Patent Publication Number: US-2023151894-A1

Title: Axial three-way modulating valve

Description:
FIELD OF THE INVENTION 
     The disclosed concept relates generally to a flow control device, and more particularly to a valve for controlling the flow of fluid in a system. The disclosed concept further relates to a system including a valve for controlling the fluid in the system. 
     BACKGROUND OF THE INVENTION 
     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 may rotate a gear train or other arrangement that is coupled to the piston to cause the piston to move. 
     SUMMARY OF THE INVENTION 
     These needs, and others, are met by embodiments of the disclosed concept. In a first example embodiment, a valve assembly is provided. The valve assembly comprises: a valve body defining a cylindrical passage therein disposed about a longitudinal axis of the valve body; an inlet port defined in or near a first end of the valve body; a first outlet port defined in the valve body, the first outlet port extending radially with respect to the longitudinal axis outward from the cylindrical passage; a second outlet port defined in the valve body, the second outlet port extending radially with respect to the longitudinal axis outward from the cylindrical passage; and a cylindrical valve spool positioned within, and sealingly engaged with, the cylindrical passage, the valve spool defining a central passage therethrough, wherein the valve spool is moveable along the longitudinal axis among: a first position wherein the inlet port is in fluid communication with the first outlet port but not the second outlet port, a second position wherein the inlet port is in fluid communication with the second outlet port but not the first outlet port, and an intermediate position between the first position and the second position wherein the inlet port is in fluid communication with both of the first outlet port and the second outlet port. 
     The inlet port may be defined in the first end of the valve body and extend axially along the longitudinal axis outward from the cylindrical passage. 
     The valve assembly may further comprise a linear drive coupled to the valve spool, wherein the linear drive is structured to selectively position the valve spool among the first position, the second position, and the intermediate position. 
     The linear drive may comprise an axial drive stepper motor. 
     The valve spool may comprise a dowel pin extending across the central passage, and the linear drive may be coupled to the valve spool via the dowel pin. 
     The valve spool may be sealingly engaged with the cylindrical passage via a number of seal arrangements positioned between the valve spool and the valve body. 
     The valve assembly may further comprise a number of circumferential grooves defined in the valve body opening into the cylindrical passage, and each seal arrangement of the number of seal arrangements may comprise: an o-ring positioned in a corresponding circumferential groove of the number of circumferential grooves, and a seal ring positioned radially inward from the o-ring. Each seal ring may have a rectangular cross-section. Each seal ring may be made from PTFE. 
     The first outlet port may be closer to the inlet port than the second outlet port. 
     The first outlet port and the second outlet port may be clocked 180 degrees apart with respect to the longitudinal axis. 
     The valve body may comprise an end cap selectively coupled to the remainder of the valve body and the inlet port may be defined in the end cap. 
     The end cap may be selectively coupled to the remainder of the valve body via a threaded connection. 
     The valve body may be formed from a brass material and the valve spool may be formed from a stainless steel material. 
     The valve assembly may further comprise a sight glass selectively coupled to a port formed in the valve body. 
     In another example embodiment, a refrigeration system is provided that comprises a valve assembly such as previously described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
         FIG.  1    is an exemplary heat reclaim system having a valve assembly in accordance with one example embodiment of the disclosed concept; 
         FIG.  2    is a perspective view of a valve assembly in accordance with one example embodiment of the disclosed concept showing a top portion of the valve assembly and a first outlet port defined in a side of the valve assembly; 
         FIG.  3    is another perspective view of the valve assembly of  FIG.  2    showing a bottom portion of the valve assembly having an inlet port defined therein and a second outlet port defined in the side of the valve assembly; 
         FIG.  4    is an elevation view of the valve assembly of  FIGS.  2  and  3    showing the first outlet port; 
         FIG.  5    is a partially schematic, first sectional view of the valve assembly of  FIGS.  2 - 4    taken along line  5 - 5  of  FIG.  4    showing a valve spool thereof positioned in a first position; 
         FIG.  6    is a partially schematic, second sectional view of the valve assembly of  FIGS.  2 - 4    taken along line  5 - 5  of  FIG.  4    showing the valve spool thereof positioned in a second position; 
         FIG.  7    is a partially schematic, third sectional view of the valve assembly of  FIGS.  2 - 4    taken along line  5 - 5  of  FIG.  4    showing the valve spool thereof positioned in a third position between the first position of  FIG.  5    and the second position of  FIG.  6   ; 
         FIG.  8    is a perspective view of the valve spool of  FIGS.  5 - 7   ; 
         FIG.  9    is a perspective view of a portion of the valve body of the valve assembly of  FIGS.  2 - 7    shown with sealing arrangements of the valve assembly; 
         FIG.  10    is an exploded view of the valve assembly of  FIGS.  2 - 7   ; 
         FIG.  11    is a detail view of a portion of the arrangement of  FIG.  5    as indicated therein; and 
         FIG.  12    is a detail view of a portion of the arrangement of  FIG.  6    as indicated therein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As used herein, the singular form of “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. As used herein, the statement that two or more parts or components are “coupled” shall mean that the parts are joined or operate together either directly or indirectly, i.e., through one or more intermediate parts or components, so long as a link occurs. As used herein, “directly coupled” means that two elements are coupled directly in contact with each other (i.e., touching). As used herein, “fixedly coupled” or “fixed” means that two components are coupled so as to move as one while maintaining a constant orientation relative to each other. 
