Abstract:
An anode is mounted to the top of a water heater tank which has a spud with external threads welded to the top thereof. The spud extends above insulation which surrounds the water tank and covers the top of the water heater. An anode rod is inserted into the water tank through the spud and has a steel core welded to a flat cylindrical steel disk which extends radially outwardly of a magnesium cylinder formed about the core. A water sealing gasket is positioned between the disk and the annular surface formed by the open end of the spud. A nut fits over the disk and engages the threads on the spud, and clamps the anode to the spud so that the threads are isolated from water in the tank, allowing easy removal of the anode after the passage of time.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   Not applicable. 
   STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   The present invention relates generally to water heaters and water tanks and more particularly to the sacrificial anode in a water tank. 
   Water heaters have a variety of applications. A common use is for the heating of water in a residential structure. A water heater has a water tank, typically manufactured of steel. The water tank is typically cylindrical to withstand pressure and for simplicity of manufacture. The tank is oriented with the axis of the cylinder vertical so that a firebox may be positioned beneath the water tank and an exhaust stack may extend along the cylindrical axis through the water tank. To decrease heating costs, the water tank is often insulated. 
   To protect a steel water heater tank from corrosion, the interior of the tank is coated with a glass lining formed by coating the tank interior with an enamel and heating the tank to form the glass lining. However, small voids or cracks may be present as manufactured or may form later in the glass coating, possibly exposing the metal tank walls to corrosion. To protect against corrosion a sacrificial metal anode rod attached to a threaded fitting is screwed into a threaded boss at the top of the tank. 
   Cathodic corrosion is an electro-chemical phenomenon in which a metal tends to return to its native oxide state. This corrosion can be slowed, and even stopped, by making the surface to be protected the cathode of an electrochemical cell. Thus, an anode must be supplied that has a more negative electrochemical potential than the potential of the steel surface to be protected. Anodes are typically made of alloys of zinc, magnesium, and aluminum to protect steel surfaces. 
   Because of the sacrificial nature of the anode, it is necessary to replace the anode periodically as it is depleted. However, access to the anode mounting is hampered when the fitting is buried in insulation which covers the top of the tank. Moreover, if threads on the anode and the tank are not isolated from the water in the tank, the threads could become corroded, making the removal of the anode difficult. What is needed is a sacrificial anode which mounts with good electrical contact to the tank yet which is readily and expeditiously replaceable. 
   SUMMARY OF THE INVENTION 
   The invention is an anode and an arrangement for mounting the anode to the top of a water heater water tank. The water heater tank has a short vertical pipe or spud welded at one end to the top of the tank and forming an opening at the other end. The spud extends vertically from the top of the water tank, and gives access to the interior volume of the water tank through the open end. The spud extends above insulation which surrounds the water tank and covers the top of the water heater. The spud has external threads on the portion of the spud that protrudes beyond the tank insulation. An anode rod is inserted into the water tank through the spud. The anode rod is constructed of a magnesium cylinder and has a steel core that extends along the axis of the magnesium cylinder. The steel core extends through and is welded to a flat cylindrical steel disk terminating one end of the anode rod. The weld electrically connects the flat steel disk to the anode rod. The magnesium cylinder surrounding the steel core extends below the flat steel disk for the entire length of the anode rod. The flat steel disk extends radially outwardly of the magnesium cylinder giving the anode rod a T-shaped vertical cross-section. The flat steel disk has an annular, i.e. circumferential, or ringlike, surface that surrounds and faces the magnesium cylinder and is without threads. 
   When the anode rod is installed in the spud the annular surface faces a corresponding annular surface formed by the open end of the spud. A water sealing gasket is positioned between the flat steel disk and the annular surface formed by the open end of the spud. The gasket is made of an elastomer in the shape of a ring or washer. The gasket is held in sealing contact between the annulus of the flat steel disk and the flat end face of the spud threaded end by a hexagonal nut with internal threads which fits over the steel disk of the anode, the internal threads of the nut engage the external threads on the spud. By tightening the nut the gasket is clamped between the annular surface formed by the open end of the spud and the annular surface face of the disk at the top of the anode. The nut has a recess in the center or has a central hole to receive a bump on the anode disk where the steel core is welded to the disk. Electrical continuity is provided between the magnesium of the anode and the water heater tank by way of the steel core, to the disk, to the nut, to the spud which is welded to the water tank. 
   It is an object of the present invention to provide a water heater with longer service life. 
   It is another object of the present invention to provide a water heater anode mounting arrangement that is easier to service and maintain. 
