Patent Publication Number: US-6707988-B2

Title: Universal drain plug heater for livestock water tanks

Description:
RELATED APPLICATIONS 
     This application is related to, and claims priority from, Provisional Application No. 60/297,961 filed Jun. 13, 2001, titled “Universal Drain Plug heater For Livestock Water Tanks,” the complete subject matter of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to electric water heaters, and more particularly to electric water heaters for use in livestock water tanks exposed to low temperature extremes. 
     Livestock require large amounts of water throughout the year. In order to provide livestock with needed water during winter months, exterior livestock watering tanks are seasonally equipped with electric water heaters to prevent the water contained therein from icing over during cold temperatures. These heaters either float in the tank or rest on the bottom of the tank. The power cord extends from the heater and over the side wall of the tank for connection to a power outlet. Because the heater is not fixed in the tank in these prior designs, it is possible for the heater to be thrown from the tank when an animal drags on the power cord. 
     Commercially available water tanks typically include a drain opening in their side wall so that the tanks can be drained, e.g. for transporting or so it can be refilled with fresh water. It is desirable to have a tank heater in which the power cord extends from the tank through the drain opening so that cord is out of reach of the livestock. However, the size of the drain plug opening varies depending on the manufacturer, and in many instances the drain openings are too small to permit the male plug of the power cord to be inserted through the opening. As a result, there is a need for a tank heater that can be mounted through a variety of sizes of drain plug openings without modifying the drain plug or the water heater. 
     In response to this problem, U.S. Pat. No. 6,151,448 discloses the use of “split” cord construction. However, this split cord construction requires the use of extra components, and, hence, it is relatively expensive to manufacture. Additionally, if the detachable section of the power cord is damaged or misplaced the heater will be rendering inoperable. 
     BRIEF SUMMARY OF THE INVENTION 
     According to certain aspects of an embodiment of the present invention, an electric heater for mounting through the drain plug opening of a livestock water tank includes an electrical heating element sized for insertion through the drain plug opening, a male plug adapted for connection to a conventional electrical outlet, and a power cord extending between the electrical heating element and the male plug. A drain plug fitting is connected to the proximal end of the heating element and is adapted for insertion into the drain plug opening, the drain plug fitting include a seal adapted to seal the drain plug opening to prevent water leakage though the opening. 
     According to one embodiment, the heating element may have a maximum outer cross sectional dimension of 0.75 inches or smaller. 
     The heater may also include a temperature regulating device interconnected between the power cord and the heating element, which is adapted to regulate the heating element so as to maintain the contents of the tank within a preselected temperature range. 
     According other aspects of an embodiment of the present invention, an electric water heating apparatus for mounting in a water tank having a drain plug opening includes a housing having a back wall which is larger than the drain plug opening and body portion extending from the back wall, the body portion being sized for insertion through the drain plug opening including a threaded portion. An electric heating element extends from the end of the body portion opposite the back wall. The heating element is sized for insertion through the drain plug opening and is configured for immersion into the contents of the tank. A power cord has one end mechanically and electrically connected to a male plug. The other end of the power cord extends into the housing is electrically interconnected with the heating element for delivering power thereto. A fastener, such as a nut, threads onto the threaded portion of the housing from inside the tank to secure the heating element within the tank. A seal is provided to seal the drain plug opening around the housing to prevent leakage therethrough. A temperature regulating device is interconnected between the power cord and the heating element. The temperature regulating device is adapted to regulate the heating element so as to maintain the contents of the tank within a preselected temperature range. 
     The seal may be an annular washer which is compressed between the water tank side wall and the back wall as the nut is threaded onto the boss. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a perspective view of a drain plug heater in accordance with certain aspects of an embodiment of the present invention, showing the heater installed through the drain plug opening of a watering tank. 
     FIG. 2 is a cross sectional view showing the drain plug heater of FIG. 1 installed through the drain plug opening of a watering tank. 
     FIG. 3 is a partial cross-sectional view of the drain plug heater of FIG.  1 . 
