Patent Publication Number: US-9840803-B2

Title: Pump assembly for appliance

Description:
FIELD OF THE INVENTION 
     The present disclosure relates generally to pump assemblies for appliances, and more particularly to improved sensing of pump assembly operation. 
     BACKGROUND OF THE INVENTION 
     Many appliances include pumps for flowing fluid therethrough during operation of the appliance. One example is a washing machine appliance, which includes a pump for draining fluid from a tub of the washing machine appliance. Washing machine appliances generally include a cabinet which supports a tub for containing wash fluid, e.g., water and detergent, bleach and/or other wash additives. A basket is mounted within the tub and defines a wash chamber for receipt of a load of articles for washing. During operation of such washing machine appliances, wash fluid is directed into the tub and onto articles within the wash chamber of the basket. The basket or an agitation element can rotate at various speeds to agitate articles within the wash chamber in the wash fluid, to wring wash fluid from articles within the wash chamber, etc. The fluid can then be drained from the tub, and a pump is typically provided for facilitating such drainage. Another example of an appliance which utilizes a pump is a dishwasher appliance which can utilize a pump for drainage and/or recirculation purposes. 
     One issue with many presently known pumps is that the pumps generally run continuously during a drain cycle of the appliance. In some cases, insufficient fluid levels may flow through the pump during a portion of the drain cycle. For example, there may be blockage in the system which prevents or reduces fluid flow through the pump, or the amount of fluid to be drained may be low, resulting in a majority of the fluid being flowed through the pump in a faster than expected time period. These situations may result in the pump running “dry” for period of time, which can cause damage to the pump and can utilize excess energy. In some cases, pressure sensors are provided for detecting blockages in the system, but these sensors typically only provide a blockage indication to the user when a full blockage is detected in the appliance. 
     Accordingly, improved appliance pump operation is desired. In particular, pump assemblies, methods and appliances which facilitate sensing of low fluid flow levels within pumps would be advantageous. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In accordance with one embodiment, a pump assembly for an appliance is provided. The pump assembly includes a pump, the pump including a body and an impeller disposed within the body, the body including an inlet portion, an outlet portion, and an impeller portion disposed between the inlet portion and the outlet portion. The pump assembly further includes a motor connected to the impeller for driving the impeller. The pump assembly further includes a sensor assembly for sensing fluid flow through the pump, the sensor assembly including a first electrical contact and a second electrical contact in electrical communication with each other. The pump assembly further includes a controller in communication with the sensor assembly and the motor. The controller is configured for actuating the motor to begin operation of the pump, receiving an electrical signal level between the first electrical contact and the second electrical contact, and deactuating the motor when the electrical signal level falls outside of a predetermined electrical signal range. 
     In accordance with another embodiment, a washing machine appliance is provided. The washing machine appliance includes a cabinet, a tub positioned within the cabinet, and a basket rotatably mounted within the tub, the basket defining a chamber for receipt of a load of items for washing. The washing machine appliance further includes a pump for draining fluid from the tub. The pump includes a body and an impeller disposed within the body, the body including an inlet portion, an outlet portion, and an impeller portion disposed between the inlet portion and the outlet portion. The washing machine appliance further includes a motor connected to the impeller for driving the impeller. The washing machine appliance further includes a sensor assembly for sensing fluid flow through the pump, the sensor assembly including a first electrical contact and a second electrical contact in electrical communication with each other. The washing machine appliance further includes a controller in communication with the sensor assembly and the motor. The controller is configured for actuating the motor to begin operation of the pump, receiving an electrical signal level between the first electrical contact and the second electrical contact, and deactuating the motor when the electrical signal level falls outside of a predetermined electrical signal range. 
