Abstract:
A thermostatic control valve assembly for use in continuously mixing a hot first fluid with a cold second fluid to continuously produce a mixed fluid at a constant temperature. The valve assembly includes an improved mixing dome defining a mixing chamber that facilitates thorough mixing of the hot and cold fluids over a wide range of flow rates, including rates as low as two gallons per minute. The improved mixing performance is accomplished by a plurality of baffles sequentially disposed along the flow path within the mixing chamber and extending at an angle in opposition to the flow path. Each baffle exhibits a paisley shape and is angularly displaced from the adjacent baffles to turn the fluid flow, thereby optimally mixing the hot and cold fluids over a wide range of flow rates while minimizing the pressure drop between the valve inlet and outlet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to the field of fluid mixing valve assemblies. More particularly, the invention concerns an improved thermostatically controlled mixing valve assembly in which a thermostat is immersed in the fluid flowing through the valve.  
           [0002]    Thermostatic control valve assemblies are well known in the art and have long been utilized in various applications including group showers, washing stations, hospital hydrotherapy installations and in many industrial applications where precision thermostatic water blending is essential. In order to operate properly, the hot and cold water entering such a valve assembly must be thoroughly blended before the temperature of the mixture is sensed by the thermostat. If the hot and cold water are not adequately mixed, the valve assembly can behave erratically because the temperature sensor sees pockets of hot and cold water instead of a mixture that is at a single temperature throughout. One problem that has long persisted in the art is the inability of most valve assemblies to adequately mix the hot and cold water over a wide range of flow rates. Consequently, multiple valves often have to be used to satisfy flow requirements.  
           [0003]    Another problem that has persisted in the art is the physical size of the valve assembly required for a specific application. Often, the valve assembly is simply too large because of the need for a large mixing chamber to adequately mix the hot and cold water. What is needed is a thermostatic control valve assembly having an improved mixing chamber that has the ability to thoroughly mix the hot and cold water over a wide range of flow rates, and which does so in a smaller physical space than valve assemblies currently known in the art.  
           [0004]    One such valve assembly featuring an improved mixing chamber is disclosed in U.S. Pat. No. 5,203,496 which is assigned to the assignee of the present invention. It is now desired to improve the operation of such valve assemblies by providing a mixing valve assembly which operates with reduced pressure drop across the valve assembly, while still thoroughly mixing the hot and cold fluids.  
         SUMMARY OF THE INVENTION  
         [0005]    A thermostatic control valve assembly for continuously mixing a hot first fluid with a cold second fluid to continuously produce a mixed fluid at a constant temperature according to one embodiment of the present invention comprises a cold fluid inlet, a hot fluid inlet, a mixing dome defining a mixing chamber, a thermostatically controlled flow control valve and an operably connected thermostat for adjusting the flow of the hot and cold fluids into the mixing chamber. The mixing dome includes a plurality of baffles sequentially placed in the flow path to promote better mixing of the hot and cold fluids before the mixed fluid contacts the thermostat disposed in the fluid flow path.  
           [0006]    In one aspect of the invention, each baffle projects into the flow stream and is angled from the mixing dome wall in a direction contrary to the direction of flow. The mixing performance is further improved by angularly displacing the each baffle with respect to each other to impart a twisting movement to the fluid. The mixing dome includes means for supporting the thermostat between the baffles and the fluid outlet of the dome.  
           [0007]    A general object of the present invention is to provide an improved thermostatic control valve assembly. A specific object is to provide a valve assembly that more efficiently mixes hot and cold fluids for accurately sensing the temperature of the mixture.  
           [0008]    A further objective is to provide a valve assembly that provides effectively mixed hot and cold fluids with reduced pressure drop between the valve and valve outlet. Related objects and advantages of the present invention will be apparent from the following description.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 shows a side cross-sectional view of a thermostatic control valve assembly according to a preferred embodiment of the present invention.  
         [0010]    [0010]FIG. 2 shows a side cross-sectional view of a housing defining an improved mixing chamber for the valve assembly shown in FIG. 1.  
         [0011]    [0011]FIG. 3 is a top view along section  3 — 3  of FIG. 2 showing a first baffle according to the present invention.  
         [0012]    [0012]FIG. 4 is a top view along section  4 — 4  of FIG. 2 showing a second baffle according to the present invention.  
         [0013]    [0013]FIG. 5 is a top view along section  5 — 5  of FIG. 2 showing a third baffle according to the present invention.  
         [0014]    [0014]FIG. 6 shows a side cross-sectional view of a housing defining an improved mixing chamber for a second embodiment of the present invention.  
         [0015]    [0015]FIG. 7 is a top view along section  3 - 3  of FIG. 6 showing a first baffle according to the present invention.  
         [0016]    [0016]FIG. 8 is a top view along section  4 - 4  of FIG. 6 showing a second baffle according to the present invention.  