     FIG. 4 is a partial perspective view of a drain plug fitting of the drain plug heater of FIG.  1 . 
     FIG. 5 is a partial perspective view of the heater side of potting box of the drain plug heater of FIG.  1 . 
     FIG. 6 is a partial perspective view of the cable side of the potting box of FIG.  5 . 
     FIGS. 7A-7C illustrate some of the alternative shapes for the heating element employed in the heater of FIG.  1 . 
     FIG. 8 is an electrical diagram for the heater of FIG.  1 . 
     FIGS. 9 and 10 show front and back views of a nut employed in accordance with certain aspects of the present invention. 
     FIG. 11 illustrates certain aspects of an alternate embodiment of the water tank heater. 
    
    
     The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, certain embodiments. It should be understood, however, that the present invention is not limited to the arrangements and instrumentality shown in the attached drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, an electric drain plug heater  10  in accordance with certain aspects of an embodiment of the present invention includes a heating element  12 , a housing  14 , and a power cord  16 . The power cord  16  is interconnected with the heating element  12  through a temperature control device, e.g. a thermostat, for delivering electrical power to the heating element  12  in a controlled fashion so as to regulate the temperature of the contents of the tank  20 . The power cord  16  extends from the housing  14  and terminates in a conventional male plug  22 , which is configured for insertion into a conventional power outlet (not shown). The heater housing  14  hermetically seals the interconnection temperature control device  18 , the power cord  16 , and the heating element  12  from moisture infiltration. The heating element  12  and at least a portion of the housing  14  are configured for insertion through the drain plug opening  23  from the outside of the tank  20 . 
     The housing includes a drain plug fitting  24  for affixing the heater  10  to the tank  20  through the drain plug opening in a sealed manner, thereby preventing inadvertent removal of the heater  10  and also preventing the contents of the tank  20  from leaking out of the drain plug opening  23 . The fitting  24  includes a threaded portion or boss  26 , which is sized for insertion through the drain plug opening  23 . The housing  14  also includes a back wall or plate  28  having a diameter which is larger than that of the drain plug opening. The power cord  16  extends from the back wall  28  of the housing  14  opposite the boss  26 . The heating element  12  extends from housing  14  on the side opposite that of the power cord  16 . The heater  10  is installed into the drain plug opening by inserting the heating element  12  and the housing  14  through the drain plug opening from the outside of the tank  20  until the back wall  28  abuts the outer surface of the tank  20 . A rubber gasket or washer  30  is positioned between the back wall  28  and the wall  32  of the tank  20  to seal around the drain plug opening  23 . A reciprocal nut or fastener  34  threads onto the threaded portion  26  of the housing  14  from inside of the tank  20  to secure the housing  14  to the tank  20 . 
     The nut  34  may be constructed in accordance with the nut described in U.S. Pat. No. 6,151,448, the disclosure of which is hereby incorporated by reference. The nut  34  includes a slot (see FIGS. 9 and 10) which is sized to slide over a necked down portion  38  of the housing  14 . The necked down portion  38  is located at the distal end of the threaded portion  26 . The nut  34  is installed by sliding its slot  36  over the necked down portion  38  and then threading it onto the threaded portion  26  to tighten it against the wall  32  of the tank  20 . The rubber gasket  30  fits around the threaded portion  26  and, as is shown in FIG. 2, is compressed between the housing  14  and the tank wall  32  as the nut  34  is tightened onto the threaded portion  26  of the housing  14 . Alternatively, the gasket  30  may be positioned on the inside of the tank  20 , between the nut  34  and the tank wall  32 . The gasket  30  can also be slotted to allow it to be slid laterally into place over the threaded portion  26 . The heating element  12  can also be formed of a smaller diameter to allow the nut  34  to be slid over the distal end of the heating element  12  and tighten onto the housing  14 , thereby eliminating the need for a “slotted” nut. 
