Control device and pump apparatus

Abstract

A programmable electronic device prevents mechanically switched pumps as well as wastewater and / or viscous pumps to provide anti-ragging functionality while providing traditional electrical pump protections. An apparatus comprises a pump and a controller, the pump being a mechanically switched pump having a forward and a reverse direction and a controller comprising a torque monitoring mechanism and a control mechanism adapted to selectively directing the pump to (i) stop, (ii) operate in a reverse, and (iii) operate in a forward direction. Blockage clearing initiates upon the measured torque exceeding a first predetermined value, whereby the control mechanism is adapted to control the pump to complete a series of cycles, each cycle comprising (a) stopping, (b) operate in a reverse direction, (c) stopping, and (d) operating in a forward direction. A second predetermined value may be set below the first predetermined value to sense partial-blockage conditions.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part, and claims the benefit, of co-pending U.S. patent application Ser. No. 15 / 017,987, filed Feb. 8, 2016, entitled “Control Device And Pump Apparatus”, now U.S. Pat. No. 12,212,265, which in turn is a continuation, and claims the benefit, of U.S. patent application Ser. No. 14 / 000,086, filed Aug. 16, 2013, entitled “Control Device And Pump Apparatus”, which in turn is a national stage conversion of PCT / GB 2012 / 051083, filed May 16, 2012, entitled “Control Device And Pump Apparatus”, which in turn claims priority to Great Britain Patent Application No. 1108171.8, filed May 17, 2011, and to Great Britain Application No. 1121293.3, filed Dec. 12, 2011, each of which is incorporated by reference in its entirety herein.TECHNICAL FIELD

[0002] This invention relates to a controller for pumps and to a pump control apparatus and, in particular, a controller for a mechanically switched pump using first and second pre-determined values that may be the same or different to efficiently operate the pump to eliminate various types of blockages.BACKGROUND

[0003] Pump blockages contribute a significant cost to water authorities'operational spend by requiring a truck crew to unblock the site in order to avoid floods to the local area and any associated reputational damage to the operator. It would be beneficial to mitigate the amount of maintenance used for certain pumps, especially those pumping wastewater. Moreover, it would be beneficial to improve the power efficiency of wastewater pumps.SUMMARY

[0004] An object of the present invention is to mitigate the maintenance requirements and / or improve the power efficiency of pumps. U.S. Pat. No. 6,254,353 discloses a method and apparatus for controlling operation of a submersible pump and discloses a variable speed pump, evidenced by FIG. 2 which shows a rectifier circuit and a 3 phase H-bridge. According to a first aspect of the present invention, there is provided a pump control apparatus comprising a pump and a pump controller, the pump being a mechanically switched pump and capable of being operated in a forward and a reverse direction, and the controller comprising a monitoring mechanism to monitor the torque of the pump and a control circuit adapted to direct the pump to (a) stop and (b) operate in a reverse direction when the monitoring mechanism detects that the torque of the pump exceeds a first pre-determined value. The controller may direct other devices, such as alarms.

[0005] The present invention claims a mechanically switched pump, as opposed to the relatively complex variable speed pump shown in U.S. Pat. No. 6,254,353. Moreover, the present invention monitors the torque of the pump whereas U.S. Pat. No. 6,254,353 monitors the frequency of the pump (as detailed in e.g. FIG. 11, FIG. 13 and claim 1). The inventor of the present invention has discovered an important benefit of such an approach. The present invention can detect when a pump is laboring (but the output is not necessarily changing) because of a blockage starting to occur and can take remedial action at an early stage. In contrast, relying on monitoring the frequency of a pump will only suggest a blockage when the pump is unable to maintain the desired frequency (not merely laboring), which will often be when the blockage is more severe. Embodiments of the present invention therefore can take remedial action at an earlier stage of a blockage, which is more effective at clearing the blockage and / or minimizing the time taken to clear the blockage.

[0006] A mechanically switched pump is one which is activated by a mechanical switch and so can take up the forward, stop, or reverse modes. Suitable mechanically switched pumps include direct online pumps or Star / Delta pumps. In contrast, soft start and Variable Speed Drive (VSD) pumps can gradually ramp up the speed of the pump and are not mechanically switched pumps. The pump may have a power rating less than 25 kW, optionally less than (but not totally restricted to less than) 9 kW, and sometimes less than 7.5 kW. The pump may be a pump for pumping viscous fluids such as sewage and sludge, wastewater, grit etc.

