A temperature-actuated mixing valve for controlling outlet temperature in a fluid flow system including a valve housing having first and second fluid supply inlets for introducing first and second respective supply fluids and a fluid outlet for dispensing a fluid at a predetermined outflow temperature. The mixing valve includes a shuttle assembly positioned in the housing. The shuttle assembly includes a valve member mounted for movement within the housing responsive to the temperature of the supply fluids to vary the mixture ratio of the first and second supply fluids as required to dispense fluid at the predetermined outflow temperature. A shuttle member is positioned within the valve member and is moveable as a unit therewith within a predetermined range of motion responsive to supply fluid temperature variation. A thermal actuator is provided of the type which converts thermal energy into mechanical movement by movement of a piston. A first end of the thermal element engages the movable shuttle member and an opposing second end engages a stationary portion of the housing whereby movement of the piston of the thermal actuator produces corresponding movement of the valve member. An overtravel spring is captured in a tensioned condition between the valve member and the shuttle member for maintaining the shuttle member and the valve member in a stationary condition relative to each other within the predetermined range of motion of the valve member and for permitting movement of the shuttle member relative to the valve member sufficient to accommodate movement of the piston of the thermal actuator when the valve member has reached its limit of travel without accommodating the full extent of movement of the piston of the thermal actuator.

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION
 This invention relates to a temperature-actuated mixing valve of the
 general type used to control in-line water temperature in potable hot
 water systems. Such valves are typically used at the hot water source,
 such as at a gas or electric hot water heater or boiler. The temperature
 of the water allowed to flow downstream from the mixing valve is
 maintained within a predetermined range of temperature by mixing hot and
 cold water entering the valve on the upstream end. The invention is
 therefore described with reference to such a hot water system. However,
 principles of the invention also have application with other liquids and
 with gases, and for this reason the application is intended to encompass
 both liquids and gases, and liquids other than water.
 Most prior art mixing valves utilize a thermal actuator, which acts as the
 "motor" of the valve. Such actuators convert thermal energy into
 mechanical movement. The operating principle of most such devices is based
 upon the large increase in volume of a thermosensitive material such as
 wax which, when heated, changes from a solid to a liquid. When such a
 thermosensitive material is enclosed within a confined space, heating
 causes the material to expand against a piston to perform work. In some
 cases such actuators are either provided with two oppositely-acting
 pistons to increase the range of motion, or two such actuators are placed
 end-to-end to accomplish the same function. By incorporating a thermal
 actuator into a mixing valve, hot and cold supply pressures and
 temperatures can be regulated.
 A common problem in the use of such devices is that if the shuttle has
 moved as far as it can move within the valve, but the piston of the
 thermal actuator is still trying to move, there must be some means of
 consuming this extra travel. Otherwise the valve can be damaged or
 destroyed. This is most often accomplished in the prior art by the use of
 an overtravel spring mounted around an adjusting bolt in the top of the
 valve. This solution creates several additional problems. First, this
 arrangement adds height to the mixing valve, which may prevent or restrict
 use in confined areas, or promote breakage under impact. Second, the
 overtravel spring must be preloaded, requiring a means for retaining the
 spring on the adjusting bolt. Finally, in applications where two thermal
 actuators are used back-to-back, there must be some way to retain both
 elements in the shuttle.
 In addition, mixing valves are often difficult to disassemble for repair or
 maintenance, and require the use of tools, often in confined spaces.
 The design features of the present invention solve the known prior art
 problems simply and efficiently.
 SUMMARY OF THE INVENTION
 Therefore, it is an object of the invention to provide a mixing valve which
 is compact.
 It is another object of the invention to provide a mixing valve which is
 easy to disassemble.
 It is another object of the invention to provide a mixing valve in which
 the overtravel spring is integral with the shuttle assembly.
 It is another object of the invention to provide a mixing valve in which
 the shuttle cages the thermal element or elements, which permitting
 unrestricted movement within the full range of movement.
