Patent Publication Number: US-6708910-B2

Title: Pump and grinder assembly for use with a steam producing device

Description:
BACKGROUND 
     1.0 Field of the Invention 
     The present invention is directed to pump and grinder assemblies and, more particularly, to a pump and grinder assembly for use with a steam producing device, with the pump and grinder assembly being effective for pumping scale out of the steam producing device and grinding the scale into relatively smaller pieces. 
     2.0 Related Art 
     Steam producing devices such as steam generators, boilers, coffee makers and others, are well known in the art. Steam generators, which are vented to atmosphere, and boilers, which are pressurized to various gauge pressures, have a variety of applications including multiple applications in the cooking industry. For instance, steam generators and boilers are commonly used with convection-type steamer ovens such as those used in restaurants and other commercial establishments. The water supplied to these steam producing devices typically contains various minerals such as calcium, sodium, iron and magnesium. When the water is heated to its boiling temperature, the molecular bonds of the water break down causing these minerals to be deposited upon various interior surfaces of the housing of the steam producing device and components, such as water level sensors, disposed at least partially within the steam producing device. The minerals are typically deposited on any surface which is exposed to boiling water or steam, which constitutes essentially all interior surfaces of steam generators and boilers. The mineral deposits are referred to herein generically as “scale”. The buildup of scale within the steam producing device has a variety of adverse effects including increased operating costs and possible failure of the steam producing device. 
     Gas-fired steam producing devices typically include an outer housing and a firetube assembly contained within the outer housing. During operation, water is disposed in the space between the outer housing and the firetube assembly. Buildup of scale on the exterior walls of the firetube assembly reduces the thermal efficiency of the steam producing device, and therefore increases operating costs, by reducing the heat transfer from the metal walls of the firetube assembly to the surrounding water. The walls of the firetube assembly are heated by hot gas flowing within the assembly. The reduction in heat transfer through the water results in longer cooking times, with regard to steam producing devices used in the cooking industry, which is not desirable. The thermal efficiency of electrically-heated units is reduced when scale accumulates on the electrical resistance heating rods which are disposed within the water contained within the outer housing of the steam producing device and are used to transfer heat to the water. 
     Another problem with scale build up of this type is that it may lead to distortion or failure of the firetube assembly, which is typically made of stainless steel. This may occur as follows. The scale may accumulate on the exterior surfaces of the firetube assembly unevenly, with the thickness of the scale varying from top to bottom of the firetube assembly. Typically, the scale thickness increases with the temperature of the surface. The walls of the firetube assembly are generally hotter near the bottom where the gas burners are typically located, and are cooler near the top since the “hot air” cools down, due to heat transfer, as it flows through the firetube assembly from bottom to top, typically through a tortuous flowpath. Locally thicker areas of scale build up create “hot spots” in the metal walls of the firetube assembly. As an example, an average local metal temperature may be about 300° F., with a gas flame temperature of about 1000° F. under normal circumstances. As a result of scale build up, less heat is transferred to the surrounding water, so that the local metal temperature rises significantly, such as to about 700° F. by way of example. This may cause the wall of the firetube assembly to distort locally. Also, as one skilled in the art may appreciate, the presence of multiple hot spots may cause the metal wall of the firetube assembly to move to the extent that various seam or spot welds are pulled apart causing expensive repair or replacement of the unit. For instance, the spot welds attaching various interior heat transfer baffles to the walls of the firetube assembly may fail, causing water leaks into the combustion chamber of the firetube assembly. Additionally, the welds which attach the firetube assembly to the outer housing of the steam producing device may fail, which may result in water leaking externally of the steam producing device. 
     Operational costs may also be increased due to scale buildup on the water level sensors. When this occurs to the extent that the sensors are “limed over”, the sensors malfunction and are no longer able to detect the water level within the steam producing device. Typically, these sensors are part of a control circuit used to control water fill valves and the operation of the gas burners or electrical resistance heating elements within the steam producing device. Accordingly, when this occurs it may be necessary to shutdown and “de-lime” the device, which has been the industry standard for de-scaling water level sensors and attempting to de-scale the heat transfer surfaces within the steam producing device. A “de-liming” procedure is typically completed by pouring a chemical solution into the device, mixing it with water and running a cleaning cycle which adds to operating costs. The de-liming procedure may require the assistance of a service repairman or technician which further adds to operating costs. 
     Although de-liming procedures may be effective for cleaning the water level sensors and recovering thermal efficiency, by de-scaling various heat transfer surfaces such as the outer surfaces of the walls of a firetube assembly, other problems are created. During de-liming, pieces of scale, which may also be referred to as chips or chunks and vary in size and shape, are released and drop to the bottom of the steam producing device where they accumulate. Pieces of scale may also fall off during normal operation or during water filling and draining operations. When wet, these pieces tend to bond to one another forming a large mass of scale particles. When dry, the mass of scale particles is hard and brittle. Repeated de-liming procedures causes the accumulated mass of scale to grow in size which reduces the steam-generating capacity of the device due to reduced internal volume available for containing water. This also increases operating costs. Such an accumulation of scale may adversely affect water circulation within the steam producing device. As one skilled in the art may appreciate, when water boils, the water tends to rotate en masse, which mixes relatively hotter water with relatively cooler water within the steam producing device. However, the presence of significant scale build up within the unit may interrupt this natural convective flow of water, thereby reducing the efficiency of the unit. 
