Patent Document

PRIORITY TO RELATED APPLICATION 
     This application claims benefit of U.S. Provisional Application No. 61/523,478 filed Aug. 15, 2011, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF INVENTION 
     This invention relates to centrifugal pumps and particularly to an anti-air locking system for such a pump. 
     BACKGROUND OF THE INVENTION 
     Centrifugal pumps are well known devices employed to pump fluids from one location to another. Many pumps today are called upon to operate on critical projects over a wide range of capacities without any manual intervention. For these applications, the pumps must be able to operate continuously without interruption. 
     A common problem with centrifugal pumps is that they do a very poor job of pumping gas or multiphase fluids and can easily become air-locked or “vapor-locked” causing them to deliver reduced performance and ultimately lose prime without warning. Centrifugal pumps can become air bound from many sources such as vortexing from improper suction line submergence, leaks on the suction side of the pump, entrained air in the pumping fluid, cavitation due to poor suction conditions and from suction recirculation. Some of these problems can be controlled to some extent by various means but all of them cannot be completely eliminated. 
     Suction recirculation is one of the major causes of air-locking in centrifugal pumps and is very difficult to prevent. Suction recirculation is a phenomenon that occurs in all centrifugal pumps when operated at off-peak performance. The capacity at which suction recirculation occurs is directly related to the design suction specific speed of the pump. The higher the suction specific speed, the closer will be the beginning of recirculation to the capacity at best efficiency. 
     Suction recirculation is the reversal of flow at the impeller eye. At operation away from best efficiency, a portion of the flow is redirected out of the impeller eye (instead of through the impeller exit vane tips) in a swirling motion due to the mismatch between the incoming fluid flow and the rotation of the impeller inlet blades. The swirling fluid travels out of the impeller eye upstream of the impeller inlet into the suction piping causing a distortion of the fluid pressure field. In the fluid pressure field, the heavier fluid is thrown outward by the centripetal action of the rotating impeller blades while the lighter vapor (air) is centrifuged toward the center of rotation. This creates a vapor bubble or blockage directly in the eye of the impeller preventing any new liquid from passing through the eye to the discharge side of the impeller. At this point, the pump will stop pumping (lose prime) and is said to be air-locked. In addition to not being able to perform its required task of pumping the fluid, air-locking also causes excessive noise and vibration and can damage the internals of the pump. Damaging the internals of the centrifugal pump could include pitting the impeller, wear ring of casing, rupturing the mechanical seals, excessively loading the bearings or bending or breaking the pump shaft. 
     The problem with air locking is very common for pumps that are used on varying capacity applications with back pressure such as sewer bypass projects where the pump&#39;s pumping capacity can often exceed the incoming fluid rates (called “snore” condition) during non-peak hours and the pump is required to pump through a pressurized forcemain. When this occurs, the fluid level in the sump drops below the minimum submergence level of the suction entrance allowing air to enter the suction piping. The air in the suction piping reduces the overall flow rate into the pump causing the pump to undergo suction recirculation. Once the suction recirculation cycle begins, the pump is no longer able to develop enough centrifugal head to penetrate the forcemain and the pump becomes air bound. 
     DESCRIPTION OF PRIOR ART 
     Many attempts have been made to solve this dilemma with limited results. 
     One method that has been tried is to manually turn the centrifugal pump off thus breaking the suction recirculation cycle and allowing the trapped air at the inlet of the impeller to escape. The pump is then restarted and in theory, the pump should regain normal pumping. The problem is that in practice, this does not always work because the conditions that existed to air-lock the pump in the first place usually are still present and the pump soon air-locks again. Also this method requires manual intervention to be able to discover the problem and manually start and stop the pump. One method to remove the manual intervention component is to incorporate a device to detect whether the pump is air-locked and stop and start it automatically but this method still has the same problem of not changing the conditions for which the pump will continually air lock. 
     Another method that has been tried is to provide a vent line at the high point of the pump casing to release the trapped air from the impeller. The problem with this method is that while the pump is running, the pressure field around the inlet of the impeller traps the air bubble at the eye preventing it from escaping through to the pump casing. 
