Abstract:
Provided is a three-way valve having and actuator ( 66 ) and first ( 100 ) and second ( 102 ) piston assemblies movable by the actuator ( 66 ) and arranged in tandem, wherein each piston assembly ( 100,102 ) has a backside ( 104,106 ) in fluid communication with a common pressure source for pressure balancing the piston assemblies ( 100,102 ). By having the backsides ( 104,106 ) in fluid communication with a common pressure source and by isolating the piston assemblies ( 100,102 ) from a main chamber, an axial load on the actuator ( 66 ) is minimized, thereby allowing for more compact valve designs.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/764,723 filed Feb. 14, 2013, which is hereby incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates generally to a flow control device, and more particularly to a valve for controlling the flow of fluid in a system 
       BACKGROUND 
       [0003]    Flow control devices, such as motor controlled electric valves may be provided in heating/cooling systems to control the flow of fluid through the system. For example, motor controlled valves may be used at nodes of diverging loops of circuits to provide refrigerant for heat reclaim or for defrosting evaporators. The motor controlled valves may include a piston which is movable by an electric motor to vary the flow of fluid through the valve. The motor may be rotated by a signal sent by a controller. The motor rotates a gear train that is coupled to the piston to cause the piston to move. 
       SUMMARY OF INVENTION 
       [0004]    The present invention provides a three-way valve having and actuator and first and second piston assemblies movable by the actuator and arranged in tandem, wherein each piston assembly has a backside in fluid communication with a common pressure source for pressure balancing the piston assemblies. By having the backsides in fluid communication with a common pressure source and by isolating the piston assemblies from a main chamber, an axial load on the actuator is minimized, thereby allowing for more compact valve designs. 
         [0005]    According to one aspect of the invention, a modulating balance ported three-way valve is provided that includes a valve body having an inlet port, a chamber, and first and second outlet ports in fluidic communication with the inlet port via the chamber, an actuator having an output shaft, a connection rod disposed in the valve body and coupled to the actuator such that the actuator effects longitudinal movement of the connection rod, and first and second piston assemblies coupled to the connection rod and each having a backside in fluid communication with a common pressure source for pressure balancing the piston assemblies, wherein the first and second piston assemblies are movable between a first position allowing fluid entering the inlet port to flow through the first outlet and preventing fluid flow through the second outlet, a second position preventing fluid flow through the first outlet and allowing the fluid to flow through the second outlet, and a plurality of third positions allowing a varying amount of the fluid to flow through the first and second outlets. 
         [0006]    The connection rod includes a passage in fluid communication with the backside of each piston assembly and the common pressure source. 
         [0007]    The common pressure source is the fluid entering the inlet port. 
         [0008]    The connection rod includes at least one port through which the fluid in the chamber enters the passage. 
         [0009]    When the first and second piston assemblies are in the first position, the second piston assembly is seated against a second valve seat in the valve body, and when the first and second piston assemblies are in the second position, the first piston assembly is seated against a first valve seat in the valve body. 
         [0010]    According to another aspect of the invention, a modulating balance ported three-way valve is provided that includes a valve body having an inlet port, a chamber, and first and second outlet ports in fluidic communication with the inlet port via the chamber, a connection rod disposed in the valve body and movable axially in the valve body, and first and second piston assemblies coupled to the connection rod and movable therewith to engage first and second seats respectively in the valve body, the first and second piston assemblies being axially spaced from one another such that while the first piston assembly is seated against the first seat to prevent fluid flow through the first outlet the second piston assembly is unseated from the second seat to allow fluid flow through the second outlet, while the second piston assembly is seated against the second seat to prevent fluid flow through the second outlet the first piston assembly is unseated from the first seat to allow fluid flow through the first outlet, and while the first and second piston assemblies are unseated from the first and second seats respectively fluid flows through both the first and second outlets. 
         [0011]    Each of the first and second piston assemblies has a backside in fluid communication with a common pressure source for pressure balancing the piston assemblies. 
         [0012]    The connection rod includes a passage in fluid communication with the backside of each piston assembly and the common pressure source. 
         [0013]    The connection rod includes at least one port through which the fluid in the chamber enters the passage. 