     In accordance with another embodiment, a method for operating a pump assembly of an appliance is provided. The method includes actuating a motor of the pump assembly to begin operation of a pump of the pump assembly, receiving an electrical signal level between a first electrical contact and a second electrical contact provided for sensing fluid flow through the pump, and deactuating the motor when the electrical signal level falls outside of a predetermined electrical signal range. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  is a front perspective view of a washing machine appliance with a door in a closed position in accordance with one embodiment of the present disclosure; 
         FIG. 2  is a front cross-sectional view of a washing machine appliance in accordance with one embodiment of the present disclosure; 
         FIG. 3  is a perspective view of a pump assembly in accordance with one embodiment of the present disclosure; 
         FIG. 4  is a schematic top view of a pump assembly in accordance with one embodiment of the present disclosure; 
         FIG. 5  is a schematic top view of a pump assembly in accordance with another embodiment of the present disclosure; 
         FIG. 6  is a schematic cross-sectional view of a pump assembly in accordance with one embodiment of the present disclosure; and 
         FIG. 7  is a flow chart illustrating a method in accordance with one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
       FIG. 1  is a perspective view of a washing machine appliance  50  according to an exemplary embodiment of the present subject matter. As may be seen in  FIG. 1 , washing machine appliance  50  includes a cabinet  52  and a cover  54 . A backsplash  56  extends from cover  54 , and a control panel  58  including a plurality of input selectors  60  is coupled to backsplash  56 . Control panel  58  and input selectors  60  collectively form a user interface input for operator selection of machine cycles and features, and in one embodiment, a display  61  indicates selected features, a countdown timer, and/or other items of interest to machine users. A door  62  is mounted to cover  54  and is rotatable between an open position (not shown) facilitating access to a wash tub  64  ( FIG. 2 ) located within cabinet  52  and a closed position (shown in  FIG. 1 ) forming an enclosure over tub  64 . 
     Door  62  in exemplary embodiment includes a transparent panel  63 , which may be formed of for example glass, plastic, or any other suitable material. The transparency of the panel  63  allows users to see through the panel  63 , and into the tub  64  when the door  62  is in the closed position. In some embodiments, the panel  63  may itself generally form the door  62 . In other embodiments, the door  62  may include the panel  63  and a frame  65  surrounding and encasing the panel  63 . Alternatively, panel  63  need not be transparent. 
       FIG. 2  provides a front, cross-section view of washing machine appliance  50 . As may be seen in  FIG. 2 , tub  64  includes a bottom wall  66  and a sidewall  68 . A wash drum or wash basket  70  is rotatably mounted within tub  64 , defining an annulus  85  between the tub  64  and basket  70 . In particular, basket  70  is rotatable about a central axis  69 , which may when properly balanced and positioned in the embodiment illustrated be a vertical axis. Thus, washing machine appliance is generally referred to as a vertical axis washing machine appliance. Basket  70  defines a wash chamber  73  for receipt of a load of articles for washing and extends, e.g., vertically, between a bottom portion  80  and a top portion  82 . Basket  70  includes a plurality of openings or perforations  71  therein to facilitate fluid communication between an interior of basket  70  and tub  64 . 
     A nozzle  72  is configured for flowing a liquid into tub  64 . In particular, nozzle  72  may be positioned at or adjacent top portion  82  of basket  70 . Nozzle  72  may be in fluid communication with one or more water sources  75 ,  76  in order to direct liquid (e.g. water) into tub  64  and/or onto articles within chamber  73  of basket  70 . Nozzle  72  may further include apertures  79  through which water may be sprayed into the tub  64 . Apertures  79  may, for example, be tubes extending from the nozzles  72  as illustrated, or simply holes defined in the nozzles  72  or any other suitable openings through which water may be sprayed. Nozzle  72  may additionally include other openings, holes, etc. (not shown) through which water may be flowed, i.e. sprayed or poured, into the tub  64 . 
     A main valve  74  regulates the flow of liquid through nozzle  72 . For example, valve  74  can selectively adjust to a closed position in order to terminate or obstruct the flow of liquid through nozzle  72 . The main valve  74  may be in fluid communication with one or more external liquid sources, such as a cold water source  75  and a hot water source  76 . The cold water source  75  may, for example, be a commercial water supply, while the hot water source  76  may be, for example, a water heater. Such external water sources  75 ,  76  may supply water to the appliance  50  through the main valve  74 . A cold water conduit  77  and a hot water conduit  78  may supply cold and hot water, respectively, from the sources  75 ,  76  through valve  74 . Valve  74  may further be operable to regulate the flow of hot and cold liquid, and thus the temperature of the resulting liquid flowed into tub  64 , such as through the nozzle  72 . 
