Patent Publication Number: US-9903395-B2

Title: Proportional pressure controller with isolation valve assembly

Description:
FIELD 
     The present disclosure relates to proportional pressure controllers adapted for use in pneumatic systems and particularly to proportional pressure controllers with a isolation valve assembly. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Proportional pressure controllers often include main internal valves which are moved to permit a pressurized fluid to be discharged to a pressure controlled device. Such proportional pressure controllers regulate the operating pressure of the pressurized fluid at the pressure controlled device. The main valves are commonly repositioned using solenoids operators. This configuration increases weight and expense of the proportional pressure controller and requires significant electrical current to reposition the main valves. 
     Known proportional pressure controllers are also often susceptible to system pressure undershoot or overshoot. Due to the mass and operating time of the main valves, signals controlling the main valves to reduce or stop pressurized fluid flow to the pressure controlled device may occur too soon or too late to avoid either not reaching or exceeding the desired operating pressure. When this occurs, the control system operating the solenoid actuators begins a rapid opening and closing sequence as the controller “hunts” for the desired operating pressure. This rapid operation known as “motor-boating”, increases wear and the operating costs associated with the proportional pressure controller. 
     Known proportional pressure controllers often include an inlet port, an outlet port, and an exhaust port. A high pressure fluid is typically supplied to the inlet port, after passing through the proportional pressure controller, the fluid exits to the pressure controlled device through the outlet port, and excess fluid pressure is vented from the proportional pressure controller through the exhaust port. Another problem associated with known proportional pressure controllers is that it is difficult to achieve zero pressure at the outlet port of the proportional pressure controller even when a zero pressure condition at the outlet port is desired. The inability to create zero pressure at the outlet port of the proportional pressure controller can negatively affect the operation and/or performance of the pressure controlled device. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In accordance with one aspect of the subject disclosure, a proportional pressure controller is provided that minimizes the likelihood of having pressure at an outlet port of the proportional pressure controller when a zero pressure condition at the outlet port is desired. The proportional pressure controller generally includes a body, an inlet poppet valve, an exhaust poppet valve, a isolation valve assembly, and an actuator that controls the isolation valve assembly. The body of the proportional pressure controller has an inlet flow passage, an outlet flow passage, an exhaust/outlet common passage, and an exhaust flow passage. An inlet port in the body opens to the inlet flow passage, the outlet port in the body opens to the outlet flow passage and the exhaust/outlet common passage, and an exhaust port in the body opens to the exhaust flow passage. An inlet valve cavity in the body connects the inlet flow passage to the outlet flow passage and an exhaust valve cavity in the body connects the exhaust/outlet common passage to the exhaust flow passage. The inlet poppet valve is slidably disposed in the inlet valve cavity and the exhaust poppet valve is slidably disposed in the exhaust valve cavity. In operation, the inlet poppet valve controls fluid flow between the inlet flow passage and the outlet flow passage and the exhaust poppet valve controls fluid flow between the exhaust/outlet common passage and the exhaust flow passage. 
     The isolation valve assembly is integrated into the body of the proportional pressure controller. The isolation valve assembly generally includes an isolation valve cavity and a isolation valve member that is situated in the isolation valve cavity. The isolation valve cavity is disposed in the body in fluid communication with the outlet port. The isolation valve member is slidably disposed in the isolation valve cavity. In operation, the isolation valve member moves relative to and within the isolation valve cavity between a isolation valve closed position and an isolation valve open position. The actuator of the proportional pressure controller controls the movement of the isolation valve member between the isolation valve closed position and the isolation valve open position. In the isolation valve closed position, the isolation valve member prevents fluid from flowing through the outlet port in the body of the proportional pressure controller. By contrast, in the isolation valve open position, the isolation valve member permits fluid flow through the outlet port. Advantageously, this arrangement is compact and provides a zero pressure condition at the outlet port, which can be configured to connect to the pressure controlled device. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a side cross-sectional view of an exemplary proportional pressure controller constructed in accordance with the subject disclosure; 
