Abstract:
A piston for a control valve of a water treatment apparatus includes a body having a central portion from which at least one flange projects radially outward. Each flange has an outer peripheral surface extending around the central portion with an annular groove therein. The annular groove is undercut thereby having a width that increases from the peripheral surface radially inward into the flange. A separate sealing ring is molded into the groove of each flange and is captivated therein by the undercut of the groove. That captivation better enables each sealing ring to resist forces produced by the water flowing through the control valve without becoming dislodged from the flange.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to apparatus for softening water; and more particularly to systems for controlling regeneration of the resin in a water softening apparatus. 
     It is quite common for water drawn from a well to be considered “hard” in that it contains di-positive and sometimes tri-positive ions which have leached from mineral deposits in the earth. Such ions form insoluble salts with common detergents and soaps producing precipitates that increase the quantity of detergent or soap required for cleaning purposes. When hard water is used in boilers, evaporation results in the precipitation of insoluble residues that tend to accumulate as scale. 
     It is standard practice to install a water softener in the plumbing system of a building that is supplied with hard water. The most common kind of water softener is an ion exchange apparatus that has a tank which holds a bed of resin through which the hard water flows to remove undesirable minerals and other impurities. Binding sites in the resin bed initially contain positive ions, commonly unipositive sodium or potassium ions. As hard water enters the resin, competition for the binding sites occurs. The di-positive and tri-positive ions in the hard water are favored due to their higher charge densities and displace the unipositive ions. Two or three unipositive ions are displaced for each di-positive or tri-positive ion, respectively. 
     The capacity of the rein bed to absorb minerals and impurities is finite and eventually ceases to soften the water when a large percentage of the sites become occupied by the di-positive and tri-positive ions. When this occurs, it becomes necessary to recharge or regenerate the resin bed by flushing it with a regenerant, typically a solution of sodium chloride or potassium chloride. The concentration of unipositive ions in the regenerant is sufficiently high to offset the unfavorable electrostatic competition and the binding sites are recovered by unipositive ions. The interval of time between regeneration periods during which water softening takes place is referred to as a service mode of operation. 
     Regeneration of early types of water softeners was affected manually only after it was discovered that the treatment capacity of the resin bed has been exceeded and the water flowing there through is no longer “soft.” In an effort to eliminate the need for manual regeneration, water softener control systems were provided with a mechanical clock which initiated water softener regeneration on a periodic basis. The frequency of such regeneration was set in accordance to the known capacity of the resin bed and the anticipated daily usage of soft water. Although mechanical clock-type water softener controllers alleviated the need for manually regenerating the resin bed, such controllers are subject to the disadvantage that regeneration at fixed intervals may occur too often or not often enough depending upon water usage. Regenerating the water softener resin bed when sufficient capacity to treat water still exists wastes the regenerant and the water used in regeneration. Conversely, failure to regenerate the water softener after the resin bed capacity has diminished to a point below that required to treat hard water may result in hard water leaving the water softener. 
     In an effort to better regulate the frequency of water softener regeneration, demand-type water softener controls have been developed which determine the remaining capacity of the resin bed to soften water. One type of such an improved control system employed a flow meter that measures the volume of water being treated and regenerates the resin bed when a specified volume of water has flowed through the softener since the previous regeneration. While this type of system is adequate in many installations, municipal systems alternately may draw water from several wells which contain water having different degrees of hardness. In that case, the exhaustion of the resin bed is not a direct function of the volume of water which has been treated since the previous regeneration. 
     Other types of control systems were developed which detect the exhaustion of the resin bed directly. Electronic controllers utilize electrodes to measure the electrical conductivity of the resin bed at two spaced apart locations. The ratio of the conductivity measurements, along with the minimum and maximum ratio values that occurred since the previous resin bed regeneration, are used to determine a probability of resin bed exhaustion and this triggers regeneration. 
     Regardless of the type of control system used to determine when to regenerate the resin bed, that control system activates a motor that drives a valve. The valve has several positions corresponding to the backwashing, brining, rinsing and brine replenishing steps of the regeneration process. The conventional valves have a body with a bore that has several chambers to which the inlet, outlet and internal passages of the water softener are connected. A piston with recesses and lands slides within the bore to selectively interconnect the different chambers and thereby direct water in different paths through the valve depending on the stage of operation. Separate sealing rings are placed in annular grooves in the bore between chambers. The seals engage the lands of the piston to block undesired water flow between the chambers. Several manufacturing steps are required to accurately place each sealing ring in the respective groove. 
