casing 116 can be coupled to a stuffing box 119 at the pressure side 102a of the impeller 100.

[00030] As shown in Fig. 1(b), there may be a front-clearance gap 120a between the front-shroud plate 104a and the volute casing 116. Similarly, there may be a back- clearance gap 120b between the back- shroud plate 104b and the stuffing box 119. The back- shroud plate 104b can also comprise a balancing ring 122 which is in close- clearance with the stuffing box 119.

[00031] In operation, rotation of the rotary shaft 118 causes the fluid to enter the volute casing 116 through a suction nozzle 124. Due to rotation of the rotary shaft 118 the fluid is transferred from the suction nozzle 124 to the impeller 100. The fluid gains kinetic energy on rotation of the plurality of impeller vanes 108 and the plurality of back vanes 110. The fluid then exits through a discharge outlet 126. The fluid can exit in a radial direction or in a direction perpendicular to the rotary shaft 118.

[00032] While the fluid flows as explained above, a part of the fluid separates from this normal flow and leaks into the front-clearance gap 120a. The leaked fluid in the front-clearance gap 120a gets transferred to a front-end position 128 which is close to the suction nozzle 124. The leaked fluid, therefore, again flows into the volute casing 116 via the suction nozzle 124. Velocity of the leaked fluid is controlled by an area of the front-clearance gap 120a. The area of the front-clearance gap 120a is, therefore, modified to maintain the velocity of the leaked fluid such that it does not cause any mixing losses during pumping of the fluid.

[00033] Similarly, at the pressure side 102a, another part of the fluid leaks into the back-clearance gap 120b. The leaked fluid can enter and be retained in the back- clearance gap 120b. Fluid retained in the back-clearance gap 120b causes increase in pressure at the pressure side 102a. The increase in pressure causes unbalanced pressure distribution between the suction side 102b and the pressure side 102a. Fluid retained in the back-clearance gap 120b also causes volumetric losses. Fluid retained in the back-clearance gap 120b also increases axial thrust on the rotary shaft 118. Therefore, the fluid retained affects performance of the pump and also affects the mechanical integrity of the pump.

[00034] To drain the fluid retained in the back-clearance gap 120b, the back-shroud plate 104b is provided with the plurality of balance holes 107. To further improve the reduction in axial thrust, a flow passage 130 can be provided in each of the plurality of back vanes 110. The flow passage 130 comprises the inlet 112 towards the central annular opening of the impeller 100. The inlet 112, therefore, is at a position opposite to a radial tip of the back vane 110. The fluid retained in the back-clearance gap 120b is taken into the flow passage 130 through the inlet 112. The fluid then flows through the flow passage 130. The flow passage 130 transfers fluids retained in the back- clearance gap 120b from the first side 106a to the second side 106b of the back-shroud plate 104b. Various aspects of the plurality of balance holes 107 and the flow passage 130 are explained with respect to the Fig.(s) 2(a)-2(e) and Fig.(s) 3(a)-3(c).

[00035] Fig. 2(a) depicts the first side 106a of the back- shroud plate 104b, in accordance with an implementation of the present subject matter. Fig. 2(a) illustrates the plurality of balance holes 107 provided in the back-shroud plate 104b. The plurality of balance holes 107 may be drilled into the back-shroud plate 104b. Fig. 2(a) depicts three balancing holes 107. However, it is to be understood that any number of balancing holes may be provided. As previously described, the plurality of balance holes 107 allow the retained fluids to be removed through the balance holes 107.

[00036] Fig. 2(a) also depicts the plurality of back vanes 110 disposed on the first side 106a of the back-shroud plate 104b. Fig. 2(a) depicts curved back vanes. However, it is to be understood that other configurations and shapes are possible. Further, Fig. 2(a) depicts six back vanes. It is to be understood that any number of back vanes may be disposed on the first side 106a of the back-shroud plate 104b. As previously explained, the flow passage 130 can be provided in each of the plurality of back vanes 110. [00037] Fig. 2(b) depicts a lateral cross-section of the back- shroud plate 104 depicting the flow passage 130, in accordance with an implementation of the present subject matter. The flow passage 130 comprises the inlet 112 towards the central annular opening 103 the impeller 100. In one example, the inlet 112 may be provided on the rim 105 (not shown) towards the central annular opening 103 of the back-shroud plate 104b. As will be understood, position and dimensions of the rim 105 around the central annular opening 103 can depend on design considerations.

[00038] The fluid retained in the back-clearance gap 120b (Fig. 1(b)) can be taken into the flow passage 130 through inlet 112. The fluid then flows through the flow passage 130. The fluid within the flow passage 130 then exits through an outlet (not shown in Fig. 2b) into the discharge outlet 126. Therefore, the retained fluid flows from the first side 106a to the second side 106b through the flow passage 130.

[00039] The flow passage 130 can be fabricated such that the flow of the fluid within the passage is smooth. The flow passage 130 can have a circular or polygonal cross- section. In one example, the flow passage 130 can extend throughout a length of the each of the plurality of back vanes 110. In another example, the flow passage 130 extends through a partial length of each of the plurality of back vanes 110. In an example, the outlet is close to an impeller vane of the plurality of impeller vanes 108. In one example, the outlet is away from a radial tip of the back vane 110. In another example, the outlet is at the radial tip of the back vane as shown in Fig. 2(c)-2(e).