         [0014]    According to still another aspect of the invention, a method of modulating a three-way valve is provided, the valve having a valve body, an actuator, a connection rod disposed in the valve body and first and second piston assemblies arranged in tandem and coupled to the connection rod. The method includes controlling the tandem piston assemblies such that while the first piston assembly is seated against a first seat in the valve body to prevent fluid flow through a first outlet the second piston assembly is unseated from a second seat in the valve body to allow fluid flow through a second outlet, while the second piston assembly is seated against the second seat to prevent fluid flow through the second outlet the first piston assembly is unseated from the first seat to allow fluid flow through the first outlet, and while the first and second piston assemblies are unseated from the first and second seats respectively fluid flows through both the first and second outlets, and delivering fluid to a backside of each piston assembly in fluid communication with a common pressure source for pressure balancing the piston assemblies. 
         [0015]    While the first and second piston assemblies are unseated from the first and second seats respectively, the method further includes controlling the tandem piston assembly to vary the percentage of flow between the outlets. 
         [0016]    According to yet another aspect of the invention a modulating balance ported three way valve is provided that includes two balance ported piston assemblies, a connecting rod coupled to the ported piston assemblies having a passageway that is in fluid communication with a main chamber of the valve and respective sides of the piston assemblies opposite the main chamber of the valve to communicate pressure from the main chamber to the respective opposite sides of the pistons, and a motor actuator for controlling the position of the piston assemblies. 
         [0017]    According to a further aspect of the invention, a modulating balance ported three-way valve is provided that includes a valve body having an inlet port, a chamber, and first and second outlet ports in fluidic communication with the inlet port via the chamber, an actuator having an output shaft, a connection rod disposed in the valve body and coupled to the actuator such that the actuator effects longitudinal movement of the connection rod, the connection rod including a passage, and first and second piston assemblies coupled to the connection rod, each piston assembly having a backside in fluid communication with the other backside via the passage for pressure balancing the piston assemblies. 
         [0018]    The first and second piston assemblies are movable between a first position allowing fluid entering the inlet port to flow through the first outlet and preventing fluid flow through the second outlet, a second position preventing fluid flow through the first outlet and allowing the fluid to flow through the second outlet, and a plurality of third positions allowing a varying amount of the fluid to flow through the first and second outlets. 
         [0019]    The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is an exemplary heat reclaim system having a modulating balance ported three-way valve in accordance with aspects of the invention. 
           [0021]      FIG. 2  is a perspective view of the exemplary modulating balance ported three-way valve. 
           [0022]      FIG. 3  is a cross-sectional view of the modulating balance ported three-way valve taken about line  3 - 3  in  FIG. 2  showing piston assemblies in a first position. 
           [0023]      FIG. 4  is another cross-sectional view of the modulating balance ported three-way valve taken about line  3 - 3  in  FIG. 2  showing the piston assemblies in a second position. 
           [0024]      FIG. 5  is still another cross-sectional view of the modulating balance ported three-way valve taken about line  3 - 3  in  FIG. 2  showing the piston assemblies in a third position. 
           [0025]      FIG. 6  is a partial cross-sectional view of a piston assembly and connection rod of an exemplary modulating balance ported three-way valve. 
           [0026]      FIG. 7  is a cross-sectional view of another exemplary modulating balance ported three-way valve. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The principles of the present application have particular application to three-way valves for refrigeration and air conditioning systems and thus will be described below chiefly in this context. It will of course be appreciated, and also understood, that the principles of the invention may be useful in other fluid transfer applications where it is desirable to direct fluid to multiple outlets of a valve. 
         [0028]    Turning now to  FIG. 1 , an exemplary heat reclaim system is shown generally at reference numeral  10 . The system includes a compressor  12 , a modulating balance ported three-way valve  14 , a first condenser  16 , a second condenser  18 , an expansion device  20 , an evaporator  22 , and, controller  24 , and a check valve  26  for preventing fluid flow from the condenser  16  to the condenser  18 . The fluid flowing through the system, which may be a suitable refrigerant, such as a two-phase refrigerant, enters the compressor  12  and is compressed. The compressed fluid then flows to the three-way valve  14 , which may deliver the fluid to one or both of the first and second condensers  16  and  18 . Fluid delivered to the first and second condensers  16  and  18  is cooled and the heat rejected. The heat rejected from the second condenser  18 , which may serve as a heat reclamation coil, is dissipated as useful heat and then the fluid flows to the first condenser  16 . The fluid exits the first condenser  16  and flows to the expansion device  20  that expands the fluid to a low pressure liquid-vapor, and then the fluid flows to the evaporator  22  where heat is absorbed from a component, the environment, etc. The controller  24  may be provided to control the valve  14 , and specifically an actuator of the valve  14  to control the flow of fluid exiting the valve. 