     Additionally, the buildup of scale in the bottom of the steam producing device may clog the drain system associated with the device. Steam producing devices such as a steam generator typically have a drain port extending through the housing of the device, which may be about two inches in diameter. However, a downstream drain valve, which is connected to the drain port by appropriate plumbing, may be much smaller, such as one-half inch diameter, due to cost considerations. Operators usually prefer remotely operated drain valves, such as electrically operated solenoid valves and, as known in the art, the price of these valves increases significantly with an increase in effective flow area. For instance, a nominal one-half inch solenoid valve may presently cost under one hundred dollars, whereas a nominal two inch solenoid valve may cost several hundred dollars. As may be appreciated, the presence of loose scale within the steam producing device may result in a relatively smaller flow area drain valve and associated plumbing becoming clogged before a relatively larger flow area drain port which may exist in the housing of the steam producing device. When the device drain is plugged, a potentially significant buildup of scale may result. This may lead to the various problems discussed previously. 
     Also, in extreme instances, the mass of accumulated scale may become so large that housing seam welds are broken or a “dry fire” may occur within the steam producing device causing the device to be replaced. The term “dry fire”, as known in the art, refers to the condition when the gas burners or electrical resistance heating rods of the steam producing device are turned on when there is no water contained within the steam producing device, as a result of the volume available to contain water being substantially filled with the scale. 
     In view of the foregoing disadvantages associated with known steam producing devices, a need exists for a cost efficient way to de-scale steam producing devices, without the intervention of a service technician or repairman. 
     SUMMARY 
     In view of the foregoing needs, the present invention is directed to a pump and grinder assembly for use with a wide variety of steam producing devices, including, but not limited to steam generators and boilers used in the cooking industry, with the pump and grinder assembly being operatively effective for pumping water and loose scale contained within the water out of the steam producing device and grinding the scale into relatively smaller pieces which may be discharged out of the drain port of the pump and grinder assembly. The present invention is also directed to the associated methodology and, in one aspect, a combination of the pump and grinder assembly and a steam producing device. Use of the pump and grinder assembly of the present invention permits significantly reduced operating costs, relatively to those associated with known steam producing devices which are not used in combination with the pump and grinder assembly of the present invention, as well as decreased capital costs. 
     Operating costs are reduced as a result of use of the pump and grinder assembly of the present invention for a variety of reasons. In the first instance, thermal efficiency of the associated steam producing device is increased due to the periodic extraction of loose scale from within the housing of the steam producing device. Scale may be released during filling, draining or de-liming operations or during normal operation of the unit. The pump and grinder assembly includes a blade assembly which is in fluid flow communication with a water chamber defined by the housing of the steam producing device. Preferably, the blade assembly is rotated during each of the filling, draining and de-liming operations. This causes water, and any loose scale suspended within the water, to be pumped out of the housing of the steam producing device into a grinding chamber of the pump and grinder assembly, where the scale is ground into relatively smaller pieces by the blade assembly, and then discharged out of a drain port of the pump and grinder assembly. Accordingly, the scale does not accumulate within the housing of the steam producing device as described previously with regard to those devices which are not used in connection with the pump and grinder assembly of the present invention. Consequently, thermal efficiency is improved due to improved heat transfer to the water within the housing of the steam producing device, which results in lower cooking times and reduced costs to the operator. Also, the use of the pump and grinder assembly of the present invention results in several additional advantages to the operator of the associated steam producing device. For instance, since there is not a significant accumulation of scale within the housing of a steam producing device, the natural convective flow of water within the housing may occur when the water starts to boil, thereby mixing the relatively hotter and cooler water and improving the overall efficiency of the steam producing device which reduces operating costs. The absence of a significant accumulation or buildup of scale in the bottom of the housing of the steam producing device also permits the nominal steam capacity of the steam producing device to be substantially maintained, which also reduces operating costs. Further, since the loose scale is ground into relatively smaller pieces, use of the pump and grinder assembly of the present invention permits the use of relatively smaller and less expensive, remotely operated main valves, which reduces overall capital costs. 
     Use of the pump and grinder assembly significantly reduces the possibility of local hot spots and dry fires due to the periodic extraction of scale from within the housing of the steam producing device. Accordingly, use of the pump and grinder assembly of the present invention results in reduced chances of failure of the steam producing device and therefore a longer service life and reduced capital costs associated with the steam producing device. 
     According to a first aspect of the present invention, a pump and grinder assembly is provided for use with a steam producing device having a housing defining a water chamber and an aperture formed in the housing and communicating with the water chamber. The pump and grinder assembly of the present invention may be used with a wide variety of steam producing devices including steam generators, boilers, coffee makers and others. The pump and grinder assembly is operatively effective for pumping water and scale contained within the water out of the steam producing device and grinding the scale into relatively smaller pieces with may be discharged out of a drain port of the pump and grinder assembly. The scale may comprise calcium carbonate, also known as lime, or other mineral-based compounds. According to one preferred embodiment, the pump and grinder assembly includes a motor having a rotatable output shaft and a pump and grinder shaft coupled to the output shaft of the motor for rotation therewith. The pump and grinder assembly also includes a blade assembly having a plurality of blades, with the blade assembly being secured to the pump and grinder shaft for rotation therewith. A housing is interconnected to a stationary portion of the motor, with the housing defining a grinding chamber. The plurality of blades is disposed within the grinding chamber. The drain port is formed in the housing and communicates with the grinding chamber. Additionally, the drain port is disposed downstream of the blades. The pump and grinder assembly is mountable on the steam producing device so that the grinding chamber communicates with the water chamber of the steam producing device, permitting water and scale contained within the water to be pumped out of the steam producing device into the grinding chamber and then subsequently discharged through the drain port. 