     Another method that has been tried is to provide a recirculation line from the pump discharge directly into the eye of the impeller to try to force the air bubble out of the eye. The problem with this idea is that there is not enough centrifugal head developed from the outlet of the impeller to overcome the dynamic head at the eye diameter to break up the air bubble. 
     Another method that has been tried is to add an external priming system such as a vacuum pump, venturi or diaphragm pump to the suction of the pump to automatically strip off any air before it enters the pump. The problem with these systems is that they are ineffective at capturing the entrained air within the fluid and they are not able to counteract the pressure field caused by suction recirculation to remove the trapped air in the center of rotation. 
     Another method that has been tried is to completely drain the discharge line each time the pump loses prime thus taking the backpressure off the pump and reducing the centrifugal head required by the impeller to move the air through to the discharge. The problem with this method is that it can only be applied to gravity systems where the discharge pressure can be reduced by stopping the pump and not pressurized discharge systems such as sewer force mains and other parallel pumping applications into the same discharge line. 
     Another method that has been tried is to place an inducer on the shaft directly in front of the impeller to boost the pressure at the eye of the impeller to theoretically force the air through the eye. The problem with this concept is that each inducer has to be specifically matched to the impeller inlet geometry and is only effective over a narrow capacity range. Operation outside this narrow range actually causes the problem to worsen. 
     Many attempts have been made to modify existing impellers or design new ones to try to release the air bubble at the eye by drilling vent holes in the eye, providing vent channels through the vanes or adding small projections from the vanes but these methods are ineffective in releasing the trapped air in the center of rotation during suction recirculation; they have a tendency to clog when handling stringy materials; they reduce the structural integrity of the impeller and they reduce the overall efficiency and performance of the pump. 
     Many attempts have been made to redesign the geometry of the impeller to change the suction specific speed but these modifications fail to be able to reproduce the same desired performance characteristics of the original impeller and only serve to move the range of the onset of suction recirculation and not totally eliminate it. 
     Since many of the above-mentioned problems cannot be totally eliminated, it would be an advantage in the art to provide a means of preventing conventional centrifugal pumps from air locking during any or all of these events. 
     SUMMARY OF THE INVENTION 
     A principle object of this invention is to prevent loss of prime or “air-locking” in a centrifugal pump. 
     Another object of the present invention is to enable a centrifugal pump to handle multi-phase fluids without air locking, losing performance or causing damage to the internal parts of the pump. 
     Another object of the present invention is to enable a centrifugal pump to handle fluids with low vapor pressures without air locking, losing performance or causing damage to the internal parts of the pump. 
     Another object of the present invention is to enable a centrifugal pump to handle multi-phase fluids without air locking, losing performance or causing damage to the internal parts of the pump without requiring constant monitoring or action by the operator. 
     Another object of the present invention is to enable a centrifugal pump to handle multi-phase fluids without air locking, losing performance or causing damage to the internal parts of the pump without requiring any external means such as vent lines, air release valves, discharge drain lines, etc. 
     Another object of the present invention is to enable a centrifugal pump to handle multi-phase fluids without air locking, losing performance or causing damage to the internal parts of the pump without requiring any modifications to the centrifugal pump impeller. 
     Another object of the present invention is to enable a centrifugal pump to handle multi-phase fluids without air locking, losing performance or causing damage to the internal parts of the pump while operating against a positive discharge head. 
     Another object of the present invention is to enable a centrifugal pump to handle multi-phase fluids without air locking, losing performance or causing damage to the internal parts of the pump while handling fluids containing solids and stringy material. 
     Another object of the present invention is to enable a centrifugal pump to operate during off-peak performance/suction recirculation without air locking. 
     Another object of the present invention is to enable a centrifugal pump to operate without air locking when the internal parts become worn and the clearance between the impeller and wear plate/rings increases. 
     Another object of the present invention is to enable a centrifugal pump to operate during “snore” conditions where air enters the suction line via the vortex created from improper suction line submergence in the sump without air locking. 
     Another object of the present invention is to enable a centrifugal pump to operate without air locking without causing adverse affects such as excessive suction pressure loss or reduction in flow to the centrifugal pump. 
