Abstract:
A single control device is operational to control the flow of gas to a water heater as well as to protect against excessive temperature and pressure. The control device requires only a single fitting to be attached to the water heater tank to expedite the assembly process, eliminate a number of potential sources of leakage and reduce heat loss.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is generally directed to control devices for gas-fired water heaters and more particularly pertains to gas flow control valves as well as safety mechanisms that guard against the build-up of excess heat and/or pressure within water heaters. 
     Gas fired water heaters typically rely on a gas valve that controls the flow of gas to the burner in order to maintain the temperature of the water contained in the tank within preselected limits. As the water temperature drops below a preselected lower limit, the valve opens to permit the flow of gas to the burner where it is ignited by a pilot flame or electronic means. When the temperature of the water exceeds a preselected upper limit, the valve shuts off the flow of gas. Such temperature regulation is typically achieved with the use of a temperature sensor that must be immersed in the water within the tank and therefore requires the wall of the tank to be penetrated. In common use is an Invar rod type sensor which extends through the tank wall into the water contained therein, wherein the distal end of an Invar rod is affixed to the distal end of a concentrically positioned copper sleeve. The disparate rates of thermal expansion of the two materials causes the proximal ends of the rod and sleeve to undergo relative movement which is advantageously employed to open and close the gas valve. 
     Water heaters are usually additionally fitted with a pressure relief (PRV) valve that serves to vent water from within the tank should it exceed a preselected pressure. Such safety device prevents a build up of excessive pressures that could cause catastrophic failure of the tank. When the water pressure exceeds the preselected limit, the PRV valve opens to relieve excessive pressure to a vent line that conducts the released water to a safe location. The fitting of a PRV valve inherently requires another penetration of the tank wall. 
     Water heaters are typically also protected against the build up of excessive temperatures with the use of a relief valve that is actuated by a temperature sensor. The sensors in common use must be immersed in the water and therefore another penetration of the tank wall is required. Such device may be combined with the pressure relieve valve wherein a single valve mechanism is actuatable by either the temperature sensor or directly by water pressure thereby achieving both functions with a single perforation of the water tank. 
     Another device fitted to most water heaters is a drain valve that allows the water to be drained from the tank. This is necessary to enable the tank to be moved or to be flushed. The valve is typically located near the bottom of the tank in an easily accessible location. 
     A disadvantage of the prior art approach to the use of these various control and safety devices is inherent in the fact that each requires a separate hole to be formed in the water heater tank, the welding of a threaded fitting thereto and the threading of the respective device thereinto. Not only is such manufacturing process relatively labor intensive, but the mounting of each of such device then poses a potential for leakage throughout the service life of the water heater. Additionally, each device that protrudes from the tank not only serves as a conduit for heat loss but may also serve to disrupt the continuity of insulation that is fitted about the tank to further compromise the ability of the water heater to retain heat. Finally, the protrusion of these various devices through the outer skin of a water heater is unsightly which may be problematic for installations wherein the water heater is positioned in plain sight. 
     It would therefore be advantageous to reduce the number of devices that must be attached to a water heater in order to properly and safely control its operation. Such improvement would expedite the assembly process, reduce the potential for leaks and reduce heat loss to improve the overall efficiency of the water heater. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages associated with prior art control and safety devices utilized on water heaters. The control device of the present invention may integrate any combination of the gas flow control valve actuator, pressure relief valve, temperature relief valve and drain cock in a single housing that requires only a single fitting to be attached to the tank. This greatly reduces the potential for leakage, reduces manufacturing costs, reduces heat loss to improve the overall efficiency of the water heater and provides for a smoother, less cluttered outward appearance. 
     A preferred embodiment of the control device of the present invention employs an Invar rod mechanism to sense water temperature and actuate the gas valve. The interior of the housing through which the Invar rod extends from the gas valve into the interior of the tank is in fluid communication with the tank. A port is formed in such housing which is sealed off by a relief valve that is biased against a valve seat by a spring. The spring is oriented and configured such that in the event the water pressure within the tank and hence within the housing rises to a level that overcomes the biasing action of the spring, the relief valve opens to release water through the port. The force of the spring may also be overcome by manual means so as to enable the same relief valve to be used as a drain cock. A temperature sensor also manipulates the relief valve. A temperature in excess of a preselected amount causes the spring tension to be overcome and the valve to open. The same valve is therefore used to manually drain the tank as well as to automatically reduce excessive water temperature or pressure. 
     These and other features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment which, taken in conjunction with the accompanying drawings, illustrates by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged perspective view of a preferred embodiment of the control device of the present invention; 
     FIG. 2 is a cross-sectional view taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a perspective view of a water heater fitted with prior art devices; and 
     FIG. 4 is a perspective view of a water heater fitted with the control device of the present invention; 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The control device of the present invention controls the temperature and pressure of the water contained in a water heater. The device controls the operation of a gas valve that regulates the flow of gas to the burner to heat the water and automatically opens a relief valve in the event the internal pressure or temperature of the tank exceeds certain limits. Additionally, the device allows the tank to be manually drained there through. As a result only a single hole must be formed in the tank to accommodate all of these various functions. 
     FIG. 3 illustrates a prior art water heater  12 , having a separate gas control valve  14 , a combination pressure and temperature relief valve  16  and a drain cock  18 . Each such component is tapped into the interior of the tank necessitating a separate hole forming operation, welding operation and assembly operation during the manufacture of the water heater. In addition to being unsightly, each component contributes to heat loss as each such component conducts and radiates heat and compromises the continuity of any insulation in place about the tank. 
