Patent Publication Number: US-2013228579-A1

Title: Expansion tank with a piston

Description:
TECHNICAL FIELD 
     This invention relates generally to water systems and more particularly to a water system expansion tank and method for use with a hot water heater. 
     BACKGROUND 
     Modern indoor plumping generally has a backflow preventer installed at or near the water meter to prevent water from a structure&#39;s water system from flowing out. The presence of a backflow preventer creates a closed system within the structure where the water system exists. Most interior water systems rely on a hot water heater to provide hot water to the structure. As the water continues to be warmed its density decreases and its volume increases, thereby generating pressure within the hot water heater&#39;s tank. To alleviate some of this pressure an expansion tank is made apart of the system thus providing more volume to contain the heated water. Without the expansion tank, pressure within the hot water heater can increases until the structural integrity of the heater is compromised. If the hot water heater becomes structurally compromised then severe water leakage can occur. Thus, the need for an expansion tank on closed water systems is known in the prior art. 
     An expansion tank is typically linked by a pipe to the hot water heater. The expansion tank is designed to contain excess water which is the result of thermal expansion. Thermal expansion occurs as a result of water being heated in the tank of the hot water heater. A prior art expansion tank typically uses a rubber diaphragm to divide the tank. One side of the tank is designed to receive expanding water from the water system to which it is attached. The other side of the diaphragm contains air under pressure. Water is not compressible, while air is. When heated water enters the expansion tank due to the resulting increase of water pressure it causes the diaphragm to flex against and compress the air cushion thereby allowing water to enter the tank. When the water system is opened through the use of a faucet or similar device, or the water cools, water leaves the tank and returns to the water system at large. This cycle occurs at a minimum, as frequently as the burner of the hot water heater is activated. As the rubber diaphragm flexes repeatedly under routine use it eventually tears or is otherwise compromised. Once the diaphragm wears out or ruptures the system fails resulting in pressurized water being expelled from the system into the surrounding area. The water leak could result in expensive water damage being caused to both the dwelling and other property contained therein. The cost of repair for such damage can range from $5,000-$70,000, or even more, with the average claim for water damage being $15,000 according to State Farm Insurance. As such the need for an expansion tank with a more robust means of receiving and releasing pressurized water exist. 
     An object of the present invention is to provide an expansion tank which overcomes the deficiencies found in the prior-art rubber diaphragm with a more robust spring-operated piston mechanism to regulate the flow of water into and out of the expansion tank. 
     SUMMARY 
     The preferred embodiment of the present invention consists of a cylindrical housing which has an extension at one end that is configured to be connected to a water system. The interior of the cylindrical housing contains an aluminum piston which is in contact with the interior walls of the housing, effectively dividing the housing into two separate areas. The piston has two o-rings that occupy parallel planes about its periphery. The o-rings serve the purpose of preventing water from seeping around the face of the piston and collecting behind it, within the spring compartment. The walls of the housing are lubricated with an insoluble lubricant. The piston is acted on by a spring thereby pressing the piston towards the extension located at the bottom of the housing. The area between the back of the piston and the interior of the cylindrical housing contains the spring and is vacuum sealed. This area is generally referred to as the spring compartment. The piston face has a quasi-crescent shape which creates an air gap between itself and the water system. As expanding water enters through the provided opening into the interior of the cylindrical housing, the piston and spring are compressed thereby allowing the water to occupy the interior volume of the provided tank. When the system is opened, or the water cools, pressure within the system is thereby reduced. Water is expelled from the expansion tank once the force of the spring on the piston exceeds the force exerted by the water on the piston. Through the use of a spring powered aluminum piston the inherent weakness of a flexible rubber diaphragm are over come. 
     The foregoing it a broad outline of the significant features of the present invention, more pertinent and specific details of these features are discussed in the detailed description of the invention that follows. It should be understood by those skilled in the art that the disclosed preferred embodiment may be modified or used as a basis for designing other methods of constructing a similar device which is capable of fulfilling the same purpose. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of preferred and alternative embodiments is better understood when read in conjunction with the appended drawings. For the purposes of illustration, there is shown in the drawings exemplary embodiments; however, the subject matter is not limited to the specific elements and instrumentalities disclosed. In describing the preferred and selected alternate embodiments of the present invention, as illustrated in the Figures, specific terminology is employed for the sake of clarity. The invention, however, is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish similar functions. 
