SELF-ADJUSTING LINER FOR CENTRIFUGAL PUMP

Abstract

A self-adjusting liner assembly for installation within a centrifugal pump of the type having an impeller and a pump casing having a suction inlet is provided, comprising a liner having a sealing end, the sealing end having at least one substantially planar outer most surface for contacting an outer surface of the impeller; and a resilient member disposed in the liner, said resilient member providing a force so that the at least one outer most surface remains in substantially continuous contact with the outer surface of the impeller.

Description

FIELD OF THE INVENTION

The present invention relates to centrifugal pumps in general and more specifically to a self-adjusting liner assembly for centrifugal pumps for substantially reducing recirculation damage to the impeller.

BACKGROUND OF THE INVENTION

Centrifugal pumps are commonly used to move mixtures of solids and liquids through piping. The mixture enters the pump impeller along or near the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute (casing) which surrounds the impeller from where it exits into the downstream piping.

Most centrifugal pumps which handle mineral slurries, for example, oil sand slurries, run into problems with respect to solid particles of the slurry becoming trapped between the rotating impeller and the surrounding volute during operation, thereby causing wear and abrasion of both the impeller and the volute. This results in downtimes for repair and ultimately reduces the life of the pump and its hydraulic efficiency. The problem tends to be more serious on the suction side of the impeller, where the high pressure liquid inside the discharge portion of the volute tends to flow towards the low pressure zone in the suction portion of the pump. This is commonly referred to as suction-side recirculation, which results in a loss of pump hydraulic performance and efficiency.

In particular, increase in suction-side recirculation may directly contribute to loss of efficiency. Since efficiency is a ratio of output work against input power, and since output work (flow and head) is less with the same amount of input power, efficiency is lower. Furthermore, as wear increases, the gap between the impeller and the volute becomes larger if unaddressed and a higher rate of flow can pass through the gap, speeding the deterioration process. Thus, the pump life span will be reduced.

Many centrifugal slurry pumps are now equipped with an annular suction liner (also referred to as an annular wear ring), which is located between the suction side of the impeller and the volute to decrease the wear due to recirculation. However, these suction liners still create a gap where solids can cause abrasion damage. Furthermore, the entire operation (e.g., pumps) must be stopped in order to replace the suction liner when it has become sufficiently worn. Also, it is somewhat unpredictable as to when the suction liner will need to be replaced, which may result in unexpected pump failures.

In an attempt to at least partially remedy some of the problems encountered above, CA 2,214,415 and U.S. Pat. No. 5,921,748 teach a wear ring which is axially adjustable by means of one or more adjustment screws. The adjustment screws are located outside of the pump and, thus, the wear ring (suction liner) can be adjusted while the pump is in operation. However, one will still have to rely on human intervention to adjust the wear ring according to a schedule or a particular criterion. Furthermore, in between these adjustments, wear will occur, allowing a continuing increase in recirculation.

U.S. Pat. No. 7,189,054 teaches a wear ring which is axially self-adjusting by means of balanced flush water pressures. However, in this design, physical contact between the wear ring and the impeller is expressly avoided. When pressurized water is applied to the water inlet end of the seal, the seal will move to a self-compensating balance between the pump casing and the impeller of the pump. Therefore, the seal cannot be independently adjusted.

It would be desirable to have a suction liner assembly which would automatically adjust according to the wear thereon so that a proper seal between the suction side of the impeller and the volute can always be maintained, resulting in substantially reduced suction-side recirculation for longer periods of time. While the design in U.S. Pat. No. 7,189,054 has this feature, the driving force to create the adjustment is limited by the use of balanced hydraulic forces to locate the adjustable component. If, as seems likely, solid material were to accumulate in the gaps on either side of the adjustable component, the hydraulic force required to advance towards the impeller may not be sufficient to overcome the friction due to solids accumulation; the adjustment mechanism seems vulnerable to loss of function.

SUMMARY OF THE INVENTION

The present invention relates to centrifugal pumps in general and more specifically to a self-adjusting liner assembly for a centrifugal pump.

In one aspect of the present invention, a self-adjusting liner assembly for installation within a centrifugal pump of the type having an impeller and a pump casing having a suction inlet is provided, comprising:

• • a liner having a sealing end, the sealing end having at least one substantially planar outer most surface for contacting an outer surface of the impeller; and
  • a resilient member disposed in the liner, said resilient member providing a force so that the at least one outer most surface remains in substantially continuous contact with the outer surface of the impeller.

