Abstract:
An automatic filtering system for filtering a cooking medium in a fryer, includes a frypot; a filter manifold having removable filter; a pump, that supplies cooking medium from the filter manifold to the frypot; a pressure sensor that senses a pressure of the cooking medium supplied by the pump; and a controlling mechanism that controls an operation of the pump in response to the sensed pressure data. The control mechanism halts the operation of the pump after sensing a drop in the pressure of the cooking medium pressure that is greater than or equal to a predetermined pressure drop threshold. The systems and methods of the invention provide automatic filtering that may reduce or eliminate an incorrect refilling operation after the filtering of cooking medium, so that the filtering process may be performed correctly each time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 12/475,051 filed on May 29, 2009, now U.S. Pat. No. 8,551,331, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to systems and methods for automatically filtering a cooking medium in a cooking apparatus, such as a fryer. 
     2. Description of Related Art 
     Known fryers, e.g., open-well fryers and pressure fryers, are used to cook various food products, e.g., poultry, fish, or potato products. Such fryers include a cooking vessel, e.g., a frypot, and the cooking vessel is filled with a cooking medium, e.g., an oil, a liquid shortening, or a meltable-solid shortening. Such fryers also include a heating element, e.g., an electrical heating element, such as a heating coil, or a gas heating element, such as a gas burner and gas conveying tubes, which heat the cooking medium in the cooking vessel. After the cooking medium reaches a preset cooking temperature, the food product is placed into the cooking medium, such that the food product is cooked in the cooking medium. For example, the food product may be positioned inside a product holder, e.g., a wire basket, and submerged in the cooking medium for a predetermined amount of time sufficient to cook or to complete the cooking of the food product. The amount of time sufficient to cook or to complete the cooking of the food product at a given cooking temperature depends on the type of food product which is cooked. Moreover, the cooking medium is used during several cooking cycles before the cooking medium inside the cooking vessel is filtered, replaced, or supplemented with a new or filtered supply of cooking medium. 
     Cooking medium may be filtered periodically to maintain cooking quality and to prolong the operational lifetime of the cooking medium. The filtering process removes cooking by-products, e.g., suspended food particles, ranging from dust-sized particles to larger pieces of crackling and small pieces of food product. Known contemporary filtering systems require the operator to manipulate valves to route the cooking medium through the filter and to return it to a cooking vessel, e.g., a frypot, disposed within the fryer. Even experienced operators may open or close the valves incorrectly, which increases operating expenses through lost time. Periodically, the drain pan under the fryer may be removed for cleaning or to discard the cooking medium. If the operator fails to replace the drain pan and opens the drain valve, the cooking medium drains out of the fryer and may be wasted, which greatly increases operating expenses. Moreover, it is generally desirable to filter the cooking medium for an appropriate time period. Consequently, if the filter time is too short, the cooking medium may not be not adequately filtered. If the filter time is too long, operating efficiency may be impaired, and cooking medium quality may be degraded unnecessarily by mechanical agitation and oxidation. 
     After filtering, the cooking medium may be returned to the frypot for further cooking. Known systems require an operator to operate a pump to refill the frypot with cooking medium. The amount of cooking medium in the frypot may vary based on the experience level of the operator, which may lead to inconsistencies in the quality of cooked food product. Moreover, such a refilling process requires the operator to supervise the refilling process, which reduces overall efficiency. 
     In addition, multiple frypots may be connected to a single drypan. Each frypot may be designated for cooking a different food product, e.g., chicken, french-fried potatoes, and fish. The flavor characteristics of each of these food products may become infused in the cooking medium. As a result, mixing cooking medium from frypots designated for different food products during filtering may adversely affect food quality, e.g., cooking chicken in a significant quantity of fish-flavored cooking medium may result in “fishy” chicken. Known filtering systems may permit an operator to simultaneously filter cooking medium for frypots designated for different food products, which may reduce the quality of cooked food product for the reasons noted above. 