   It is a further object of the present invention to provide a water heater anode that is more easily accessed and replaced. 
   It is another object of the present invention to provide a water heater anode where the anode mounting arrangement has a reduced tendency to corrode. 
   Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevational cross-sectional partially exploded view of the water heater anode mounting arrangement interface with a water tank of this invention. 
       FIG. 2  is a side elevational cross-section plan view of the assembled water heater anode mounting arrangement of  FIG. 1 . 
       FIG. 3  is a side elevational cross-sectional view of the anode of the device of  FIG. 2 . 
       FIG. 4  is an side elevational cross-sectional view of the water heater tank and anode mounting arrangement of this invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring more particularly to  FIGS. 1-4 , wherein like numbers refer to similar parts, a water heater  20  is shown in  FIG. 4 . The water heater  20  has a water tank  22  which is separated from a combustion chamber  24  by a bottom dome  26 . A central steel flue  28  extends between an opening  30  in the bottom dome  26  and a top dome  34  of the water heater tank  22 . A burner, not shown, is positioned below the water tank  22 . The burner may operate on oil, natural gas, propane or other fuel. The exhaust gases from the burner flow upwardly through the central flue  28  to the flue outlet  32 , exchanging heat with the water  36  contained within the water tank  22 . Heat is also exchanged between the dome  26 , and the water  36  contained in the water tank  22 . Portions of water tank  22  are covered by a layer of insulation  38  that helps to prevent heat losses to the surrounding air. The insulation  38  is in turn surrounded by a sheet metal cover  39 . The thickness of the insulation  38  depending upon the type of material the insulation  38  is made of and is generally in the range of 0.5 inch to 2 inches. 
   The water tank  22  has a cold water inlet  40 , on the top dome  34  where cold water is introduced through a pipe that extends to near the bottom of the water tank  22 . A hot water outlet  41  is also located on the top dome  34 . The hot water outlet  41  extends into the water  36  near the top of the water tank  22 . As hot water leaves through the outlet  41  of the water tank  22 , cold replacement water enters through the cold water inlet  40  into the bottom of the water tank  22 . 
   Because water  36  is an ionic compound, it promotes the oxidation of materials in contact with it. Ferrous materials, such as steel, are especially prone to cathodic corrosion because of this oxidation. Common practice is to coat all surfaces coming in contact with water, including the steel water tank  22 , the bottom dome  26 , the top dome  34 , and the outside surface of the flue  28 , with an enamel material to prevent this corrosion from taking place. The enamel is painted or coated onto the steel surface. The enamel coating is then fired to form a protective, glass-like lining on the steel surface. However, small defects may exist in the coating or small cracks may develop in the coating over time. These defects or cracks allow water  36  to come in contact with the steel surface of the water tank  22  thus promoting cathodic corrosion, and reducing the operational life of the water heater  20 . 
   Cathodic corrosion is an electrochemical process that occurs when water  36  comes in contact with the steel water tank  22 , causing the steel to oxidize. To protect the steel water tank  22  cathodic protection supplied by an anode  42  of sacrificial material is used. The anode  42  is formed of cast or extruded magnesium cylinder  44  surrounding a steel core  46  or wire as shown in  FIG. 3 . The magnesium cylinder  44  is more electronegative than steel and acts as a sacrificial material, corroding in place of the steel water tank  22 . Electrons leave the magnesium cylinder  44  which is electrically part of the anode  42  and travel a grounded path to the steel water tank  22  which serves as a cathode. This will occur as long as there is good electrical conductivity between the anode  42 , the water  36 , and the water tank  22 , and as long as the magnesium cylinder  44  remains attached to the steel core  46 . As the magnesium of the cylinder  44  erodes from the anode  42 , the steel core  46  prevents the magnesium from separating from the anode and maintains electrical contact with the wall of the tank  22 . When no magnesium material remains on the anode  42 , the anode  42  must be replaced to protect the steel water tank  22  from corrosion. 
   The construction of the anode  42  is shown in  FIG. 3 . A cylinder of magnesium  44  surrounds a steel core  46  and is topped by a flat steel disk  48 . The length of the anode  42  is selected to ensure that the rod extends from the top of the water tank  22  to nearly the bottom of the water tank  22 , typically a distance of three to four feet, e.g. 42 inches. The steel core  46  extends through the flat steel disk  48  and is welded to the disk forming a weldment which has a steel nub  52  in the center of the flat steel disk  48 . The weld between the steel core  46  in the disk  48  forms a mechanical and electrical connection between the core and the disk. Once the flat steel disk  48  is attached, the anode rod  42  has a T-shaped cross-section. The bottom side  47  of the flat steel disk  48  forms an annulus around the magnesium cylinder  44  that serves as a sealing surface. The top side of the flat steel disk  48  is engaged by and compressed by a corresponding annular surface  61  of a nut  62 , shown in  FIG. 1 . 