 It is another object of the invention to provide a mixing valve wherein the
 overtravel spring is remote from and operates independently of the
 adjustment bolt.
 These and other objects of the present invention are achieved in the
 preferred embodiments disclosed below by providing a temperature-actuated
 mixing valve for controlling outlet temperature in a fluid flow system
 including a valve housing having first and second fluid supply inlets for
 introducing first and second respective supply fluids and a fluid outlet
 for dispensing a fluid at a predetermined outflow temperature. The mixing
 valve includes a shuttle assembly positioned in the housing. The shuttle
 assembly comprises a valve member mounted for movement within the housing
 responsive to the temperature of the supply fluids to vary the mixture
 ratio of the first and second supply fluids as required to dispense fluid
 at the predetermined outflow temperature. A shuttle member is positioned
 within the valve member and is moveable as a unit therewith within a
 predetermined range of motion responsive to supply fluid temperature
 variation. A thermal actuator is provided of the type which converts
 thermal energy into mechanical movement by movement of a piston. A first
 end of the thermal element engages the movable shuttle member and an
 opposing second end engages a stationary portion of the housing whereby
 movement of the piston of the thermal actuator produces corresponding
 movement of the valve member. An overtravel spring is captured in a
 tensioned condition between the valve member and the shuttle member for
 maintaining the shuttle member and the valve member in a stationary
 condition relative to each other within the predetermined range of motion
 of the valve member and for permitting movement of the shuttle member
 relative to the valve member sufficient to accommodate movement of the
 piston of the thermal actuator when the valve member has reached its limit
 of travel without accommodating the full extent of movement of the piston
 of the thermal actuator.
 According to one preferred embodiment of the invention, the valve member is
 generally cylindrical and includes sealing means for sealing the valve
 member against fluid flow between the valve member and adjacent
 cylindrical walls of the valve housing.
 According to another preferred embodiment of the invention, the shuttle
 member includes retaining means for retaining the thermal actuator within
 the shuttle member while permitting movement of the piston responsive to
 the temperature of the inlet fluids.
 According to yet another preferred embodiment of the invention, the
 retaining means comprises a plurality of elongate fingers axially aligned
 with the longitudinal axis of the thermal actuator, each of the fingers
 having a radially inwardly-extending detent for interfering with movement
 of the thermal actuator beyond a predetermined range of motion for
 movably-capturing the thermal actuator within the shuttle member.
 According to yet another preferred embodiment of the invention, the shuttle
 member includes an elongate grip pad for permitting the shuttle member to
 be manually removed from the valve housing without the need for tools.
 According to yet another preferred embodiment of the invention, the grip
 pad extends along the longitudinal axis of the shuttle member.
 According to yet another preferred embodiment of the invention, the valve
 member includes an annular shoulder defining a support for the overtravel
 spring. The valve member includes locking means for receiving and locking
 the shuttle member within the valve member. The locking means cooperates
 with the overtravel spring for tensioning the shuttle member in the
 stationary condition relative to each other.
 According to yet another preferred embodiment of the invention, the locking
 means comprises a plurality of locking channels formed within the area of
 the valve member accommodated by the overtravel spring, each of the
 locking channels having a first segment communicating with an
 inwardly-facing end of the valve member, a second segment communicating
 with the first segment and extending peripherally around inner wall of the
 valve member and a third segment spaced apart from the first segment,
 communicating with the second segment and terminating at a blind end
 within the inner walls of the valve member, the plurality of locking
 channels adapted to receive respective ones of a plurality of locking tabs
 carried by the shuttle member and lock the shuttle member in the valve
 member by compressing the overtravel spring and passing the plurality of
 locking tabs through the first and second segments and to the blind end of
 the third segment of the locking channels.
 According to yet another preferred embodiment of the invention, the shuttle
 member comprises an elongate stem having an annular bore for receiving the
 thermal actuator therein for movement therein, retaining means for
 retaining the thermal actuator in the bore and locking means for locking
 the stem in the valve member.
