Patent Publication Number: US-5833434-A

Title: Device for regulating the output of a verticle-axis centrifugal pump

Description:
FIELD OF THE INVENTION 
     The present invention pertains to a device for regulating the output of constant-speed vertical-axis centrifugal pumps. 
     REVIEW OF RELATED TECHNOLOGY 
     In lifting stations with fluctuating quantities of water to be lifted, for example municipal wastewater or rainwater, a simple device serves to regulate the output according to the varying quantities of accumulating liquid, without requiring adjustment of the revolutions of the pump, by providing for a functional design of the pump sump. 
     The device comprises an open-top cylinder placed in the suction sump, having an inlet opening tangential to the direction of rotation of the pump, ending above the bottom of the cylinder; and a coaxial suction pipe, the upper end of which is attached to the suction side of the pump, projecting into the cylinder. This device is described in the Swiss Patent 533 242. 
     If enough water has accumulated for the water line to rise sufficiently high above the edge of the cylinder, the water flows over said edge into the cylinder and straight to the suction pipe of the pump, without resulting in a noticeable difference in the water levels inside and outside the cylinder; and the pump thus achieves its full output according to its characteristic curve. If the quantity of accumulating water decreases, less and less water can flow over the edge of the cylinder, and the water level inside the cylinder drops below the water level outside the cylinder. This results in increasing quantities of water entering the cylinder through the tangential inlet opening, causing a swirling movement of the water inside the cylinder that accelerates as the difference between the water levels increases. This resulting swirling flow in the direction of rotation of the pump causes a proportionate reduction in the output of the pump, so that the output is adjusted to the respective reduced quantity of accumulating water. With this method, the output of a pump can be reduced from 100% to approximately 50%. The lowest lifting level is predetermined by the cross-section of the tangential inlet opening. 
     To expand the regulating range to a lower quantity, the tangential inlet opening was replaced by a downward sloped channel extending from a point slightly below the level of the cylinder edge and tangentially protruding through the cylinder wall. The lowest lifting level was thus no longer limited by the entrance cross section of a pipe; however, in practical application it was found that the inlet flow tangentially entering the swirling flow via the channel produced an undesirable effect. Air entrapped due to waves and cross-currents, entering the suction pipe of the pump, caused unexpected disruptions in the output flow of the pump. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has an object, among others, to overcome deficiencies in the prior art such as noted above. 
     The present invention is aimed at improving the above device so as to attain a smooth flow that is free from cross-currents and is not subject to unexpected disruptions and to attain a substantially lower minimum output. 
     In the present invention the gyroscopic movement, of both the inlet flow and also the swirling flow of the liquid inside the casing, are intensified before they are forced together, so that the current of the tangential inlet flow forces the transported medium against the outer wall of the inlet channel in the form of a coaxial spiral prior to discharging it into the cylindrical casing, thus placing the open liquid level in a roughly vertical level. 
     The swirling liquid inside the cylindrical casing, in turn, also forms a vertical surface when it crosses the inlet opening in the casing wall and is forced together, at an acute angle, with the above-described approximately vertical liquid level of the inlet flow, whereby said inlet flow accelerates the swirling flow inside the casing without causing any cross-currents. The gyroscope movement inside the casing is further intensified and concentrated in the same direction based on the formation of a channel in the cylindrical casing wall at the height of the suction opening, or the pump suction port, respectively, that is coaxially encased by the suction opening, with the upper wall of the channel reducing the diameter of the casing to a small diameter. 