     Referring to  FIGS. 1 and 2 , a fryer apparatus  10  comprising a known manual cooking medium filtering system and a known method for operating such a filtering system are depicted. Fryer apparatus  10  includes a frypot  16  having an open top  14  for receiving a food product. A cabinet  20 , shown without a door for illustrative purposes, has brackets  32  supporting a drain pan  30  having a filter (not shown). Drain pan  30  includes a handle  34  that allows drain pan  30  to be removed from cabinet  20  for cleaning. Drain pan  30  is fluidly connected to frypot  16  via a drain hose  24  and a filter pipe  28 . Disposed on filter pipe  28  is a filter pump  27  for drawing cooking medium to frypot  16  from pan  30 . Frypot  16  includes a drain valve handle  22  that operates a drain valve (not shown) for selectively permitting cooking medium to drain from frypot  16  via hose  24 . Frypot  16  also includes a filter valve handle  26  that operates a filter valve (not shown) for selectively permitting the introduction of cooking medium to frypot  16  from drain pan  30 . Fryer apparatus  10  further may include a power supply  40  for powering filter pump  27 , which may be actuated via a switch on control panel  18 . 
     Referring to  FIG. 2 , a method for operating a known filtering system is depicted. To filter the cooking medium of fryer apparatus  10 , the operator first ensures that the filter valve is closed  50 . The operator turns drain valve handle  22  clockwise to manually open the drain valve  55 , which uses gravity to permit the cooking medium to drain into drain pan  30 . Next, the operator turns the filter valve handle  26  counter-clockwise to manually open the filter valve  60 . The operator then turns drain valve handle  22  counter-clockwise to manually close the drain valve  55 . The operator then actuates filter pump  70  using a switch that may be located on control panel  18 . Next, the operator de-actuates the filter pump  75  to end the filtering process. Finally, the operator turns filter valve handle  26  in a clockwise direction to manually close the filter valve  80 , so that operation of the fryer apparatus may resume. 
     Handles  22 ,  26  may be located in cabinet  20  beneath frypot  16 . The above-described procedure is not intuitive unless the operator understands the logic and plumbing of the filter system, which generally is not the case for untrained operators. In known filtering systems, handles  22 ,  26  may be turned opposite directions to achieve the same result, in part because of design limitations within cabinet  20 , which may add another element of complexity that may lead to operator error. Further, if one of the sequence of steps is omitted or executed out of order, then, at best, the operating efficiency of the fryer apparatus is impaired, and, at worst, the pump or frypot may be damaged. Even trained, experienced operators may omit or switch steps during peak cooking periods, e.g., the “lunch-rush.” 
     SUMMARY OF THE INVENTION 
     Therefore, a need has arisen for filtering systems and methods for a cooking apparatus that overcome these and other shortcomings of the related art. A technical advantage of the present invention is that automatic filtering prevents incorrect valve operation, so that the filtering process is performed substantially correctly each time. Another technical advantage of the invention is that operating profits may be increased by reducing the personnel training needed by providing an automatic filtering system where the operator need only actuate a single switch to accomplish filtering. Yet another technical advantage of the invention is that precise control of the filtering cooking medium may be achieved, including automatic refilling of the frypot after a filtering operation is performed. Still another technical advantage of the invention is that mixing of significant amounts of cooking medium from frypots used to cook different food products, which may adversely affect cooked food product quality, may be reduced or eliminated. 
     The systems and methods of the invention are suitable for use with automatic filtering control systems and methods, such as those disclosed in U.S. patent application Ser. No. 11/563,656, filed on Nov. 27, 2006, entitled “AUTOMATIC OIL LEVEL CONTROL SYSTEMS AND METHODS,” and U.S. patent application Ser. No. 11/563,597, filed on Nov. 27, 2006, entitled “AUTOMATIC COOKING MEDIUM FILTERING SYSTEMS AND METHODS,” the disclosures of which are hereby incorporated by reference in their entirety. 
     According to an embodiment of the present invention, an automatic cooking medium filtering system includes a cooking vessel having an opening for receiving food product, the cooking vessel is configured to accommodate a cooking medium; a filter container having a removable filter configured to filter cooking medium, the filter container is fluidly connected to the cooking vessel; a fill manifold disposed on a fluid communication path between the filter container and the cooking vessel; a supply mechanism configured to supply cooking medium from the filter container to the cooking vessel; a pressure sensor configured to sense a pressure of the cooking medium supplied from the filter container; and a controlling mechanism receiving sensed pressure data from the pressure sensor, the controlling mechanism configured to control the supply mechanism in response to the sensed pressure data to provide the cooking medium from the filter container to the cooking vessel. The control mechanism is configured to stop the supply mechanism when the pressure sensor senses a drop in the pressure of cooking medium that is greater than or equal to a predetermined pressure drop threshold. 