 According to yet another preferred embodiment of the invention, the valve
 housing includes an adjusting bolt engaging an end of the thermal actuator
 remote from the valve member for permitting longitudinal adjustment of the
 thermal actuator relative to the valve member.
 According to yet another preferred embodiment of the invention, the thermal
 actuator comprises a pair of thermal actuators for increasing the
 effective range of temperature-responsive motion.
 According to yet another preferred embodiment of the invention, the
 retaining means comprises a cage within which the thermal actuator is
 captured.
 An embodiment of the method according to the invention controls outlet
 temperature in a fluid flow system including a valve housing having first
 and second fluid supply inlets for introducing first and second respective
 supply fluids and a fluid outlet for dispensing a fluid at a predetermined
 outflow temperature, the mixing valve including a shuttle assembly
 positioned in the housing. The method comprises the steps of mounting a
 valve member for movement within the housing responsive to the temperature
 of the supply fluids to vary the mixture ratio of the first and second
 supply fluids as required to dispense fluid at the predetermined outflow
 temperature. A shuttle member is positioned within the valve member as a
 unit with the valve member within a predetermined range of motion
 responsive to supply fluid temperature variation and a thermal actuator is
 provided of the type which converts thermal energy into mechanical energy
 by movement of a piston wherein a first end of the thermal element engages
 the movable shuttle member and an opposing second end engages a stationary
 portion of the housing whereby movement of the piston of the thermal
 actuator produces corresponding movement of the valve member. The shuttle
 member and the valve member are maintained in a stationary condition
 relative to each other within the predetermined range of motion of the
 valve member while permitting movement of the shuttle member relative to
 the valve member sufficient to accommodate movement of the piston of the
 thermal actuator when the valve member has reached its limit of travel
 without accommodating the full extent of movement of the piston of the
 thermal actuator.
 Another embodiment of the method according to the invention comprises the
 step of retaining the thermal actuator within a cage forming a part of the
 shuttle member for permitting movement of the thermal actuator within its
 range of motion while preventing the thermal actuator from falling out of
 the shuttle assembly.
 According to another preferred embodiment of the invention, a method is
 disclosed for controlling outlet temperature in a mixing valve of a fluid
 flow system includes a valve housing having first and second fluid supply
 inlets for introducing first and second respective supply fluids and a
 fluid outlet for dispensing a fluid at a predetermined outflow
 temperature, the mixing valve including a shuttle assembly positioned in
 the housing and carrying a thermal actuator responsive to the temperature
 of fluid entering the mixing valve for controlling the ratio of the
 respective supply fluids to regulate the outflow temperature of the fluid.
 The method comprises the steps of forming the shuttle assembly from a
 shuttle member and a valve member releasably-attached together, retaining
 an overtravel spring between the shuttle member and the valve member,
 moving the shuttle member and the valve member as a unit responsive to the
 thermal actuator when regulating the flow of fluid flowing into the mixing
 valve, and moving the shuttle member relative to the valve member when
 compensating for overtravel of the thermal actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENT AND BEST MODE
 Referring now specifically to the drawings, a prior art
 temperature-responsive mixing valve 10 is shown. Note generally that the
 prior art shuttle assembly 11 is moved by a thermal actuator 12 which is
 maintained in a tensioned condition by a spring 13, which returns the
 thermal actuator 12 to its initial position. Another spring 16 captured on
 the other side of the thermal actuator 12 by an adjustment bolt 17
 provides overtravel protection to the shuttle assembly 11. This
 arrangement results in a valve housing which is relatively large, as is
 evident from the overall length taken up by the shuttle assembly, spring
 13 and spring 16. The shuttle assembly 11 is rigidly attached via a
 threaded connection to the thermal actuator 12.
