Abstract:
Apparatus and method to provide run-dry protection to semi-positive and positive displacement pumps is disclosed, including a resettable fuse placed in line with the motor of said pump to interrupt the supply of electrical power to the pump in response to sensing a run-dry condition. The resettable fuse prohibits pump operation until manual resetting, which occurs only upon interrooting and re-applying electrical power to the resettable fuse.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    (Not Applicable)  
         STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT  
         [0002]    (Not Applicable)  
         FIELD OF THE INVENTION  
         [0003]    The present invention is directed to the field of pumps and, more particularly, to devices and methods for providing run-dry protection for semi-positive and positive displacement pumps.  
         BACKGROUND OF THE INVENTION  
         [0004]    The use of semi-positive and positive displacement pumps for fluid transport applications is well known in the art. Presently, a large number of such pumps are used to drain various fluids from storage tanks used in numerous general purpose pumping applications such as industrial, recreational vehicle and/or marine marketplaces. By way of example and not limitation, a typical marine application may comprise drain/transfer applications, such as in recreational boating bilge pumps and/or on board sewage storage tanks. In this regard, such pumps are typically located in remote, difficult to access locations and use the fluid to lubricate the pump impeller while the motor-pump is in operation.  
           [0005]    Due to such semi-positive and positive displacement pumps utilizing the pumped fluid to lubricate pump components such as the pump impeller, there exists a substantial concern when the pump experiences a run-dry condition. Such run-dry conditions occur when the fluid level within the tank falls below the inlet conduit leading to the pump, whereby the pump no longer pumps fluid, but rather pumps air. During such a run-dry condition, excessive heat is built up within the pump, which additionally results with the swelling of the pump impeller and associated increase in amperage drawn by the pump motor. Through prolonged duration, such increase heat load permanently damages pump components such as the pump impeller and/or pump motor.  
           [0006]    In recognizing this deficiency, the prior art has recently introduced safety devices to such pumps which comprise either current-sensing interrupt switches and/or thermal fuses which momentarily interrupt the application of DC power to the pump upon encountering a run-dry condition. Although such prior art solutions have proven useful, they have not eliminated the possibility of damage to the pump impeller and/or pump motor.  
           [0007]    This is due to the fact that such prior art amperage-detecting circuit breakers and/or thermal fuses typically only momentarily interrupt the flow of power to the motor. In this regard, once the temperature of the device reduces to a proper operating level, then such circuit breaker or fuse automatically resets, whereby pump operation is reinitiated. However, in view of the fact that the run-dry condition still exists, the pump and motor will again continue to experience increase in thermal and amperage values until such time as excessive amperage and/or temperature values are exceeded, where again the circuit breaker and/or fuse will momentarily interrupt pump operation. However, until such time as the main on/off switch to the circuit is opened to eliminate further pump operation, the continuous, repetitive cycle-on/cycle-off condition of the pump is continued.  
           [0008]    In addition, as a practical matter, conventional manually-resettable fuses and/or circuit breakers typically cannot be utilized in such applications for pump protection, since such pumps are typically located in remote, difficult to access locations, thereby making it difficult and/or impossible for a user to manually reset the fuse.  
           [0009]    As such, a substantial need in the art exists for an improved apparatus and method to provide run-dry protection to a semi-positive and/or positive displacement pump which insures against undesirable cycle-on/cycle-off repetitive conditions and which further enables selected reset of the protection device from a physical location remote to the pump.  
         SUMMARY OF THE INVENTION  
         [0010]    These and other objects are achieved by the various apparatus and associated method of the present invention.  
           [0011]    In a broad aspect, the present invention provides a motor-pump protection device to protect a motor-pump assembly and pump components such as the pump impeller from damage occurring in run-dry conditions. The protector device includes a resettable fuse device placed in line with a power source supplying electrical power to the fuse and the motor-pump assembly, with the fuse serving to interrupt supply of electrical power to the motor-pump assembly in response to the occurrence of a run-dry condition. Thereafter the fuse remains open to discontinue operation of the pump until such time as the main on-off switch to the pump is opened thereby automatically resetting the fuse. As such, the protection device of the present invention eliminates unintended cycle-on and cycle-off conditions encountered in the prior art and permits pump reactivation only after a user opens and then closes the main on-off switch to the pump circuit, i.e., by an intentional act of the user.  
