Abstract:
A tempering valve is connected to hot and cold water supplies. The tempering valve has first and second thermal valves, each of which mixes hot and cold water flows to produce a tempered flow at a selected temperature. the mixed flow from the first thermal valve bypasses through the second thermal valve. A small valve assembly is responsive to the flow rate therethrough. At low flow rates, direct hot and cold water flow paths to the second thermal valve are blocked. At or above a selected transition flow rate, the small valve assembly opens to permit direct hot and cold water flows from hot and cold water inlets to the second thermal valve. The tempering valve may include a failure protection valve which shuts off all flow in case of a cold water supply failure.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to a fluid tempering valve and more particularly to a tempering valve which accurately controls the temperature of a fluid at both high and low flow rates. 
   Tempered fluid mixing systems are used in a variety of commercial and industrial applications, for example, in gang showers. A typical system includes a thermostatic mixing valve or tempering valve which automatically blends hot and cold water supply streams to produce a mixed water output stream having a selected temperature. This tempered water is supplied through a common manifold to a plurality of fixtures such as shower heads. 
   Such tempered water mixing systems must be able to maintain the desired temperature regardless of the flow rate demanded. For example, a system could have a single fixture in use, or more than 20 fixtures could be in use simultaneously. It is difficult to design a tempering valve which accurately maintains a set temperature at widely varying flow rates. Attempts have been made in the prior art to provide accurate mixing at all flow rates. For example, some systems use a pair of mixing valves, one sized for a low flow rate and the other sized for a high flow rate, connected together with a pressure regulating valve or check valve between the outlets of the two mixing valves. However, when the larger valve does open, it is still only flowing a small percentage of the total flow. Such a system tends to have a “dead zone” of intermediate flow rates where the tempering is inaccurate. Accordingly, there is a need for a fluid tempering valve which accurately controls temperature at both high and low flow rates. 
   BRIEF SUMMARY OF THE INVENTION 
   Therefore, it is an object of the invention to provide a tempering valve which provides accurate temperature control at varying flow rates. 
   It is another object of the invention to provide a tempering valve in which all of the mixed water flow passes through the main valve regardless of flow rate. 
   It is another object of the invention to provide a tempering valve which is responsive to a loss of cold fluid supply pressure to shut off all fluid flow. 
   It is another object of the invention to provide a tempering valve which is easily adjusted to a desired temperature. 
   These and other objects of the present invention are achieved in the preferred embodiments disclosed below by providing a fluid tempering valve, having a housing defining a first fluid inlet for receiving fluid at a first temperature, the first fluid inlet being in fluid communication with a spaced-apart first fluid port, and a second fluid inlet for receiving fluid at a second temperature higher than the first temperature, the second fluid inlet being in fluid communication with a spaced-apart second fluid port. First valve means receiving fluid from the first and second fluid inlets and mix the fluid to maintain a preselected temperature. Second valve means receiving fluid from the first and second fluid ports and mix the fluid to maintain a preselected temperature. Bypass means direct the mixed fluid from the first valve means to the second valve means. 
   Third valve means are responsive to the flow rate through the first valve means. The third valve means block flow communication between the first fluid inlet and the first fluid port, and between the second fluid inlet and the second fluid port, when the flow rate is less than a preselected value, and the third valve means permit fluid communication from the first fluid inlet to the first fluid port, and from the second fluid inlet to the second fluid port, when the flow rate is equal to or greater than the preselected value. 
   In another embodiment of the present invention, the first valve means are adapted to a preselected first flow rate; and the second valve means are adapted to a preselected second flow rate greater than the first flow rate. 
   In another embodiment of the present invention, the tempering valve includes means for blocking all flow through the tempering valve in response to an absence of fluid pressure in the first fluid inlet. 
   In another embodiment of the present invention, a tempering valve has a housing defining: first and second spaced-apart bores; a cold fluid inlet for receiving a fluid at a first temperature, the cold fluid inlet having a cold fluid check valve disposed therein which allows flow from the cold fluid inlet to the first bore but prevents flow in the opposite direction; a hot fluid inlet for receiving a fluid at a second temperature greater than the first temperature, the hot fluid inlet having a hot fluid check valve disposed therein which allows flow from the hot fluid inlet to the first bore but prevents flow in the opposite direction; a hot fluid port spaced-apart from the hot fluid inlet and connected in flow communication with the first and second bores; a cold fluid port spaced-apart from the cold fluid inlet and connected in flow communication with the first and second bores; an outlet port; and a bypass passage connecting the first and second bores. 