         [0017]    [0017]FIG. 9 is a top view along section  5 - 5  of FIG. 6 showing a third baffle according to the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0019]    Referring now to FIG. 1, there is shown a thermostatic control valve assembly  10  with fluid mixing according to the preferred embodiment of the present invention. Valve assembly  10  includes a hot inlet  11 , a cold inlet  12  and an outlet  13 . Inlets  11  and  12  are connected to opposite sides of flow control valve  14  and open to annular cavities  15  and  16 , respectively, within the flow control valve. The inner wall of annular cavities  15  and  16  is defined by a cylindrically shaped liner  17 . Liner  17  is open at both ends and includes a plurality of openings or slots  18  which are distributed around its circumference in communication with cavities  15  and  16 .  
         [0020]    Slidably mounted within liner  17  is a cylindrically shaped piston  19  which is open at its upper end. Piston  19  is preferably pressure balanced and includes a plurality of openings or slots  20  that are distributed around its circumference. Preferably, each opening  20  through piston  19  has a counterpart opening  18  in liner  17 . Modulation of the piston  19  within the liner  17  variably opens the cavities  15  and  16  to the interior of the piston  19 , which communicates the combined hot and cold fluid to the outlet  14   a  of the flow control valve.  
         [0021]    Flow control valve  14  also includes a bottom plug  21  which can be removed to allow access to repair, replace or clean the interior parts of flow control valve  14 . Bottom plug  21  defines a cavity  22  therein which substantially receives compressed valve spring  23 . Valve spring  23  is supported at one end by bottom plug  21  and is connected at its other end to the base  24  of piston  19 . The spring  23  applies a return force to piston  19 .  
         [0022]    A push rod  25  extends through the liner  17  and piston  19  to engage the base  24 . The opposite end of push rod  25  is connected to a thermostat  26 . Thermostat  26  can be of many types known in the art, such as a thermal coil or a temperature sensitive bellows. Such a thermostat is designed to expand or contract along the axis defined by push rod  25  in linear proportion to a change in the temperature of fluid surrounding the thermostat. In this embodiment, thermostat  26  is connected to adjustment screw  27  via shaft  28 . Adjustment screw  27  acts against spring  23  and thus allows the vertical position of the thermostat  26 , and ultimately of the piston  19 , to be adjusted, which in turn alters the relative proportions of hot and cold fluid passing through openings  20 .  
         [0023]    One problem that has persisted in the art is the inability of valve assemblies to operate properly over a wide range of flow rates. In other words, a flow control valve assembly is only useful over the range of flow rates that the device is able to thoroughly blend the hot and cold fluids before the mixture contacts the thermostat. While many known mixing valve assemblies are capable of adequate fluid mixing at high flows, a need remains for a valve assembly that is also capable of thorough hot and cold fluid mixing at low flow rates, such as below 10 g.p.m.  
         [0024]    [0024]FIG. 1 illustrates one form of control valve assembly that may utilize the features of the present invention. It is understood that the invention can have application with a variety of thermostat control valve configurations. In the illustrated embodiment, a mixing dome  29  is engaged over the outlet  14   a  of the flow control valve  14 . The mixing dome  29  defines a mixing chamber  30  therein which is preferably cylindrical in configuration. An important feature of the present invention is the incorporation within the mixing dome  29  of means for turning or rotating the fluid flow through the mixing chamber  30  to ensure complete mixing of the hot and cold fluid before it reaches the thermostat  26 . Complete fluid mixing assures a uniform temperature throughout the fluid discharged through outlet  13 . Most importantly, the mixed fluid accurately reflects the exiting temperature of the fluid so the thermostat can accurately regulate the movement of the valve control elements.  
         [0025]    According to the invention, the means for turning the fluid includes a plurality of baffles  31  that are integrally formed as part of the housing  32  forming the mixing dome. The shape and relative arrangement of baffles  31  are intended to induce more thorough blending of the hot and cold fluids in mixing chamber  30  before the mixture contacts thermostat  26 , particularly at low flow rates where the problem of inadequate mixing is most prevalent.  
         [0026]    In order to reliably react to a change in the temperature of the fluid mixture, the thermostat must be immersed in the mixture, and the mixture must have a substantially uniform temperature throughout rather than consisting merely of hot and cold pockets. Baffles  31  of the present invention create a vortex in the fluid flow so that the hot and cold fluids remain in contact longer, leading to complete mixing resulting in a substantially uniform fluid mixture and temperature prior to flowing around the immersed thermostat. In this manner, higher flow rates are achieved with only a minimal pressure drop between the valve inlet and outlet.  
         [0027]    The mixing dome  29  is shown in more detail in FIG. 2. The housing  32  defines the mixing chamber  30  therein and a flow path  33  therethrough. The housing  32  is provided with a mating surface  35  and an annular flange  36  that enable the housing to be mated to flow control valve  14  by conventional means. Housing  32  also defines an opening  37  at its top which permits an adjustment means, such as screw  27  and shaft  28 , to be connected to the thermostat, as better shown in FIG. 1. In operation, the fluid leaving flow control valve  14  enters housing  32  through inlet  34 . Immediately afterwards, the fluid encounters baffles  38 ,  39  and  40  in successive order. The fluid mixture then continues upward along flow path  33  until finally exiting housing  32  through outlet  13 .  