         [0029]    Turning now to  FIGS. 2 and 3 , the valve  14  includes a valve body  30  having an inlet port  32 , a chamber  34 , and first and second outlet ports  36  and  38  in fluidic communication with the inlet port  32  via the chamber  34 . The inlet port  32  and outlet ports  36  and  38  may be longitudinally spaced and have coupled thereto or integral therewith respective fluid conduits  40 ,  42  and  44 . The valve body  30  may be open at its first and second ends  46  and  48 , and the first end  46  may be closed by an adapter  50  and the second end  48  may be closed by a plug  52 . The adapter  50  and plug  52  may be coupled to the valve body  30  in any suitable manner, such as by a threaded connection. 
         [0030]    Coupled to the adapter  50  is a motor housing  60 , which may include a top housing member  62  and a bottom housing member  64  coupled together and to the adapter  50  in any suitable manner, such as a threaded connection. The motor housing  60  may enclose a suitable actuator, such as a motor. In the illustrated embodiment, the motor housing  60  encloses a motor  66 , such as an electric motor, such as an electric stepper motor. To provide power to the motor  66 , the motor  66  may be coupled to pins  68  by suitable wires  67 , and the pins  68  may be coupled to a strain relief  70  by suitable wires  71 . The strain relief  70  is coupled to a nut  72  in any suitable manner, such as by a threaded connection, and the nut  72  is coupled to the top housing member  62  in any suitable manner, such as by a threaded connection. The pins  68  are constrained in sintered glass to isolate each pin, and the glass is constrained in a frame constrained between the nut  72  and the top housing member  62 , which are sealed by a suitable seal, such as o-ring  74 . 
         [0031]    The motor  66  includes an output shaft  80  extending longitudinally towards the inlet and outlet ports  32 ,  34  and  36 . The output shaft  80  is rotatably coupled to a drive screw  82  via a reduction gear assembly  84 , such as a cluster gear assembly, and the drive screw  82  is coupled to a plunger  86 . The plunger  86  is supported in the valve body  30  for longitudinal movement along the drive screw  82  such that rotation of the drive screw  82  effects longitudinal movement of the plunger  86 . The plunger includes a head  88  coupled to a first end of a connection rod  90  in any suitable manner, such as a threaded connection, such that the connection rod  90  moves longitudinally with the plunger  86 . 
         [0032]    The connection rod  90  is disposed in the valve body  30  and coupled to first and second piston assemblies  100  and  102 . The first piston assembly  100  is coupled to the first end of the connection rod  90  and the second piston assembly  102  is coupled to a second end of the connection rod  90 . A backside  104 ,  106  of each piston assembly  100 ,  102 , respectively, is in fluid communication with a common pressure source, for example the fluid entering the chamber  34  via the inlet port  32 , to pressure balance the piston assemblies  100  and  102 . 
         [0033]    Fluid flowing through the chamber  34  enters a passage  108  in the connection rod  90  via one or more ports  110 , which passage  108  is in fluid communication with the backside  104 ,  106  of each piston assembly  100 ,  102  and the common pressure source. The fluid then flows through the passage  108  to an area  112  between the backside  104  and the adapter  50 , and to an area  114  between the backside  106  and the plug  52 . The fluid flowing through the passage  108  may exit the passage  108  into the areas  112  and  114  via axial or radial passages at the ends of the connection rod  90 , or via radial passages  116  and  118  in the plunger  86  and a retainer  120 , respectively. The radial passages  116  and  118  may be, for example, cross-holes machined into the plunger  86  and retainer  120 . 