     The pump and grinder assembly may further include a motor mount bracket having a first end portion attached to the motor, and a second opposite end portion. The assembly may also include a seal disposed between, and in sealing engagement with, the second end portion of the motor mount bracket and the housing. The seal, motor mount bracket and housing are secured to one another and, preferably, are fastened to one another. 
     The pump and grinder assembly may also include a hollow connecting member which may be used to mount the pump and grinder assembly on the steam producing device. Accordingly, the hollow connecting member may have various configurations, depending upon the particular steam producing device on which the pump and grinder assembly is mounted. The hollow connecting member has a downstream, proximal end secured to the housing of the pump and grinder assembly and an upstream, distal end terminating in a mount flange. The mount flange has a plurality of mount holes formed therein, with the mount holes being effective for receiving fasteners to attach the pump and grinder assembly to the steam producing device. The mount flange also has a generally centrally disposed aperture formed therein, with the aperture of the mount flange being substantially aligned with the aperture or drain port formed in the housing of the steam producing device when the pump and grinder assembly is attached to the steam producing device. Accordingly, an interior portion of the hollow connecting member and the grinding chamber are in communication with the water chamber of the steam producing device. The motor preferably comprises an electric motor and even more preferably comprises an alternating current electric motor. However, the motor may also comprise a direct current electric motor. 
     In one embodiment, the blade assembly further includes a first blade-supporting portion and a second blade-supporting portion, with the first and second blade-supporting portions being secured to the pump and grinder shaft for rotation therewith. In this embodiment, the plurality of blades includes first and second pluralities of blades, with the first plurality of blades being integral with the first blade supporting-portion and the second plurality of blades being integral with the second blade-supporting portion. Preferably, the blades are made as a one piece construction with the corresponding blade-supporting portion. 
     The first blade-supporting portion is disposed forward, or upstream of the second blade-supporting portion. In one embodiment the first plurality of blades extend radially outwardly and forwardly or upstream from the first blade-supporting portion and the second plurality of blades extend radially outwardly and rearwardly, or downstream, from the second blade-supporting portion. However, it should be understood that a wide variety of blades are suitable for use in the pump and grinder assembly of the present invention, provided that they are effective for pumping water and loose scale contained in the water out of the steam producing device and then grinding the loose scale contained within the water into relatively smaller pieces. In this embodiment, the first plurality of blades comprises a pair of blades, each having a blade tip, with the blade tips being separated by a first distance. A lateral or transverse internal dimension of the downstream, proximal end of the hollow connecting member is preferably less than or equal to this first distance separating the pair of blade tips so that the scale does not bypass the blades as water and the included scale is pumped through the blade assembly. The downstream, proximal end of the hollow connecting member has a circular cross-section in one embodiment, with the lateral or transverse internal dimension of this portion of the hollow connecting member being an internal diameter. 
     The pump and grinder assembly may further include a gasket which is disposed between the mount flange of the connecting member and the steam producing device when the pump and grinder assembly is mounted to the steam producing device. The gasket has a plurality of mount holes equal in number to, and alignable with, the mount holes formed in the mount flange of the connecting member. The gasket also has a generally centrally disposed aperture which is substantially equal in size to the generally centrally disposed aperture formed in the mount flange of the connecting member. 
     In one preferred embodiment, the pump and grinder shaft includes a first substantially cylindrical portion having a first outside diameter, and a second substantially cylindrical portion having a second outside diameter. The first and second substantially cylindrical portions are integral with one another, with the second outside diameter being less than the first outside diameter. The blade assembly is secured to the first substantially cylindrical portion of the pump and grinder shaft at an end opposite the second, reduced diameter substantially cylindrical portion of the shaft. In this embodiment, the pump and grinder shaft further includes a threaded portion, having external threads, which is integral with the second substantially cylindrical portion at an end opposite the first, relatively larger diameter substantially cylindrical portion of the shaft. In this embodiment, the assembly further includes a hollow coupling having a first end portion with internal threads which are engaged with the threaded portion of the pump and grinder shaft. Additionally, a set screw is provided, which protrudes through a hole in the wall of the hollow coupling and engages the rotatable output shaft of the motor, whereby the hollow coupling and set screw combine to rotatably couple the pump and grinder shaft to the rotatable output shaft of the motor. In other embodiments, the rotatable output shaft of the motor may be threadedly engaged with the coupling, with the pump and grinder shaft being secured to the coupling via the set screw. Also, it is noted that a flexible coupling may be used within the scope of the present invention. As known in the art, a flexible coupling refers to a coupling which may be used to accommodate some misalignment between shafts being coupled, in this case the rotatable output shaft of the motor and the pump and grinder shaft. 