     According to another embodiment of the present invention, a method for automatically filtering cooking medium in a cooking vessel includes the steps of: draining cooking medium from a cooking vessel; filtering cooking medium through a filter; supplying the filtered cooking medium back to the cooking vessel with a supplying mechanism; sensing a pressure of cooking medium supplied to the cooking vessel; and controlling the supplying of filtered cooking medium based on the sensed pressure of the filtered cooking medium. The sensing step includes the substeps of: sensing the pressure of cooking medium at a first interval; sensing the pressure of cooking medium at a second interval; and determining a change in the pressure of cooking medium between the first interval and the second interval. The controlling step includes halting the supply of cooking medium when sensing that the change in cooking medium pressure is a pressure drop that is greater than or equal to a predetermined pressure drop threshold. 
     According to yet another embodiment of the invention, a system for automatically filtering a cooking medium of a cooking apparatus includes: a cooking vessel having an opening formed therein for receiving food product, the cooking vessel is configured to accommodate a cooking medium; a filter container having a removable filter configured to filter cooking medium in fluid communication with the cooking vessel; a means for supplying cooking medium along a fluid communication path between the filter container and the cooking vessel; an expansion chamber disposed on the fluid communication path between the filter container and the cooking vessel; a means for sensing a pressure of the cooking medium supplied from the filter container to said cooking vessel; a means for controlling an operation of the supply means in response to sensed pressure of the cooking medium, the control means halts the operation of the supply means when said sensing means senses a drop in the pressure of cooking medium that is greater than a predetermined pressure drop threshold; and a means for indicating that the cooking vessel is filled with cooking medium after sensing the predetermined pressure drop threshold. 
     Other objects, features, and advantages of the present invention will be apparent to persons of ordinary skill in the art in view of the foregoing detailed description of the invention and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following description taken in connection with the accompanying drawings. 
         FIG. 1  is a front view of a fryer utilizing a known filtering system. 
         FIG. 2  is a flow chart showing a known method for operating the filter system shown in  FIG. 1 . 
         FIG. 3  is a schematic view of an automatic cooking medium filtering system according to an embodiment of the invention. 
         FIG. 4A  is a perspective view of a cooking vessel according to an embodiment of the invention. 
         FIG. 4B  is a plan view of a cooking vessel according to another embodiment of the invention. 
         FIG. 5  is a schematic view of an automatic cooking medium filtering system according to another embodiment of the invention. 
         FIG. 6  is a flow chart showing a method for automatically filtering a cooking medium according to an embodiment of the invention. 
         FIG. 7  schematic view of an automatic cooking medium filtering system according to still yet another embodiment of the invention. 
         FIG. 8  is an elevational view of an automatic cooking medium filtering system according to still yet another embodiment of the invention. 
         FIG. 9  is a flow chart showing a method for automatically refilling a cooking vessel with cooking medium after a filtering operation according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention, and their features and advantages, may be understood by referring to  FIGS. 3-9 , like numerals being used for corresponding parts in the various drawings. 
     Referring to  FIG. 3 , a filtering system  100  according to an embodiment of the present invention is depicted. Filtering system  100  may comprise at least one cooking vessel  116 , e.g., a frypot, which may be configured to hold a cooking medium, e.g., an oil, a liquid shortening, a meltable-solid shortening, or the like. Cooking vessel  116  may include an opening  114  for receiving a food product. A heating element (not shown), which may be a heating coil, is disposed within cooking vessel  116  for heating the cooking medium within vessel  116 . Filtering system  100  may be utilized in a gas or electric fryer.  FIG. 3  depicts vessel  116  suitable for an open-well fryer, but filtering system  100  also be used in a pressure fryer. 