         FIG. 1  shows a side view of the expansion tank; 
         FIG. 2  shows a cutaway view of the expansion tank shown in  FIG. 1 ; 
         FIG. 3  shows the cutaway view of  FIG. 2  with the piston compressing the spring; 
         FIG. 4  shows a side view of the expansion tank installed on a hot water heater; and 
         FIG. 5  shows an alternative embodiment of the expansion tank. 
         FIG. 6  shows an additional alternate embodiment of the expansion tank. 
     
    
    
     It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended to define the limits of the invention. 
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
     Turning now to the figures in which like reference characters indicate corresponding elements throughout the several views, there is shown an expansion tank, generally designated by reference numeral  10 , which consists of a cylindrically shaped housing, generally designated by reference numeral  20 , that contains a piston  30  which is biased into position by a spring  50 . The expansion tank is configured to be connected to a water system  60  through a threaded extension  28 . As used herein, the word “bottom” corresponds to the portion of the housing  20  where the threaded extension  28  is located as shown in  FIG. 1 ; “top” corresponds to the portion of the housing  20  which is opposite the threaded extension  28 , also shown in  FIG. 1 . 
     Shown in  FIG. 1  is an illustration of the expansion tank  10  wherein an embodiment of the cylindrical housing&#39;s  20  exterior is shown. The side of housing  20  which is not shown in the drawing is substantially identical to the view therein illustrated. In general the housing is constructed from a stainless steel alloy, but other material compositions which are suitable for containing pressurized water that are currently in use or may come into use would make acceptable substitutes. At the bottom of the housing is a threaded extension  28  which in the preferred embodiment has ¾ inch threads configured to interface with a pipe fitting and thereby connect the housing  20  to a water system  60 . The threaded extension  28  can easily be configured with an array of thread pitches which are suitable for use in securing an expansion tank  10  to a water system  60 . 
       FIGS. 2 and 3  show cutaway view of the expansion tank  10  illustrated in  FIG. 1 . The housing  20  consists of a top tank portion  44  and a bottom tank portion  46 . The interior of the housing  20  is divided into two general sections by the piston  30 . The piston  30  is constructed from aluminum and has a face  32  which has a quasi-crescent shape. The backside  40  of the piston  30  is smooth in the preferred embodiment. It should be known that any metallic compound or synthetic material which is suitable for use as a piston in an aqueous environment would be an acceptable substitute from which to manufacture the piston  30 . Located about the periphery of the piston  30  are two grooves  36  each of which houses an o-ring  38 . The area between the backside  40  of the piston  30  and the top of the housing  20  is the spring compartment, while the area between the face  32  of the piston  30  and the bottom of the housing  20  is referred to as the water pocket  24 . A spring  50  is in operational contact with the backside  40  of the piston  30  and is wholly contained within the spring compartment  22  of the housing  20 . The spring  50  places 80 lbs of force against the backside of the piston  30 . Further, the spring compartment  22  is isolated from the water pocket  24  through the use of o-rings  28  present about the exterior of the piston  30  and as a result of the close fit between the piston&#39;s  30  exterior and the interior of the housing  20 . Present, but not illustrated, is an insoluble lubricant which is used on the interior walls of the housing  20  to aid the piston  30  during its movement cycles. Located near the top of the housing  20  is a port  42  which is used during assembly to vacuum seal the spring compartment  22 . 
     The spring  50  used with the preferred embodiment expansion tank  10  has a max load of 80 lbs and is manufacture from a stainless steel. It should be understood that any material suitable for use as a spring may be substituted. Further, the load weight of the spring may be selected based on the pressure generated by the water system  60  to which the expansion tank  10  is being incorporated. 
       FIG. 2  shows the piston  30  being biased into position against the bottom of the housing&#39;s  20  interior, as is the case when no water is present within the interior of the expansion tank  10 .  FIG. 3  shows the piston  20  compressed towards the top interior portion of the housing  20 , as is the case when sufficient pressure is generated by the water system  60  to force water into the expansion tank  10 . 
       FIG. 4  shows a side perspective view of the expansion tank  10  installed on a water system  60 . The housing&#39;s  20  interior is placed into communication with the water system  60  through the threaded extension  28  located on the bottom of the housing  20 . The threaded extension  28  consists of a cylindrical tube which is hollow that has at least a portion of its exterior threaded. The water system  60  generally consists of a hot water heater, pipes, water which originates from a well or municipal water system and a series of faucets or other pressure release mechanisms. 