         FIG. 2A  is another side cross-sectional view of the exemplary proportional pressure controller of  FIG. 1  where an exemplary isolation valve assembly is preventing fluid from entering an inlet port in a body of the exemplary proportional pressure controller; 
         FIG. 2B  is another side cross-sectional view of the exemplary proportional pressure controller of  FIG. 1  where the exemplary isolation valve assembly is supplying the inlet port in the body of the exemplary proportional pressure controller with fluid and where fluid is being discharged through an outlet port in the body of the exemplary proportional pressure controller; 
         FIG. 2C  is another side cross-sectional view of the exemplary proportional pressure controller of  FIG. 1  where fluid pressure in an outlet flow passage and an exhaust/outlet common passage in the body of the exemplary proportional pressure controller is being relieved by expelling fluid from the outlet flow passage and the exhaust/outlet common passage through an exhaust flow passage and an exhaust port in the body of the exemplary proportional pressure controller; 
         FIG. 3  is a side cross-sectional view of another exemplary proportional pressure controller constructed in accordance with the subject disclosure; 
         FIG. 4A  is another side cross-sectional view of the exemplary proportional pressure controller of  FIG. 3  where an exemplary isolation valve assembly is preventing fluid from exiting the outlet port in the body of the exemplary proportional pressure controller; 
         FIG. 4B  is another side cross-sectional view of the exemplary proportional pressure controller of  FIG. 3  where the exemplary isolation valve assembly is discharging fluid exiting the outlet port in the body of the exemplary proportional pressure controller; 
         FIG. 4C  is another side cross-sectional view of the exemplary proportional pressure controller of  FIG. 3  where fluid pressure in the outlet flow passage and the exhaust/outlet common passage in the body of the exemplary proportional pressure controller is being relieved by expelling fluid from the outlet flow passage and the exhaust/outlet common passage through the exhaust flow passage and the exhaust port in the body of the exemplary proportional pressure controller; 
         FIG. 5  is a side cross-sectional view of another exemplary proportional pressure controller constructed in accordance with the subject disclosure; 
         FIG. 6A  is another side cross-sectional view of the exemplary proportional pressure controller of  FIG. 5  where an exemplary isolation valve assembly is preventing fluid from exiting the outlet port in the body of the exemplary proportional pressure controller; 
         FIG. 6B  is another side cross-sectional view of the exemplary proportional pressure controller of  FIG. 5  where the exemplary isolation valve assembly is discharging fluid exiting the outlet port in the body of the exemplary proportional pressure controller; and 
         FIG. 6C  is another side cross-sectional view of the exemplary proportional pressure controller of  FIG. 5  where fluid pressure in the outlet flow passage and the exhaust/outlet common passage in the body of the exemplary proportional pressure controller is being relieved by expelling fluid from the outlet flow passage and the exhaust/outlet common passage through the exhaust flow passage and the exhaust port in the body of the exemplary proportional pressure controller. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on”, “engaged to,” “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     Referring to  FIG. 1 , a proportional pressure controller  10  includes a body  12  having a first end cap  14  and a second end cap  16  that is oppositely arranged on the body  12  relative to the first end cap  14 . The first and second end caps  14 ,  16  can be releasably fastened or fixedly connected to body  12 . A spacer member  18  can also be included with body  12  whose purpose will be discussed in greater detail below. A controller operator  20  can be connected such as by fastening or fixed connection to a central body portion  22 . Body  12  can further include an inlet body portion  24  connected between central body portion  22  and spacer member  18 , with spacer member  18  positioned between inlet body portion  24  and second end cap  16 . Body  12  can further include an exhaust body portion  26  positioned between central body portion  22  and first end cap  14 . Optionally, the proportional pressure controller  10  can be provided in the form of a generally rectangular-shaped block such that multiple ones of the proportional pressure controllers  10  can be arranged in a side-by-side configuration. This geometry also promotes use of the proportional pressure controller  10  in a manifold configuration. 