In one embodiment, the at least one outer most surface comprises a wear ring. In another embodiment, the liner includes a recessed portion for housing the resilient member and the wear ring. The wear ring may vary in diameter relative to the liner and, in one embodiment, may have an outer diameter essentially the same as the outer diameter of the liner itself.

In one embodiment, the resilient member is a spring such as a wave spring.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:

FIG. 1 is a cross-sectional view of the interior of a conventional single stage centrifugal pump.

FIG. 2 is a cross-sectional view of the interior of a single stage centrifugal pump having an embodiment of a self-adjusting liner assembly of the present invention.

FIG. 3 is a cross-sectional view of an embodiment of a self-adjusting liner assembly of the present invention prior to wear of the liner.

FIG. 4 is an isometric exploded view of the embodiment of the self-adjusting liner assembly of FIG. 3.

FIG. 5 is an isometric exploded view of the embodiment of the insert as shown in FIG. 3.

FIG. 6 is a cross-sectional view of another embodiment of a self-adjusting liner assembly of the present invention prior to wear of the liner which includes a lubricating and cooling system.

FIG. 7 shows a sealing arrangement for a wear ring of the present invention.

FIG. 8 shows an embodiment of the sealing face of an impeller useful in the present invention.

FIG. 9 is an isometric exploded view of another embodiment of a self-adjusting liner assembly of the present invention.

FIG. 10a is a cross-sectional view of a portion of the self-adjusting liner assembly of FIG. 9 where the spring is fully contracted.

FIG. 10b is a cross-sectional view of a portion of the self-adjusting liner assembly of FIG. 9 where the spring is fully expanded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The detailed description set forth below in connection with the appended drawing is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

FIG. 1 is a cross-sectional view of a prior art conventional single stage centrifugal pump 10. Centrifugal pump 10 comprises a stationary casing (volute) 20 having a suction inlet 22 which is the point of entry of the slurry. Housed within the stationary casing 20 is an impeller 14 and a shaft 12 for rotating the impeller 14. Typically, the shaft is coupled to a motive power such as an electric motor (not shown). Impeller 14 has a gland side shroud 31 and a suction side shroud 32. The impeller vanes 24 are located in between the gland side shroud 31 and the suction side shroud 32, and serve to accelerate the fluid towards the high-pressure region 28.

The slurry to be pumped enters the pump via suction inlet 22 (see arrows 13) and is forced at high pressure through the rotating impeller 14 into the high pressure region 28 inside the pump casing 20 from where it is discharged via a discharge pipe (not shown). However, some of the slurry will tend to flow from the high pressure region 28 back into the low pressure region 30 in the suction inlet 22. Therefore, the suction surface 18 of impeller 14 typically wears more quickly than the gland surface 16 due to the recirculation of the incoming slurry (see arrows 11). Thus, a suction liner 26 is provided, which liner can be made from a variety of materials such as chrome white iron, elastomers and the like, as is known in the industry. The suction liner 26 takes up some of the clearance at the suction side 18 of the impeller 14 to reduce suction side 18 recirculation and the possibility of abrasive solids being trapped between the rotating impeller 14 and the casing 20 and suction liner 26.

However, during use of the pump 10, both the suction liner 26 and the impeller 14 wears and the space between the suction liner 26 and the impeller 14 increases, leading to increased recirculation and eventually the pump 10 needs to be shut down so that both the suction liner 26 and the impeller 14 can be replaced. It would be desirable to avoid the number of shut downs of the pump 10 which are necessary for replacing the suction liner 26 and/or impeller 14. One way to accomplish this would be to provide a self-adjusting suction liner assembly which would adjust during operation to continuously ensure that the space between the suction liner and the suction side of impeller is eliminated or kept at a minimum.

FIG. 2 shows one embodiment of a pump 110 which has been fitted with a self-adjusting suction liner assembly 180 of the present invention. In this embodiment, self-adjusting suction liner assembly 180 comprises suction liner 126 having an insert 142, which insert 142 can be seen more clearly in FIG. 5, and in the cross-sectional of self-adjusting suction liner assembly 180 in FIG. 3. As can be seen in FIG. 2, the substantially planar outer most surface 160 of inset 142, which comprises wear ring 154, lies essentially flush with impeller 114 and therefore prevents recirculation by blocking the flow of slurry (see arrows 115).