     Cooking vessel  116  may comprise a drain at an inlet of a drain path  124  fluidly connecting vessel  116  to a filter container  130 , e.g., a drain pan or a filter canister. A drain valve  122 , which may be a solenoid valve, may be disposed on drain path  124  to permit selectively cooking medium to drain from vessel  116  in response to a control signal from a controller C. Preferably, drain valve  122  is a linearly actuated valve to reduce the likelihood that cooking by-products may obstruct valve  122 . Cooking medium may pass through filter container  130  holding a removable filter pad, such as a Henny Penny SmartFilter™ or other known permeable filters for filtering a cooking medium. Subsequently, the cooking medium may return to vessel  116  via a fill path  128 . A second filter container (not shown) that may serve as a backup filter also may be connected to paths  124 ,  128 , when a filter in container  130  requires replacing or otherwise malfunctions. A fill valve  126 , which also may be a solenoid valve, may be disposed on fill path  124  to selectively permit cooking medium to be introduced into vessel  116  in response to a control signal from controller C. 
     Referring to  FIG. 3 , a filter pump  127  is disposed on drain path  124  to convey the cooking medium along drain and fill paths  124 ,  128 , but pump  127  also may be disposed on fill path  128 . Pump  127  actuates and de-actuates in response to a control signal from controller C. Any suitable pump may be used. In one embodiment, pump  127  may be a roller pump, such as a series 0500 roller pump, manufactured by Hypro, Inc., of New Brighton, Minn. Controller C may comprise a processor coupled to a physical memory, an operator input, e.g., a push-button manual switch or an electronic switch, and a mechanism to detect whether the cooking medium is in suitable condition for filtering. Controller C may be coupled to an indicator  142 , e.g., a visual or audible alarm that indicates either that a filtering process is being performed by system  100  or that the cooking medium in vessel  116  is not in suitable condition for filtering. Indicator  142  may be a light, e.g., incandescent, fluorescent, LED, or the like, or indicator  142  may be incorporated into the fryer&#39;s current display, such as on an LCD screen. If indicator  142  is an LED light, it may be on to indicate filtering of the cooking medium, and may blink or flash to indicate the cooking medium is not available, i.e., not ready for, filtering. 
     Drain and fill manifolds (not shown) may be disposed on the respective drain and fill paths, such an arrangement may permit the use of a smaller filter container that has an insufficient capacity to hold the entire volume of cooking medium within vessel  116 , or may allow multiple vessels to be connected to the same filter container wherein a multiple vessel, fryer may use a single filtering system, as shown, for example, in  FIG. 5 . 
     Referring to  FIG. 4A  and  FIG. 4B , arrangements for cooking medium inlets fluidly connected to fill path  128  according to embodiments of the invention are depicted. As shown in  FIG. 4A , a pair of inlets  226 A,  226 B may be formed within a surface of cooking vessel  116  disposed at opposite ends of a longitudinal axis, i.e., a length, of vessel  116 . For example, inlets  226 A,  226 B are shown here as formed within opposing sidewalls of vessel  116 . Inlets  226 A,  226 B may be separated by a lateral distance that is substantially a width of vessel  116 . Arranging inlets  226 A,  226 B in this configuration may facilitate a spiral flow, e.g, swirling, of the cooking medium on a bottom surface  216  of vessel  116  to clean bottom surface  216 , wherein cooking by-product or any other particles may exit vessel  116  through a drain  220 . Bottom surface  216  may be sloped towards drain  220  to assist cooking medium, and any cooking by-product therein, to exit vessel  116 . Preferably, inlets  226 A,  226 B are disposed proximate to bottom surface  216 . 
     Referring to  FIG. 4B , an alternative inlet arrangement is depicted. A pair of linear diffuser headers  236 A,  236 B may extend along opposing sides of bottom surface  216 . Diffuser headers  236 A,  236 B also may be disposed on opposing sidewalls of vessel  116  proximate to bottom surface  216 . Preferably, diffuser headers  236 A,  236 B extend substantially parallel to a longitudinal axis, i.e., along a length, of vessel  116 . Diffuser headers  236 A,  236 B may comprise a plurality of inlet holes  238  for introducing cooking medium via filter path  128 . Preferably, inlet holes  238  are configured to direct cooking medium towards a center axis of bottom surface  216  to promote the spiral flow of cooking medium for the reasons described above. Again, bottom surface  216  may be sloped towards drain  220 . 