         [0034]    The connection rod  90  is movable longitudinally to move the first and second piston assemblies  100  and  102  between a first position shown in  FIG. 4 , a second position shown in  FIG. 5 , and a plurality of third positions, one of which is shown in  FIG. 3 . When the first and second piston assemblies  100  and  102  are in the first position, fluid entering the inlet port  32  flows into the chamber  34  and exits the valve via the first outlet port  36 , and the second piston assembly  102  is seated against a second valve seat  132  in the valve body  30  to prevent fluid flow through the second outlet port  38 . When the first and second piston assemblies  100  and  102  are in the second position, fluid entering the inlet port  32  flows into the chamber  34  and exits the valve via the second outlet port  38 , and the first piston assembly  100  is seated against a first valve seat  130  in the valve body  30  to prevent fluid flow through the first outlet port  36 . When the first and second piston assemblies  100  and  102  are in one of the third positions, neither piston assembly  100  or  102  is seated against the respective valve seat  130 ,  132 , thereby allowing a varying amount of the fluid to flow through the first and second outlet ports  36  and  38 . 
         [0035]    Referring now to the first piston assembly  100  in detail, the first piston assembly  100  includes a piston body  140  and a nose piece  142  through which an end of the connection rod  90  extends, a seal  144 , such as a lip seal near the backside  104  for isolating the area  112  from the chamber  34  and for retaining the pressure from the common pressure source in the area  112 , and a seal retainer  146  coupled to a backside of the piston body  140  to secure the seal between the piston body  140  and the seal retainer. The connection rod  90  may be sealed to the nose piece  142  in any suitable manner, such as by an o-ring  148 , and the seal retainer  146  may be coupled to the piston body  140  in any suitable manner, such as by a threaded connection. The first piston assembly  100  may also include a seat disc  150  disposed between the nose piece  142  and the piston body  140 , which is sealed to the piston body  140  in any suitable manner, such as by an o-ring  152 . 
         [0036]    To vent fluid in the passage  108  in the connection rod  90  to equalize pressure, the nose piece  142  includes a radial passage  160  in communication with the passage  108 , for example by a radial passage  162  in the connection rod  90 . The fluid vented from the passage  108  puts pressure on the backside of the o-ring  152 , which prevents a large pressure drop by fluid flowing through the passage  108  and prevents the o-ring  152  from being blown out or being pushed in. 
         [0037]    To connect the piston assembly  100  to the connection rod  90 , the piston body  140  includes at least one ledge in the piston body, and in the illustrated embodiment first and second ledges  170  and  172  that are configured to be abutted by corresponding stepped portions  174  and  176  of the nose piece  142  and a third ledge  178  that is configured to be abutted by the plunger head  88 . The nose piece  142  is inserted into the piston body  140  until the portions  174  and  176  abut the corresponding ledges  170  and  172 , and the connection rod  90  is inserted through the nose piece  142  and the piston body  140 . The end of the connection rod  90  is then coupled to the plunger head  88 , such as by a threaded connection, causing the plunger head  88  to abut the ledge  178  and causing a stepped portion  180  of the connection rod  90  to abut a ledge  182  in the nose piece  142 . 
         [0038]    Referring now to the second piston assembly  102  in detail, the second piston assembly  102  includes a piston body  190  and a nose piece  192  through which an end of the connection rod  90  extends, a seal  194 , such as a lip seal near the backside  106  for isolating the area  114  from the chamber  34  and for retaining the pressure from the common pressure source in the area  114 , and a seal retainer  196  coupled to a backside of the piston body  190  to secure the seal between the piston body  190  and the seal retainer. The connection rod  90  may be sealed to the nose piece  192  in any suitable manner, such as by an o-ring  198 , and the seal retainer  196  may be coupled to the piston body  190  in any suitable manner, such as by a threaded connection. The second piston assembly  102  may also include a seat disc  200  disposed between the nose piece  192  and the piston body  190 , which is sealed to the piston body  190  in any suitable manner, such as by an o-ring  202 . 
         [0039]    To vent fluid in the passage  108  in the connection rod  90  to equalize pressure, the nose piece  192  includes a radial passage  210  in communication with the passage  108 , for example by a radial passage  212  in the connection rod  90 . The fluid vented from the passage  108  puts pressure on the backside of the o-ring  202 , which prevents a large pressure drop by fluid flowing through the passage  108  and prevents the o-ring  202  from being blown out or being pushed in. 