     An additive dispenser  84  may additionally be provided for directing an additive, such as detergent, bleach, liquid fabric softener, etc., into the tub  64 . As illustrated, dispenser may be in fluid communication with annulus  85 , such that additive added to the dispenser  84  may flow directly from the dispenser  84  into the annulus  85 . In alternative embodiments, dispenser may be in fluid communication with nozzle  72  such that water flowing through nozzle  72  flows through dispenser  84 , mixing with additive at a desired time during operation to form a liquid or wash fluid, before being flowed into tub  64 . In still other alternative embodiments, nozzle  72  and dispenser  84  may be integral, with a portion of dispenser  84  serving as the nozzle  72 . 
     A pump assembly  90  (shown schematically in  FIG. 2 ) is located beneath tub  64  and basket  70  for gravity assisted flow to drain tub  64 . An agitation element  92 , shown as an impeller in  FIG. 2 , may be disposed in basket  70  to impart an oscillatory motion to articles and liquid in chamber  73  of basket  70 . In various exemplary embodiments, agitation element  92  includes a single action element (i.e., oscillatory only), double action (oscillatory movement at one end, single direction rotation at the other end) or triple action (oscillatory movement plus single direction rotation at one end, singe direction rotation at the other end). As illustrated in  FIG. 2 , agitation element  92  is oriented to rotate about vertical axis V. Alternatively, basket  70  may provide such agitating movement, and agitation element  92  is not required. Basket  70  and agitation element  92  are driven by a motor  94 . Motor  94  may, for example, be a pancake motor, direct drive brushless motor, induction motor, or other motor suitable for driving basket  70  and agitation element  92 . As motor output shaft  98  is rotated, basket  70  and agitation element  92  are operated for rotatable movement within tub  64 , e.g., about vertical axis V. Washing machine appliance  50  may also include a brake assembly (not shown) selectively applied or released for respectively maintaining basket  70  in a stationary position within tub  64  or for allowing basket  70  to spin within tub  64 . 
     Operation of washing machine appliance  50  is controlled by a processing device or controller  99 , that is operatively coupled to the input selectors  60  located on washing machine backsplash  56  (shown in  FIG. 1 ) for user manipulation to select washing machine cycles and features. Controller  99  may further be operatively coupled to various other components of appliance  50 , such as main valve  74 , pump assembly  90 , motor  94 , and other suitable sensors, etc. In response to user manipulation of the input selectors  60 , controller  99  may operate the various components of washing machine appliance  50  to execute selected machine cycles and features. 
     Controller  99  may include a memory and microprocessor, such as a general or special purpose microprocessor operable to execute programming instructions or micro-control code associated with a cleaning cycle. The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor. Alternatively, controller  99  may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software. Control panel  58  and other components of washing machine appliance  50 , such as the door  62 , pump assembly  90 , motor  94 , valve  74 , etc. may be in communication with controller  99  via one or more signal lines or shared communication busses. 
     In an illustrative embodiment, a load of laundry articles are loaded into chamber  73  of basket  70 , and washing operation is initiated through operator manipulation of control input selectors  60 . Tub  64  is filled with liquid, such as water, and may be mixed with detergent to form a wash fluid. Main valve  74  can be opened to initiate a flow of liquid and resulting wash fluid into tub  64  via nozzle  72 , and tub  64  can be filled to the appropriate level for the amount of articles being washed. Once tub  64  is properly filled with wash fluid, the contents of the basket  70  are agitated with agitation element  92  or by movement of the basket  70  for cleaning of articles in basket  70 . More specifically, agitation element  92  or basket  70  is moved back and forth in an oscillatory motion. 