     According to several embodiments, the inlet and exhaust body portions  24 ,  26  are releasably and sealingly connected to the central body portion  22 . The proportional pressure controller  10  can include each of an inlet port  28 , an outlet port  30 , and an exhaust port  32  each created in the central body portion  22 . A pressurized fluid  33  such as pressurized air can be discharged from the proportional pressure controller  10  via outlet port  30 . The outlet port  30  is open to and operably receives the pressurized fluid  33  from an outlet flow passage  34  that is defined within the body  12 . The outlet flow passage  34  includes a pressure balancing segment  34   a . Flow to the outlet flow passage  34  can be isolated using an inlet poppet valve  36 . The inlet poppet valve  36  has a longitudinal cavity  39   a  and a vent passageway  39   b . The inlet poppet valve  36  is normally seated against an inlet valve seat  38  and is held in the seated position shown in  FIG. 1  by a biasing member  40  such as a compression spring. When the inlet poppet valve  36  is closed, no fluid flow can pass into the outlet flow passage  34 . The biasing member  40  can be held in position by contact with an end wall  41  of inlet body portion  24 , and oppositely by being partially received in the longitudinal cavity  39   a  that is defined within the inlet poppet valve  36 . Inlet poppet valve  36  is received within an inlet valve cavity  42  in the body  12  such that the inlet poppet valve  36  can axially slide within the inlet valve cavity  42  in each of an inlet valve closing direction “A” extending biasing member  40  and an opposite inlet valve opening direction “B”. When the inlet poppet valve  36  moves in the inlet valve opening direction “B”, the inlet poppet valve  36  compresses the biasing member  40 . An inlet valve stem  43  is integrally connected to the inlet poppet valve  36 , extending axially from inlet poppet valve  36 . A free end of inlet valve stem  43  contacts a piston  44 . Inlet valve stem  43  is slidably disposed through a first boundary wall  45  before contacting piston  44  to help control an axial alignment of inlet poppet valve  36  and to promote a perimeter seal of an inlet poppet seat engagement member  46   a  with inlet valve seat  38  in the closed position. The inlet poppet valve  36  has an opposing face  46   b , opposite the inlet poppet seat engagement member  46   a , that faces the pressure balancing segment  34   a  of the outlet flow passage  34 . The inlet poppet seat engagement member  46   a  and opposing face  46   b  of the inlet poppet valve  36  have equal surface areas. Accordingly, the inlet poppet valve  36  operates in a pressure balanced condition. Pressurized fluid  33  can free-flow through first boundary wall  45  via at least one hole  47  and/or through the bore that permits passage of inlet valve stem  43 . A size and quantity of the at least one hole  47  controls the time required for pressure in outlet flow passage  34  to act on piston  44  and therefore the speed of piston movement. The pressure acting through the at least one hole  47  creates a pressure biasing force acting to move piston  44  toward the closed position. Piston  44  can be provided with at least one, and according to several embodiments, a plurality of resilient U-cup seals  48  which are individually received in individual seal grooves  49  created about a perimeter of piston  44 . U-cup seals  48  provide a fluid pressure seal about piston  44  as piston  44  axially slides within a cylinder cavity  50  that is defined within the body  12 . 
     Piston  44  moves coaxially with the inlet poppet valve  36  in inlet valve closing direction “A” or the inlet valve opening direction “B”. First boundary wall  45  defines a first boundary (a non-pressure boundary) and piston  44  defines a second boundary (a pressure boundary) of the cylinder cavity  50 . Piston  44  can move in the inlet valve opening direction “B” until an end  51  of piston  44  contacts first boundary wall  45 , since the first boundary wall  45  is fixed in position. Piston  44  is retained within cylinder cavity  50  by contact with first boundary wall  45  by the previously described pressure biasing force created by pressurized fluid  33  freely flowing through the holes  47 . Piston  44  is also retained within cylinder cavity  50  by contact at an opposite end of cylinder cavity  50  with portions of spacer member  18 , which extend radially past a cylindrical wall of cylinder cavity  50  as shown in  FIG. 1 . An elastic seal member  52   a  such as an O-ring can be positioned within a slot or circumferential groove  53   a  created externally about a perimeter of inlet poppet valve  36 . Elastic seal member  52   a  seals the inlet poppet valve  36  against the inlet valve cavity  42 . 
     The longitudinal cavity  39   a  in the inlet poppet valve  36  is open to and disposed in fluid communication with the pressure balancing segment  34   a  of the outlet flow passage  34 . The vent passageway  39   b  extends between the longitudinal cavity  39   a  and the inlet valve cavity  42 . Another elastic seal member  52   b  such as an O-ring can be positioned within a slot or circumferential groove  53   b  created externally about a perimeter of the inlet poppet valve  36 . The vent passageway  39   b  opens into circumferential groove  53   b  such that the elastic seal member  52   b  blocks the vent passageway  39   b  and prevents fluid in the inlet valve cavity  42  from entering the vent passageway  39   b . When pressure in the longitudinal cavity  39   a  of the inlet poppet valve  36  is greater than pressure in the inlet valve cavity  42 , the pressure differential slightly expands the elastic seal member  52   b  allowing fluid to flow out from the vent passageway  39   b . Accordingly, the elastic seal member  52   b  acts as a check valve for the vent passageway  39   b , allowing fluid to flow through the vent passageway  39   b  in one direction from the longitudinal cavity  39   a  in the inlet poppet valve  36  to the inlet valve cavity  42 , but not in the opposite direction (from the inlet valve cavity  42  to the longitudinal cavity  39   a  in the inlet poppet valve  36 ). Therefore, the vent passageway  39   b  in combination with the elastic seal member  52   b  neutralizes pressure differences between the pressure balancing segment  34   a  of the outlet flow passage  34  and the inlet valve cavity  42 . 