         [0040]    To connect the piston assembly  102  to the connection rod  90 , the piston body  190  includes at least one ledge in the piston body, and in the illustrated embodiment first and second ledges  220  and  222  that are configured to be abutted by corresponding stepped portions  224  and  226  of the nose piece  192  and a third ledge  228  that is configured to be abutted by a retainer  230 . The nose piece  192  is inserted into the piston body  190  until the portions  224  and  226  abut the corresponding ledges  220  and  222 , and the connection rod  90  is inserted through the nose piece  192  and the piston body  190 . The end of the connection rod  90  is then coupled to the retainer  230 , such as by a threaded connection, causing the retainer  230  to abut the ledge  228  and causing a stepped portion  232  of the connection rod  90  to abut a ledge  234  in the nose piece  192 . 
         [0041]    During operation of the heat reclaim system  10 , fluid flows from the compressor to the modulating balance ported three-way valve  14 . To deliver refrigerant to the first condenser  16  and not the second condenser  18 , the first and second piston assemblies  100  and  102  are moved axially until the second piston assembly, and specifically the seat disc  200  is seated against the valve seat  132  thereby preventing fluid flow through the second outlet port  38 . When the second piston assembly  102  is seated against the valve seat  132 , the first piston assembly  100  is not seated on the first valve seat  130  thereby allowing all of the flow entering the inlet port  32  to flow through the first outlet port  36 , thereby bypassing the second condenser  18 . The check valve  26  prevents fluid from flowing from the first condenser  16  to the second condenser  18 . 
         [0042]    To deliver refrigerant to the second condenser  18  and not the first condenser  16  the first and second piston assemblies  100  and  102  are moved axially until the first piston assembly, and specifically the seat disc  150  is seated against the valve seat  130  thereby preventing fluid flow through the first outlet port  36 . When the first piston assembly  100  is seated against the valve seat  130 , the second piston assembly  102  is not seated on the second valve seat  132  thereby allowing all of the flow entering the inlet port  32  to flow through the second outlet port  38 , thereby bypassing the first condenser  16 . 
         [0043]    As the first and second piston assemblies  100  and  102 , which have diameters that are substantially similar to the valve seats  130  and  132 , are being moved, a portion of the fluid in the chamber  34  enters the passage  108  via the port  110  and flows to the areas  112  and  114 , which are isolated from the chamber  34  by the seals  144  and  194 , respectively, thereby minimizing the axial load on the actuator required to move the first and second piston assemblies  100  and  102 . By reducing the axial load, smaller actuators may be used allowing for a more compact valve design. 
         [0044]    To deliver refrigerant to both the first and second condensers  16  and  18  without having to use multiple valves, for example in a heat reclaim system where a precise amount of flow is desired to be delivered to the heat reclaim condenser  18 , the connection rod  90  and thus the piston assemblies  100  and  102  are moved to one of the plurality of third positions. When in one of the third positions, a percentage of the flow entering the inlet port  32  flows through both the first and second outlet ports  36  and  38 . The piston assemblies  100  and  102  may be moved to allow equal flow through both the outlet ports  36  and  38  or to positions allowing for varying flow through the outlet ports  36  and  38 . 
         [0045]    Turning now to  FIG. 6 , an exemplary embodiment of the second piston assembly of the modulating balance ported three-way valve  14  is shown at  302 . The second piston assembly  302  is substantially the same as the above-referenced second piston assembly  102 , and consequently the same reference numerals but indexed by 200 are used to denote structures corresponding to similar structures in the valve. In addition, the foregoing description of the second piston assembly  102  and components of the valve is equally applicable to the second piston assembly  302  except as noted below. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the second piston assemblies may be substituted for one another or used in conjunction with one another where applicable. 
         [0046]    The second piston assembly  302  includes a piston body  390  and a nose piece  392  through which an end of the connection rod  290  extends, a seal  394 , such as a lip seal disposed in a seal groove  396  near the backside  306  for isolating the area  314  from the chamber  34  ( FIG. 3 ) and for retaining the pressure from the common pressure source in the area  314 . The connection rod  290  may be sealed to the nose piece  392  in any suitable manner, such as by an o-ring  398 . The second piston assembly  302  may also include a seat disc  400  disposed between the nose piece  392  and the piston body  390 , which is sealed to the piston body  390  in any suitable manner, such as by an o-ring  402 . 