     As employed herein, the statement that two or more parts or components “engage” one another shall mean that the parts exert a force against one another either directly or through one or more intermediate parts or components. As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality). Directional phrases used herein, such as, for example and without limitation, left, right, upper, lower, front, back, on top of, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. 
     The principles of the disclosed concept 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 disclosed concept may be useful in other fluid transfer applications where it is desirable to direct fluid to multiple outlets of a valve. 
     Referring first to  FIG.  1   , an exemplary heat reclaim system  10  including a valve assembly  12  in accordance with one example embodiment of the disclosed concept is generally shown. System  10  may be generally be broken down into an outdoor unit section  10 A and an indoor unit section  10 B. System  10  further includes a compressor  14 , a condenser  16 , a heat reclaim coil  18 , a tee  20 , an expansion valve  22 , an evaporator coil  24 , and a controller  26 . System  10  may optionally include a check valve  28  for preventing fluid flow from condenser  16  to the heat reclaim coil  18 . System  10  may also optionally include a purge valve  30  provided between a heat reclaim return line from heat reclaim coil  18  and the suction line of compressor  14 . 
     The fluid flowing (as shown by the arrows in  FIG.  1   ) through system  10 , which may be a suitable refrigerant, such as a two-phase refrigerant, enters compressor  14  and is compressed. The compressed fluid then flows to valve assembly  12 , which may deliver the fluid to one or both of condenser  16 , via tee  20 , and/or heat reclaim coil  18 . Fluid delivered to condenser  16  is cooled and the heat rejected. The heat rejected from heat condenser  16 , is dissipated (e.g., assisted via an outdoor fan  32 ) and then the fluid flows to expansion valve  22  that expands the fluid to a low pressure liquid-vapor. The fluid then flows to evaporator coil  24  where heat is absorbed by the fluid. The fluid delivered to heat reclaim coil  18  is cooled by rejecting heat to the air stream derived from evaporator coil  24  (e.g., assisted via an indoor fan  34 ). The fluid exits heat reclaim coil  18  and passes to condenser  16  via tee  20  (optionally via check valve  28 ), and/or optionally to the suction side of compressor  14  via purge valve  30 . Controller  26  may be provided to control valve assembly  12 , and specifically an actuator (discussed below) of valve assembly  12  to control the flow of fluid exiting valve assembly  12 . 