[0007] The invention satisfies a long felt need to provide a responsive pump control without the expense of a VSD system and, according to the embodiments, resulting in improved functionality is provided in the same controller used to monitor the potential overloading of the pump. Thus, additional functionality may be provided to the pump apparatus within the often-limited confines of the existing pump apparatus. Other desirable features and characteristics will become apparent from the subsequent detailed description, the abstract, the drawings, and the appended claims, when considered in view of this background.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings. In the drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified.

[0009] For a better understanding of the present disclosure, reference will be made to the following Detailed Description, which is to be read in association with the accompanying drawings, which are incorporated in and constitute a part of this specification, show certain aspects of the subject matter disclosed herein and, together with the description, help explain some of the principles associated with the disclosed implementations, wherein:

[0010] FIG. 1 illustrates an embodiment of the controller in accordance with the present invention;

[0011] FIG. 2 illustrates an environmental view of the controller in accordance with the present invention;

[0012] FIG. 3 illustrates a flowchart showing the functional stages of a controller in accordance with the present invention;

[0013] FIG. 4 illustrates a schematic diagram indicating current levels useful for setting pre-determined values in accordance with the present invention; and

[0014] FIG. 5 illustrates a circuit diagram indicating electrical connections and a typical retro-fit installation in accordance with the present invention.DETAILED DESCRIPTION

[0015] Non-limiting embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals represent like elements throughout. While the invention has been described in detail with respect to the preferred embodiments thereof, it will be appreciated that upon reading and understanding of the foregoing, certain variations to the preferred embodiments will become apparent, which variations are nonetheless within the spirit and scope of the invention. For a better understanding of the present invention, reference will be made to the following Detailed Description, which is to be read in association with the accompanying drawings, which are incorporated in and constitute a part of this specification, show certain aspects of the subject matter disclosed herein and, together with the description, help explain some of the principles associated with the disclosed implementations.

[0016] The terms “a” or “an”, as used herein, are defined as one or as more than one. The term “plurality”, as used herein, is defined as two or as more than two. The term “another”, as used herein, is defined as at least a second or more. The terms “including” and / or “having”, as used herein, are defined as comprising (i.e., open language). The term “coupled”, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.

[0017] Reference throughout this document to “some embodiments”, “one embodiment”, “certain embodiments”, and “an embodiment” or similar terms means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of such phrases or in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments without limitation.

[0018] The term “or” as used herein is to be interpreted as an inclusive or meaning any one or any combination. Therefore, “A, B or C” means any of the following: “A; B; C; A and B; A and C; B and C; A, B and C”. An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive.

[0019] The drawings featured in the figures are provided for the purposes of illustrating some embodiments of the present invention, and are not to be considered as limitation thereto. The term “means” preceding a present participle of an operation indicates a desired function for which there is one or more embodiments, i.e., one or more methods, devices, or apparatuses for achieving the desired function and that one skilled in the art could select from these or their equivalent in view of the disclosure herein and use of the term “means” is not intended to be limiting.

[0020] In the context of this disclosure, the term “stop”, as applied to a mechanically switched pump, refers to a pump wherein the impeller has both zero angular speed and zero angular momentum.

[0021] The controller 10, shown in FIGS. 1 and 2, represents a hardware and software solution. The controller 10 measures real time current on the three conductors supplying a pump via current transducers (CT's). From this current, the parameter Ipump as illustrated in FIG. 4, the controller 10 can measure the instantaneous torque (the torque is indicative of the degree to which the pump is laboring to meet its desired setpoint condition(s), such as meeting instantaneous flow rate and / or external static pressure requirements that characterize the operation of the system) of the motor during operation. Upon completion of a newly installed pumping system, retrofit, or the like, an engineer may commence commissioning of the pump by recording the low and high current consumptions under normal operation to establish base operating conditions. A set point of around 10% may be added to the high level and 10% subtracted from the low level to widen the operating range. Alternatively, any desired and appropriate percentages may be applied to the high- and low-level current values, such as 1%, 5%, 15%, 20%, or higher percentage. Furthermore, the high- and low-level current values may have different percentages applied, such as 10% added to the high level, and 5% subtracted from the low level. These high- and low-level current set point values may then be entered into the controller 10 to provide predetermined “activation levels,” and this disclosure generally refers to the high-level current value as Imax, and the low-level current value as Imin unless otherwise specified.