[00040] Fig. 2(c) depicts a cross-section of the one of the plurality of back vanes 110 to illustrate the flow passage 130 in greater detail. Fig. 2(c) is a cross-section along line A - A of Fig. 2(b) and depicts an outlet 202 of the flow passage 130 in greater detail. The fluid flows through the flow passage 130 and exits the back vane at the outlet 202. The outlet 202 can be provided such that it does not hinder the normal flow of fluid into the discharge outlet 126. The velocity of the fluid exiting out the outlet 202 can be maintained by modifying the diameter of the outlet 202 as will be understood. The outlet 202 can be designed such that mixing of the fluid with the normal fluid discharge causes negligible to no mixing losses.

[00041] In one example, as shown in Fig. 2(c), the flow passage 130 terminates close to a radial tip 204 of the back vane 110. In said example, the retained fluid is transferred from the first side 106a to the second side 106b and discharged into the discharge outlet 126. Therefore, in said example, the outlet 202 is away from the radial tip 204 of the back vane 110. In another example, the flow passage 130 terminates at the radial tip 204 of the back vane 110 as shown in Fig. 2(d). Therefore, in said example, the outlet 202 is at the radial tip 204. In one example, the radial tip 204 may coincide with an impeller tip. The impeller tip can be understood as a radial tip of the impeller. In another example, the radial tip 204 may be away from the impeller tip. Other configurations of the flow passage 130 are possible as will be understood by a person skilled in the art.

[00042] Fig. 2(e) depicts yet another cross-section of impeller 100 having a curved back vane, in accordance with an implementation of the present subject matter. In operation, with reference to Fig. 2(a)-(e), fluid retained in the back-clearance gap 102b is taken into the flow passage 130 through the inlet 112 which is away from the radial tip of the back vane 110. The fluid flows through the flow passage 130 and can then be transferred to the discharge outlet 126 through the outlet 202. Therefore, the flow passage 130 helps in removing fluid retained in the back-clearance gap 102b from the first side 106a to the second side 106b of the back-shroud plate 104b.

[00043] Therefore, in addition to reduction of volumetric losses by the balance holes 107, the flow passage 130 further helps in reducing volumetric losses by removing the retained fluid. The axial thrust on the rotary shaft is also reduced. Therefore, the impeller 100 comprising flow passage 130 helps in improving the performance and mechanical stability of the pump. While Fig. 2(a)-2(e) is explained with reference to the plurality of back vanes 110 being curved, it is to be understood that the back vanes 110 can have other configurations. [00044] Fig. 3(a) depicts isometric view of yet another impeller 300, in accordance with an implementation of the present subject matter. As shown in Fig. 3(a), the back- shroud plate 104a has straight back vanes 110 disposed thereon. While Fig. 3(a) depicts six back vanes, it is to be understood that any number of back vanes may be disposed on the back- shroud plate 104b.

[00045] As can be seen from Fig. 3(a), to reduce axial thrust and volumetric losses, the impeller 300 comprises the plurality of balance holes 107 provided around the central annular opening 103 of the back-shroud plate 104b and the flow passage 130 (not shown in Fig. 3(a)) in each of the plurality of back vanes 104b. The inlet 112 of the flow passage 130 can also be provided close to the central annular opening 103 of the back-shroud plate 104b, away from the radial tip of the back vane 110, on the first side 106a of the back-shroud plate 104b. In one example, the inlet 112 may be provided on a rim 302. In an example, the rim 302 is a ring-like structure which is provided co- axially with the front-shroud plate 104a and the back- shroud plate 104b. In another example, the rim 302 may be a ring-like protrusion formed continuously with the back- shroud plate 104b. The inlet 112 provided on the rim 302 can be fluidly coupled to the flow passage 130.

[00046] Fig. 3(b) depicts the first side 106a of the back-shroud plate 104b, in accordance with an implementation of the present subject matter. Fig. 3(c) depicts section of one of the plurality of back vanes 110 of the impeller 300 with straight vanes. The section is taken along line A - A of Fig. 3(b). As can be seen from Fig. 3(c), the flow passage 130 comprises the inlet 112 substantially close to the central annular opening 103 of the back-shroud plate 104b. The flow passage 130 exits at the outlet 202. In an example, as shown in Fig. 3(c), the flow passage 130 extends throughout a length of the back vane 110 and terminates at the outlet 202 at the radial tip of the back vane 110. It is to be understood, that the flow passage 130 may extend only partially through the back vane 110 in other implementations. [00047] In the example as shown in Fig. 3(c), the outlet 202 is closer to the plurality of impeller vanes 108 than an impeller tip 303. In said example, therefore, as the outlet 202 is close to the plurality of impeller vanes 108, the fluid retained in the back- clearance gap 102b is transferred from the first side 106a to the plurality of impeller vanes 108 on the second side 106b. In operation, the retained fluid flows through the flow passage 130 through the inlet 112 and is delivered within the impeller 300 at the plurality of impeller vanes 108 and is transferred to discharge gap 126 due to rotation of the impeller 300. Therefore, as shown in Fig.(s) 2(a)-2(e) and Fig 3(a)-3(b) different configurations of the plurality of back vanes 110 and flow passage 130 are possible. Further, it is to be understood that the same principle can be applied to helical impellers, and the like.

[00048] Thus, the flow passage 130 in each of the plurality of back vanes 110 helps in removing the retained fluid from behind the impeller 100, 300. This further helps in improving the performance of the pump by reducing volumetric losses and axial thrust on the rotary shaft. Therefore, volumetric efficiency of the pump is enhanced.

[00049] Although the subject matter has been described in considerable detail with reference to certain examples and implementations thereof, other implementations are possible. As such, the scope of the present subject matter should not be limited to the description of the preferred examples and implementations contained therein.