     In a preferred embodiment, a bearing is provided having a flange portion and a substantially cylindrical portion integral with the flange portion. The substantially cylindrical portion extends longitudinally through the second end portion of the motor mount bracket which is disposed away from the motor, and the flange portion of the bearing is disposed in contacting engagement with a first surface of this portion of the motor mount bracket, which faces away from the motor. An annular, elastomeric seal is disposed longitudinally between the first, relatively larger, substantially cylindrical portion of the pump and grinder shaft and the flange portion of the bearing. This seal is disposed in surrounding relationship with the second, relatively smaller, substantially cylindrical portion of the pump and grinder shaft. A combination of this seal and the gasket which is disposed in sealing engagement with the bearing and hollow coupling substantially prevent water from entering the chamber defined by the motor mount bracket. 
     According to a second aspect of the present invention, an assembly is provided which includes a steam producing device and a pump and grinder assembly mounted on the steam producing device. The pump and grinder assembly may include the various features of the previously discussed embodiments of the present invention. The steam producing device includes a housing defining a water chamber and a fill port formed in the housing and communicating with the water chamber such that the fill port is effective for receiving water therethrough. The steam producing device further includes a drain port formed in the housing and communicating with the water chamber, and a heating device disposed at least partially within the water chamber. The heating device is effective for transferring heat to the water contained within the water chamber during operation of the heating device. In one embodiment, the heating device includes one or more electrical resistance heating rods. In other embodiments, the steam producing device may be gas-fired, with the heating device including a gas manifold, gas burners and an associated firetube assembly disposed within the housing of the steam producing device. In this case, air is heated by the gas burners, with the air then flowing through the firetube assembly which results in heat being transferred through the metal walls of the firetube assembly to the water contained within the housing between an interior surface of the housing and the firetube assembly. 
     The pump and grinder assembly is operatively effective for pumping water and scale, which is loose and disposed or contained within the water, out of the housing of the steam producing device and grinding the scale into relatively smaller pieces. This scale is typically lying on a bottom of the housing of the steam producing device. Preferably, the fill port and a drain port of the steam producing device are longitudinally spaced apart. This relative positioning of the fill port and drain port assists in moving water and the included scale toward the pump and grinder assembly during periods when the blade assembly is rotated within the grinding chamber. 
     According to a third aspect of the present invention, a method is provided for extracting loose scale contained in water from within a water chamber of a steam producing device and processing the scale for draining. According to one preferred embodiment, the method comprises the steps of: pumping at least a portion of the water and the scale contained therein out of the water chamber of the steam producing device; and grinding at least some of the scale into relatively smaller pieces. 
     The method according to the present invention may further include the step of mounting a pump and grinder assembly to a housing of the steam producing device, with the housing defining the water chamber of the steam producing device, and the pump and grinder assembly including a grinding chamber and a plurality of rotatable blades disposed within the grinding chamber. The method may also include the step of providing communication between the water chamber of the steam producing device and the grinding chamber of the pump and grinder assembly. This permits water and loose scale contained within the water to be pumped from the water chamber to the grinding chamber. Additionally, at least one of the step of pumping and the step of grinding may include the step of rotating the plurality of rotatable blades disposed within the grinding chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings wherein: 
     FIG. 1 is an isometric view of a double-oven type steamer apparatus which includes two steam producing devices and associated pump and grinder assemblies, according to the present invention; 
     FIG. 2 is a side elevation view of one of the steam producing devices and associated pump and grinder assemblies shown in FIG. 1; 
     FIG. 3 is a top plan view taken along line  3 — 3  in FIG. 2; 
     FIG. 4 is a front elevation view taken along line  4 — 4  in FIG. 2; 
     FIG. 5 is an enlarged isometric view of a pump and grinder assembly according to the present invention; 
     FIG. 6 is a longitudinal view, partially in cut-away view and partially in cross-section, of the pump and grinder assembly shown in FIG. 6; 
     FIG. 7 is another longitudinal view, partially in cut-away view and partially in cross-section, rotated relative to FIG. 6, further illustrating the pump and grinder assembly shown in FIGS. 5 and 6; 
     FIG. 8 is an end view of the pump and grinder assembly shown in FIGS. 5-7; 
     FIG. 9 is an isometric view of a sub-assembly of the pump and grinder assembly shown in FIGS. 5-8, further illustrating a portion of the pump and grinder assembly; 
     FIG. 10 is an end view of the sub-assembly shown in FIG. 9; 
     FIG. 11 is a top view, partially in cross-section, of the sub-assembly shown in FIGS. 9 and 10; and 
     FIG. 12 is a side view of the sub-assembly shown in FIGS.  9 - 11 . 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, FIG. 1 is an isometric view illustrating a double-oven steamer apparatus  10  which includes a pair of convection-type steamer ovens  12  and a corresponding pair of steam producing devices  14 . Each of the steam producing steam devices  14  of apparatus  10  is an atmospheric steam generator and, as subsequently discussed, the water within each of the steam producing devices  14  is heated to a boiling temperature by a heating device  16 , best seen in FIG.  2 . The heating device  16  included in apparatus  10  is an electrical heating device. As shown in FIG. 1, the ovens  12  and steam generators  14  are supported by a structure indicated generally at  18 . Each of the steam generators  14  is used in conjunction with a pump and grinder assembly  20 , according to the present invention. 