     After the agitation phase of the wash cycle is completed, tub  64  is drained, such as through use of pump assembly  90 . Laundry articles can then be rinsed by again adding fluid to tub  64 . Depending on the particulars of the cleaning cycle selected by a user, agitation element  92  or basket  70  may again provide agitation within basket  70 . After a rinse cycle, tub  64  is again drained, such as through use of pump assembly  90 . Further, in exemplary embodiments, one or more extractions, or spin cycles, may be performed. In particular, a spin cycle may be applied after the wash cycle(s) and/or after the rinse cycle(s) in order to wring excess wash fluid from the articles being washed. During a spin cycle, basket  70  is rotated at relatively high speeds, as discussed further herein. 
     While described in the context of specific embodiments of washing machine appliance  50 , using the teachings disclosed herein it will be understood that washing machine appliance  50  is provided by way of example only. Other washing machine appliances having different configurations (such as horizontal-axis washing machine appliances), different appearances, and/or different features may also be utilized with the present subject matter as well. 
     It should further be understood that an appliance in accordance with the present disclosure is not limited to a washing machine appliance. Any suitable appliance which utilizes a pump for flowing fluid therethrough, such as for example a dishwasher appliance, is within the scope and spirit of the present disclosure. 
     Referring now to  FIGS. 3 through 6 , embodiments of pump assemblies  90  for use in appliances  50  are provided. In general, a pump assembly  90  in accordance with the present disclosure may include a pump  100  for flowing fluid therethrough, such as for drainage as discussed above, for recirculation, or for another suitable use. Advantageously, a pump assembly  90  in accordance with the present disclosure may further include apparatus for sensing fluid flow levels through the pump assembly  90 , and for operating the pump assembly  90  accordingly. 
     As shown, pump  100  may include a body  102  and an impeller  104 . The impeller  104  may be disposed within an interior  106  of the body  102 , and may be rotatable to direct fluid (i.e. wash fluid, which in exemplary embodiments includes a liquid) flow therepast. Body  102  may include an inlet portion  110  (which may define an inlet  111  of the body  102 ), an outlet portion  112  (which may define an outlet  113  of the body  102 ), and an impeller portion  114  (in which the impeller  104  is disposed) between the inlet and outlet portions  110 ,  112 . Fluid may flow into the inlet portion  110  through the inlet  111 , from the inlet portion  110  to the impeller portion  114 , past the impeller  104  and into the outlet portion  112 , and from the outlet portion  112  through the outlet  113 . 
     Pump assembly  90  may additionally include a motor  120  (which may for example be motor  94  or be separate from motor  94 ). The motor  120  may drive the impeller  104  and thus operate the pump  100 . Actuation of the motor  120  may operate the pump  100  may causing rotation of the impeller  104 , and deactuation of the motor  120  may stop operation of the pump  100  (and impeller  104  thereof). Motor  120  may be connected, such as via a shaft  122 ) to the impeller  104  for driving the impeller  104 . 
     Pump assembly  90  may further include a sensor assembly  130  for sensing fluid through the pump  100 . Sensor assembly  130  may include a first electrical contact  132  and a second electrical contact  134 , and may further include a third or more electrical contacts. The contacts  132 ,  134  may be in electrical communication with each other, such that there is an electrical signal, such as a voltage, current, and/or capacitance, between the contacts  132 ,  134  that can be measured. For example, the contacts  132 ,  134  may be connected to a power source and to each other. 
     In exemplary embodiments, the contacts  132 ,  134  may be formed from steel, such as a stainless steel, or another suitable metal. Alternatively, other suitable conductive materials may be utilized. The contacts  132 ,  134  may, in exemplary embodiments, be disposed within the body  102 , such as in the interior  106 . In some embodiments, as illustrated in  FIG. 4 , the contacts  132 ,  134  may be disposed within the inlet portion  110 . In other embodiments, as illustrated in  FIG. 5 , the contacts  132 ,  134  may be disposed within the outlet portion  112 . In still other embodiments, the contacts  132 ,  134  may be disposed within the impeller portion  104 . Alternatively, the contacts  132 ,  134  may be disposed upstream or downstream of the pump  100  in the flow path of fluid through the pump  100 , such as in a conduit connected to the pump  100  for flowing fluid to or from the pump  100 . 