     SUMMARY OF THE INVENTION 
     A piston for a control valve of a water treatment apparatus includes a body with a central portion from which one or more flanges project radially outward. Each flange has an outer peripheral surface extending around the central portion with an annular groove therein. The annular groove in undercut, thereby having a width that increases from the outer peripheral surface radially inward into the flange. A separate sealing ring is located within the annular groove of each flange and is captivated therein by the increasing width of the groove. 
     The control valve piston can be fabricated by forming the body using an investment casting process in which the grooves are defined by lost material, such as wax for example. This enables each groove to be undercut thereby forming a structure to captivate the sealing ring. After the body has hardened, it is placed in a second mold to form the sealing rings. This second mold has a cavity in which the valve piston body fits leaving small voids around each flange, that then are filled with the material for the sealing rings which flows into the flange grooves. After the sealing rings have hardened, the second mold is opened and the completed valve piston is removed. 
     By over molding the sealing rings into the grooves of the piston body, the sealing rings become locked within the grooves and are not easily removed, such as due to the force from the water flowing through the assembled control valve. This is a design concern because as the piston moves within the valve body to open and close paths through the control valve, water rushes past the piston flange edges creating forces that tend to dislodge the sealing rings. 
    
    
     
       DESCRIPTION OF THE OF THE DRAWINGS 
         FIG. 1  is a cross sectional view through components of a water softener that incorporates a valve piston according to the present invention; 
         FIG. 2  is a cross sectional view through the valve piston; and 
         FIGS. 3-5  are enlarged views of three embodiments of seals integrated into the valve piston. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to  FIG. 1 , a water softener  10  includes a treatment tank  12  which contains a bed  14  of ion exchange resin particles. A control valve  16  is fixed to the top of the treatment tank  12 . In the service mode, hard water to be softened is supplied to an inlet passage  18  from which water flows to inlets  20  at the top of the treatment tank and then flows through the resin bed to absorb minerals from the water. An outlet conduit  22  extends through the bed  14  from a point adjacent the bottom of the treatment tank  12  to an outlet passage  24  in the control valve  16 . Water that has been treated in the resin bed  14  flows through the outlet conduit  22  into the valve&#39;s outlet passage  24  from which the water exits the water softener  10  into the pipes in a building. 
     The resin bed  14  eventually becomes exhausted and no longer is capable of softening the water. Either periodically in response to a timer or in response to sensors detecting depletion of the resin bed, a controller  26  initiates a standard regeneration process. The controller  26  is fixed to the top of the valve and has a motor  28  that is adapted to drive a valve piston  30  within a circular bore  15  of the control valve  16  through a slowly moving and uninterrupted reciprocating cycle. As the piston  30  moves, the passages of the control valve  16  are connected in several combinations to direct water through different paths for the various stages of the regeneration process. 
     A typical resin bed regeneration process commences with a backwash step in which hard water is directed from the control valve into the outlet conduit  22  and upwards through the resin bed  14  finally exiting the water softener via a drain passage (not shown). The backwash step is followed by a brining step. The control valve  16  has an injector  32  that is connected by a conduit  34  through a shut-off valve  36  and a tube  38  to a brine tank  40 . The brine tank  40  contains a brine solution  42  of a common salt, such as a sodium chloride or potassium chloride. In this stage of generation, a partial vacuum created by the flow of hard water through the injector  32  withdraws brine from the brine tank  40  through conduits  29  and  27  and into the treatment tank  12 . The concentrated brine solution replaces the di-positive and tri-positive ions in the resin bed  14  with unipositive ions recharging the bed. When the contents of the brine tank  40  have been exhausted, a check valve  44  closes to prevent air from being injected into the system and water continues to flow through the injector  32  free of brine. This water propels the brine solution from the treatment tank  12  and then rinses the bed  14  to remove residual brine. 