     The pump and grinder assemblies  20  illustrated in FIG. 1 are used in conjunction with electrically heated steam generators  14 . However, it should be understood that this application of the pump and grinder assembly  20  is shown by way of illustration, and not of limitation. For instance, the pump and grinder assemblies  20  may be used in conjunction with a pair of gas-fired steam generators, otherwise similar to steam generators  14 . Additionally, the pump and grinder assemblies  20  may be used in combination with a pair of steam boilers, either electrically heated or gas fired, in lieu of the atmospheric steam generators  14 . Furthermore, a single pump and grinder assembly may be used with a single steam generator or boiler, either electrically heated or gas-fired which is used in conjunction with a single convection-type steamer oven. 
     Water is supplied to each of the steam producing devices  14  in a conventional manner. The heating device  16 , is an electrical resistance heating device in the illustrative embodiment and is used during cooking cycles to heat the water contained within the steam producing devices  14  to a boiling temperature such that steam is produced. Steam is discharged out of each of the steam producing devices  14  by a steam discharge port  22  and a steam discharge conduit (not shown) which communicates with a steam inlet housing (not shown) of the corresponding oven  12 , in a manner well known in the art. The steam then passes through the steam inlet housing into the cooking chamber (not shown) of the oven  12 . The manner in which steam is conveyed from steam producing devices  14  to ovens  12 , as well as the various features of the ovens  12 , do not comprise a part of the present invention. 
     Various included features of each of the steam generators  14  are illustrated with regard to one of the steam generators  14 , in FIGS. 2-4. Steam generator  14  includes a housing  24  which has a bottom  26 , a pair of sidewalls  28  supported by the bottom  26  and extending upwardly therefrom, and a top  30  secured to each of the sidewalls  28 . 
     Housing  24  is hollow and defines a water chamber  32 , which is suitable for containing water within housing  24 . The steam generator  14  further includes a fill device indicated generally at  34  which includes a connector  36 , suitable for attachment to a water fill hose (not shown) and a fill port indicated generally at  38  and formed in the bottom  26  of housing  24  which communicates with the water chamber  32 . Accordingly, the fill device  34  is effective for supplying water from a source of water to the water chamber  32 . The water level within the water chamber  32  is sensed by a pair of water level sensors  40 , of conventional construction. As known in the art, the water level sensors  40  are mounted on housing  24  and extend therethrough, with a tip (not shown) of each sensor  40  used to sense the presence of water within chamber  32 . 
     The electrical heating device  16  of steam generator  14  includes one or more electrical resistance heating elements  42 . In the illustrative embodiment, the heating device  16  includes a pair of the elements  42 , as shown in the partial cutaway view of FIG. 2, which extend into the water chamber  32 . At appropriate times during the operation of the apparatus  10 , electrical power may be supplied to the heating device  16 , which may be controlled by the water level sensors  40  as known in the art, so that heat is transferred from the elements  42  to water (not shown) contained within the water chamber  32 . This causes the water to be heated to a boiling temperature, which produces steam. The steam is discharged through discharge port  22 , flowing to the corresponding oven  12  as discussed previously. 
     Steam generator  14  further includes a high limit sensor  44 , shown in FIG. 2, which senses metal temperature and is used to detect conditions indicating a possible future dry fire, in the absence of maintenance activities to eliminate the condition. It is further noted that dry fires are very rare within the industry. The steam generator  14  further includes a pressure relief port  46  shown in FIG. 3 which may used in conjunction with a pressure relief valve (not shown). 
     Referring now to FIGS. 5-8, the various features of one of the pump and grinder assemblies  20  is further illustrated, according to one embodiment of the present invention. The pump and grinder assembly  20  includes a motor, indicated generally at  50 , having a housing  52  and a rotatable output shaft  54 . Motor  50  further includes a shaft seal  56  disposed in surrounding relationship with shaft  54  at the interface with housing  52 . 
     In the illustrative embodiment, the motor  50  is an alternating current electric motor, with electric power being provided to motor  50  from a source of electric power (not shown) via an electrical connector (not shown), such as a plug adaptable for engaging a wall outlet for instance, and wires  58  shown in FIG.  5 . In the illustrative embodiment, the electrical power provided to motor  50  may be 110 VAC or alternatively 24 VAC. In one embodiment, the inventor has determined that a single speed motor, having a rated speed of about 1200 rpm and one-third horse power, is sufficient for use since this motor has sufficient torque to grind scale with the subsequently described blade assembly included in the pump and grinder assembly  20 . 
     The pump and grinder assembly  20  further includes a pump and grinder shaft  60  coupled to the rotatable output shaft  54  of the motor  50 , for rotation therewith. A blade assembly, indicated generally at  62 , is secured to the pump and grinder shaft  60 , for rotation therewith as subsequently discussed in greater detail. 
     The pump and grinder assembly  20  also includes a motor mount bracket  64  having a first end portion  66  which is secured to the stationary housing  52  of motor  50  via a plurality of fasteners, such as bolts or screws  68  and nuts  70 . The motor mount bracket  64  further includes a notch  72  formed therein which is effective for receiving the electrical wires  58  therethrough, as shown in FIG.  5 . 