     An object of the stationary vanes mounted in the centrifugal pump intake structure and priming chamber is to break up the swirling fluid that back flows from the suction eye of the impeller into the suction inlet by generating small vortices or swirls opposite to the main swirl. This produces rigorous cross stream mixing between the swirling fluid and main incoming fluid which breaks up the air pocket at the entrance of the impeller thus allowing the air to be effectively purged by the priming chamber. 
     An object of the present invention is that it has an automatic self cleaning feature in that as the centrifugal pump impeller becomes clogged with rags or stringy material, the flow to the impeller will be lessened and the pump will begin to operate farther and farther away from BEP (best efficiency point) causing the impeller to undergo suction recirculation. The force of the back flowing swirl of fluid from the impeller during this suction recirculation will then clear any debris from the impeller or stationary vanes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will hereinafter be described with reference to the accompanying drawing in which: 
         FIG. 1  is a perspective view of the elements of the present invention with the lower priming chamber and suction cover partially shown to view vanes therewithin. 
         FIG. 2  is a longitudinal cross sectional view of the elements of the present invention. 
         FIG. 3  is an exploded view of the elements of the present invention. 
         FIG. 4  is a partial view taken generally along line  1 - 1  in  FIG. 3 . 
         FIG. 5  is an illustration showing the direction of fluid flow across one of the replaceable secondary anti-rotation vanes of the present invention. 
         FIG. 6  is an illustration showing the direction of fluid flow across one of the stationary primary anti-rotation vanes located in the lower section of the priming assembly of the present invention. 
         FIG. 7  is a partial view of another embodiment of the replaceable secondary anti-rotation vanes mounted in the pump suction cover of the present invention where the fluid flow  70 ′ is directly into the suction cover  25 ′. 
         FIG. 8  is an illustration showing the direction of fluid across another embodiment of one of the replaceable secondary anti-rotation vanes. 
         FIG. 9  is a partial view of another embodiment of the stationary primary anti-rotation vanes located in the lower section of the priming assembly. 
         FIG. 10  is a schematic illustration showing the direction of fluid across another embodiment of a stationary primary anti-rotation vane located in the lower section of the priming assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A centrifugal pump system according to the present invention is shown generally at  100  in  FIG. 1 . Pump system  100  includes a centrifugal pump  9 , a priming device  5 , a priming chamber assembly  8  and discharge non return valve  55 . The centrifugal pump  9  may contain a separate suction cover  25  or it can be an integral part of the pump casing  10  to permit the mounting of one or more strategically located replaceable anti-rotation vanes  65 . The priming device  5  can consist of any vacuum producing mechanism including, but not limited to, a vacuum pump, venturi, or diaphragm primer. The priming chamber assembly  8  consists of two sections; an upper section  50  and lower section  35  so that the upper portion  50  may be removed to allow access to the pump for inspection, cleaning, maintenance, etc. The upper section  50  is attached to the top of the lower section  35  about midway of the length of the lower section  35  of the priming chamber assembly  8 . However, certain embodiments may include the upper section  50  intersecting into the lower section  35  at any point along the length of the lower portion of the priming chamber  8 . The lower portion  35  of the priming chamber assembly  8  contains one or more strategically located anti-rotation vanes  60  that are positioned relative to the anti-rotation vanes  65  in the centrifugal pump suction cover  25  or casing  10  to remove air and prevent the centrifugal pump  9  from air locking. 
     The size, shape, number and exact placement of the stationary anti-rotation vanes  60  and removable anti-rotation vanes  65  are determined based on the specific geometry of the centrifugal pump impeller. Test data appears to indicate that impellers with a higher rotational velocity require more anti-rotation vanes then those with a lower rotational velocity. One possibility for this outcome has to do with the higher energy required by impellers with greater rotational velocities to generate head (pressure) inside the pump casing due to the axial components of the flow vector. It is possible that other factors may play a part in this determination. 
     The stationary anti-rotation vanes  60  may also be referred to as the primary stationary vanes  60 . The replaceable anti-rotation vanes  65  may also be referred to as secondary replaceable vanes  65 . The lower section  35  may also be described as an intake plenum  35 . The fluid flow  70  is shown entering the entrance of the lower section  72 . The fluid flow  70  may include fluid  70  with entrained air along with other possible substances (not shown) which may include suspended dirt, rags or stringy material (not shown). The primary stationary vanes  60  includes a curved forward section  60   a  (best shown in  FIG. 6 ) proximal to the entrance  72  of the lower section  35 . The primary stationary vanes  60  with their curved forward section  60   a  help to prevent rags and stringy material from catching and accumulating on the surface, while the primary stationary vanes  60  aid in the removal of air to prevent the centrifugal pump system  100  from air locking. 