 As is shown in FIGS. 2-13, the mixing valve 20 according to a preferred
 embodiment of the invention is simple, compact, efficient and easy to
 assemble and disassemble. As is generally shown in FIGS. 2 and 3, mixing
 valve 20 includes a cast housing 21 which includes a hot water supply
 inlet 22, and cold supply water inlet 23 and an outlet 24 for discharging
 a mixture of the hot and cold water downstream. A removable threaded plug
 25 positioned in a threaded bore 26 in the housing 21 permits access to
 the internal parts of the mixing valve 20, as described below.
 As is generally shown in FIG. 3, a shuttle assembly 30 is positioned within
 the mixing valve 20 and regulates the temperature of water flowing from
 the outlet 24. Shuttle assembly 30 includes an annular, hollow valve
 member 40 which is releasably locked to a shuttle member 50. The shuttle
 member 50 carries a pair of thermal actuators 70A, 70B which move the
 valve member 40 responsive to the temperature of the water flowing into
 the housing 21 through the inlets 22 and 23. The thermal actuators 70A,
 70B are rigidly coupled together, with, for example, a brass collar 71. An
 adjustment screw 80 is threaded into the top of the housing 21 and is
 seated against an adjustment plug 81 which also engages the top end of the
 thermal actuator 70A. The adjustment screw 80 is used to calibrate the
 adjustment of the valve member 40. A spring 82 is seated in the plug 25
 and urges the shuttle member 50 and the thermal actuators 70A, 70B
 upwardly into engagement with the adjustment plug 81.
 An overtravel spring 85 is positioned within the hollow bore of the valve
 member 40 and cooperates with the shuttle member 50 to accommodate
 movement of the thermal actuators 70A, 70B beyond the range of the travel
 of the valve member 40 within housing 21. Further explanation of the
 operation of the mixing valve 20 follows a more specific description of
 the shuttle assembly 30.
 While the shuttle member 50 and valve member 40 can be fabricated from many
 suitable materials, which must be moldable or machinable, and
 dimensionally stable over a wide range of temperatures, one suitable
 material is a glass-filled plastic such as modified polyphenylene ether
 ("PTE") such as sold under the trademark "Noryl."
 Referring now to FIGS. 4 and 5, the shuttle assembly 30 is shown in two
 different views with (FIG. 4) and without (FIG. 5) the thermal actuators
 70A, 70B and overtravel spring 85 in place. Valve member 40 includes an
 interior shoulder 41 on which one end of the overtravel spring 85 rests.
 An annular groove 42 on the outer surface accommodates an O-ring 43 which
 seals the valve member 40 against the interior walls of the housing 21.
 (See FIG. 3). Valve member 40 also includes four three-segment locking
 channels 44A-D on the interior walls. Each locking channel 44A-D
 communicates with the top end of the valve member 40 and is adapted to
 receive one of four integrally-formed locking tabs 51A-D. Each locking
 channel 44A-D is generally U-shaped and extends along the longitudinal
 axis of the interior wall of the valve member 40, laterally across the
 inner periphery of the inner wall of the valve member and then along the
 longitudinal axis of the interior wall of the valve member 40 to a blind
 end.
 The shuttle member 50 is locked into the valve member 40 by inserting one
 of the locking tabs 51A-D into a respective one of the locking channels
 44A-D. Significant force must be applied to force the locking tabs 51A-D
 into the locking channels 44A-D against the force of the overtravel spring
 85. When the locking tabs 51A-D reach the level of the laterally-extending
 segment of the locking channels 44A-D the shuttle member 50 is twisted
 relative to the valve member 40, moving the locking tabs 51A-D along the
 periphery of the valve member 40 to the respective blind ends of the
 channels 44A-D. The tension of the overtravel spring 85 securely locks the
 shuttle member 50 in the valve member 40 while still allowing longitudinal
 movement of the shuttle member 50 relative to the valve member 40 when
 necessary to accommodate overtravel of the thermal actuators 70A, 70B.
 Within the normal range of movement of the valve member 40, the shuttle
 member 50 and the valve member 40 move together in fixed relation to each
 other.