           [0012]    Preferably and not by way of limitation, the resettable fuse device is mounted within the motor housing of the pump. However, those skilled in the art will recognize that the resettable fuse device could be configured as a separate after market retrofit device for pump systems. The aforementioned summary description is intended to only provide an overview of the exemplary embodiments of the present invention. A more detailed understanding of these features, and of additional features, objects, and advantages of the present invention will be provided to those skilled in the art from a consideration of the following Detailed Description of the Invention, taken in conjunction with the accompanying Drawings, which will now first be described briefly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a side view of a typical prior art motor-pump assembly in a typical marine operational environment to drain fluid from a storage reservoir;  
         [0014]    [0014]FIG. 2 is a circuit diagram of the motor-pump in a typical marine application; and  
         [0015]    [0015]FIG. 3 is an end view of the motor-pump of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    The present invention comprises a device for protecting positive and/or semi-positive displacement pumps from damage occurring during run-dry conditions.  
         [0017]    Referring to FIG. 1, a typical application environment for use of the present invention is depicted. By way of illustration and not by limitation, the application depicts a storage tank such as an onboard sewage storage tank  10  disposed below deck  12  of a recreational pleasure boat (not shown). Reservoir  10  includes an inlet  14  and an outlet conduit  16 . The outlet conduit  16  is located near the lowermost region of the reservoir  10  and leads to a positive displacement pump  20  which can be mounted at differing locations relative the reservoir  10  and which draws liquid  22  contained within the reservoir  10  and transfers the same to an outlet conduit  24  which can communicate via flexible tubing or the like (not shown) to a desired transfer location. In operation, the pump  20  is initiated by a user to evacuate the reservoir  10 . Typically, such operation is initiated by the closing of an on-off toggle switch typically positioned at a remote location from the reservoir  10 , such as the bridge of a boat, such that selected operation of the pump  20  can be easily facilitated.  
         [0018]    Through pump operation, fluid is drawn from the reservoir  10  through the pump  20  and discharged through the outlet  24 . During such pumping operation, the internal components of the pump  20  such as the impeller are lubricated via the liquid passing therethrough. When the liquid level within the reservoir  12  drops below the reservoir outlet conduit  16 , pump operation continues, causing air to enter the pump, as opposed to liquid, i.e., causing a run-dry condition for the pump  20 .  
         [0019]    Heretofore it has been required for the user to continuously monitor pump operation. Upon confronting a run-dry condition, the user then simply opened the on-off toggle switch at the vessel&#39;s bridge, causing the pump operation to cease. However, if the user was not in a “standby” waiting condition to turn off the pump  20 , the pump  20  continued to operate, wherein, due to failure of liquid lubricating the same, the impeller of the pump could be damaged by heat swelling and/or the motor associated with the pump could overheat and be damaged.  
         [0020]    In recognizing this deficiency, it has been known to insert a thermal fuse in the pump circuit which senses heat buildup occasioned by pump operation during run-dry conditions which thermal fuse opens at a predetermined temperature value, causing the pump  20  operation to cease. However, after a prolonged period wherein the temperature of the fuse reduces back to proper operating conditions, the thermal fuse will automatically close, causing the pump  20  to again operate under run-dry conditions. This sequential cycling-off and cycling-on of the pump has been found to additionally damage the impeller of the pump  20 . As such, unless the user of the pump  20  is present to open the main on-off switch to the pump&#39;s circuit, such thermal fuses fail to prevent pump damage.  
         [0021]    Referring more particularly to FIGS. 2 and 3, the apparatus and method to provide run-dry protection to semi-positive and positive displacement pumps is schematically depicted. More particularly, the present invention contemplates the use of a selectively resettable fuse  30  to be disposed upon the pump  20  and be placed in line with the pump circuitry. The resettable fuse is designed to remain closed during proper current values within the pump&#39;s circuit. However, when current values increase within the circuit such as upon encountering a run-dry condition within the reservoir  12 , the resettable fuse automatically opens, therefore providing an automatic pump operation shut-off.  