     As shown in  FIG. 2 , the centrifugal pump  9  is comprised of a shaft and bearing assembly  13  connected to an impeller  12  via a washer  16  and bolt  17 . A pump casing  10  with replaceable wear ring  20 , rear plate  14  and suction cover  25  is mounted to the shaft and bearing assembly  13 . The suction cover  25  permits mounting of one or more replaceable strategically located anti-rotation vanes  65 . In some embodiments the suction cover  25  may be an integral part of the pump casing  10 . The priming chamber assembly  8  is comprised of an upper section  50  and lower section  35  with a removable baffle  45  in between to prevent any fluid from splashing into the upper section  50  and possibly passing through to the priming device  5 . The lower section  35  of the priming chamber assembly  8  contains one or more strategically located anti-rotation vanes  60  that are positioned relative to the anti-rotation vanes  65  in the centrifugal pump suction cover  25  or casing  10 , if suction cover  25  is integral to pump casing  10 , to remove air and prevent the centrifugal pump  9  from air locking. In one embodiment, the lower section  35  has 3 vanes, these vanes are oriented with the flowing fluid which is heading to the suction cover  25  and then to the rotating pump impeller  12 . 
     The centrifugal pump system  100  is shown with its components in an exploded perspective view in  FIG. 3 . The component assembly of the centrifugal pump  9  may generally comprise a rotating pump impeller  12 , with pump casing  10 , wear ring  20 , suction cover gasket,  15  and suction cover  25 . The suction cover  25  or casing  10  contains one or more replaceable strategically located anti-rotation vanes  65  and anti-rotation vane bolts  66  for fastening the anti-rotation vanes  65 . The component assembly of the priming chamber assembly  8  may generally comprise an upper section  50 , lower section  35 , removable baffle  45  in between with gaskets  40 . Intermediate the suction cover  25  and the lower section  35  is a lower section gasket  30 . The lower section  35  may also be referred to as the input plenum  35 . The lower section  35  of the priming chamber assembly  8  contains one or more strategically located anti-rotation vanes  60  that are positioned relative to the anti-rotation vanes  65  in the centrifugal pump suction cover  25  or casing  10  to remove air and prevent the centrifugal pump  9  from air locking. 
     As best seen in  FIG. 4 , the replaceable anti-rotation vanes  65  in the suction cover  25  or pump casing  10  are positioned relative to the stationary anti-rotation vanes  60  in the lower section  35  of the priming chamber assembly  8 . The lower section  35  of the priming chamber assembly  8  is connected to the upper section  50 , and includes a replaceable baffle  45  sandwiched in between. The replaceable baffle  45  permits air to enter the priming system upper section  50  for removal, while allowing the water flow to continue into the rotating impeller  12 . The size, shape, number and exact placement of the stationary vanes  60  and the replaceable vanes  65  are determined based on the specific geometry of the centrifugal pump impeller. 
     In one embodiment the geometry of the stationary anti-rotation vanes  60 , are arranged such that the three longer vanes  60  affixed to the inner wall of the intake plenum or the priming device lower section  35  are arranged at the 3, 6 and 9 o&#39;clock positions. In a circular cross-section of the priming device lower section  35 , where 12 o&#39;clock position is considered 0 (zero) degrees, the three longer vanes  60  would be located at 90 degrees, 180 degrees and 270 degrees in the clockwise direction respectively. It is to be understood that the plurality of longer vanes  60  may be positioned at other angular separations then discussed above and further the number of the plurality of longer vanes  60  is not limited to 3 (three). 