     The tank heater  10  may be configured for use in water tanks having drain plug openings ranging from 0.75 inches in diameter to 2.0 inches in diameter. In this respect, both the housing  14  and the heating element  12  preferably have a respective maximum outer cross-sectional dimension (see, e.g., reference number  35  in FIG. 5) which is less than 0.75 inches, and most preferably on the order of 0.65 inches or less. The gasket  30  preferably has an inner diameter which approximates the outer diameter of the threaded portion  26 , and an outer diameter which is greater than the largest drain plug opening for which the heater is designed to accommodate. Therefore, in the present example the gasket  30  has an outer diameter which is greater than 2.0 inches. The back wall  28  of the housing  14  is also configured to extend beyond the edge of a 2 inch diameter drain plug opening. In this respect, the outer diameter of both the nut  34  and the back wall  28  may be on the order of between 2.75 and 3.25 inches. 
     Although the housing  24  has been illustrated with a planar, circular back wall  28 , it will be appreciated that other housing configurations are also suitable. For example, the back wall can be rectangular. Alternatively, the housing  14  can have a cone-shaped back wall (not shown) which configured to fit into drain plug openings of varying diameters. In such a design, a cone-shaped gasket (not shown) can be provided to fit over the cone-shaped back wall to seal the drain opening. The gasket can be a separate component from the housing or it can be in the form of a layer of gasket material bonded to the outside of the housing. Alternatively, the nut could be cone or funnel shaped. 
     The power cord  16  includes an outer insulating sheath  100  enclosing a line or “hot” conducting wire  102 , a neutral conducting wire  104 , and a ground conducting wire  106 . Each wire is further provided with its own insulating sheath. The distal end of the power cord is connected to conventional three-prong electrical plug  22 . Three prongs extend from the front face of the plug  22  and are oriented for insertion into a convention power outlet. In particular, the plug includes a line prong  112 , a neutral prong  114 , and a ground prong  116 . The power cord  16  extends from the rear of the plug  22  with the sheath  100  of the power cord being encapsulated within the body of the plug  22 . Within the plug  22 , the sheath has been removed to allow the wires to be separated for interconnection with the appropriate conductive prongs. In particular, the line wire  102  is electrically and mechanically interconnected with the line prong  112 , the neutral wire  104  is electrically and mechanically interconnected with the neutral prong  114 , and the ground wire  106  is electrically and mechanically interconnected with the ground prong  116 . 
     The proximal end of the power cord extends into the housing  14  where it is electrically interconnected with the heating element  12  and the temperature control device  18 . (See generally FIGS.  3  and  8 ). The housing  14  may include an outer shell or potting box  40 , which defines an inner cavity  42  enclosing the interconnection between the power cord  16 , the temperature control device  18 , and the heating element  12 . The outer shell may be formed from a suitable material such as plastic in a conventional manner such as injection molding. The inner cavity  42  is hermetically sealed by filling it with a suitable waterproof sealant such as epoxy resin or a silicone sealing material. 
     The heating element  12  is in the form of an elongated tubular member which is looped back along itself such that the first and second ends of the heating element are positioned within the housing  14  where they are appropriately interconnected with the power cord  16 . In particular, the first end of the heating element  12  is connected to the proximal end of the line wire  102  through the temperature control device  18  and the second end of the heating element  12  is connected to the neutral conductor wire  104 . The ground conductor wire is connected to a thermally conductive temperature feedback strap  44 . FIGS. 7A-7C illustrate some of the suitable alternative shapes for the heating element  12 . Preferably, the legs of the heating element substantially abut one another or are in close proximity, so as to minimize the outer cross-sectional dimension of the heating element  12 . The heating element in FIGS. 7B and 7C are curved, which is preferable because it increases the overall length of the heating element which can be used, thereby increasing heat distribution within the tank. 