     Referring to  FIG. 5 , a filtering system  300  according to another embodiment of the present invention is depicted. Filtering system  300  may comprise a plurality of cooking vessels  316 ,  356 ,  376 , e.g., frypots. Each vessel  316 ,  356 ,  376  may comprise a drain path  324 ,  364 ,  384  fluidly connected to a common, drain manifold  340 . If two vessels, e.g., vessels  316  and  356 , are designated for a same first food product, and the third vessel, e.g., vessel  376 , is designated for a different second food product, then vessels  316 ,  356  may be connected fluidly to a first drain manifold, while vessel  376  may be connected fluidly to a second drain manifold to segregate further the flavors infused in the cooking mediums for the respective first and second food products. A drain valve  322 ,  362 ,  382 , responsive to a control signal from controller C, may be disposed along each drain path  324 ,  364 ,  384 . 
     Drain manifold  340  may be connected fluidly to filter container  330  on a manifold drain path  345 . An outlet (not shown) of the filter container  330  may be connected fluidly to a fill manifold  350  through a manifold fill path  355 . A pump  327  may be disposed along either manifold path  345 ,  355  to draw cooking medium through filter container  330 , which may hold a removable filter media for filtering cooking medium, such as a filter pad. In this exemplary embodiment, pump  327 , which may be responsive to a control signal from controller C, is shown as disposed on manifold drain path  345 . Fill manifold  350  may be fluidly connected to each vessel  316 ,  356 ,  376  via a respective fill path  328 ,  368 ,  388 . A fill valve  326 ,  366 ,  386 , responsive to a control signal from controller C, may be disposed along each fill path  326 ,  366 ,  386 . 
     Controller C may be actuated by an operator using a single switch  344 , e.g., a mechanical or an electronic switch. An indicator  342  coupled to controller C may give a visual or audible indication that filtering of cooking medium from at least one vessel  316 ,  356 ,  376  is being performed, or that the cooking medium in at least one of the vessels is not available, i.e., ready, for filtering for filtering. Indicator  342  also may indicate that the cooking medium needs filtering, and such indication may be based on a predetermined number of cooking cycles for which the cooking medium has been used or sensing the condition of the cooking medium to determine that it is no longer efficient for cooking food product and requires filtering or changing. 
       FIG. 6  shows an exemplary embodiment of a method for automatically filtering a cooking medium of a cooking vessel, e.g., a frypot. First, the operator may request the cooking medium in a cooking vessel to be filtered, e.g., by actuating a switch. Next, a controller may determine whether the cooking medium in the vessel is not available, i.e., ready, for filtering. Parameters used for determining whether the cooking medium is ready for filtering may include, but are not limited to, the temperature of the cooking medium, any turbulence detected in the cooking medium, or whether food product is within the vessel. Further, if the method is used with a fryer apparatus having a plurality of cooking vessels, not more than one vessel may be suitable for filtering at any time, so that multiple vessels will not be filtered concurrently, in part, to prevent mixing of a significant amount of cooking medium from different vessels. Once it is determined that the cooking medium is ready for filtering, then filtering of the cooking medium may begin. 
     Referring to  FIG. 6 , a method  400  for automatically filtering the cooking medium according to one embodiment of the invention now is described. First, in step  410 , a drain valve may be opened automatically to permit cooking medium to exit, or drain, the cooking vessel. Next, in step  415 , a filter valve may be opened automatically to permit introduction of cooking medium into the vessel. Subsequently, a filter pump may be energized in step  420  to pass the cooking medium through a container, such as a drain pan or filter canister, to filter the cooking medium. Both the drain valve and the filter valve may be open concurrently when the pump is energized to enable a flow of cooking medium to coat or swirl on a bottom surface of the cooking vessel for cleaning purposes. After letting the cooking medium clean the bottom surface of the vessel for a predetermined period, the drain valve may be closed automatically in step  425  to allow purging of the filter container and filling of the vessel with cooking medium in step  430 . Next, the pump may be de-energized in step  435  after filling the vessel. Finally, the filter valve may be closed automatically in step  440  to prevent drainage of cooking medium into the filter container and complete the filtering of cooking medium from the cooking vessel. 
     Referring to  FIG. 7 , a filtering system  500  according to yet another embodiment of the present invention is depicted. Filtering system  500  may comprise a plurality of cooking vessels  516 ,  556 ,  576 , e.g., frypots. Each vessel  516 ,  556 ,  576  may comprise a drain path  524 ,  564 ,  584  fluidly connected to a common, drain manifold  540 . A drain valve  522 ,  562 ,  582 , responsive to a control signal from controller C, may be disposed along each drain path  524 ,  564 ,  584 . 