     In this embodiment, the four replaceable anti-rotation vanes  65  are affixed to the inner wall of the suction cover  25  are arranged at the 2, 5, 8 and 11 o&#39;clock positions which appear to be a configuration which permits maximum effectiveness. In a circular cross section of the suction cover  25 , where 12 o&#39;clock position is considered 0 (zero) degrees, the four replaceable anti-rotation vanes  65  would be located at 60 degrees, 150 degrees, 240 degrees and 330 degrees in the clockwise direction respectively. This places the four replaceable anti-rotational vanes about 90 degrees apart from one another. It is to be understood that the plurality of shorter vanes  65  may be positioned at other angular separations then discussed above and further the number of the plurality of shorter vanes  65  is not limited to 4 (four). 
     It can be seen that the two types of anti-rotation vanes  60  and  65  are proximal to each other, and both are located joined to the wall of a specific pump intake structure in a radial fashion, both projecting outwardly into the fluid flow path  70 , the primary stationary anti-rotation vanes  60  on the lower section  35  and the removable secondary anti-rotation vanes  65  on the adjacent suction cover  25 , or in some embodiments in the entrance to the centrifugal pump housing itself. 
     Tests show that an acceptable range for the placement of the replaceable shorter anti-rotation vanes  65  relative to the longer anti-rotation vanes  60  is a about 15 to 35 degrees from each other. The optimum angle for the 2, 5 and 8 o&#39;clock positions is about 30 degrees clockwise from the three longer anti-rotation vanes  60  and the shorter anti-rotation vane at 11 o&#39;clock position is about 30 degrees from 12 o&#39;clock position of the suction cover  25 . It is to be understood that primary anti-rotation vanes  60  do not move. 
     The secondary anti-rotation vanes  65  are secured by mechanical fastener to the interior cylindrical sidewall of the suction cover  25 . Once secured, the anti-rotation vanes  65  do not move either. They can be replaced or may be placed in another position, but once fastened they remain stationary. 
       FIG. 5  shows the general configuration of the replaceable anti-rotation vane(s)  65  that are mounted in the suction cover  25  or pump casing  10  which contain a mounting pad  65   a  and one or more mounting holes  65   b . The replaceable anti-rotation vane  65  includes a curved or angularly cut section at the entrance  65   c  to prevent rags or stringy materials from catching and accumulating on the surface. The size, shape, number and exact placement of the replaceable anti rotation vanes  65  are determined based on the specific geometry of the centrifugal pump impeller or other centrifugal pump system  100  considerations. This diagram also shows the relationship of the incoming fluid flow  70  and the rotating reversing flow of fluid  80  from the impeller  12  onto the anti-rotation vane  65 . 
       FIG. 6  shows the general configuration of the stationary anti-rotation vane(s)  60  in the lower section  35  of the priming chamber assembly  8 . The anti-rotation vane(s)  60  include a curved section at the entrance  60   a  to prevent rags and stringy materials from catching and accumulating on the surface. The size, shape, number and exact placement of the stationary vanes  60  are determined based on the specific geometry of the centrifugal pump impeller or other centrifugal pump system  100  considerations. This diagram also shows the relationship of the incoming fluid flow  70  and the rotating reversing flow of fluid  80  from the impeller  12  onto the anti-rotation vane  60 . 
       FIG. 7  shows another embodiment of the invention whereby the replaceable anti-rotation vanes  65 ′ in the in the centrifugal pump suction cover  25 ′ have a curved shape opposite of the direction to the swirling fluid  80 ′ to create vortices which counteract the low pressure zone in the center of the fluid flow  70 ′. In  FIG. 7  six of the smaller replaceable anti-rotation vanes  65 ′ are shown each separated by 60 degrees. The number of smaller replaceable anti-rotation vanes  65  is not limited to 4 as shown in  FIG. 4 or 6  as shown in  FIG. 6 , but is chosen appropriately to meet the requirements of the centrifugal pump system  100  and variances in the components thereof, such as the impeller. In  FIG. 5 , a replaceable anti-rotation vane  65  is shown and it should be noted that it does not have a curvature  65   d  (best seen in  FIG. 8 ) as the replaceable anti-rotation vanes  65 ′. It is to be understood that circumstances may exist where a mixture of the 2 different replaceable anti-rotation vanes  65  and  65 ′ may be desirable and such a configuration is contemplated as part of this invention. 