   The anode mounting arrangement is shown in  FIG. 1 . The anode rod  42  is fitted to a short spud  54  that has a first end that is preferably welded to the top  34  of the water tank  22 . The spud  54  has external threads  56  on the open end  57  of the spud. The length of the spud  54  is selected to be greater than the thickness of the insulation  38  which covers the top dome  34  of the water tank  22  and so that the external threads  56  are clear of the insulation  38 . The spud  54  has an internal diameter selected to be greater than the diameter of the anode  42 . The diameter of the anode  42  is typically ¾ or one inches. The spud  54  has a second end that terminates in an end face  58  which forms a flat water sealing surface. The anode  42  is passed through the spud  54  and extends into the water tank  22  making contact with the water  36 . A gasket  60  in the form of an elastomeric washer, or other sealing material, is placed between the bottom sealing surface  47  of the flat steel disk  48  and the end face  58  of the spud  54 . The gasket  60  is preferably made of an elastomer or rubber material to facilitate water tight sealing and to conform to the sealing surfaces of the spud  54  end face  58  and the flat steel disk  48 . 
   The anode  42  is clamped against the end face  58  of the spud  54  by a hexagonal nut  62  that covers the flat steel disk  48 . Internal threading  64  of the nut  62  engages the external threading  56  of the spud  54 , as shown in  FIG. 1 . The gasket  60  prevents water from reaching the engaged threads  56 ,  64 , which prevents corrosion which would make removal and replacement of the anode difficult. The nut  62  has a downwardly opening central recess  66  to receive the welding nub  52  on the anode  42 . The nut  62  compresses the flat steel disk  48  against the gasket  60  and provides electrical continuity between the anode  42  and the water heater tank  22 . The nut  62  is a cap nut, or acorn nut, having a cap  74  on the interior of which the annular surface  61  which engages the steel disk  48  is formed. 
   The anode  42  gradually dissolves over time to protect the water tank  22  and should be replaced periodically, for example yearly. The arrangement illustrated in  FIG. 1  overcomes the prior art difficulties of gaining access to the anode and of corrosion of the threads which attach the anode to the water tank. The threads  56  on the spud  54  which are engaged with the threads  64  of the nut  62  are isolated from the water contained within the water tank by the gasket  60  so threads do not become corroded, allowing the nut to be readily loosened and removed. Once the nut  62  is removed, the anode is no longer attached to the water heater but simply rests on the gasket  60  by means of the steel disk  48  and thus may be easily removed from the water tank. A new anode  42  together with the new gasket  60  is installed and the nut  62  is replaced and tightened, compressing the steel disk of the new anode against the gasket. 
   An alternative nut  68  is shown in  FIG. 2 . The nut  68  has portions forming an opening  70  centered over the anode rod  42 . The nut  68  has a partial cap  76  which has an annular surface  72  which surrounds the opening  70  and which engages portions  78  of the steel disk  48  near its periphery  80 . A portion of the disc  48  compresses the gasket  60  between the sealing surface  47  of the disk  48  and a sealing end face surface  58  of the spud  54 . The open nut design prevents the nut from engaging the nub  52 . 
   It should be understood that the magnesium cylinder  44  could be any sacrificial metal used to protect steel, such as zinc or aluminum. It should further be understood that the cylinder of sacrificial metal may be flexible, or formed as discontinuous pieces attached to the core so that the anode rod can be bent to facilitate insertion into a water heater mounted beneath a low ceiling. It should be understood that although the disk  48  and the core  46  are described as constructed of steel it should be understood that steel as used in the claims includes pure iron, alloys of iron with carbon, and alloys of iron with other alloy materials. It should also be understood that the annular sealing surface  58  of the spud, and the sealing surface  47  on the steel disk  48  could have shapes other than the flat parallel surfaces illustrated in the figures, including any arrangement which functions to engage the gasket  60  to form a watertight seal. 
   It should be understood that wherein nuts  62 ,  68  are described and claimed as having portions that engage the steel disk  48  and bias the steel disk against the gasket  60  and the second end of the spud  54 , a washer or other electrically conductive spacer placed between the nut and the spud is intended. It should also be understood that the water tank described and claimed is the water tank of a direct fired or indirect fired water heater or is a water storage tank. 
   It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces all such modified forms thereof as come within the scope of the following claims.