   A small valve assembly disposed in the first bore includes an outer sleeve having upper and lower ends and being movable between a closed position wherein fluid flow is blocked from the first fluid inlet to the first fluid port, and from the second fluid inlet to the second fluid port, and an open position wherein fluid flow is permitted from the first fluid inlet to the first fluid port, and from the second fluid inlet to the second fluid port; and a first thermal valve disposed in the outer sleeve, the small thermal valve operative to control the relative proportions of fluid flows from the hot and cold water inlets to the bypass passage for maintaining a preselected fluid temperature. 
   A large valve assembly is disposed in the first bore, including a second thermal valve. The second thermal valve is operative to control the relative proportions of flow from the hot and cold water ports to the outlet port for maintaining a preselected fluid temperature. The small valve assembly moves to the closed position when the flow therethrough is less than a preselected rate, and the small valve assembly moves to the open position when the flow therethrough is equal to or greater than the preselected rate, and wherein the flow from the first thermal valve passes from the bypass passage to the outlet port through the second thermal valve regardless of the position of the small valve assembly. 
   In another embodiment of the present invention, the small valve assembly includes: a first surface having a first area in fluid communication with the cold fluid inlet; a second surface having a second area in fluid communication with the hot fluid inlet, the second area being equal to the first area; and a third surface having a third area in fluid communication with the bypass passage, the third area being equal to the sum of the first and second areas. 
   In another embodiment of the present invention, the tempering valve further includes biasing means for urging the small valve assembly towards the closed position. 
   In another embodiment of the present invention, the biasing means comprise a spring disposed between the bypass passage and the third surface. 
   In another embodiment of the present invention, the first thermal valve comprises a first cylinder disposed in the first bore in fluid communication with the cold fluid inlet, the hot fluid inlet, and the bypass passage, the first cylinder having first upper and lower sealing edges and a first cylinder seal which prevents fluid communication between the hot and cold water inlets; and a first temperature-responsive element connected to the first cylinder and operative to move the first cylinder so for controlling the relative proportions of flow from the hot and cold water inlets to the bypass passage for maintaining a preselected fluid temperature. 
   In another embodiment of the present invention, the second thermal valve comprises: a second cylinder disposed in the second bore in fluid communication with the cold fluid port, the hot fluid port, the bypass port, and the outlet port, the second cylinder having second upper and lower sealing edges and a second cylinder seal which prevents fluid communication between the hot and cold water ports; and a second temperature-responsive element connected to the second cylinder and operative to move the second cylinder for controlling the relative proportions of flow from the hot and cold water ports to the outlet port for maintaining a preselected fluid temperature. 
   In another embodiment of the present invention, the small valve assembly includes a movable adjusting screw disposed therein for controlling a temperature set point of the second thermal valve. 
   In another embodiment of the present invention, the small valve assembly includes a movable adjusting stem disposed therein for controlling a temperature set point of the first thermal valve. 
   In another embodiment of the present invention, the adjusting stem is in threaded engagement with the small valve assembly, and includes a first set of splines disposed at an end thereof. 
   In another embodiment of the present invention, the tempering valve further includes an adjusting shaft mounted in the housing, the adjusting shaft having a first end including a second set of splines complementary to the first set of splines; and a second end including means for turning the adjusting shaft. The adjusting shaft is movable between a first position in which the first set of splines engages the second set of splines, and a second position in which the first set of splines is disengaged from the second set of splines. 
   In another embodiment of the present invention, the tempering valve further includes a failure protection valve for blocking all flow through the tempering valve in response to an absence of fluid pressure in the cold fluid inlet. 
   In another embodiment of the present invention, the failure protection valve blocks flow through the bypass passage in response to an absence of fluid pressure in the cold fluid inlet. 