     Turning now to  FIGS.  2 - 7   , valve assembly  12  includes a valve body  40  defining a cylindrical, main passage  42  therein disposed about a longitudinal axis  43  ( FIGS.  5 - 7   ). In some example embodiments, valve body  40  is machined from a brass cylinder or brass forging, however, it is to be appreciated that other material or materials may be employed without varying from the scope of the disclosed concept. Valve body  40  includes an inlet port  44  defined in or near a first end  45  of valve body  40 . In the example embodiment illustrated, inlet port  44  is defined in first end  45  and extends axially along longitudinal axis  43  between main passage  42  and the exterior of valve body  40 . In the example embodiment illustrated in  FIGS.  2 - 7   , first end  45  of valve body  40  is formed as a separate end cap which is then coupled (e.g., via a threaded or other suitable arrangement) and sealed (e.g., via an O-ring or other suitable arrangement) to a main cylindrically shaped portion (not numbered) of valve body  40 , alternatively, the end cap can be formed as an integral part of the cylindrical body, without being formed as a separate part. Valve body  40  further includes a first outlet port  46  defined in valve body  40  extending radially with respect to longitudinal axis  43  outward from main passage  42 , as well as a first annular cavity  47  ( FIGS.  5 - 7 ,  9  and  12   ) defined in valve body  40  extending outward from main passage  42 . First outlet port  46  and first annular cavity  47  are positioned generally in the same first axial position along longitudinal axis  43  such that first outlet port  46  opens into first annular cavity  47  and first annular cavity  47  axially encompasses first outlet port  46 . Similarly, valve body  40  also includes a second outlet port  48  defined in valve body  40  extending radially with respect to longitudinal axis  43  outward from main passage  42 , as well as a second annular cavity  49  ( FIGS.  5 - 7 ,  9  and  11   ) defined in valve body  40  extending outward from main passage  42 . Second outlet port  48  and second annular cavity  49  are positioned generally in the same second axial position along longitudinal axis  43 , longitudinally spaced from the aforementioned first axial position, such that second outlet port  48  opens into second annular cavity  49  and second annular cavity  49  axially encompasses second outlet port  48 . In the example illustrated embodiment, first and second outlet ports  46  and  48  are clocked generally 180 degrees about longitudinal axis  43 , however, it is to be appreciated that first and second outlet ports  46  and  48  may be clocked generally at any other angular relationship without varying from the scope of the disclosed concept. Additionally, in embodiments wherein inlet port  44  is defined near first end  45  of valve body  40  (e.g., extending radially with respect to longitudinal axis  43 ), inlet port  44  may likewise be clocked generally at any angular relationship with either of first and second outlet ports  46  and  48  without varying from the scope of the disclosed concept. Each of first and second outlet ports  46  and  48  are in fluid communication with inlet port  44  via main passage  42 . Each of inlet port  44 , and first and second outlet ports  46  and  48  may have fluid conduits (not shown) coupled thereto (e.g., via any suitable method) or integrally formed with valve body  40  extending generally outward from main passage  42 . 
     As shown in  FIGS.  5 - 8   , valve assembly  12  further includes a valve spool  50  positioned within main passage  42  and axially movable along longitudinal axis  43  of valve body  40 , as described in detail below. Valve spool  50  includes a cylindrical spool body  52  extending between a first end  52 A and an opposite second end  52 B. Valve spool  50  is positioned about longitudinal axis  43  and defines a central passage  54  therein that extends between first end  52 A and second end  52 B and provides for axial gas flow along longitudinal axis  43 . In some example embodiments of the disclosed concept, spool body  52  has been formed from brass or stainless steel depending on the wear, friction and pressure requirements, with stainless steel being more durable for the sliding surface. It is to be appreciated, however, that spool body  52  may be formed from other suitable material or materials without varying from the scope of the disclosed concept. Central passage  54  is sized to allow an axial flow path, and to provide sufficient wall thickness to spool body  52  in order to support a drive linkage (described below), and for pressure and mechanical stresses on spool body  52 . Each of first and second ends  52 A and  52 B of spool body  52  are tapered to protect the seal edges during assembly and operation. 
     In the example embodiment illustrated, valve spool  50 , and more particularly spool body  52  thereof, is sealingly engaged with the walls of main passage  42  of valve body  40  via a plurality of seal arrangements  56  (the four seal arrangements  56  shown in  FIGS.  5 ,  6 ,  7 ,  9  and  10    include the further designations A-D so as to distinguish each seal arrangement  56  in the accompanying description). As described further below, valve spool  50  slides through seal arrangements  56 A- 56 D in order to close off either one of first or second outlet ports  46  or  48 , and thus allow for refrigerant gas to pass to the other of first or second outlet ports  46  or  48 , or to allow for refrigerant gas to pass to both of first and second outlet ports  46  and  48  in proportion to the axial position of spool body  52  of valve spool  50 . The illustrated example embodiment utilizes four seal arrangements  56 A- 56 D, with each seal arrangement  56  being positioned/fixed in a respective circumferential groove  58  defined in valve body  40  extending around and radially outward from main passage  42 . Each seal arrangement  56  may include one or more pieces and may be of any suitable form. In the illustrated example embodiment, each seal arrangement  56  is a two-part design that includes an elastomeric O-ring  60  and a seal ring  62  of semi-rigid composition, such as polytetrafluoroethylene—PTFE, disposed radially inward (with respect to longitudinal axis  43 ) from O-ring  60 . In an example embodiment, seal ring  62  has a rectangular cross section, although other cross-sectional shapes may be employed without varying from the scope of the disclosed concept. In such arrangements, O-ring  60  provides a radially inward force on seal ring  62  which in-turn provides a durable low friction, sliding surface against spool body  52  of valve spool  50 . 