         [0047]    To vent fluid in the passage  308  in the connection rod  290  to equalize pressure, the nose piece  392  includes a radial passage  410  in communication with the passage  308 , for example by a radial passage  412  in the connection rod  290 . The fluid vented from the passage  308  puts pressure on the backside of the o-ring  402 , which prevents a large pressure drop by fluid flowing through the passage  308  and prevents the o-ring  402  from being blown out or being pushed in. To allow fluid flowing through the passage  308  to exit the passage directly into the area  314 , the end of the connection rod  290  may extend beyond the retainer  430 , which may be a nut. 
         [0048]    Turning now to  FIG. 7 , an exemplary embodiment of the modulating balance ported three-way valve is shown at  515 . The modulating balance ported three-way  515  is substantially the same as the above-referenced modulating balance ported three-way  14 , and consequently the same reference numerals but indexed by 500 are used to denote structures corresponding to similar structures in the valve. In addition, the foregoing description of the modulating balance ported three-way  14  is equally applicable to the modulating balance ported three-way  514  except as noted below. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the valves may be substituted for one another or used in conjunction with one another where applicable. 
         [0049]    The valve  514  includes a valve body  530  having an inlet port  532 , a chamber  534 , and first and second outlet ports  536  and  38  in fluidic communication with the inlet port  532  via the chamber  534 . The inlet port  532  and outlet ports  536  and  538  may have coupled thereto or integral therewith respective fluid conduits  540 ,  542  and  544 . The valve body  530  may be coupled to an adapter  550  in any suitable manner, such as by a threaded connection. Coupled to the adapter  550  is a motor housing  560  that encloses a suitable actuator, such as a motor  566  that is coupled be coupled to pins  568  by suitable wires (not shown), and the pins  568  may be coupled to a strain relief  570  by suitable wires (not shown). 
         [0050]    The motor  566  includes an output shaft  580  extending longitudinally towards the inlet and outlet ports  532 ,  534  and  536 . The output shaft  580  is rotatably coupled to a drive screw  582  via a reduction gear assembly  584 , and the drive screw  582  is coupled to a plunger  586 . The plunger includes a head  588  coupled to a first end of a connection rod  590  in any suitable manner, such as a threaded connection, such that the connection rod  590  moves longitudinally with the plunger  586 . 
         [0051]    The connection rod  590  is disposed in the valve body  530  and coupled to first and second piston assemblies  600  and  602 . The first piston assembly  600  is coupled to the first end of the connection rod  590  and the second piston assembly  602  is coupled to a second end of the connection rod  590 . A backside  604  of the piston assembly  600  is in fluid communication with a backside  606  of the piston assembly  602  via a passage  608  in the connection rod  590 . The fluid enters the passage  608  via a port  610 , and flows through the passage  608  to an area  612  between the backside  606  and the adapter  550 . 
         [0052]    The connection rod  590  is movable longitudinally to move the first and second piston assemblies  600  and  602  between a first position, a second position, and a plurality of third positions, one of which is shown in  FIG. 7 . When the first and second piston assemblies  600  and  602  are in the first position, fluid entering the inlet port  532  flows into the chamber  534  and exits the valve via the first outlet port  536 , and a bottom portion of the second piston assembly  602  is seated against a second valve seat  632  in the valve body  530  to prevent fluid flow through the second outlet port  538 . When the first and second piston assemblies  600  and  602  are in the second position, fluid entering the inlet port  532  flows into the chamber  534  and exits the valve via the second outlet port  538 , and a top portion of the second piston assembly  602  is seated against a first valve seat  630  in the valve body  530  to prevent fluid flow through the first outlet port  536 . When the first and second piston assemblies  600  and  602  are in one of the third positions, neither the top nor the bottom portion of the second piston assembly  602  is seated against the respective valve seat  630 ,  632 , thereby allowing a varying amount of the fluid to flow through the first and second outlet ports  536  and  538 . 