   In another embodiment of the present invention, the failure protection valve includes a body having a valve inlet, a valve outlet, and a sensing port, the sensing port being connected in fluid communication with the cold fluid inlet; a piston disposed in the body, the piston movable between a closed position wherein flow from the valve inlet to the valve outlet is blocked, and an open position wherein flow from the valve inlet to the valve outlet is permitted; and biasing means for urging the piston towards the closed position. The valve inlet is connected to the bypass passage and the valve outlet is connected to the large valve assembly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
       FIG. 1  is a cross-sectional view of an exemplary tempering valve including a constructed in accordance with the present invention, during a low-flow operating condition; 
       FIG. 2  is a view of the valve of  FIG. 1 , during a high-flow operating condition; 
       FIG. 3  is a cross-sectional view of the tempering valve of  FIG. 1  having a supply failure protection valve added thereto, during normal operation; a 
       FIG. 4  is a view of the tempering valve of  FIG. 3  in a condition where the cold water supply has failed; and 
       FIG. 5  is an enlarged cross-sectional view of a portion of the small valve assembly depicted in  FIGS. 1–4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIGS. 1 and 5  illustrate an exemplary tempering valve  10  constructed in accordance with the present invention. It should be noted that the present invention is equally applicable to systems which handle fluids other than water, and therefore the terms “water” and “fluid” are used interchangeably herein when describing the invention. The tempering valve  10  has a housing  12  including a first bore  14  containing a first valve assembly generally referred to as a “small valve assembly”  16 , and a second bore  18  containing a second valve assembly referred to as a “large valve assembly”  20 . The housing  12  also includes a hot fluid inlet  22  for receiving fluid from a hot fluid supply H, a cold fluid inlet  24  for receiving fluid from a cold fluid supply C, a hot fluid port  26  extending between the first and second bores  14  and  18 , a cold fluid port  28  extending between the first and second bores  14  and  18 , an outlet port  30 , and a bypass passage  32  connecting the small valve assembly  16  and the large valve assembly  20 . 
   The hot fluid inlet  22  contains a hot fluid check valve  34  which allows flow from the hot fluid inlet  22  to the first bore  14  but prevents flow in the opposite direction. The cold fluid inlet contains a cold fluid check valve  36  which allows flow from the cold fluid inlet  24  to the first bore  14  but prevents flow in the opposite direction. The small valve assembly  16  has a hollow outer sleeve  38  with upper and lower ends  40  and  42 , that slides in the first bore  14  and is sealed by upper and lower seals  44  and  46 . A stationary hollow inner sleeve  48  is inserted into the upper end  40  of the outer sleeve  38 . A biasing spring  50  urges the small valve assembly  16  upwards towards a closed position. An elongated adjusting stem  52  is threaded into the interior of the inner sleeve  48 . The adjusting stem includes a shaft with external splines  54  protruding from its upper end. The lower end of the adjusting stem  52  contains an overtravel spring  56  and a disk  58 . 
   A small thermal valve  60  is disposed in the outer sleeve  38  below the adjusting stem  52 . The small thermal valve  60  is adapted to a relatively low flow rate, meaning that its components are sized such that it can provided the desired flow of mixed fluid, for example a flow sufficient for one or a few shower fixtures, without excessive pressure loss or choking of the flow. The small thermal valve  60  includes a —hollow small cylinder  62  with circumferential upper and lower sealing edges  64  and  66 . The small cylinder  62  is disposed in fluid communication with the cold fluid inlet  24  through a circumferential array of cold fluid openings  68  formed through the upper portion of the outer sleeve  38 , and with the hot fluid inlet  22  through a circumferential array of hot fluid openings  70  formed through the lower portion of the outer sleeve  38 . A small cylinder seal  72  disposed around the periphery of the small cylinder  62  prevents leakage between the hot and cold water flowpaths to the small cylinder  62 . 
   A first temperature-responsive element  74  is located inside the small cylinder  62  and connected to the small cylinder  62  by a circumferential array of struts  76 . For illustrative clarity only one such strut  76  is shown in  FIGS. 1–4 . In this example the first temperature-responsive element  74  is a known type of thermomechanical unit such as a sealed, wax-filled capsule. However, any other type of device capable of moving the small cylinder  62  in response to a temperature change may be used. An annular turbulator  78  having a plurality of holes  80  formed therethrough is mounted on the first temperature-responsive element  74 . A first return spring  82  is disposed between the turbulator  78  and a seat  83  located at the bottom of the outer sleeve  38 . 
   An adjusting shaft  84  passes through a hole  86  in the housing  12 . The lower end of the adjusting shaft  84  contains female splines  88  which engage the male splines  54  of the adjusting stem  52 . Means for turning this adjusting shaft  84  are provided, such as the illustrated handle  90 . The adjusting shaft slides up and down in the hole  86  to engage or disengage the adjusting stem  52  as required, as explained in more detail below. 