     Drain manifold  540  may be connected fluidly to filter container  530  on a manifold drain path  545 . Filter container  530 , which may hold a removable filter media for filtering cooking medium, such as a filter pad, may be connected fluidly to a fill manifold  550  via a manifold fill path  555 . A filter pump  527  may be disposed on either manifold path  545 ,  555  to draw cooking medium through filter container  530  and return to cooking medium to a selected vessel  516 ,  556 ,  576 . Pump  527 , which may be responsive to a control signal from controller C, is shown as disposed along manifold fill path  555 . Fill manifold  550  may be fluidly connected to each vessel  516 ,  556 ,  576  via a respective fill path  528 ,  568 ,  588 . A fill valve  526 ,  566 ,  586 , responsive to a control signal from controller C, may be disposed along each fill path  526 ,  566 ,  586 . A pressure sensor  600 , such as a pressure transducer, or the like, may be provided to sense the pressure of the cooking medium supplied through fill path  555  or manifold  550 . In the exemplary embodiment of  FIG. 7 , pressure sensor  600  is set up to sense the pressure of cooking medium in fill manifold  550 . While pump  527  is operating to refill one of vessels  516 ,  556 ,  576 , after a filtering operation, pressure sensor  600  will sense a pressure of cooking medium. When a selected vessel nearly is refilled, there may be little or no cooking medium in the fill path  555  or manifold  550 , which results in a drop in the pressure of the cooking medium. Pressure sensor  600  may sense the drop in pressure in this cooking medium, and controller C may determine that the vessel is refilled, and a filtering operation is complete. 
     Controller C may be actuated by an operator using a single switch  544 , e.g., a mechanical or an electronic switch. An indicator  542  coupled to controller C may give a visual or audible indications regarding the status of the cooking medium or vessel, as described with respect to indicator  342 . Moreover, in response to the pressure data sensed by sensor  600 , indicator  542  may give a visual or audible indication that one of the vessels is refilled with cooking medium after a filtering operation. In addition, if the selected vessel is not refilled before the expiration of a predetermined fill time or if the cooking medium does not achieve a minimum fill pressure, controller C may send a signal to indicator  542  to indicate that a filter requires changing. 
     During a refilling operation after the cooking medium is filtered, in some instances there may be no outlet for the cooking medium supplied by pump  527  due to a fault in the system, such as failure of one of the solenoid valves or an obstruction in one of the manifolds. This condition is known as a deadhead condition which may result in the generation of high pressures in fill manifold  550 ; such pressures may reach 400-600 p.s.i. (about 2800-4200 kPa). These deadhead pressures may cause the pressure sensor to fail as these pressures greatly exceed the known proof pressure of a transducer having deformable diaphragm, such as a Ashcroft G2 pressure transducer, used in one exemplary embodiment of the invention, which may have a proof pressure of about 90 p.s.i. (about 630 kPa) and a burst pressure of about 450 p.s.i. (about 3150 kPa). 
     In the event of a deadhead condition, pump  527  will attempt to transit cooking medium from the filter pan  530  back to a selected vessel  516 ,  556 ,  576  via fill manifold  550 . Because there is no outlet for the cooking medium, pressure within the fill manifold  550  may start to build up. If pressure sensor  600  senses that the air pressure exceeds a predetermined burst threshold, controller C may halt the operation of pump  527  to prevent a build up of deadhead pressure that could damage the pressure sensor. After pressure sensor  600  senses a predetermined drop in pressure of cooking medium below the burst threshold, controller C may reactivate pump  527  and recommence the refilling operation. 
     In order to mitigate the effects of deadheads, the system may also include an expansion chamber  605  in fluid communication with fill manifold  550 , into which cooking medium expands as pump  527  pressurizes cooking medium, so that it may be supplied to a selected vessel  516 ,  556 ,  576  after a filtering operation. The geometry of expansion chamber  605  may vary, but chamber  605  should encompass a sufficient volume to slow pressure build-up during a deadhead. Pressure sensor  600  may be located above an expansion chamber to prevent immersion in the cooking medium within expansion chamber. Moreover, expansion chamber may be configured to permit cooking medium to drain out to preserve an air charge within expansion chamber  605  that may reduce a build-up of deadhead pressure. 