     In this manner all floating matter, such as scum and liquids with a lighter specific weight, can be suctioned off by the pump in a larger stable area before the output flow is disrupted. This self-cleaning effect is utilized especially in wastewater pumping stations to reduce undesirable odors and eliminate the need for purification efforts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects and the nature and advantages of the present invention will become more apparent from the following detailed description of an embodiment taken in conjunction with drawings, wherein: 
     FIG. 1 is a vertical section, along the line I--I in FIG. 2, through a centrifugal pump with a volume control device between 100% and a mean control range; 
     FIG. 2 is a plan view of FIG. 1; 
     FIG. 3 is a vertical section along the line IV--IV in FIG. 4, for a volume regulation down to the minimum range; and 
     FIG. 4 is a horizontal section, along the line III--III in FIG. 3, illustrating the minimum output. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The vertical-axis, end-suction circumferential pump 1 shown in FIG. 1 and 2, has a suction pipe 2 connected to the suction connection 1a, with the flared, non-attached suction opening 2a of the suction pipe 2 located at a distance above the bottom 3a of a cylinder 3 that coaxially encompasses the suction pipe 2 at a radial clearance. At the height of the pump suction port of the suction opening 2a, an inlet pipe 4 tangential to the direction of rotation of the pump 1 opens into the wall of the cylinder 3. A channel 4a, sloping downward from a higher elevation, is formed in the wall of the cylinder 3, penetrating the same in the area 4b and forming the inlet opening into the inlet pipe 4. 
     When the liquid level X in the suction sump 5 is high, the channel 4a and the upper edge 3b of the cylinder are sufficiently flooded so that the transported medium inside the cylinder 3 flows to the suction opening 2a in the direction of the arrow a, without any noticeable drop in pressure, where it is suctioned off by the pump 1 operating at its maximum output based on its characteristic curve. 
     If the inflow quantity decreases, the liquid level drops from X to Y. In the process, less and less water can flow over the cylinder edge 3b, causing the liquid level inside the cylinder 3 to drop even lower than the level inside the suction sump 5 and resulting in a difference of level δh from the level Y in the suction sump 5. As a result, increasing quantities of liquid enter the cylinder 3 via the tangential inlet pipe 4, causing an intensifying swirling movement of the liquid inside the cylinder, in the direction of the pump rotation. This decrease in the relative velocity inside the impeller results in a reduced output of the pump, until the output corresponds to the accumulating quantity of liquid. 
     If the accumulating quantity of liquid decreases even further, a partial filling of the entrance cross-section of the inlet pipe 4 results, which, in the case of a straight-line discharge of the flow, would produce turbulence in the liquid ring swirling inside the cylinder, and result in air entrapments, which is prevented by the following means: In FIG. 4, the boundary lines of the jet flow of the entering liquid are shown in the form of lines of alternating long and double short dashes. The inlet pipe spirals downward at an incline (helically) to the lower portion of the cylinder 3, and penetrates the wall 4b of said cylinder. The outer wall 4c of the inlet pipe 4 continues to spiral downward in the form of a channel to the end of the penetration area at point 3c and discharges through the cylinder wall in a tangential direction. The liquid that enters through the inlet pipe 4, is subjected to a centrifugal force in the curved section 4c of the outer wall, causing the liquid to be forced against the outer wall 4c of the pipe, so that the inner, open level 4d of the liquid is located in an approximately vertical position. 
     The liquid swirling inside the casing, marked with a line of separated close dots, crosses the suction pipe section 4b with its outer open level of the liquid, as shown by the knotted line of dots strung along a line (forming a straight flow). The inlet flow with its level 4d and the swirling flow with its outer level 4e are united, free of turbulence, at an acute angle α at the point 4f, providing for an optimum transfer of the energy from the inlet flow to the swirling flow. 
     The effect of concentrating the flow and enhancing the swirling movement is intensified by the design of the lower cylinder wall at the height of the suction opening 4b, or suction port 2a, respectively, in the form of a channel 3d, the upper wall of which reduces the diameter of the cylinder 3 to a small diameter 3e and stabilizes the lowest liquid level with its open inner level 4g, both regarding position and angle, and prevents air from unpredictably entering into the suction opening 2a. The upper wall of the casing 3, which reduces the diameter of the casing to a smaller diameter 3e, includes a lip (seen as a circle in FIG. 2 and as a cusp in FIGS. 1 and 3). Below this lip the channel 3d preferably is shaped as a portion of a toroid, as seen in the drawing. A toroid defines a central geometric axis, which is denoted herein as a channel center. 
     The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without undue experimentation and without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. The means and materials for carrying out various disclosed functions may take a variety of alternative forms without departing from the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.