     Referring to  FIG. 6 , the contacts  132 ,  134  may be disposed within the interior  104  of pump  100  at suitable height- or width-wise locations spaced from the inner surface of the body  102 . For example, a height within the interior  104  of the pump  100  may be measured along a vertical direction V from the inner surface of the body  102 , such as from a low-point of the inner surface of the body  102 . As shown, contacts  132  and  134 , such as the ends thereof, may be at heights  133 ,  135  respectively, which may be identical or different heights. Accordingly, when a typical fluid flow through the pump  100  is occurring, the contacts  132 ,  134  may be submerged in the fluid, as shown for example by fluid at height  137 . When the contacts  132 ,  134  are both submerged, the electrical signal between the contacts  132 ,  134  may increase or decrease (depending on the type of signal being measured), such as to outside of a predetermined electrical signal range as discussed herein. When fluid flow has stopped, the fluid level within the pump  100  may drop such that one or both contacts  132 ,  134  are no longer submerged. For example, fluid may be at height  139 . In this case, the electrical signal between the contacts  132 ,  134  may decrease or increase, such as to within the predetermined electrical signal range as discussed herein. Such electrical signal changes can thus advantageously be utilized to monitor fluid flow through the pump assembly  90  and operate the pump  100  accordingly. 
     Pump assembly  90  may additionally include a controller, such as controller  99  as discussed above. The controller  99  may generally be in communication with other components of the pump assembly  90 , such the sensor assembly  130  (i.e. the first and second contacts  132 ,  134 ) and the motor  120 . As discussed herein, controller  99  may in exemplary embodiments advantageously be configured to control operation of the pump assembly  90  based on inputs from the contacts  132 ,  134 . 
     Referring now to  FIG. 7 , the present disclosure is further directed to methods  200  for operating pump assemblies  90  of appliances. In general, the various steps of methods as disclosed herein may in exemplary embodiments be performed by the controller  99 , which may receive inputs and transmit outputs from various other components of the appliance  50  as discussed herein. Such operation of pump assemblies  90  in accordance with the present disclosure may advantageously facilitate reductions in time periods during which the pump  100  is run dry, thus reducing the risk of damage to the pump  100  and reducing the energy usage of the pump assembly  90  generally. 
     A method  200  may, for example, include the step  210  of actuating the motor  120  to begin operation of the pump  100 . When actuated, the motor  120  may operate to rotate the impeller  104 , thus operating the pump  100  generally to encourage fluid flow therethrough. Such operation may continue until the motor  120  is deactuated. Actuation  210  may occur, for example, at the beginning of a drain cycle of the appliance  50  or during another suitable cycle during operation of the appliance  50 . Further, such actuation  210  may occur for a predetermined time period, or may occur for an unspecified time period that may terminate due to operation of the sensor assembly  130  and resulting motor  120  deactuation as discussed herein. 
     Method  200  may further include, for example, the step  220  of receiving an electrical signal level between the first electrical contact  132  and the second electrical contact  134 . Such receiving step  220  may occur during operation of the pump  100  after actuation  210  occurs. For example, a signal associated with an electrical level (i.e. voltage, current, capacitance, etc.) may be transmitted to the controller  99 , which may receive such signal. In exemplary embodiments, the receiving step  220  may occur repeatedly at a predetermined time interval during operation of the pump  100 . The predetermined time interval may, for example, be between 1 and 30 seconds, such as between 1 and 20 seconds, such as between 2 and 10 seconds, such as between 3 and 5 seconds. 
     As discussed, during operation of the pump  100 , the electrical signal level may fall outside or inside of a predetermined electrical signal range based on the level of fluid flow through the pump  100 . Accordingly, method  200  may further include, for example, the step  230  of deactuating the motor  120 , thus terminating operation of the pump  100  to encourage flow therethrough, when the electrical signal level falls outside of the predetermined electrical signal range. Such step may advantageously reduce instances of the impeller  104  running dry, thus reducing the risk of damage to the impeller  104  and pump  100  generally. When the actuation  210  has been set for a predetermined time period, such deactuation  230  may occur within the predetermined time period to prevent running dry during, for example, an end portion of the predetermined time period when operation of the pump  100  is no longer necessary. 