[0022] According to a first aspect of the present invention, when the monitoring mechanism detects a first pre-determined value in the torque of the pump the response of the controller may be initially to direct the pump to stop. That is, power to the pump may be cut and the pump is allowed to coast to a rest. Preferably the pump may then be directed to run in a reverse direction. The pump may be stopped again, allowed to coast to a rest, and then run in a forward direction. The stopping before direction change reduces stress on the pump. The controller may direct the pump through a series of stop / reverse / stop / forward cycles until the torque detected by the monitoring mechanism is below a second pre-determined value, or the number of cleaning attempts exceeds a predefined maximum, whichever comes first. Typically, each stage in the stop / reverse / stop / forward cycle may last for 3 to 20 seconds, though the interval is not limited thereto. The first and second pre-determined values may be the same or they may be different.

[0023] The monitoring mechanism typically measures the torque of the pump by measuring the current at which the pump is operating, Ipump. As the current demanded by the motor is directly proportional to torque, the inventor considers this the most suitable variable to monitor. Nevertheless, a torque instrument could be put on the motor's shaft, although this may have a slower reaction time and so is less preferred. A current increase may be indicative of a blockage, such as a rag, which is inhibiting pump operation. Once the rag causes an increase in Ipump above the first pre-defined level, the controller may proceed to direct the pump into a series of stop / reverse / stop / forward cycles to remove the rag or other debris. The stop / reverse / stop / forward cycles described herein may be referred to as anti- or de-ragging functionality.

[0024] The controller may be programmed to provide anti-ragging functionality whilst providing traditional electrical pump protections. The monitoring mechanism may also be adapted to monitor Ipump with regard to potential thermal overloading of the pump. Standards directed to pumps are often imposed by regulatory authorities to safeguard against overheating. These standards may include limits, which depend on a number of different variables, and which can be stored by the controller. The controller may be adapted to control the pump or another controller in response to Ipump breaching a pre-determined safety level, which is indicative of the pump overheating. Preferably the components for monitoring the torque of the pump and the components adapted to monitor the potential overheating of the pump are provided on the same controller. Any feature of any aspect of the present invention may be combined with any other feature of any other aspect of the present invention. For example, the monitoring mechanism may also comprise a monitoring means to detect any sudden change in the current supplied to the motor, such as that induced by a short circuit, and the controller may be adapted to suitably respond to such an event, for example by shutting down the pump.

[0025] Preferably the pump starts at full power, without a restriction in power supplied. Preferably on start-up, the pump proceeds through one or more stop / reverse / stop / forward cycles. An advantage of the invention is that a pump may be cleared of debris without manual intervention, reducing pump downtime and costs associated with pump maintenance. A further advantage of the invention is that the pumps may be more efficient because any blockages may be cleared more frequently than by manual intervention. A further advantage of the invention is that the control and thermal overload sensing functions may be provided on a single controller, thus saving space.

[0026] According to a second aspect of the present invention there is provided a method of fitting a controller, as herein described, to a pump. The physical size of the controller may be minimized, which enables greater use of the product. Indeed, the present invention allows such a controller to be retrofitted into existing pump installations as, for example, a direct replacement for thermal / electronic overload monitoring devices. Preferably the size is less than 104 mmH×45 mmW×200 mmD. The controller is particularly useful for small to medium pumping stations, such as those operated with pumps having a power of less than 9 kW, optionally less than 7.5 kW. Traditionally larger pumping stations would be controlled with Variable Speed Drives (VSD) which is less preferred than the smaller (<9 kW) mechanically switched pumps of the present invention.