     The blade assembly  62  includes a first blade-supporting portion  74  (shown in FIGS.  6  and  8 - 11 ) and a second blade-supporting portion  76  best seen in FIGS. 7,  9  and  12  which are secured to the pump and grinder shaft  60 , for rotation therewith, via a retainer  78  which is integral with the pump and grinder shaft  60 . In the illustrative embodiment, pump and grinder shaft  60  and retainer  78  are made as a one piece construction. As best seen in FIGS. 8-10, the retainer  78  includes a pair of spaced apart tabs  79  which extend through apertures formed in the blade-supporting portions  74  and  76 . These tabs  79  may be spread apart somewhat after insertion through the blade-supporting portions  74  and  76 , so as to secure the blade assembly  62  to the pump and grinder shaft  60 , for rotation therewith. 
     The blade assembly  62  also includes a first plurality of blades  80  which are integral with the first blade-supporting portion  74 , and a second plurality of blades  82  which are integral with the second blade-supporting portion  76 . Preferably, blades  80  are formed as a one piece construction with blade-supporting  74  and similarly blades  82  are preferably formed as a one piece construction with blade-supporting portion  76 . In the illustrative embodiment, blade assembly  62  includes two of the blades  80  and two of the blades  82 . It should be understood that blade assembly  62  may include additional blades  80  and  82 , and further that various other configurations of blades, with regard to size, shape and number of blades, may be used in lieu of blades  80  and  82  provided that the alternative configurations are substantially rotatably balanced and are effective for pumping water and loose scale disposed within the water out of the steam producing device  14  and grinding the scale into relatively smaller pieces as subsequently discussed in greater detail with regard to blades  80  and  82 . The blades  80  extend radially outwardly and forwardly, or upstream, from the first blade-supporting portion  74  and the blades  82  extend radially outwardly and rearwardly, or downstream, from the second blade-supporting portion  76 . 
     The pump and grinder assembly  20  further includes a housing  90  which is interconnected to the stationary housing  52  of motor  50 . The assembly further includes a gasket  92  having a plurality of holes (not shown) formed therein, which are equal in number and substantially equal in size and spacing to a plurality of holes  94  formed in a second end portion  96  of the motor mount bracket  64 . The housing  90  includes a first, upstream flange  98 , a second, downstream flange  100  and an intermediate portion  102  extending between and secured to the flanges  98  and  100 . In a preferred embodiment, the intermediate portion  102  is made of metal tubing. The flange  100  of housing  90  includes a plurality holes (not shown) formed therein having a pattern which substantially matches the hole pattern in gasket  92  and the pattern of holes  94  formed in the second end portion  96  of motor mount bracket  64 . The gasket  92  and the flange  100  of housing  90  are secured to the second end portion  96  of motor mount bracket  64  via a plurality of fasteners such as bolts  104  and nuts  106 . 
     The housing  90  defines a grinding chamber  108 , with the pump and grinder shaft  60  extending into the grinding chamber  108 . Blade assembly  62  is disposed within chamber  108  for rotation therein. The pump and grinder assembly  20  further includes a drain port  110  formed in the housing  90  and communicating with the grinding chamber  108 . A connecting member  112 , which is a pipe coupling in the illustrative embodiment, is secured to the housing  90 . Preferably, the coupling  112  is welded to housing  90 . An elbow  114  is threadedly secured to coupling  112 . When assembly  20  is mounted on the steam producing device  14 , the elbow  114  may be connected to a drain conduit  116  as shown schematically in FIG.  3 . Conduit  116  is secured to a remotely-operated electrical solenoid drain valve  118 . Another conduit  120  is plumbed or connected to a discharge port of the solenoid valve  118  and is connected to a drain of the facility utilizing apparatus  10 . Solenoid valve  118  and conduits  116  and  120  are not a part of the pump and grinder assembly  20 . 
     The pump and grinder assembly  20  further includes a hollow connecting member  122  having a downstream, proximal end portion  124  secured to the housing  90  of the pump and grinder assembly  20 . In one embodiment, the proximal end portion  124  is welded to the flange  98  of the housing  90 . The connecting member  122  further includes an upstream, distal end terminating in a mount flange  126  having a plurality of mount holes  128  formed therein, with the mount holes  128  being effective for receiving fasteners (not shown) to attach the pump and grinder assembly  20  to the steam producing device  14 . The mount flange  126  further includes a generally centrally disposed aperture  130  which is substantially aligned with a drain port (not shown) extending through the housing  24  of the steam producing device  14  when the pump and grinder assembly  20  is attached to the steam producing device  14 . Accordingly, an interior portion  132  of the hollow connecting member  122  and the grinding chamber  108  are in communication with the water chamber  32  of the steam producing device  14 . Each of the blades  82  includes a blade tip  84 , with the tips  84  being separated by distance  86 . In the illustrative embodiment, the proximal end portion  124  of the connecting member  122  has a lateral or transverse internal dimension  87  which, in the illustrative embodiment, is an internal diameter. The diameter  87  is preferably less than or equal to the distance  86  separating the blade tips  84  of blades  80 , so that the water and scale contained within the water may not bypass blades  80  as the water and scale flow through the blade assembly  62 . 