         [0053]    Referring now to the first piston assembly  600  in detail, the first piston assembly  600  includes a piston body  640  through which an end of the connection rod  590  extends, a seal  644 , such as a lip seal near the backside  604  for isolating the area  612  from the chamber  534  and for retaining the pressure from the passage  608  in the area  612 , and a seal retainer  646  coupled to a backside of the piston body  640  to secure the seal between the piston body  640  and the seal retainer. 
         [0054]    To connect the piston assembly  600  to the connection rod  590 , the piston body  640  includes a ledge  678  in the piston body that is configured to be abutted by the plunger head  588 . The connection rod  590  is inserted through the piston body  640  and the end of the connection rod  590  is coupled to the plunger head  588 , such as by a threaded connection, causing the plunger heat  588  to abut the ledge  678  and causing a radially outwardly projecting portion  688  of the connection rod  590  to abut the piston body  640 . 
         [0055]    Referring now to the second piston assembly  602  in detail, the second piston assembly  602  includes a piston body  690 , an upper nose piece  692  and a lower nose piece  693  through which an end of the connection rod  590  extends, and a retainer  730  coupled to the end of the connection rod  590 . The second piston assembly  602  may also include a seat disc  700  disposed between the nose piece  692  and the piston body  690  and a seat disc  701  disposed between the nose piece  693  and the piston body  690 , which are sealed to the piston body  690  in any suitable manner, such as by respective o-rings  702  and  703 . Each nose piece may optionally include a radial passage to vent fluid in the passage  608 . A spacer  706  may be provided that surrounds the piston body  690  to guide the piston body  690 , and a vent may extend through the piston body  690  to relieve pressure behind the seals. 
         [0056]    To connect the piston assembly  602  to the connection rod  590 , the upper and lower nose pieces  692  and  693  are inserted into the piston body  690  until respective portions on the nose pieces abut respective ledges in the piston body  690 , and the connection rod  590  is inserted through the nose piece  692 , the piston body  690 , and the nose piece  693 . The end of the connection rod  590  is then coupled to the retainer  730 , such as by a threaded connection, causing the retainer  730  to abut the nose piece  693  and causing a radially outwardly projecting portion  704  of the connection rod  590  to abut the nose piece  692 . 
         [0057]    To deliver refrigerant to the first condenser  16  and not the second condenser  18 , the first and second piston assemblies  600  and  602  are moved axially until the seat disc  701  is seated against the valve seat  632  to prevent fluid flow through the second outlet port  538 . When the seat disc  701  is seated against the valve seat  632 , the seat disc  700  is not seated on the first valve seat  630 , thereby allowing all of the flow entering the inlet port  532  to flow through the first outlet port  536 , thereby bypassing the second condenser  18 . Pressure between the inlet port  532  and the outlet port  536  acts on the bottom portion of the first piston assembly  600  and the top portion of the second piston assembly  602 , and pressure in the outlet port  538  and chamber  534  below the second piston assembly  602  enters the passage  608  and flows to the area  612  to pressure balance the piston assemblies. 
         [0058]    To deliver refrigerant to the second condenser  18  and not the first condenser  16 , the first and second piston assemblies  600  and  602  are moved axially until the seat disc  700  is seated against the valve seat  630  thereby preventing fluid flow through the first outlet port  536 . When the seat disc  700  is seated against the valve seat  630 , the seat disc  701  is not seated on the second valve seat  632 , thereby allowing all of the flow entering the inlet port  532  to flow through the second outlet port  538 , thereby bypassing the first condenser  16 . Pressure in the outlet port  536  and chamber  534  above the second piston assembly  602  acts on the bottom portion of the first piston assembly  600  and the top portion of the second piston assembly  602 , and pressure from the fluid flowing through the outlet port  538  enters the passage  608  and flows to the area  612  to pressure balance the piston assemblies. 
         [0059]    To deliver refrigerant to both the first and second condensers  16  and  18 , the connection rod  590  and thus the piston assemblies  600  and  602  are moved to one of the plurality of third positions shown in  FIG. 7 . When in one of the third positions, a percentage of the flow entering the inlet port  532  flows through both the first and second outlet ports  536  and  538 . The piston assemblies  600  and  602  may be moved to allow equal flow through both the outlet ports  536  and  538  or to positions allowing for varying flow through the outlet ports  536  and  538 . 
         [0060]    Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.