     Notably, when the electrical signal level remains within the predetermined electrical signal range after actuation  210 , pump  100  may continue to operate. 
     In exemplary embodiments, the motor  120  may be deactuated in step  230  after a predetermined delay time period when the electrical signal level remains outside of the predetermined electrical signal range. Accordingly, when the electrical signal level falls outside of the predetermined electrical signal range, the motor  120  may continue to operate, and deactuation may not occur, for a predetermined delay time period. If the electrical signal level remains outside of the predetermined electrical signal range during the predetermined delay time period, the motor  120  may be deactuated after the predetermined delay time period has expired. The predetermined delay time period may, for example, be between 1 and 30 seconds, such as between 1 and 20 seconds, such as between 2 and 10 seconds, such as between 3 and 5 seconds. Further, in exemplary embodiments, the predetermined delay time period may be equal to the predetermined time interval. 
     In some embodiments, method  200  may further include, for example, the step  240  of reactuating the motor  120  to operate the pump  100 . Such step  240  may, for example, occur when the electrical signal level falls within the predetermined electrical signal range after, for example, deactuation  230  has occurred (such as within the predetermined time period for pump  100  operation). For example, such step  240  may occur when the electrical signal level falls within the predetermined electrical signal range within the predetermined delay time period. Accordingly, operation of the pump  100  may resume when the fluid level therein is again sufficient for pump  100  operation. 
     Notable, in exemplary embodiments, the predetermined electrical signal range may include and be determined based on a predetermined electrical signal threshold. In some embodiments, electrical signals above the threshold may be within the range and electrical signals below the threshold may be outside of the range. Alternatively, electrical signals below the threshold may be within the range and electrical signals above the threshold may be outside of the range. In some exemplary embodiments, for example, the electrical signal level is a voltage level. Voltage levels above a predetermined voltage threshold may be considered within the range, and voltage levels below the predetermined voltage threshold may be considered outside of the range. Alternatively, other suitable electrical signals, such as current or capacitance, may be measured and utilized in accordance with the present disclosure. 
     In some embodiments, method  200  may further include, for example, the step  250  of beginning a timer upon actuation of the motor  120  in step  210 . The timer may, for example, be integrated into the controller  99 . Method  200  may further include, for example, the step  260  of transmitting a blockage signal when the motor  120  remains actuated (and the pump  100  thus continues to operate) and a time period measured by the timer exceeds a predetermined actuation time threshold. Such step  260  may, for example, occur when the deactuating step  230  has not occurred during the time period measured by the timer and the time period exceeds the predetermined actuation time threshold. When the time period exceeds the predetermined actuation time threshold, this may indicate that a partial or full blockage exists in the pump  100  which is preventing fluid from sufficiently flowing through the pump  100 . The blockage signal thus indicates to the user that a blockage may exist, and allows the user to determine if a blockage indeed exists and to remove the blockage if necessary. 
     In some embodiments, the signal is transmitted to a signal output device  252  of the appliance  50 , which may for example, be included in the control panel  58 . For example, the signal output device  252  may be a portion of the display  61 , or may be a separate device  252  devoted to providing an output for the signal  202 . The signal output device  252  may emit an alert when the signal is received. The alert may, for example, be auditory and/or visual. Accordingly, the device  252  may, for example, be a speaker or a light. 
     Notably, in exemplary embodiments, the various time thresholds and electrical signal ranges as discussed herein may be stored in the controller  99 . In some embodiments, the thresholds and ranges may be user adjustable (i.e. via control panel  58  and input selectors  60 ). Additionally or alternatively, the thresholds and ranges may be calibrated based on an initial operation of the appliance  50 , such as upon installation or after a loss of power. For example, the predetermined actuation time threshold may be calibrated based on the time period measured during an initial operation of the appliance  50 , with the assumption that no blockage exists during this operation. Accordingly, methods and apparatus in accordance with the present disclosure may advantageously be utilized with a wide variety of drain pipe heights, and are calibrated for any particular drain pipe height, pump flow, etc. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.