[0027] An advantage of certain embodiments of the invention is that the controller of the present invention may be less expensive to manufacture, compared with VSD controllers, which may be ten times the cost of mechanical switching controllers. Thus, embodiments of the invention provide a benefit of having a responsive pump control without the expense of a VSD system. A benefit of certain embodiments is that this functionality is provided in the same controller used to monitor the potential overloading of the pump. Thus, additional functionality may be provided to the pump apparatus within the often-limited confines of the existing pump apparatus. Thus, embodiments of the invention provide de-ragging functionality akin to VSD at a fraction of the cost, therefore making it more economical for smaller stations. Also, the controller is preferably designed to be retrofitted into existing stations and is physically much smaller (<250 cm2) than a VSD.

[0028] As shown in FIG. 3, when the pump is first turned on 1 it may run through a start-up clean cycle for a pre-determined number of direction changes of a pre-defined duration 2. The pump may then run as normal 3. An increased load on the pump may be detected 4 by the motor drawing a higher level of current which may be indicative of the motor's torque increasing because it is attempting to maintain speed against a larger force, such as ragging. A series of cleaning cycles 5-8 may be initiated upon a Ipump value that exceeds a first pre-determined value. The series of cycles may continue 5-8 until the current drops below a second pre-determined value, or until the pre-determined maximum number of cycles is reached, whichever occurs first. This approach results in an improved control strategy having several advantages with respect to clearing a blockage of a wastewater pump. For example, when the second pre-determined value is set lower than the first pre-determined value, the difference can assure a more effective clearing of the blockage.

[0029] By way of example and as illustrated schematically in FIG. 4, upon installation and / or commissioning, the pump operates under unblocked conditions; the range of Ipump is established with the low-level and high-level current values noted as Imin and Imax, respectively. One skilled in the art will appreciate that the high-level current consumption measured during the commissioning process may correspond to the maximum design flow rate of the system, that is GPMmax, measured in gallons per minute, while operating at the design external static pressure of the system into which the pump apparatus is installed. This flow rate is essentially a measure of how much media the system can convey, for example, based on the number of residences served. The piping, pump, controls, and the overall system, are sized accordingly. Consequently, such maximum flow rate may correlate to maximum current drawn, i.e. GPMmax→Imax. When commissioning the pump after installation or retrofit, a set point of around 10%, for example, may be added to the high level, Imax. This exemplary value, 1.1×Imax=Itrip, may then be programmed as the first pre-determined value—the threshold that tells the control system to initiate the series of cycles. If, for example, the value of the second predetermined value, Iresume, is also set to Itrip, then the blockage may not actually have been fully cleared. In this scenario, the pump may still be running in an overloaded condition, such as, for example, 5% over Imax. This partial blockage condition may stress the pump during a period of time when the partial blockage remains undetected by the electric current sensor, resulting in a reduced lifetime of the pump and / or associated components.

[0030] In contrast, if the value of the second predetermined value is set to a value that is less than or equal to Imax, for example, Iresume=0.99×Imax, the cleaning cycle can ensure that the system blockage has actually been cleared, and that the system will run clean and as intended upon resuming normal operation. Additionally, a second predetermined value selectable by the user may allow the user to calibrate the system in accordance with on-site conditions, such that the system is not running under the aforementioned duress, i.e. with a partial blockage, after the cleaning cycle is completed. This successful clearing via cycling according to the present invention may, among other benefits, (1) promote the lifetime of the system by reducing intermittent stress conditions on the pump, (2) provide for a tailored calibration, and / or (3) provide accurate cleaning cycles.

[0031] FIG. 3 outlines the steps taken by the controller under various operating conditions. When Ipump is under or, more likely, above the normal operating range, and Ipump>Itrip, a cleaning process may be initiated by the controller 10. The controller 10 may start a cleaning cycle by cutting power 5 to the pump. Typically, the inertia of the pump and the fluid continuing to pass therethrough may keep the pump running in the same direction for a short period of time after the power is cut. In this case the pump 20 may coast to a rest. Thus, after the power is cut to the motor, the controller may wait 5 for a pre-determined amount of time A before progressing to the next step as shown in FIG. 3. The time A may be varied by the user and is typically larger for larger pumps. After this time elapses the pump may go into reverse, 6, also for a pre-determined amount of time B which may also be varied by the user. The controller 10 may stop the pump again 7 by cutting power and allowing it to coast to a rest. After a further period of time A the pump may go into a forward direction for a pre-determined amount of time C.