         [0028]    The outlet  13  is positioned at the end of the mixing chamber or fluid flow path to ensure that the thermostat  26  is substantially immersed in the fluid exiting the valve assembly  10 . Moreover, the thermostat  26  is disposed downstream of the sequential baffles, preferably by a distance greater than the distance between successive baffles. Thus, the hot and cold fluids are substantially mixed prior to the thermostat, and substantially all of the thermostat is exposed to the fluid mixture to assure that the thermostat receives a proper indication of the temperature of the exiting fluid.  
         [0029]    A more detailed view of each baffle is provided in the sectioned views of FIGS. 3, 4 and  5 . Although not shown in FIG. 2, it should be noted that if the vertical spacing of the baffles is sufficiently close, the baffles will overlap so that a section taken through the housing will encompass more than one baffle. As best shown in FIG. 5, each baffle is preferably curved in shape having a rounded first end  44  and a second end  46  that tapers into the wall of the housing  32 . The baffles run about 210 degrees end to end. Each baffle is angled downward counter to the direction of fluid flow, preferably at an angle of about 70 degrees as shown in FIG. 2. This arrangement imparts a turning action on the fluid stream, facilitating mixing of the hot and cold fluids. The baffles are most preferably arranged so that the tapered end  46  of the baffles meet the fluid first. This minimizes turbulence and reduces pressure drop as the fluid maintains laminar flow along the gradually widening baffle. The housing  32  and baffles may be manufactured by conventional casting techniques, such as sand casting.  
         [0030]    Each baffle is rotationally displaced from each adjacent baffle to produce a helical arrangement of baffles  38 ,  39  and  40  in flow path  33 . In this embodiment, each successive baffle is rotated through an angle  48 , which in the illustrated embodiment is 120 degrees, to produce a generally helical flow path through the baffles. The helical pattern of successive baffles creates an overall amount of mixing which is greater than the sum of the individual baffles acting alone and without excessive pressure drop.  
         [0031]    In one specific embodiment of the invention, the housing  32  is of sand-cast bronze and defines a cylindrical mixing chamber 2.0 inches in diameter and about 10.0 inches in length from the base of the mixing chamber to the center of the outlet opening  13 . The baffles in this specific embodiment can be spaced about 1 inch apart. Each baffle can have a maximum width of about ⅝ inches. Each baffle can have a total surface area that is about one-half the cross sectional area of the chamber.  
         [0032]    Preferably, the baffles define an unobstructed center opening  49  along the subtended length of the housing. In a specific embodiment, this opening  49  can have a diameter of ¾ inches for a 2 inch housing In a most preferred embodiment, the baffles assume a “paisely” shape to create the center opening and provide a smooth flow transition up each baffle. The valve assembly  10  of the specific embodiment is capable of accurately controlling the outlet fluid temperature at flows of 2-80 g.p.m. The fluid mixing provided by the baffles is particularly important at the low flow rates since the fluid flow can “short-circuit” the thermostat in which the entire thermostat is not immersed in the fluid flow prior to the outlet  13 .  
         [0033]    Another embodiment of the invention is shown the mixing dome  29  shown in FIG. 6. The housing  32  defines the mixing chamber  30  therein and a flow path  33  therethrough as previously described.  
         [0034]    A more detailed view of each baffle in this embodiment is provided in the sectioned views of FIGS. 7, 8 and  9 . Each baffle is crescent shaped and is angled downward counter to the direction of fluid flow, preferably at an angle of between 45 and 70 degrees. Again, the housing  32  and baffles  38 ′,  39 ′, and  40 ′ may be manufactured by conventional casting techniques, such as sand casting.  
         [0035]    Each baffle is rotationally displaced from each adjacent baffle to produce a helical arrangement of baffles  38 ′,  39 ′ and  40 ′ in flow path  33 . In this embodiment, each successive baffle is rotated through an angle  48 ′, which in this case is about 45 degrees, to produce a generally helical flow path through the baffles. Each baffle defines a chord  41 ,  42 , and  43  between its end points which is useful in illustrating the helical arrangement of the baffles in the flow path. In FIGS.  7 - 9 , chords  42 ,  42 , and  43  are show with their respective perpendicular bisectors successively rotated by an angle of about 45 degrees. The helical pattern of successive baffles creates an overall amount of mixing which is greater than the sum of the individual baffles acting alone and without excessive pressure drop.  
         [0036]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.  
         [0037]    For instance, in the preferred embodiment, the baffles  38 ,  39  and  40  are integrally formed in the housing  32  by known casting techniques. The invention further contemplates that each baffle constitutes a separate element that is suitably mounted within a cylindrical cavity in the housing. For instance, the separate baffles could be snap fitted within grooves formed in the housing.  
         [0038]    Moreover, the invention contemplates incorporating additional baffles sequentially disposed along the flow path. Multiple housing sections can be combined, and more baffles can be added to the longer chamber. The additional baffles would preferably be arranged in the helical pattern described above. Thus, while the baffles of the preferred embodiment are rotated 120 degrees relative to each other, the addition of more baffles permit smaller relative angular displacements between consecutive baffles.