   The large valve assembly  20  comprises a large thermal valve  92  disposed in the second bore  18 . The large thermal valve  92  is adapted to a relatively high flow rate, meaning that its components are sized such that it can provided the desired flow of mixed fluid, for example a flow suitable for many shower fixtures, without excessive pressure loss or choking of the flow. The large thermal valve  92  includes a -hollow large cylinder  94  with circumferential upper and lower sealing edges  96  and  98 . The large cylinder  94  is disposed in fluid communication with the cold fluid port  28 , the hot fluid port  26 , the bypass passage  32 , and the outlet port  30 . A large cylinder seal  100  disposed around the periphery of the large cylinder  94  prevents leakage between the hot and cold water ports  26  and  28 . 
   A second temperature-responsive element  102  is located above the large cylinder  94  and connected to the large cylinder  94  by an annular adapter  104  having a plurality of radially-extending struts  106 . In this example the second temperature-responsive element  102  is a known type of thermomechanical unit such as a sealed, wax-filled capsule. However, any other type of device capable of moving the large cylinder  94  in response to a temperature change may be used. A second return spring  108  is disposed between the adapter  104  and a seat  110  located at the bottom of the second bore  18 . A threaded adjusting screw  112  is mounted in the housing  12  above the upper end of the second temperature-responsive element  102 . 
   The small thermal valve  60  operates as follows: Water flows into the small thermal valve  60  through both the hot and cold fluid openings  70  and  68 , from the hot and cold fluid inlets  22  and  24 . It flows past the upper and lower sealing edges  64  and  66  of the small cylinder  62 , past the first temperature-responsive element  74 , and through the lower end  42  of the outer sleeve  38 . At temperatures below a selected metering range, the small cylinder  62  is urged upward by the first return spring  82  so that the upper sealing edge  64  contacts an upper sealing surface  114 . Therefore, most of the flow of water will be from the hot fluid openings  70 , past the lower sealing edge  66 , and into the bypass passage  32 . As the temperature increases, the first temperature-responsive element  74  expands upward until its upper end contacts the disk  58 . Further expansion of the first temperature-responsive element  74  causes it to displace the small cylinder  62  downward, opening a flow path between the upper sealing edge  64  and the upper sealing surface  114 , and simultaneously reducing the size of the flow path beneath the lower sealing edge  66 . The mixed water flow passes through the holes  80  in the turbulator  78 . This causes a turbulent flow pattern which improves the mixing of the hot and cold flows. 
   As the temperature further increases, the small cylinder  62  is finally moved all the way to its lowest position in which the lower sealing edge  66  contacts a lower sealing surface  116 , thus cutting off all hot water flow. Under normal operation, the disk  58  does not move. However, if the small thermal valve  60  should be heated beyond its intended operating range, the excess force generated by the first temperature-responsive element  74  will displace the disk  58  and compress the overtravel spring  56 . This prevents damage to the first temperature-responsive element  74 . 
   The temperature of the mixed water can be selected by moving the adjusting stem  52  to move it up or down, which changes the distance the first temperature-responsive element  74  must move before it contacts the disk  58 . The adjusting stem  52  is moved by pushing down on the handle  90  until the female splines  88  of the adjusting shaft  84  engage the male splines  54  of the adjusting stem  52 . The handle  90  may then be used to rotate the threaded adjusting stem  52 . Once the adjustment is complete, water pressure in the small valve assembly  16  pushes the adjusting shaft  84  back up. 
   At low flow rates, the force on the third surface  154  is nearly equal to the sum of the forces on the first and second surfaces  150  and  452 . There is a small net downward force on the small valve assembly. This downward force is overcome by the biasing spring  50 , so that the small valve assembly  16  remains in the upper or closed position. In this position, the flow paths from the cold fluid inlet  24  to the cold fluid port  28 , and from the hot fluid inlet  22  to the hot fluid port  26 , are cut off. All of the flow thus passes through the small thermal valve  60  where it is mixed to the correct temperature. The mixed flow then passes out through the bypass passage  32  and into the bottom of the large thermal valve  92 . The mixed flow then moves up past the second temperature-responsive element  102  and the adapter  104 , and out of the outlet port  30 . In this flow condition, the large thermal valve  92  has no effect on the temperature of the outgoing flow, because all of the flow bypasses the operating part of the large thermal valve  92 . However, because the flow is directed past the second temperature-responsive element  102 , the large thermal valve  92  is “primed” by sensing the bypass flow, and the large cylinder  94  is moved to the correct mixing position for the temperature of the flow passing through it. 