[0032] The above cleaning cycle (steps 5-8) may be repeated up to a pre-defined number of times which may be varied by the user. After each reverse and forward cycle 5-8 as shown in e.g., FIG. 3, the controller 10 may check Ipump. If the blockage is cleared as indicated by Ipump≤Iresume in the forward direction, then it may continue pumping as normal 3. If not, the controller 10 may attempt to clean again by running the cleaning cycle 5-8. The controller 10 may continue to attempt cleaning until either the blockage is cleared, or until a maximum number of cleaning cycles has been reached, at which point it may stop the pump and trip an alarm 9. In this event, a manual intervention such as a service call may be required. Also, a counter tracking the number of cleaning processes may be automatically reset by the controller 10.

[0033] The cleaning cycle may be fully customizable. It may consist of, but is not limited to, a reverse rotation time period, a forward rotation time period, and / or a stop time period; not necessarily in that order, and wherein each time period may be user adjustable as desired. Furthermore, the maximum number of cycles may be changed by the user.

[0034] As the real time current of the pump is monitored, the controller 10 may also act to protect the motor as it contains a thermal model thereof. This may allow the controller 10 to act like a traditional thermal overload protection circuit.

[0035] An advantage of certain embodiments of the present invention is that they may provide an economical de-ragging solution for wastewater pumps, where the unit detects a change in current and immediately reverses the pump to dislodge debris built up during normal operation. As shown in FIG. 1, the controller 10 may be sized such that it is capable of being retrofitted into existing pump control panels.

[0036] FIG. 5 shows an exemplary schematic diagram of the control circuit 30 for the controller 10. The pre-existing pump motor 20 is supplied by a three-phase power supply L1, L2, L3. A contactor K1 may engage the motor 20 into a forward direction, or to disengage the power from the motor 20 and allow it to stop. The system may include a contactor K2 in parallel to the K1 contactor. The contactor K2 may direct the motor 20 into a reverse direction. A current sensor 22 may be disposed downstream of the contactors K1 and K2 and upstream of the motor 20 to monitor the current being supplied to the motor 20. The current sensor 22 and contactors K1, K2 may be connected to the control circuit 30.

[0037] The control circuit 30 may have an input interface 32, an output interface 34 and a power supply 36. The input signals may be received and processed by the input interface 32 and the appropriate outputs may be activated, as described above with respect to FIG. 3. The outputs 01 and 02 from the output interface 34 may control the contactors K1 and K2, which in turn may control the motor 20. The existing coil connection to the contactor K1 may be rerouted to the de-ragger control circuit 30 by the use of an interposing relay 1314, which provides the run signal. The control circuit 30 may then take control of the pump 20.

[0038] While certain configurations of structures have been illustrated for the purposes of presenting the basic structures of the present invention, one of ordinary skill in the art will appreciate that other variations are possible which would still fall within the scope of the appended claims. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

1. A system comprising:a pump, being a mechanically switched, constant-speed pump; anda controller for the pump comprising:an electric current sensor measuring electric current drawn by the pump, andat least one switch being adapted to selectively direct the pump among three conditions consisting of: (i) stop, (ii) a constant-speed forward direction, and (iii) a constant-speed reverse direction;the pump further comprises a current range including a minimum operating current and a maximum operating current, each being measured during unblocked pump operation,the controller characterized by:while the current is above a first pre-determined value, the first pre-determined value being measurably greater than the maximum current, the controller directs the at least one switch to complete a series of cycles, each cycle comprising (a) stopping by stopping power to the pump and allowing it to coast to a rest, (b) operating in the constant-speed reverse direction, (c) stopping by stopping power to the pump and allowing it to coast to a rest, and (d) operating in the constant-speed forward direction, with a user-adjustable stopping period between direction changes; andwhile the number of cycles is less than or equal to a pre-determined maximum number of cycles, the controller directs the switch to cycle, until the current is below a second pre-determined value, where the second pre-determined value is measurably less than the first pre-determined value.

2. The system of claim 1, wherein the first pre-determined value is a multiple of 1.1× the value of the maximum current.

3. The system of claim 2, wherein the second pre-determined value is a multiple of 0.95× the value of the maximum current.

4. The system as claimed in claim 1, wherein each constant-speed forward and reverse direction in the cycle lasts for a time interval which may be set and varied by a user.