         [0022]    However, in contrast to prior art systems, the resettable fuse  30  remains open even after operating temperatures of the pump  20  drop below excessive levels and will not reset unless and until power to the resettable fuse  30  is interrupted, such as by opening the main on-off toggle switch located at the bridge of the boat. Thus, sequential on-off cycling of the pump is eliminated and operation of the pump is prohibited unless and until the user purposely resets the resettable fuse  30  by opening and subsequently closing the main on-off toggle switch for the pump&#39;s circuit.  
         [0023]    In the preferred embodiment, the resettable fuse  30  may comprise a poly-switch resettable fuse such as that manufactured by Tyco Electronics Corporation of Menlo Park, Calif. under its trademark Raychem. However, those skilled in the art will recognize that other resettable fuses are contemplated herein. Additionally, as shown, in FIG. 2, a pair of resettable fuses  30  may be utilized in parallel to achieve desired amperage limitations. However, those skilled in the art will recognize that a single resettable fuse is contemplated without departing from the spirit of the present invention. Although such resettable fuse  30  can be implemented to provide protection to all positive and/or semi-positive displacement pumps, in the preferred embodiment it is contemplated that the same will be utilized on a positive displacement pump manufactured by the assignee of the subject application, ITT Industries Jabsco, known as the Macerator pump.  
         [0024]    In the preferred embodiment, the resettable fuses  30  are mounted within the motor housing of the pump  20 . FIG. 3 depicts a brush card assembly  40  of the pump  20  which is disposed on the rear axial end of the motor housing of the pump  20 . As will be recognized, such pumps include a motor drive formed integral with the pump which is sold as a motor pump assembly. Electrical leads  42  supply power to the motor  50  of the pump  20 . One of the leads  42   a  is provided with the resettable fuse  30  which is disposed in line. As previously mentioned, the resettable fuse is preferably maintained within the housing of the pump  20 .  
         [0025]    Referring again to FIG. 2, the pump  20  having the resettable fuse  30  disposed within the housing is hard wired to the main pump circuitry. In this regard, a power supply such as a battery  60  and a main on-off toggle switch  62  is provided. As previously mentioned, the power switch  62  is typically located at a position remote from the pump  20  such as at the bridge of the boat.  
         [0026]    When it is desired to operate the pump  20 , a user merely closes the on-off toggle switch  62  at the bridge of the vessel wherein the pump  20  operates to begin evacuation of the fluid within the reservoir  10 . During such operation, liquid passing through the pump  20  lubricates the internal components of the pump, such that damage to the impeller of the pump  20  is prohibited. When the fluid level falls below the outlet  16  of the reservoir  10 , i.e., a run-dry condition, the pump  20  and, more particularly, the motor associated with the same, will increase in temperature and draw more current in the circuit. Upon encountering a preselected overcurrent value, the resettable fuses  30  automatically open the circuit, causing operation of the pump  20  to cease. As such, the resettable fuse  30  provides an automatic shut-off condition for the pump  20  upon encountering a run-dry condition.  
         [0027]    In contrast to prior art systems, after a sufficient period of time wherein operating temperature of the pump and motor decline, the resettable fuses  30  remain in an open condition provided that power is supplied to the same via the circuit. As such, prior art cycling-on and -off of the pump  20  during run-dry conditions is eliminated.  
         [0028]    Only upon manually opening of the main on-off toggle switch  62  will the resettable fuses  30  automatically reset, whereby pump operation can be reinitiated by manual re-closing of the switch  62 . Thus, the user of the system must purposefully reset the fuses  30  to allow pump reactivation.  
         [0029]    It should also be noted that only the fundamental features of the motor-pump assembly  20  are illustrated in the figures. Other embodiments, features, and advantages of the present invention will be apparent to those skilled in the art from a consideration of the foregoing specification as well as through practice of the invention and alternative embodiments and methods disclosed herein. Therefore, it should be emphasized that the specification and examples are exemplary only, and that the true scope and spirit of the invention is limited only by the following claims.