Patent Application
20130216366
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.
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.
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:
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.
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:
a is a cross-sectional view of a portion of the self-adjusting liner assembly of
b is a cross-sectional view of a portion of the self-adjusting liner assembly of
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.
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.
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
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.
a and 10b are partial cross-sectional views of the embodiment of the self-adjusting liner assembly 380 shown in
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.
| Number | Date | Country | |
|---|---|---|---|
| 61597332 | Feb 2012 | US |