     As shown in  FIGS.  5 - 8   , each end  52 A and  52 B of spool body  52  may include a number of tapered notches  64  (four are included in each end in the illustrated example embodiment) defined therein to provide gradual flow when valve spool  50  is closing or opening either of outlet ports  46  or  48 . Notches  64  can be sized to provide the desired, metered flow profile for each outlet port  46  and  48 . The notch flow enhances the response of the valve when opening or closing an adjacent outlet port of first and second outlet ports  46  and  48 . As perhaps best shown in  FIG.  8   , spool body  52  may include a number of recesses  66  defined therein extending inward from an outer circumferential surface  68  thereof. Each recess  66  is defined (e.g., via milling or other suitable process) at a certain axial position, depth, and length so as to align with one of seal arrangements  56 B or  56 C when a respective one of second and first outlet ports  48 ,  46  are closed, such as described in detail below. As discussed below, the purpose of each recess  66  is to allow refrigerant to vent from between middle seal arrangements  56 B and  56 C, and thus prevent entrapment of refrigerant between seal arrangements  56 B and  56 C. Liquid refrigerant, if present, can cause damage by thermal expansion. Additionally, the seal arrangement  56 B or  56 C that is vented by each recess  66  will not have pressure loads, which will reduce the force required to move valve spool  50  axially. In embodiments wherein the number of recesses  66  are not present, middle seal arrangements  56 B and  56 C are redundant. 
     Valve spool  50  can be actuated along longitudinal axis  43  via any suitable linear drive  70  coupled to valve spool via any suitable arrangement(s) that provide(s) linear motion to valve spool  50  from zero, variable, and to 100% positions such as described below. Linear drive  70  can include, for example, without limitation, a multi-step motor, servo motor, mechanical gear and linkages, pneumatic, refrigerant pressure, magnetic, piezoelectric drives, or any other suitable arrangement controllable via controller  26 . Control means of such actuator arrangements are various and commonly known in the industry. Feedback devices, such as encoders, proximity, and LVDT sensors, can be applied per the selected actuator. In addition to automated means, valve spool  50  may be actuated by manual input and by manual override arrangements. Valve spool  50  is constructed such that it can function normally if rotating motion thereof is encountered. In the example shown in the sectional views of  FIGS.  5 - 7   , linear drive  70  is a stepper motor  72  (shown schematically) in electrical communication with controller  26  and mechanically coupled (e.g., directly or indirectly via a threaded or other suitable arrangement) to a second end  74  of valve body  40  opposite first end  45 . In such arrangement, valve spool  50  further includes a dowel pin  76  that spans across central passage  54  of spool body  52  and is engaged at each end (e.g., via apertures  78  defined in spool body  52 ) thereof with spool body  52 . Dowel pin  74  is coupled to an actuatable head portion  80  of stepper motor  72  to provide for actuation of valve spool  50  by stepper motor  72 . Although shown coupled via dowel pin  74 , it is to be appreciated that stepper motor  72  may be coupled directly or via any suitable intermediate arrangement to valve spool  50  without varying from the scope of the disclosed concept. In the illustrated example embodiment shown in  FIGS.  5 - 7   , stepper motor  72  is effectively coupled and sealed to valve body  40  via an end cap  82  engaged with second end  74  of valve body  40 . 
     In use, the entire cavity of valve body  40  (except adjacent to a blocked outlet port) and internal parts are exposed to high pressure and temperature. Linear drive  70 /stepper motor  72  and end cap  82  are also filled with high pressure. The outlet port and adjacent outer areas of spool body  52  can achieve a lower pressure, depending on modulated flow pressure drop or full isolation. Linear drive/stepper motor  72  can be obtained with various step increments per revolution, with or without a gear reduction, acme screw output shaft and plunger, and stroke length. The intermediate positions of valve spool  50  are divided into small increments, as determined by the design of stepper motor  72 . Stepper motor  72  is electrically pulsed to move valve spool  50  in either axial direction along longitudinal axis  43 . When stepper motor  72  is not pulsed, the valve spool  50  stays in the last position. 