     Because pump  527  may continue to generate pressure after the controller C sends a control signal to halt operation, the deadhead pressure in expansion chamber  605  or fill manifold  550  still may exceed the predetermined burst threshold. A large hysteresis between the predetermined burst pressure and the pressure at which pump is reenergized may be desirable to prevent damage to pressure sensor  600 . In an exemplary embodiment, for example, when an Ashcroft G2 pressure transducer, which has a proof pressure of 90 p.s.i. (about 630 kPa), serves as pressure sensor  600 , the predetermined burst threshold may be set at 30 p.s.i. (about 210 kPa) but the ultimate deadhead pressure may reach 30 p.s.i. to 60 p.s.i (about 210 kPa to 420 kPa) as pump  527  is halting operation. Thus, controller C may be set to reenergize pump  527  at a pressure of 5 p.s.i. (about 35 kPa) so that a second deadhead condition would not result in pressures capable of damaging the pressure sensor. Moreover, the significant degree of hysteresis may permit cooking medium to drain from expansion chamber  605  and restore its air charge. 
     In another exemplary embodiment, as shown in  FIG. 8 , expansion chamber  605  may be set at an angle of at least 20 degrees relative to a horizontal plane of the fryer apparatus, parallel to a plane defined by an opening  517  of vessel  516 , to position pressure sensor above an inlet of expansion chamber  605  in fluid communication with fill manifold  550 . Such a configuration not only preserves the air charge within expansion chamber  605 , but also may substantially prevent cooking medium from contacting pressure sensor  600  and prevent food particles suspended in the cooking medium from clogging an inlet of pressure sensor  600 , which may increase the response time of the pressure sensor and prevent reliable sensing of cooking medium pressure. In a closed system, the air charge and the cooking medium within expansion chamber  605  may be substantially at the same pressure, and, thus, obviates the need to submerge the pressure sensor in cooking medium to accurately sense the pressure of cooking medium as it is supplied to vessels  516 ,  556 ,  576 . 
     Referring to  FIG. 9 , a refilling operation  700  of the filtering system now is described. The refilling operation  700  may take place between filling the vessel at step  430  and de-energizing the pump at step  435  of method  400  for automatic filtering of a cooking medium. When a vessel is refilled with filtered cooking medium at step  430 , the pressure of the cooking medium supplied to one of the vessel may be sensed at step  710 . The cooking medium pressure may fail to reach a predetermined minimum fill pressure due to filter reaching the end of its operational life. Thus, at step  715 , the indicator may give a “CHANGE FILTER” indication when the system fails to sense that the cooking medium pressure reaches the minimum fill pressure, which may prompt the operator to change the filter pad. In one exemplary embodiment, a fill pressure is at least about 4 p.s.i. (about 28 kPa). At step  720 , the sensor may detect a pressure drop exceeding a predetermined pressure drop threshold, such as, for example, a 3 p.s.i (about 21 kPa) drop in pressure of the cooking medium supplied to a cooking vessel. Such a pressure drop may indicate that the filtered cooking medium has been pumped out of the fill manifold back to the vessel. If the pressure drop threshold is not detected before the expiration of a predetermined fill time, such as, for example, 4 minutes, the indicator at step  715  may give a “CHANGE FILTER” indication to replaced the aged filter pad. In the case of a deadhead, when the predetermined burst pressure is sensed, the controller may de-energize the pump at step  435 . 
     After detecting the pressure drop at step  720 , the controller may continue the operation of the pump for a predetermined evacuation period to evacuate the cooking medium from the fill manifold at step  730 . In one exemplary embodiment, the predetermined evacuation period is approximately 8 seconds. After evacuation of the fill manifold at step  730 , a controller may de-energize the pump at step  435 . When a “CHANGE FILTER” condition is met, the method may continue to a subsequent step but the “CHANGE FILTER” condition is indicated to an operator. Nevertheless, when the burst pressure is sensed, the pump may be de-energized immediately at step  435 , without performing further refilling of the cooking vessel, to prevent build-up of deadhead pressures that may damage the pressure sensor. 
     While the invention has been described in connection with preferred embodiments, it will be understood by those of ordinary skill in the art that other variations and modifications of the preferred embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those of ordinary skill in the art from a consideration of the specification or practice of the invention disclosed herein. The specification and the described examples are considered as exemplary only, with the true scope and spirit of the invention indicated by the following claims.