Apparatus and method to provide run-dry protection to semi-positive and positive displacement pumps

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] 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] FIG. 2 is a circuit diagram of the motor-pump in a typical marine application; and

[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'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'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'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'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 42a 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.

Claims

1. A protector device to protect a motor-pump assembly having a pump to pump fluids and a motor to drive said pump, said protector device comprising:

a resettable fuse device placed in line with a power source supplying electrical power to said fuse and said motor-pump assembly, said fuse adapted to interrupt supply of electrical power to said motor-pump assembly in response to sensing a run-dry condition and reset only upon interruption and re-application of the supply of electrical power to said fuse.

2. The device of claim 1, said fuse device further comprising:

a plurality of resettable fuses connected to each other in a parallel circuit configuration.

3. The device of claim 1, wherein said run-dry condition comprises an increase in current level within said fuse.

4. The device of claim 1, wherein said fuse is disposed within the housing of the motor pump assembly.

5. A method for protecting a motor-pump assembly having a pump to pump fluids and a motor to drive said pump, said method comprising:

interrupting the supply of electrical power to said motor-pump assembly in response to sensing the occurrence of a run-dry condition; and

manually resetting said fuse from a remote location by interrupting and then reinitiating electrical power to said fuse.

6. In a positive and/or semi-positive displacement pump having a motor and pump disposed within a housing, the improvement comprising:

a resettable fuse disposed within said housing and placed in line with said motor;

said resettable fuse providing an automatic shut-off for said motor upon encountering a run-dry pump condition, which fuse remains open until electrical power is discontinued and subsequently re-initiated to said fuse.