     Valve assembly  12  may further include an optional sight glass/moisture indicator  90  located in an axial position between the two seal arrangements  64 C and  64 D on either side of first outlet port  46  (such as shown in  FIGS.  2 - 4   ) or between the two seal arrangements  64 A and  64 B on either side of second outlet port  48 . This allows the side hole (not numbered) for the sight glass to be part of the cavity, and not interfering with flow or sealing. The position of valve spool  50  can be viewed through sight glass/moisture indicator  90 . 
     From the further description/discussion below, it is to be appreciated that although inlet port  44  has been shown/described in the example embodiment illustrated herein as being disposed in (i.e., extending axially as illustrated) or near (i.e., extending radially similar to first outlet port  46 ) first end  45  of valve body  40 , it is to be appreciated that alternatively inlet port  44  may be positioned radially near second end  74  of valve body (e.g., between second end  74  and second outlet port  48 ) without varying from the scope of the disclosed concept. 
     Having thus described the components of the example valve assembly  12  in accordance with an example embodiment of the disclosed concept, operation of valve assembly  12  as a 3-way modulating valve within system  10  of  FIG.  1    will now be generally described. As generally previously described, gas in system  10  takes two paths within valve body  40 , depending on the position of valve spool  50 , which is controlled by controller  26 . When valve spool  50  is in a top, first position (which may be considered as the zero position of valve spool  50 ), such as shown in  FIG.  5   , second outlet port  48  is shut off from main passage  42  (and thus inlet port  44 ) by seal arrangement  56 A and seal arrangement  56 C. In such first position, seal arrangement  56 B is vented to second outlet port  48  via recess  66  of spool body  52  due to the position of seal arrangement  56 B radially over recess  66 , such as shown in the detail view of such portion of  FIG.  5    shown in  FIG.  11   . In such first position, first end  52 A of spool body  52  extends through seal arrangement  56 A. As second outlet port  48  is blocked, the downstream path connected to second outlet  48  is thus inactive. That particular path may be reduced in pressure by venting to a lower system pressure, as provided by the system. Second outlet  48  pressure is established between seal arrangements  56 A and  56 C, including second annular cavity  49 . High pressure remains in central passage  54  of valve spool  50 , without flow. Second end  52 B of spool body  52  is spaced above seal arrangement  56 D, thus allowing all gas entering inlet port  44  to flow through first outlet port  46 . The pressure drop through valve assembly  12  to first outlet port  46  is minimal. 
     As valve spool  50  moves down (i.e., toward inlet port  44 ) to allow refrigerant gas to start flowing to second outlet port  48 , hot gas begins flowing to heat reclaim coil  18 . In moving downward from the previously described first position, first end  52 A of spool body  52  moves down through seal arrangement  56 A. A small percentage of the stroke is required to fully extract spool body  52  from seal arrangement  56 A. The number of notches  64  in first end  52 A of spool body  52  ( FIG.  8   ), if present, allow a small initial flow into second outlet port  48 , prior to full extraction of spool body  52  from seal arrangement  56 A. The number and size of notches  64  can be modified to allow more or less flow at the initial positions of spool body  52 . The number of notches  64  provide a flow path with a shorter initial stroke. The number of notches  64  work in conjunction with the smooth taper on first end  52 A of spool body  52 , while seal arrangement  56 A is contracting as valve spool  50  moves away. The gradual flow to second outlet port  48  assists controller  26  in metering the correct flow. As additional flow is needed in second outlet port  48 , the control will pulse motor  72  to move valve spool  50  further down. While first end  52 A of spool body  52  is near seal arrangement  56 A, there will be more pressure drop between inlet port  44  and second outlet port  48  than that to first outlet port  46 . As valve spool  50  moves down, second outlet port  48  will receive more flow, while the flow to first outlet port  46  decreases. This is intrinsic to the ability of valve assembly  12  to modulate the flow in proportion to the unit control. As valve spool  50  reaches mid-stroke, such as shown in  FIG.  7   , the pressure drop is similar to either of first or second outlet ports  46  or  48 . The control will tend to modulate valve spool  50  in either direction incrementally, as needed by controller  26 . While first and second ends  52 A and  52 B of spool body  52  are not touching either seal arrangement  56 A or  56 D, seal arrangements  56 B and  56 C provide radial support, keeping spool body  52 , and thus valve spool  50 , centered in main passage  42  and clear from contacting valve body  40 . 