     FIG. 4 illustrates the control device  20  of the present invention in place on a water heater  22  and coupled to a gas flow valve  24 . The control device includes a single exit port  26  through which water is automatically drained in the event excessive temperature or pressure within the tank is sensed or when it is desired to manually drain the tank. The desired water temperature is set by rotation of the dial  28  associated with the gas flow valve. 
     FIG. 1 is enlarged perspective view of the control device  20  of the present invention which is shown detached from the water heater and from the gas control valve. The control device includes a housing  30  having a threaded end  32  for threaded receipt in the water heater. Visible extending from the threaded end is a first temperature sensor  34  for the control of the gas valve and a second temperature sensor  36  for the operation of the relief valve. A mounting flange  38  is disposed directly opposite the threaded end is configured to attach to the gas valve. In this particular embodiment, a square flange has four holes  40  holes formed therein for receiving fasteners that engage the gas valve. The proximal end of an Invar rod  42  is visible extending from the interior of the housing. A lateral branch  44  of the housing includes the exit port  26  and supports a rotatable control knob  46 . 
     FIG. 2 is a cross-sectional view taken along lines  2 — 2  of FIG. 1 illustrating the various internal components of the control device  20 . Temperature sensor  34  includes a copper sleeve  48  that is rigidly attached to the housing  30  at it proximal end  50 . The Invar rod  52  extends through the interior of the sleeve and is rigidly attached thereto at its distal end  54 . The disparate coefficients of thermal expansion of the sleeve and rod cause the proximal end  42  of the Invar rod  52  to move relative to the mounting flange  38  as the sensor is heated or cooled. The proximal end thereby effectively functions as a plunger which is employed to open and close the conventional gas valve (not shown) to which the control device is fastened. Alternatively, a wax pellet type temperature sensor may be used in place of the Invar rod type sensor. Such sensor relies on the expansion of a small amount of paraffin contained within a metallic housing against a piston or plunger as its temperature increases. The sensor and housing may be configured such that the plunger acts directly on the gas valve or a mechanism may be relied upon to transfer motion from the sensor to the gas valve. 
     The lateral branch  44  of the housing  30  encloses a valve mechanism that includes a valve head  56  that seals against a valve seat  58 . A valve stem  60  extends from the head and is carried in a bore  62  formed in control knob  46 . The receipt of the valve in the bore serves to maintain the valve in alignment within the housing but allows longitudinal movement. The valve head is biased against the valve seat by valve spring  64  which is in turn constrained by retainer  66 . The exertion of sufficient force on the face of the valve head will cause the valve to lift off its seat to thereby set the interior of the housing into fluid communication with the interior of the lateral branch of the housing. A flow path is thereby created through the entire control device. Water entering the housing through the threaded end flows in the space between the interior of the housing and exterior of sensor  34 , past the opened valve into the interior of the branch component and out through port  26 . 
     The valve may alternatively be opened by rotating control knob  46  so as to back it out of the housing. The lateral branch has internal threads  47  formed therein which cooperate with threads  49  formed on the knob. Rotation of the knob in a counterclockwise direction serves to shift the spring retainer  66  outwardly and enables the spring  64  to expand. By thereby relieving the force exerted by the spring on the valve, the valve is free to open. 
     The valve is additionally linked to temperature sensor  36 . Such sensor employs a small quantity of paraffin contained within a rigid housing  53  that causes an actuation rod  51  received therein to extend outwardly as the temperature rises and the wax expands. A bored and threaded boss  55  formed on the interior wall of the valve housing  32  receives the threaded proximal end of the sensor housing  53  to positively maintain the sensor in position. The proximal end  57  of rod  21  defines an inclined plane that cooperates with the rounded proximal end  59  of the valve stem  60  to transfer axial movement of the rod to a raising or lowering of the valve  56 . Heating the sensor beyond a preselected limit will cause its proximal end to extend sufficiently to thereby lift the valve off of its seat. Alternatively, an Invar rod type sensor may be employed in place of the described wax pellet type senor. 
     The attachment of the control device of the present invention to a water heater requires forming only a single hole in the water tank. A threaded fitting is welded thereto which receives the threaded end  32  of the housing  32 . Both sensors  34 ,  36  are thereby caused to extend well into the tank and are thereby fully immersed in the water contained therein. A conventional gas control valve is fastened to the flanged end  38  of the housing  30  such that the proximal end  42  of the Invar rod is able to open and close the gas valve as it shifts inwardly and outwardly as a function of the water temperature. In the event the water temperature exceeds a preselected limit, the mechanism associated with the second temperature sensor serves to lift the valve  56  off of its seat  58  to enable water to escape via the exit port  26 . The in rushing cold water that replaces the vented water quickly cools down the internal temperature of the water tank. Similarly, in the event a preselected water pressure is exceeded, the pressure bearing against the face of the valve  56  causes the force of spring  64  to be overcome and allows the valve to lift off of its seat. The escape of water immediately reduces the built up pressure while the in rushing cold water also cools the water tank to further reduce pressure. In the event it is desired to drain the tank, knob  46  is rotated to shift the retainer  66  outwardly and thereby relieve the closing force exerted on the valve. 
     While a particular form of the invention has been illustrated and described, it will also be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except by the appended claims.