FIG. 4 is an isometric exploded view of the embodiment of the self-adjusting liner assembly 180 in FIG. 3. With reference now to FIGS. 3 and 4, annular liner 126 has a recess 144 which houses insert 142. Insert 142 comprises annular gasket 146, an annular bottom cartridge plate 148, annular wave spring 150, annular top cartridge plate 152 and annular wear ring 154. Wear ring 154 may be made from any wear resistant material known in the industry such as urethane, elastomers, tungsten carbide, chrome white iron and the like, or a combination thereof. Choice of material will be driven by the need to reduce friction and abrasive wear. It is understood than any resilient, compressible member such as a coil/compression spring or the like could be used, however, wave springs are more desirable as they generally reduce the spring height by as much as 50% while still exerting the same force and deflection as ordinary coil/compression springs. Each of annular gasket 146, annular bottom cartridge plate 148, annular top cartridge plate 152 and annular wear ring 154 further comprise a number of notches 162 around their respective peripheries, which, when the insert 142 is assembled, line up and slide over anti-rotation keys 164 located in the recess 144 of annular liner 126 to ensure that insert 142 does not rotate during operation of the slurry pump.

In use, initially, the wave spring 150 is essentially fully compressed and forces the outer surface 160 of wear ring 154 to be essentially flush against the suction side of impeller 114, as shown in FIG. 2. As wear ring 154 wears, however, the wave spring 150 continuously expands to provide a constant force on the wear ring 154, which allows the outer surface 160 to be continuously flush against the impeller. Thus, recirculation is continuously reduced, resulting in longer wear life for the pump parts. It is understood that the choice of annular spring, i.e., resilience member, will determine the forces desirable for the wear ring 154 on the suction side of impeller 114. Generally, excessive spring force is to be avoided, as this may result in excessive wear of the wear ring 154 and overheating due to excessive friction. Thus, generally, a relatively weak spring is desirable.

FIG. 6 describes an additional embodiment, where a fluid for lubrication and cooling is provided via multiple nozzles 290, which are fitted closely to holes formed in the wear ring 254. The fluid is forced through the wear ring by the aforementioned close fit, and enters a small groove (not shown) created on the surface of the wear ring 254 for the purpose of distributing the fluid along the full circumference of the wear ring. This groove may be extended, in a spiral or radial fashion, to the outer diameter of the wear ring 254, so that the cooling and lubricating fluid would tend to travel in that direction and carry contaminants away from the continuous sealing surface between the groove 291 and the inner diameter of the wear ring 254. The flow and pressure of the cooling and lubricating fluid would be monitored and controlled external to the pump, so it would be possible to find the minimum pressure required to overcome the spring pressure and create a thin film of fluid between the wear ring 254 and the impeller sealing surface 18, which is likely to greatly reduce the wear rate of these two surfaces.

FIG. 7 describes the sealing arrangement 170 of the wear ring 154 in the groove 144 created in the suction liner 126, the purpose of which is twofold. First, the seal must prevent flow from travelling from the high pressure region 28 to the low pressure region 30, along a path underneath the wear ring 154 and through the wave spring 150. Second, the seal must be located so that the fluid pressure at the outer diameter of the wear ring 154 has equal access to both the sealing face and the underside of the wear ring 154. This will prevent a net pressure imbalance on these two surfaces of the wear ring, which could result in a significant force that would overwhelm the wave spring. The seal should be located at the inner diameter of the wear ring, and should allow for axial travel of the wear ring in the groove 144, while maintaining a seal. An o-ring, lip seal or similar arrangement may be appropriate.

FIG. 8 describes a possible embodiment of the sealing face of the impeller 14, which may be lined with a material 200 other than chrome white iron, such as tungsten carbide, polyurethane, or any other material with desirable properties. Either the same or different materials as those used in the wear ring 154 may be employed here. The sealing face of the impeller 14 may be flush with the impeller surface 18, or it may be recessed (as shown in FIG. 8), so as to create a circuitous path for any leakage across the sealing face.