     As more flow is needed to second outlet port  48  and less to first outlet port  46 , spool valve  50  moves downward toward a bottom, second position (which may be considered as the 100% position of valve spool  50 ), such as shown in  FIG.  6   . As second end  52 B of spool body  52  gets closer to seal arrangement  56 D, pressure drop from inlet port  44  to first outlet port  46  increases. The tapered end of spool body  52  helps to align seal arrangement  56 D, while the number of notches  64  in second end  52 B of spool body  52  ( FIG.  8   ), if present, allows some flow, thus gradually shutting off first outlet port  46 . Spool body  52  will extend partially past seal arrangement  56 D to achieve complete shut off. While the path connected to first outlet port  46  is inactive, the downstream pressure will establish between seal arrangement  56 B and seal arrangement  56 D. In such positioning, seal arrangement  56 C is vented to first outlet port  46  due to the position of seal arrangement  56 C radially over recess  66  of spool body  52 , such as shown in the detail view of such portion of  FIG.  6    shown in  FIG.  12   . In such second position, all flow through valve assembly  12  will be to second outlet port  48  through central passage  54  of valve spool  50  at minimal pressure drop. 
     From the foregoing it is to be appreciated that the two middle seal arrangements  56 B and  56 C are always in contact with spool body  52 , which keeps valve spool  50  centered and axially aligned in valve body  40 . Only one end seal arrangement  56 A or  56 D at a time will be in contact when valve spool  50  is in the closed port position or nearly open or closed. When not in contact, the end seal arrangements  56 A,  56 D tend to contract radially, due to the elasticity of the O-ring  60  thereof, and remain in place in the respective body groove  58 . The end seal ring  62 , which is not in contact or partially in contact with the spool body  52 , is protected from damage or distortion, due to having high pressure always exerted on the inside circumferential surface thereof. When spool body  52  is contacting a seal ring  62 , the overall radial spacing between the outer diameter of spool body  42  and the depth of body groove  58 , causes compression of O-ring  60 , thus providing a radial contact force on seal ring  62  and spool body  52 . This contact force and the coefficient of friction of the seal material translate to the required force load on motor/drive  70 . Sealing relies on the radial force at the seal ring  62  on the surface of spool body  52 . Most of the valve operation during modulation is in the intermediate positions with the middle seal arrangements  56 B and  56 C, and has minimal load on motor/drive  70 . When spool body  52  engages one of the end positions, there will be sliding friction in three seal arrangements (i.e., middle seal arrangements  56 B and  56 C and either of  56 A or  56 D). If there is a pressure differential while one of outlet ports  46  or  48  is inactive such as previously described, the O-rings  60  of the two active seal arrangements will tend to compress in the axial direction. O-ring  60  will conform to the sealing surfaces and exert more radial force on seal ring  62 . This in turn applies more force on spool body  52 , and more axial force will be required to overcome friction to move valve spool  50  out of the end seal arrangement  56 A or  56 D. Thus, the highest motor load is during the initial stroke under pressure differential. Once clear of the end seal arrangement  56 A or  56 D, pressure differential and frictional resistance decreases. As previously discussed, it is to be appreciated that other types of seals can be used, such as spring activated rod seals. The two middle seal locations would facilitate the proper orientation of spring or lip seals, since such seals have a preferred direction. 
     It is to be appreciated that in such arrangement of valve spool  50  within valve body  40  such as described herein, the pressure forces are balanced in a simple manner by having high pressure exposed on both ends of valve spool  50 . The radial pressure forces are balanced by having the pressure differences between the outside and inside surfaces of spool body  52  being distributed 360° around the circumference of spool body  52 . This geometry provides generous flow area, which achieves higher flow rates, compared to disk and seat mechanisms of conventional designs. This geometry also achieves pressure force balance on valve spool  50  in the axial direction which prevents excess force loads on the motor/drive, due to net pressure forces or from excessive seal friction. Motor loads due to pressure imbalances are minimal, only due to slight flow effects. 
     While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.