       FIG. 8  shows a representative replaceable vane  65 ′ with mounting tab  65   a ′ and mounting tab holes  65   b ′ for securing the tab to the centrifugal pump suction cover  25 ′. The replaceable vane  65 ′ includes a curved section  65   c ′ at the entrance to the fluid flow  70 ′ to prevent rags and stringy material from catching and accumulating on the surface. The anti-rotation vane  65 ′ has a curved shape  65   d  opposite of the direction to the swirling fluid  80 ′ to create vortices which counteract the low pressure zone in the center of the fluid flow  70 ′. 
       FIG. 9  shows the general configuration of the stationary vanes  60 ′ in the lower section  35 ′ of the priming chamber assembly. The upper section  50 ′ of the priming chamber assembly is also shown. Removable baffle  45 ′ is shown intermediate the lower section  35 ′ and the upper section  50 ′. The upper section  50 ′ may be removed to clean elements of the lower section  35 ′ with relative ease. Additionally, the removable baffle  45 ′ keeps the fluid out of the upper section  50 ′ which is part of the system which prevents the centrifugal pump from experiencing an air lock condition. It will be noted that a plurality of stationary anti-rotation vanes  60 ′ are located at about the same angular displacement from each other as previously discussed. Also, the plurality of stationary anti-rotation vanes are joined to the wall of the lower section  35 ′ projecting outward radially into the fluid flow  70 ′. The stationary anti-rotation vanes  60 ′ include a plurality of apertures or holes  60   b  present along its length. The number of apertures  60   b  is determined by any of a variety of requirements of the centrifugal pump system  100  such as variances in the components thereof, such as the impeller, fluid flow rates, composition of air-fluid froth being pumped, as well as other dynamic fluid and pump material properties. Additionally, it has been considered to employ both stationary anti-rotation vanes  60  with the stationary anti-rotation vanes  60 ′ when appropriate circumstances exist. 
       FIG. 10  shows a schematic of the stationary vanes  60 ′ that are mounted in the lower section of the priming chamber whereby the vanes  60 ′ have holes  60   b  located parallel to the swirling fluid  80 ″ that create additional discrete vortices which counteract the low pressure zone in the center of the fluid flow  70 ″. The stationary vane  60 ′ includes a curved section  60   a ′ at the entrance to the fluid flow  70 ″ to prevent rags and stringy material from catching and accumulating on the surface. 
     Finally, it is to be understood that various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements of parts without departing from the spirit or ambit of the invention. This includes, but is not limited to, the size, number and placement of both the primary and secondary vanes, the geometrical configuration of both the primary and secondary vanes, and the position of the components of the priming chamber assembly with respect to one another. 
     To recap, the invention is directed to a centrifugal pump for imparting a flow to a fluid which includes a priming chamber having an inlet for receiving a fluid, said priming chamber affixed to a centrifugal pump housing, said centrifugal pump housing including a centrally disposed rotating impeller therein, said centrifugal pump housing having an exit for discharging a fluid, a fluid flow path intermediate said inlet and said exit, said priming chamber having a cylindrical section with an air exit located through an opening through said cylindrical section, said cylindrical section having an interior wall, a plurality of primary vanes attached to said interior wall of said cylindrical section projecting into said fluid flow path toward said rotating impeller, whereby air present in a flowing fluid will be removed through said air exit. 
     Another way of stating the gist of the invention would be having a centrifugal pump which includes an intake plenum, said intake plenum have an intake plenum entrance and an intake plenum exit, a suction cover, said suction cover having a suction cover entrance and a suction cover exit, said intake plenum exit affixed to said suction cover entrance, a rotating impeller in a pump casing, said pump casing having a pump casing entrance and a pump casing exit, said suction cover exit affixed to said pump casing entrance, said intake plenum being cylindrical and having an interior cylindrical sidewall, said intake plenum having an air exit located through an opening through said cylindrical sidewall, a plurality of primary vanes, said primary vanes are affixed into said interior cylindrical sidewall, where said plurality of said primary vanes prevent air lock during operation of said centrifugal pump. 
     While the invention has been described in its preferred form or embodiment with some degree of particularity, it is understood that this description has been given only by way of example and that numerous changes in the details of construction, fabrication, and use, including the combination and arrangement of parts, may be made without departing from the spirit and scope of the invention.

Technology Category: 2