Abstract:
A self-priming centrifugal pump including a supplementary vacuum pump and a float valve. The vacuum pump serves to draw liquid to the pump for priming and the float valve shut of flow to the vacuum pump when liquid reaches a predetermined level to prevent entry of liquid into the vacuum pump. In some embodiments the float valve includes an o-ring valve seal and the vacuum pump includes an oil delivery system to distribute oil from an oil reservoir to improve lubrication.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 09/258,833, filed Feb. 26, 1999, U.S. Pat. No. 6,409,478 the disclosure of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to centrifugal pumps and more particularly to centrifugal pumps with vacuum-assisted self-priming. 
     BACKGROUND 
     Centrifugal pumps are the most common pumps for moving liquids from place to place and are used in irrigation, domestic water systems, sewage handling and many other applications. Liquid is urged through the pump by a spinning disk-shaped impeller positioned inside an annular volute. The volute has an eye at the center where water enters the pump and is directed into the center of the impeller. The rotation of the impeller flings the liquid outward to the perimeter of the impeller where it is collected for tangential discharge. As the liquid is driven outward, a vacuum is created at the eye, which tends to draw more fluid into the pump. 
     One of the principle limitations on the use of centrifugal pumps is their limited ability to draw fluid for priming when starting from an air-filled or dry condition. The impeller, which is designed to pump liquids, often cannot generate sufficient vacuum when operating in air to draw liquid up to the pump when the standing level of the liquid is below the eye of the pump. Once the liquid reaches the eye, the outward motion of the liquid away from the eye creates the vacuum necessary to draw a continuing stream of liquid. However, until liquid reaches the impeller, very little draw is generated. 
     In many applications, such as dewatering construction sites or pits, the standing water level is many feet below the level of the pump. As a result, when the pump is not in operation, there is no water in the pump. To begin pumping, the pump must first self-prime by drawing water up to the pump from the standing water lever or the pump must be manually primed by being filled with water from a secondary source. Since manual priming requires user intervention, it is generally preferable that the pump be capable of self-priming. This is particularly true in applications, such as dewatering, where pump operation is intermittent and the need for priming recurrent. 
     To supplement the limited capability of the spinning impeller to generate vacuum, an auxiliary vacuum pump is sometimes used with centrifugal pumps. This vacuum pump, which is typically a positive displacement-type pump, has an intake near the eye of the impeller. As the vacuum pump draws a vacuum, water is drawn up to the centrifugal pump for priming. A float valve is provided between the vacuum pump and the input near the eye of the impeller to close off the intake when the centrifugal pump has been primed. This valve prevents water from reaching and possibly damaging the vacuum pump. 
     In pumps used for dewatering, reliability is of critical importance. If a pump for dewatering a site fails, the site and equipment at the site may be flooded. Although centrifugal pumps are relatively simple and reliable, in the past, the valves and vacuum pumps used to for self-priming have proven less reliable. For instance, prior float valves have not reliably shut off when water reached the pump, thereby allowing water to enter and damage the vacuum pump. Similarly, prior vacuum pumps have exhibited unacceptable internal failure rates even when the float valve is operating correctly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a pump according to the present invention. 
     FIG. 2 is an enlarged view of a portion of the pump of FIG.  1 . 
     FIG. 3 is a side elevational view of a vacuum pump assembly according to the present invention. 
     FIG. 4 is a partial cross sectional view of part of a vacuum pump assembly taken along lines  4 — 4  in FIG.  3 . 
     FIG. 5 is a partial cross-sectional view of a float valve assembly according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     A pump according to the present invention is shown generally at  10  in FIG.  1 . Pump  10  includes a centrifugal section  12 , a float valve assembly  14  and a vacuum pump assembly  16 . The centrifugal section includes an intake  18  leading to an eye  20  of a volute  22 . The volute has an output  24  to which is connected a check valve  26  to prevent reverse flow when the pump is priming or idle. An impeller  28  is mounted inside the volute on a shaft  30 . The shaft is supported by a bearing housing  32 , which is mounted on a pedestal  34 . A bracket or bell housing  36  connects the bearing frame to a motor (not shown). A combustion motor is often used for dewatering applications because it eliminates the need for electrical power, although an electric motor may be used as well in which case the bell housing is not required. Shaft  30  has a drive end  38 , which is driven by the motor. 
     The portion of pump  10  described above is a standard centrifugal pump, such as a Cornell Pump Company Model No. 14NHGH-F18DB. It should be noted that this pump has a sealing system that allows the pump to safely run dry for extended periods of time. This system includes an oil reservoir to provide cooling. While the centrifugal pump will efficiently pump water or other liquids, it will not draw significant vacuum when operated dry. Priming is accomplished with the previously mentioned vacuum pump assembly and regulated by the float valve. 
     As shown in FIG. 2, vacuum pump assembly  16  is mounted to the top of bearing housing  32  on a mounting plate  50 . A housing or base  52  is bolted to the plate and supports a shaft  54  on bearings  56 . See FIGS. 2 and 3. Base  52  also contains an oil reservoir  58 . Shaft  54  projects through one end of base  52  to support a pulley  60 . A drive linkage in the form of a belt  62  connects pulley  60  to a pulley  64  mounted on drive end  38  of shaft  30 , passing through bell housing  36 . Thus, when the motor turns shaft  30  to turn impeller  28 , the belt and pulleys simultaneously turn shaft  54  in vacuum pump assembly  16 . A guard  65  covers the pulley and belt. 