5. The system as claimed in claim 1, wherein the electric current sensor measures the output of the mechanically switched, constant-speed pump by measuring the current at which the pump is operating.

6. The system as claimed in claim 5, wherein the electric current sensor is provided as part of the controller.

7. The system as claimed in claim 1, wherein the electric current sensor is adapted to monitor the electric current drawn by the mechanically switched, constant-speed pump, indicative of the torque of the pump, with regard to potential overloading of the mechanically switched, constant-speed pump.

8. The system as claimed in claim 1, wherein the switch control is adapted to control the mechanically switched, constant-speed pump, or another device, in response to the current rising above a third pre-determined value, which is indicative of the mechanically switched constant speed pump overloading or being in danger of overloading.

9. The system as claimed in claim 1, wherein upon start-up, a motor of the mechanically switched constant speed pump is adapted to proceed through a cycle.

10. The system as claimed in claim 1, wherein a motor of the mechanically switched constant speed pump starts at full power, without a restriction in the power.

11. The system as claimed in claim 1, wherein the electric current sensor is configured to detect any sudden change in the current drawn by the pump, and the switch control is adapted to respond to such an event.

12. The system as claimed in claim 1, which fits within a volume no greater than about 50 cm 3.

13. The system as claimed in claim 1, wherein the mechanically switched constant speed pump has a power rating ranging from about 1 kW to about 25 kW.

14. The system as claimed in claim 1, comprising a thermal stability monitor to monitor, directly or indirectly, thermal stability of the mechanically switched, constant-speed pump, wherein the electric current sensor and the thermal stability monitor are provided as part of the controller.

15. The system as claimed in claim 1, wherein the constant-speed forward direction and the constant-speed reverse direction each last for about 3 second to about 20 seconds.

16. The system as claimed in claim 1, wherein the mechanically switched, constant-speed pump has a power rating ranging from about 1 kW to about 9 kW.

17. The system as claimed in claim 1, wherein the mechanically switched, constant-speed pump does not include an inverter.

18. A retrofitting pump kit comprising:a controller for a pump, the pump being a mechanically switched, constant-speed pump, the controller comprising:an electric current sensor measuring electric current drawn by the pump, andat least one switch being adapted to selectively direct the pump among three conditions consisting of: (i) stop, (ii) a constant-speed forward direction, and (iii) a constant-speed reverse direction;the retrofitting pump kit further comprising a current range including a minimum operating current and a maximum operating current, each being measured during unblocked pump operation,the controller characterized by:while the current is above a first pre-determined value, the first pre-determined value being measurably greater than maximum current, the controller directs the at least one switch to complete a series of cycles, each cycle comprising (a) stopping by stopping power to the pump and allowing it to coast to a rest, (b) operating in the constant-speed reverse direction, (c) stopping by stopping power to the pump and allowing it to coast to a rest, and (d) operating in the constant-speed forward direction, with a user-adjustable stopping period between direction changes; andwhile the number of cycles is less than or equal to a pre-determined maximum number of cycles, the controller directs the switch to cycle, until the current is below a second pre-determined value, where the second pre-determined value is measurably less than the first pre-determined value.

19. A method of operating a mechanically switched, constant-speed pump, comprising:monitoring the current drawn from a mechanically switched, constant-speed pump while operating in a constant-speed forward direction, to detect whether the current exceeds a first pre-determined value which is measurably greater than a maximum current of a current range measured during unblocked pump operation;controlling a direction of the motor among three conditions consisting of: (i) stop, (ii) the constant-speed forward direction, and (iii) a constant-speed reverse direction;directing, while the current is above a first pre-determined value, the first pre-determined value being measurably greater than the maximum current, the controller directs the at least one switch to complete a series of cycles, each cycle comprising (a) stopping by stopping power to the pump and allowing it to coast to a rest, (b) operating in the constant-speed reverse direction, (c) stopping by stopping power to the pump and allowing it to coast to a rest, and (d) operating in the constant-speed forward direction, with a user-adjustable stopping period between direction changes; anddirecting, while the number of cycles is less than or equal to a pre-determined maximum number of cycles, the controller directs the switch to cycle, until the current is below a second pre-determined value, where the second pre-determined value is measurably less than the first pre-determined value.

Images