   As the flow out of the outlet port  30  increases, the pressure drop at the lower end of the small valve assembly  16  increases. At a sufficient flow rate, the pressure on the third surface  154  drops to the point that the small valve assembly  16  can compress the biasing spring  50  and move downward to a lower or open position, as shown in  FIG. 2 . This simultaneously opens both hot and cold fluid flowpaths so that hot fluid can flow directly from the hot fluid inlet  22  to the hot fluid port  26 , and from the cold fluid inlet  24  to the cold fluid port  28 . 
   Once the small valve assembly  16  opens, the small thermal valve  60  continues to mix hot and cold fluid as described above, and this mixed flow goes through the bypass passage  32  to the large valve assembly. The large thermal valve  92  also begins to function as follows. Fluid flows into the large thermal valve  92  through both the hot and cold fluid ports  26  and  28 . It flows past the upper and lower sealing edges  96  and  98  of the large cylinder  94 , past the second temperature-responsive element  102  and the adapter  104 , and out through the outlet port  30 . Because of the bypass flow from the small thermal valve  60 , the second temperature-responsive element  102  will have already expanded downward until the adapter  104  has contacted a ledge  118  in the large cylinder  64  and caused it to displace the large cylinder  94  downward. A flow path will be open between the upper sealing edge  69  and an upper sealing surface  120 , and also between the lower sealing edge  98  and a lower sealing surface  122 . 
   Thus, the large cylinder  94  will already be at approximately the correct position to mix the hot and cold fluids to the desired temperature. If the temperature decreases below a selected level, the second temperature-responsive element  102  will contract, allowing the second return spring  108  to force the large cylinder  94  upwards. This allows relatively more hot fluid to enter the large tempering valve  92 . As the temperature increases above a selected level, the large cylinder  94  will move downward reducing the size of the flow path beneath the lower sealing edge  98 . As the temperature further increases, the large cylinder  94  will finally move all the way to its lowest position in which the lower sealing edge  98  contacts the lower sealing surface  122 , thus cutting off all hot water flow. The temperature of the mixed water can be selected by moving the adjusting screw  112  up or down, which changes the static position of the second temperature-responsive element  102 . 
   Thus, the total flow through the tempering valve  10  always passes through the large valve assembly  20 . Practically this means that at flow rates just above the transition value, the percentage of the flow passing through the large tempering valve  92  is much greater than in prior art designs. This prevents the large tempering valve  92  from operating at very low flows, which are far below its design operating point, at which it controls flow inefficiently. 
     FIGS. 3 and 4  depict the addition of an optional supply failure protection valve  124  to the tempering valve  10 . The failure protection valve  124  includes a body  126  having a first passage  128 , a perpendicular second passage  130 , a valve inlet  134 , a valve outlet  136 , and a sensing port  138 . A piston  140  having a transverse passage  142  formed therethrough is disposed in the first passage  128  and is movable between an open position which permits flow from the valve inlet  134  through the second passage  130  to the valve outlet  136 , and a closed position which blocks flow from the valve inlet  134 . A closing spring  144  is installed in the first passage  128  and urges the piston  140  towards the open position. The failure protection valve  124  is connected to the tempering valve  10  so that mixed flow from the bypass passage  32  enters the valve inlet  134  and the valve outlet  136  is connected to the large valve assembly  20 . A sensing line  146  (shown schematically in  FIGS. 3 and 4 ) carries fluid from the cold fluid inlet  24  upstream of the cold fluid check valve  36  to the sensing port - 138 . Under normal operating conditions, as shown in  FIG. 3 , the fluid pressure of the cold fluid supply forces the piston  140  to the open position. The mixed flow from the small valve assembly  16  is free to pass from the valve inlet through the second passage  130  to the valve outlet  136  and then into the large valve assembly  20 . 
     FIG. 4  shows a condition in which the cold fluid supply C has failed. In this condition the pressure in the sensing port  138  will drop to zero (or a very low level) and the closing spring  144  will compress and allow the piston  140  to a closed position. This immediately cuts off the flow of mixed-temperature fluid from the small valve assembly  16  to the large valve assembly  20 . Therefore, any hot water traveling through this flowpath will be shut off. With the failure protection valve  124  closed, the pressure will build up below the small valve assembly, against the third surface  154 , until it equals the supply pressure. The first biasing spring  50  will then force the small valve assembly  16  upwards to the closed position, which closes off the flowpath from the hot and cold fluid inlets  22  and  24  to the hot and cold fluid ports  26  and  28 . Thus, all fluid flow out of the tempering valve  10  will be cut off, preventing any possible scalding of users. 
   The foregoing has described a tempering valve suitable for use at varying flow rates. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation, the invention being defined by the claims.