     Shaft  54  includes an eccentric section  66  to which is mounted a connecting rod  68 . See FIG.  4 . Connecting rod  68  is tied to a slider  70  by a pin  72 . An oil delivery system in the form of two oil flingers  74  attached to shaft  54  throws oil in the oil reservoir up onto the connecting rod, pin and slider to insure adequate lubrication. The flingers are rigid and similar to a thumb screw screwed into shaft  54 . In should be understood, that the flingers could also take many other configurations, such as flexible strips or a partially submerged disk which could likewise flip oil onto components above the oil level. Alternatively, some type of pumping system could be provided to convey oil onto the moving components that are not in contact with the oil bath. 
     Slider  70  extends upward through a sleeve section  76  that is bolted to the top of base  52 . Sleeve  76  includes two seals  78  and a bushing  80  to guide slider  70 . A grease fining  82  allows introduction of grease into a cavity  84  between the seals. 
     A diaphragm housing  86  is mounted to the top of sleeve  76  and encloses a pump chamber that houses a diaphragm  88 . Diaphragm  88  is mounted to the top of slider  70  and is driven up and down with the slider when shaft  54  rotates. As the diaphragm moves up and down in the pump chamber, air is moved by operation of three check valves. As the diaphragm moves up in the chamber, air is drawn through an intake check valve  90  positioned in an intake port  92 . The check valve includes a disk-shaped rubber seal  94 , which is positioned over a number of holes  96  in the chamber in the intake port. As the diaphragm rises and generates a vacuum, the seal is lifted and air is drawn into the lower portion of the chamber. 
     At the same time that air is being drawn into the lower portion of the chamber, the diaphragm is compressing air in the upper portion and forcing it into an output port  98  through an output check valve  100  via holes  102 . Output check valve  100  is similar to intake check valve  90  and includes a seal  104  which lifts to release air as positive pressure is generated in the upper portion of the pump chamber. The output check valve is centered over the diaphragm to maximize flow rate through the output port. 
     After the diaphragm has completed its upward motion, it begins to move down, closing both the intake and output check valves. Subsequently pressure begins to drop above the diaphragm and rise below, causing a flexible rubber seal  110  in a diaphragm check valve  106  to open, allowing air to move from below the diaphragm to above through holes  108 . It should be noted that the upper and lower portions of the pump chamber are separated by a flexible rubber seal  111  extending between the perimeter of the diaphragm and the wall of the chamber. Similarly, a flexible seal  112  extending between the slider and the wall of the chamber seals the bottom of the chamber. It should also be noted that, in contrast to prior designs, bolts  114  holding the chamber housing to the sleeve are not installed from inside the cavity, thereby eliminating a possible source of air leakage. 
     Vacuum pump assembly  16  is connected by a hose  116  to an output port  118  on float valve assembly  14 . As shown in FIG. 5, the output port is mounted atop a valve housing or float box  120 , an upper portion  122  of which is cylindrical and a lower portion  124  of which is frustro-conical in shape. The float box is mounted on the intake of the centrifugal pump. Holes  125  allow water to rise into the float box from the intake. 
     When there is no water in the float box, a float  126  hangs freely. The float is connected through linkage assembly  128  to a valve stem  130 . A seal  132 , consisting of an o-ring  134  supported by a small flange  136 , is mounted on the valve stem and positioned away from a valve seat  137  formed in the float box when the float is hanging freely. This configuration allows air to be drawn through the valve seat and into the output port for subsequent delivery to the vacuum pump. The upper portion of stem  130  is supported in a guide  138  formed in output port  118 . This guide allows the stem to move up and down freely, but restricts lateral movement. 
     As water enters the float box and lifts the float, the linkage shifts the valve stem  130  upward to push the seal against the valve seat, thereby stopping withdrawal of air from the housing. This action prevents the water from being drawn into the vacuum pump. The absence of sharp projections in the float box reduces that chance that the float ball will become hung on the side of the float box, as may occur with existing designs. 
     It should be noted that the valve tends be held closed by the vacuum that builds quickly after the valve closes because of the cross-sectional area of the seal and stem. As a result, a hysteresis effect is created whereby the valve will not open until the water drops well below the level at which the valve first closed. Similarly, after opening, the valve will not close again until the water rises well above the level where the valve opened. The amount of hysteresis can be established by balancing the cross-sectional area of the valve against the size and density of the ball. The hysteresis is important because, as the pump is being primed, water flow is turbulent and subject to surging which would otherwise cause the valve to repeatedly open and close. The small area of holes  125  also helps to reduce fluctuations in the level of water in the valve housing. 
     While the invention has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. Applicants regard the subject matter of their invention to include all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. No single feature, function, element or property of the disclosed embodiments is essential. The following claims define certain combinations and subcombinations which are regarded as novel and non-obvious. Other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such claims, whether they are broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of applicants&#39; invention.