FIG. 9 is an isometric exploded view of another embodiment of a self-adjusting liner assembly 280 of the present invention. In this embodiment, annular liner 326 has a recess 344 which houses insert 342. Recess 344 comprises a number of holes 266 for receiving anti-rotation pins 368, to prevent rotation of the insert 342 during operation of the slurry pump. Insert 342 comprises an annular bottom steel plate 348, and annular top steel plate 352 and an annular spring 350 positioned therebetween. Both the annular bottom steel plate 348 and the annular top steel plate 352 further comprise a comparable number of holes 266 as the recess 344 of the annular line 326 to also receive anti-rotation pins 368 to prevent rotation of the insert 342 during operation of the pump.

Insert 342 further comprises O-ring 368 for providing the proper sealing arrangement for assembly 380. Annular liner 326 comprises a groove 357 for receiving O-ring 368. In this embodiment, wear ring 354 comprises a recess 355 for receiving steel plate 369. Generally, the wear ring is made of rubber, polyurethane, and the like. The embedded steel ring 369 provides structure to the wear ring 354, which wear ring can be made of more flexible, non-metallic materials. Furthermore, the embedded steel ring 369 may comprise threaded holes (not shown) to receive screws for attaching the wear ring 354 and steel ring 369 to the annular top steel plate 352. The annular bottom steel plate 348 contains threaded holes to receive screws for attaching the insert 342 to the annular liner 326. The assembly 380 is installed in the pump in the same manner as a regular annular liner with no self-adjusting insert 342 would be.

FIGS. 10a and 10b are partial cross-sectional views of the embodiment of the self-adjusting liner assembly 380 shown in FIG. 9. FIG. 10a shows the annular spring 350 of insert 342 in its full contracted state and FIG. 10b shows the annular spring 350 of insert 342 in its fully expanded state.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.

Claims

1. A self-adjusting liner assembly for installation within a centrifugal pump of the type having an impeller and a pump casing having a suction inlet, comprising:

a liner having a sealing end, the sealing end having at least one substantially planar outer most surface for contacting an outer surface of the impeller; and

a resilient member disposed in the liner, said resilient member providing a force so that the at least one outer most surface remains in substantially continuous contact with the outer surface of the impeller.

2. The self-adjusting liner assembly as claimed in claim 1, wherein the at least one outer most surface comprises a wear ring.

3. The self-adjusting liner assembly as claimed in claim 1, wherein resilient member is a spring.

4. The self-adjusting liner assembly as claimed in claim 3, wherein the spring is a wave spring.

5. The self-adjusting liner assembly as claimed in claim 2, wherein the liner includes a recessed portion for housing the resilient member and the wear ring.

6. The self-adjusting liner assembly as claimed in claim 1, wherein the liner is formed from a wear resistant iron such as chrome white iron.

7. The self-adjusting liner assembly as claimed in claim 2, wherein the wear ring is made from a material selected from the group consisting of urethane, tungsten carbide and chrome white iron.

8. The self-adjusting liner assembly as claimed in claim 1, further comprising a lubricating and cooling system for providing water to the at least one substantially planar outer most surface.

9. A self-adjusting liner assembly for installation within a centrifugal pump of the type having an impeller and a pump casing having a suction inlet, comprising:

a liner having a sealing end, the sealing end having a substantially planar outer most surface comprising a wear ring for contacting an outer surface of the impeller; and

a resilient member disposed in the liner, said resilient member providing a force so that the wear ring of the outer most surface remains in substantially continuous contact with the outer surface of the impeller.

10. The self-adjusting liner assembly as claimed in claim 9, wherein resilient member is a spring.

11. The self-adjusting liner assembly as claimed in claim 10, wherein the spring is a wave spring.

12. The self-adjusting liner assembly as claimed in claim 9, wherein the liner includes a recessed portion for housing the resilient member and the wear ring.

13. The self-adjusting liner assembly as claimed in claim 9, wherein the liner is formed from a wear resistant iron such as chrome white iron.

14. The self-adjusting liner assembly as claimed in claim 9, wherein the wear ring is made from a material selected from the group consisting of urethane, tungsten carbide and chrome white iron.

15. The self-adjusting liner assembly as claimed in claim 9, further comprising a lubricating and cooling system for providing water to the at least one substantially planar outer most surface.