     The pump and grinder assembly further includes a coupling  140  and a set screw  142  which are effective for coupling the rotatable output shaft  54  motor  50  with the pump and grinder shaft  60 . The pump and grinder shaft  60  includes a first substantially cylindrical portion  144  having a first outside diameter  146  and a second substantially cylindrical portion  148  having a second outside diameter  150 . The first  144  and second  148  substantially cylindrical portions of the pump and grinder shaft  60  are integral with one another and, preferably, the first diameter  146  is larger than the second diameter  150 . Shaft  60  further includes a threaded portion  152 , having external threads which is integral with the second substantially cylindrical portion  148 . The hollow coupling  140  has a first end portion  154  with internal threads which are threadedly engaged with the external threads of the threaded portion  152  of shaft  60 . Further, in the illustrative embodiment, the set screw  142  protrudes through a hole  156  formed in a wall of the hollow coupling  140  and engages the rotatable output shaft  54  of motor  50 . Accordingly, the hollow coupling  140  and the set screw  142  combine to rotatably couple the pump and grinder shaft  60  to the rotatable output shaft  54  of motor  50 . It should be understood, that, in other embodiments, the coupling  140  may be threadedly engaged with a threaded end of the output shaft  54  of motor  50 , with the set screw  142  passing through a hole such as  156  in the wall of coupling  140  so as to engage the pump and grinder shaft  60 . 
     The pump and grinder assembly  20  further includes a bearing  158  having a flange portion  160  and a substantially cylindrical portion  162  integral with the flange portion  160 . The substantially cylindrical portion  162  extends longitudinally through the second, opposite end portion  96  of the motor mount bracket  64 . The flange portion  160  is disposed in contacting engagement with a surface  164  of the portion  96  of motor mount bracket  64 . The surface  164  faces away from the motor  50 . The pump and grinder shaft  60  extends longitudinally through the bearing  158  and is rotatable within, and relative to, the bearing  158 . 
     An annular, elastomeric seal  166  is disposed longitudinally between the first substantially cylindrical portion  144  of the pump and grinder shaft  60  and the flange portion  160  of bearing  158 . In the illustrative embodiment, the seal  166  has a generally V-shaped cross section, but other configurations of seals may be used. The seal  166  is disposed in surrounding relationship with the second, substantially cylindrical portion  148  of shaft  60 . As shown in FIG. 6, a gasket  168  is disposed in sealing engagement with the bearing  158  and the hollow coupling  140 . The seal  166  and gasket  168  combine to substantially prevent water from entering the interior space  170  defined by mount brackets  64  and motor  50 . 
     A gasket  172 , best seen in FIG. 5, is disposed between the flange portion  126  of the connecting member  122  and the steam producing device  14  when the pump and grinder assembly  20  is mounted on the steam producing device  14 . Gasket  172  has a plurality of mount holes  174  which are in equal in number to, and alignable with, the mating mount holes formed in the mount flange  126  of the connecting member  122 . Gasket  172  further includes a generally centrally disposed aperture  176  which is substantially equal in size to an aperture  178  formed in flange in  126  of connecting member  122 . 
     According to another aspect of the present invention, the invention is directed to a combination of the pump and grinder assembly  20  and the steam producing device  14 . The steam producing device  14  includes a drain port which passes through the housing  24  of device  14 , at the location where the pump and grinder assembly  20  is mounted on housing  24 . As may be appreciated from FIG. 2, this drain port and the fill port  38  are spaced longitudinally apart from one another, which facilitates directing water and scale toward the pump and grinder assembly  20  during the portion of the filling operation when the rotatable blade assembly  62  is activated, or is rotating, as subsequently discussed in greater detail. 
     According to another aspect of the present invention, the present invention is directed to a method for extracting loose scale contained in the water within the water chamber  32  of the steam producing device  14  and processing the scale for draining. The method of the present invention includes the steps of: pumping at least a portion of the water and the scale contained therein out of the water chamber  32  of the steam producing device  14 ; and grinding at least some of the scale contained in the water into relatively smaller pieces. The method may further include the steps of mounting the pump and grinder assembly  20  to the housing  24  of the steam producing device  14  and providing communication between the water chamber  32  of the steam producing device  14  and the grinding chamber  108  of the pump and grinder assembly  20  so that water and at least some of the scale contained therein may flow between the water chamber  32  and the grinding chamber  108 . At least one of the steps of pumping and grinding includes the step of rotating the blades  80  and  82  of the blade assembly  62  within the grinding chamber  108 . 
     Preferably, the blade assembly  62  of the pump and grinder assembly  20  is activated, or turned on, so that the blade assembly  62  is rotated for at least a portion of the time when the steam producing device  14  is being filled with water, water is being drained from the steam producing device  14  and when the steam producing device  14  is being de-limed by introducing a de-liming solution into the steam producing device  14 . When the blade assembly  62  is rotated, the pumping action of blades  80  and  82  cause water and at least a portion of the scale contained within the water to be pumped out of the water chamber  32  through the drain port of the steam producing device  14 , through the interior portion  132  of the connecting member  122 , and into the grinding chamber  108 . The configuration of the blades  80  and  82  are such that the scale contained with the water pumped into grinding chamber  108  is ground into relatively smaller pieces. Additionally, blades  80  act as a centrifuge, which forces the pieces of scale radially outwardly where they pass through the annular space between the tips  84  of blades  80  and the inner surface of the wall of housing  90 . The scale then flows downstream within housing  90  and out through the drain port  110  formed in housing  90 . From there, the scale flows through coupling  112 , and elbow  114  to the drain conduit  116 . The scale then passes through solenoid valve  118 , and drain conduit  120  as it flows toward the drain of the facility in which the apparatus  10  is contained. 