     During the final stage of the regeneration process, the brine tank  40  is refilled with water and the softener resin bed  14  is purged. This is accomplished by feeding water into the brine tank  40  through the open shut-off valve  36  and into the treatment tank  12  through the inlets  20 . Water passing through the resin bed  14  exits via the drain passage. Thereafter, the control valve  16  is returned to the position that places the water softener  10  into the previously described service mode in which the water for the building in treated. 
     With reference to  FIG. 2 , the control valve  16  has a novel piston  30  with a central portion, or shaft,  50  from which a plurality of circular disk-shaped flanges  51 ,  52  and  53  project radially outward, thereby forming recesses  54  and  55  between the flanges. A rod-like stem  56  extends axially from one end of the central portion  50  and is adapted for attaching to the mechanism of the controller  26 , which moves the piston  30  within the bore  15  of the control valve  16  during the regeneration mode. The central portion  50 , flanges  51 - 53  and the stem  56  form a body  60  of the valve piston  30  that preferably is fabricated of stainless steel or other corrosion resistant material. 
     Each flange  51 ,  52  and  53  has an outer circumferentially peripheral surface  57 ,  58  and  59 , respectively, extending around the central portion  50  with an annular groove in that surface. A separate sealing ring  61 ,  62  or  63  is located within each of the annular grooves in the peripheral surface  57 ,  58  and  59 , respectively. Preferably, the sealing ring  61 - 63  are made of rubber, such as a cross-linked thermal set rubber, or a resilient plastic, such as a thermoplastic elastomer. Each sealing ring  61 - 63  projects outward from the respective flange  51 - 53  and engages the inside surface of the control valve bore  15 . That engagement prevents fluid within the recesses  54  or  55  from flowing between a flange and the surface of the valve bore  15  (see  FIG. 1 ). 
       FIG. 3  illustrates the cross section through the sealing ring  61  located in the groove  66  in the peripheral surface  57  of one of the flanges  51 . The annular groove  66  has a dove tail cross section that is undercut so that the interior surface is wider than the opening of the groove through the peripheral surface  58  of the flange  52 . The undercut captivates the sealing ring  61  within the annular groove  66  and prevents the sealing ring from being pulled out of that groove by forces produced by water flowing through the assembled control valve  16 . This is a design requirement because as the piston  30  moves within the bore  15  opening and closing paths through the control valve, water rushes past the peripheral surfaces  57  of the piston flanges creating forces that tend to dislodge the sealing rings. 
       FIG. 4  illustrates a second style of sealing ring  70  located in a groove  72  in the peripheral surface  58  of one of the flanges  52 . The groove  72  has T-shaped cross section in which an inner region  74  has a width that is larger than the width of the groove in an outer region  76  at the peripheral surface  58  of the flange. The sealing ring  70  is enlarged in that inner region  74 , thereby captivating the sealing ring in the groove  72 . This style of sealing ring  70  has a pair of lobes  78  which engage the interior surface of the valve bore  15 . 
     A third style of sealing ring  80  is shown in  FIG. 5  located in an identical annular groove  72  in one of the flanges  52 . This style of sealing ring  80  has three lobes  82  which engage the interior surface of the valve bore  15 . 
     The valve piston  30  is fabricated by first producing the body  60  using an investment casting process, such as lost wax casting. The mold for this casting process includes material, such as wax, which defines the grooves in the outer circumferentially peripheral surfaces of the flanges  51 - 53 . Because this material can be easily removed after the material of the body  60  has hardened, the grooves can be undercut to provide a groove in which the sealing rings are locked in place, as described previously. After the valve body  60  has hardened, it is placed in a second mold for forming the sealing rings  61 - 63 . This second mold has a cavity in which the body  60  of the valve piston  30  fits leaving small voids around each flange, which then are filled with the material for the sealing rings which flows into the entire groove  57 - 59  in the respective flange  51 - 53 . After the sealing rings have hardened, the second mold is opened and the completed valve piston  30  is removed. 
     By over molding the sealing rings  61 - 63  into the grooves of the metal portion of the piston  30 , the sealing rings become locked within the grooves and are not easily removed, such as due to the force from the water flowing through the assembled control valve  16 . If non-locking type grooves were used with resilient sealing rings merely stretched around the flanges  51 - 56  and then released into the grooves, the sealing rings might not be held in place securely enough to resist the water flow force that tends to dislodge the sealing rings. 
     The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.