     The temperature control device  18  is in the form of a thermostat or temperature responsive switch that is interposed between the heating element  12  and the power cord  16 . The temperature control device  18  is disposed within the cavity  42  of the housing  14  and has a first terminal and a second terminal. The first terminal is connected to the proximal end of the line wire  102  and the second terminal is connected to the first end of the elongated heating element  12 . The temperature control device  18  senses the temperature of the contents of the tank  20  through the thermally conductive strap  44  and cycles the heating element  12  on and off to maintain the contents of the tank  20  within a predetermined temperature range. In particular, the temperature control device  18  turns on the heating element  12  when the temperature of the contents of the tank fall below a lower set point, which in the preferred embodiment is on the order of 40° F. Conversely, the temperature control device  18  turns the heating element  12  off when the temperature of the contents of the tank rise above an upper set point, which in the preferred embodiment is on the order of 60° F. A suitable temperature control device  18  is constructed in accordance with U.S. Pat. No. 4,835,366, the contents of which are hereby incorporated by reference. The thermally conductive strap  44  is affixed in a thermally conductive manner to the temperature control device  18  and functions as a temperature feedback strap for the thermostat. The strap  44  is exposed on its lower face to the water in the tank  20  and its distal end is affixed to the elongated heating element  12 . The thermal feedback strap  44  could be various shapes and may only be attached to the bottom of the element as opposed to the bottom three sides of the heating element, as shown. 
     The housing  14  may consist of two primary components, namely a cable holder  48  and an outer shell  40 . The cable holder, shown generally in FIG. 4, forms the threaded portion  26  and the back plate  28 . As can best be seen in FIGS. 3,  5 , and  6 , the outer shell  40  defines the hollow inner cavity  42 , which houses the interconnection between the power cord  16 , the temperature control device  18  and the heating element  12 . The outer shell  40  may include removable end plates  51 ,  53  that seal around the heating element  12  and the cable holder  48 , respectively. The end plate  51  and the main portion of the outer shell  40  define openings  55  that clamp around the ends of the heating element  12 . The bottom of the potting box  50  defines a slot  57 , which is configured to receive and support the feedback strap  44  such that the strap  44  is exposed to the contents of the tank. It will be appreciated that while the housing can take other forms from that shown. For example, the housing can be circular in cross-section, instead of round as shown. 
     The heating element  12  consists of a standard cal rod element, except that the two rods preferably are squeezed together to minimize their combined maximum outer cross-section dimension. As will be appreciated, the cal rods should be “cold ended” adjacent the housing to protect the housing  14  from damage due to overheating. Other types of heating rods, such as cast aluminum, could also be employed. In addition, the diameter of the heating rods could be reduced by forming the heating rod of two separate elements which are interconnected at their distal ends, e.g., by a wire or other conductive connector. As will be appreciated, this interconnection is sealed against moisture infiltration, e.g., with epoxy. The two elements could also remain electrically attached before sealing with epoxy. 
     As is shown generally in FIG. 1, the distal end of the heating element can be supported above the bottom of the tank  20  by a support member  58  that is connected to the heating elements after they are inserted through the drain plug opening  23 . 
     The materials used to construct the heater may be as follows: 
     1. Nut and potting box  50 : plastic. 
     2. Heating element  12 : incoly or cast aluminum. 
     3. Thermal feedback strap  44 : copper or aluminum. 
     4. Thermostat  18 : bimetal disc type. 
     It should be noted that the entire unit could also be made of cast aluminum. 
     FIG. 11 illustrates an alternative embodiment of a drain plug heater in accordance with certain aspects of the present invention. This alternative design is directed to reducing the overall cross-section width of the heating element  12 . In this embodiment, the heating element  12  is not looped back on itself as was done in the design of FIG.  1 . Instead, an insulated wire  60  is fed through a small diameter tube  62 . The wire  54  is electrically connected between the distal end of the heating element  12  and the power cord  16  to complete the electrical circuit. A connector  64  may be used to interconnect the wire  60  and the heating element  12 . A second potting box  66  is filled with epoxy to encapsulate the interconnection between the heating element  12  and the wire  60 , thereby sealing this junction against moisture infiltration. Another alternative (not shown) is to provide a second, reduced diameter heating element in place of the wire  60  and tube  62 . 
     Although the invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope and spirit of the invention. 
     While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.