     Use of the pump and grinder assembly of the present invention results in significant advantages to the operator of the associated steam producing device such as the steam producing devices  14  included in the double-oven steamer apparatus  10 . These advantages will be discussed in conjunction with the pump and grinder assembly  20 , according to one embodiment of the present invention, and steam producing device  14 . However, it should be understood that these advantages also apply to other embodiments of the pump and grinder assembly of the present invention, and when the pump and grinder assembly of the present invention is used with other steam producing devices. 
     Operating costs are reduced as a result of the use of the pump and grinder assembly  20  of the present invention for a variety of reasons. In the first instance, thermal efficiency of the associated steam producing device  14  is increased due to the periodic extraction of loose scale from within the housing  24  of the steam producing device  14 . Preferably, the blade assembly  62  is rotated during each of the filling, draining and de-liming operations since scale may be released during each of these operations. This causes water, and at least a portion of the loose scale contained within the water, to be pumped out of the housing of the steam producing device into the grinding chamber  108  of the pump and grinder assembly  20 , where the scale is ground into relatively smaller pieces by the blade assembly, and then discharged out of the drain port  110  of the pump and grinder assembly  20 . Accordingly, the scale does not buildup within the housing  24  of the steam producing device  14  as described previously with regard to those steam producing devices which are not used in connection with the pump and grinder assembly  20  of the present invention. Consequently, thermal efficiency is improved due to improved heat transfer to the water within the housing  24  of the steam producing device  14 , which results in lower cooking times and reduced costs to the operator. 
     Also, the use of the pump and grinder assembly  20  of the present invention results in several additional advantages to the operator of the associated steam producing device. For instance, since there is not a significant accumulation of scale within the housing  24  of the steam producing device  14 , the natural convective flow of water within the housing may occur when the water starts to boil, thereby mixing the relatively hotter and cooler water and improving the overall efficiency of the steam producing device  14  which reduces operating costs. The absence of a significant buildup of scale from the bottom of the housing  24  of steam producing device  14  also permits the nominal steam capacity of the steam producing device to be substantially maintained, which also reduces operating costs. Further, since the loose scale is ground into relatively smaller pieces, use of the pump and grinder assembly  20  of the present invention permits the use of relatively smaller and less expensive, remotely operated drain valves, such as solenoid valve  118 , which reduces overall capital costs. 
     Also, use of the pump and grinder assembly  20  significantly reduces the possibility of local hot spots and dry fires due to the periodic extraction of scale from within the housing  24  of the steam producing device  14 . Accordingly, use of the pump and grinder assembly  20  of the present invention results in reduced chances of failure of the steam producing device  14  and therefore a longer service life and reduced capital costs associated with the steam producing device  14 . 
     While the foregoing description has set forth the preferred embodiments of the present invention in particular detail, it must be understood that numerous modifications, substitutions and changes can be undertaken without departing from the true spirit and scope of the present invention as defined by the ensuing Claims. For instance, although the pump and grinder assembly  20  of the present invention has been illustrated for use with an atmospheric steam generator  14 , the pump and grinder assembly of the present invention may also be used with other steam producing devices, including pressurized boilers. Although the pump and grinder assembly  20  has been illustrated for use with a steam producing device which uses an electrical heating device to transfer heat to the water included therein, the pump and grinder assembly  20  may be used in conjunction with a “gas-fired” steam producing device which typically uses a gas supply system and gas burners which heat air flowing within a firetube assembly disposed within an outer housing of the steam producing device. Heat is then transferred to the water contained between the firetube assembly and the outer housing. “Gas-fired” steam producing devices are known in the art. As discussed previously, while the motor  50  shown in the illustrative embodiment is an alternating current electric motor, direct current electric motors may be used instead as part of the pump and grinder assembly of the present invention. Also, pump and grinder assembly  20  has been shown to include a motor mount bracket  64  in the illustrative embodiment. However, it should be understood that a wide variety of motor mount brackets having configurations other than that illustrated with respect to bracket  64 , may be included in the pump and grinder assembly of the present invention. Furthermore, it is possible that the motor mount bracket may be eliminated and replaced with a motor mounting housing. Also, as discussed previously, a wide variety of blades having other sizes, shapes and numbers may be used in lieu of blades  80  and  82 , as well as additional numbers of blades  80  and  82 , provided that the alternate blades are effective for pumping water and scale contained within the water out of the steam producing device and for grinding the scale into relatively smaller pieces. Further, the connecting member  122  may assume a wide variety of configurations, depending upon the configuration of the associated steam producing device. Also, in some circumstances, the connecting member  122  may be eliminated altogether. In this case, the housing  90  may be mounted directly on the associated steam producing device, with flange  98  being replaced by an appropriately configured mount flange. In still other embodiments, various other gaskets and seals may be used in lieu of those disclosed, provided that the function of sealing is maintained. Also, the coupling  112  and elbow  114  may be replaced with other drain devices effective for receiving water and scale passing through the drain port  110  formed in housing  90 . Accordingly, the invention is therefore not limited to specific embodiments as described, but is only limited as defined by the following Claims.