     The expansion tank  10  is assembled as follows. The bottom tank portion  46  and the top tank portion  44  are lubricated with an insoluble lubricant. An o-ring  38  of appropriate size is selected and placed into the o-ring grooves  36  present about the exterior side wall of the piston  30 . Next, the piston  30  is placed into the interior of the bottom tank portion  46  and oriented such that its face  32  is oriented towards the bottom. The area between the face  32  of the piston  30  and the threaded extension  28  of the bottom tank portion  44  is generally referred to as the water pocket  24 . A spring  50  is placed on top of the piston  30  and then covered by the top tank portion  44 . Where the top tank portion  44  and the bottom tank portion  46  meet a seam is formed. At the seam the two tanks portions  44 ,  46  are welded together to form the housing  20  of the expansion tank  10 . The area between the backside  40  of the piston  30  and the interior of the housing  20  is generally referred to as the spring compartment  22 . Through the use of the port  42  located on the top tank portion  44  of the housing  20  the spring compartment  22  is vacuum sealed. It is to be understood that the spring compartment  22  does not have to be vacuumed sealed during assembly. Other ways of vacating air from the spring compartment  22  which are within the scope of the present invention are described in, but not limited to, those methods outlined in the alternate embodiments below. 
     In operation the housing  20  is threadedly secured to the water system  60  by the threaded extension  28 , but other method routinely used to secure pipes together offer acceptable alternatives. After initial installation, water faucets may be opened to allow for air trapped in the water pocket  24  of the housing&#39;s  20  interior to be released from the water system  60  as a whole. The hot water heater has a thermostat which automatically activates a burner or series of burners to heat water contained within a tank. As the water heats it gradually expands through a phenomenon known as thermal expansion. This expansion of the water increases the internal pressure of the water system  60  as a whole and results in water being forced through the opening of the threaded extension  28  and into the interior of the housing  20 . Initially the piston  30  is biased into its first position by the spring  50 , shown in  FIG. 2 . As water enters the water pocket  24  of the housing  20  sufficient pressure is being generated in the water system  60  to slowly move the piston  30  and thereby compress the spring  50  towards the top of the housing  20 , shown in  FIG. 3 . When the burner of the hot water heater shuts off, a faucet is opened, or another exit is provided the water from the water system  60 , pressure within the water system  60  will decrease resulting in water flowing out of the expansion tank  10 . Water is able to exit the expansion tank  10  when the force applied by the spring  50  to the backside  40  of the piston  30  is greater than the pressure of the water against the piston face  32 . 
       FIG. 5  shows an alternate embodiment of the expansion tank  100 . This embodiment is constructed substantially similar to the preferred embodiment expansion tank  10  except for the presence of an air release valve  110 . The air release valve  110  is located on the housing  112  and provides an exit for air trapped within the spring compartment  22 . Air is vented from the spring compartment  22  through the release valve  110  as the piston  30  is compressed as a result of water entering the expansion tank  110 . This removes the need to vacuum seal the spring compartment during manufacturing. 
       FIG. 6  shows an additional alternate embodiment of the expansion tank  200  would have a check valve  210  which has been incorporated on the face  222  of a piston  220  which has been appropriately modified. The check valve  210  is oriented such that the valve flap opens towards the water pocket  24 . As the expansion tank  200  receives water from the water system  60  the air pressure within the spring compartment  232  increases. This increase in air pressure is the result of the piston  220  and the spring  50  being compressed. Once sufficient pressure has been generated within the spring compartment  232  air is released into the water pocket  24  as a result of the cracking pressure of the check valve  210  being overcome. 
     The foregoing description and drawings comprise illustrative preferred and alternate embodiments of the present invention. Having thus described exemplary embodiments of the present invention, it should be noted by those skilled in the art that the within disclosures are exemplary only, and that various other alternatives, adaption&#39;s, and modifications may be made within the scope of the present invention. Merely listing the steps of the method in a certain order does not necessarily constitute any limitation on the order of the steps of the method. Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing description and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of I imitation. Accordingly, the present invention is not limited to the specific embodiments illustrated herein, but is limited only by the following claims.