 Shuttle member 50 also includes four fingers 54A-D which extend along the
 longitudinal axis of the shuttle member 50 and surround a recess 55 within
 the thermal actuators 70A, 70B are positioned. Each of the fingers 54A-D
 have radially inwardly-directed detents 56 which engage and interfere with
 an enlarged annular ring 72 on the innermost thermal actuator 70B. This
 prevents the thermal actuator 70B from falling from the shuttle member 50.
 Rather, a pulling force must be applied to the thermal actuator 70B
 sufficient to cause the ring 72 to outwardly deform the fingers 54A-D
 sufficiently to permit the thermal actuator 70B to be removed. In
 instances where only a single thermal actuator 70B is used, it is captured
 and held in exactly the same manner.
 Finally, the shuttle member 50 also includes an integrally-formed finger
 grip pad 76 which permits the shuttle member 50 and other attached
 components to be removed merely by inserting the hand into the housing 21
 through the threaded bore 26 after removal of the plug 25. The entire
 assembly can then be removed from the housing 21.
 FIGS. 6 and 7 further illustrate the arrangement of the locking channels
 44A-D, and FIG. 6, in particular, illustrates the laterally-extending
 channel segment which extends around the inner periphery of the valve
 member 40. Note also in FIG. 7 that the overtravel spring 85 is captured
 in a compressed condition between the bottom side of the locking tabs
 51A-D and the shoulder 41 on the opposite end of the valve member 40.
 The overall assembly of the shuttle assembly 30 is shown in FIG. 8. Each of
 the elements, namely, the valve member 40, the shuttle member 50, the
 overtravel spring 85 and the thermal actuators 70A, 70B have a common
 central axis and thus a symmetrical longitudinal orientation.
 The incorporation of the shuttle assembly 30 into the mixing valve 20 is
 shown in FIG. 9. The plug 25 captures the shuttle assembly 30 and the
 spring 82 in the housing 21. The mixing valve is then ready to install in
 a water system by connecting suitable inlet and outlet piping to the
 inlets 22, 23 and the outlet 24, respectively.
 Operation of the mixing valve 20 is illustrated in FIGS. 10-13. The mixing
 valve 20 is set to produce a mixed outflow of water within a predetermined
 temperature range, taking into account the nominal temperature of the cold
 and hot water flowing into the valve 20. FIG. 10 illustrates the valve
 member position when only cold water is being supplied to the valve 20.
 This occurs transiently as necessary when too much hot water flow has
 heated the thermal actuators to the point where the temperature of the
 outlet flow is outside of limits, and when a long period of time with
 little or no flow has heated the valve 20 significantly.
 If set correctly, the mixture of hot water and cold water through the
 mixing valve 20 results in an outflow which is within the desired
 temperature range. Thus, in FIG. 11 both hot water and cold water flow
 past the valve member 40. As shown, movement of the valve member 40
 simultaneously increases the flow of hot water when the flow of cold water
 is being decreased, and vice versa. The movement of the valve member 40
 acts as a form of servo-feedback device to constantly sense and correct
 imbalances in the inflow temperature of the water.
 FIG. 12 illustrates the condition when only hot water is being passed into
 the mixing valve 20 in order to compensate for a temperature which is
 below the lower temperature range. The valve member 40 is thus at the top
 of its movement range.
 FIG. 13 illustrates the situation when a temperature imbalance on the hot
 side has called for cold water, but the temperature imbalance is such that
 the thermal actuators 70A, 70B has caused the valve member 40 to bottom
 out on the plug 25 at the bottom of the mixing valve 20, but is still
 expanding. In this case, the overtravel spring 85 is compressed by the
 further downward force by the shuttle member 50, preventing damage to the
 valve 20. Correction of the overtravel condition immediately returns the
 mixing valve 20 to normal operation.
 A temperature-actuated mixing valve is described above. Various details of
 the invention may be changed without departing from its scope.
 Furthermore, 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.