     The proportional pressure controller  10  can be operated using each of a fill valve  54  and a dump valve  56 , which can be releasably connected to central body portion  22  within controller operator  20 . Pressurized fluid  33  ( FIGS. 2A-2C ) such as pressurized air received in inlet port  28  may be filtered or purified. Fluid that can back-flow into the proportional pressure controller  10  via outlet port  30  and outlet flow passage  34  is potentially contaminated fluid. According to several embodiments, the fill and dump valves  54 ,  56  are isolated from the potentially contaminated fluid such that only the filtered, pressurized fluid  33  that is received via the inlet port  28  flows through the fill valve  54  and the dump valve  56 . An inlet flow passage  58  communicates the pressurized fluid  33  between inlet port  28  and the inlet valve cavity  42 . In other words, the inlet valve cavity  42  connects the inlet flow passage  58  to the outlet flow passage  34 . Therefore, the inlet flow passage  58  is fluidly isolated from outlet flow passage  34  by the inlet poppet valve  36 , which can be normally closed. A fluid supply port  60  communicates with and is open to the inlet flow passage  58 . The fluid supply port  60  leads to a fill inlet passage  62 , which is isolated from outlet flow passage  34  and provides pressurized fluid  33  to the fill valve  54 . A fill valve discharge passage  64  provides a path for pressurized fluid  33  flowing through the fill valve  54  to be directed to an inlet of dump valve  56  and a plurality of different passages. 
     One of these passages includes a piston pressurization passage  66 , which directs pressurized fluid  33  from the fill valve discharge passage  64  to a piston pressurization chamber  68  created in second end cap  16 . Pressurized fluid  33  in the piston pressurization chamber  68  generates a first force F 1  ( FIG. 2B ) acting on a piston end face  70  of piston  44 . A surface area of the piston end face  70  is larger than a surface area of the inlet poppet valve  36  that is in contact with inlet valve seat  38 , therefore, when the fill valve  54  opens or continues to open further, the net force created by the pressurized fluid  33  acting on the piston end face  70  causes piston  44  to initially move or move further in the inlet valve opening direction “B” and away from inlet valve seat  38 . This initially opens the inlet poppet valve  36  or further increases flow through the inlet valve cavity  42  to allow pressurized fluid  33  to flow into the outlet flow passage  34  and exit the proportional pressure controller  10  at the outlet port  30 . Therefore, the proportional pressure controller  10  can initiate flow of the pressurized fluid  33  between the inlet port  28  and the outlet port  30  if no flow is present at the outlet port  30 , or the proportional pressure controller  10  can maintain, increase, or decrease the pressure of an existing flow of the pressurized fluid  33  between the inlet port  28  and the outlet port  30  in those situations where a continuous, regulated flow of pressurized fluid  33  is required. These operations will be more fully explained below. 
     A portion of the pressurized fluid  33  that is discharged through the fill valve  54  and then through the fill valve discharge passage  64  is directed via an exhaust valve pressurization passage  72  created in a connecting wall  74  of central body portion  22  into an exhaust valve pressurization chamber  76 . When the fill valve  54  is open and the dump valve  56  is closed, the pressurized fluid  33  received in the exhaust valve pressurization chamber  76  via the exhaust valve pressurization passage  72  applies a second force F 2  ( FIG. 2B ) against an exhaust valve end face  78  of an exhaust poppet valve  80  to retain the exhaust poppet valve  80  in a seated position. 
     The exhaust poppet valve  80  is slidably disposed in an exhaust valve cavity  82  that is defined within the body  12 . The exhaust poppet valve  80  includes an exhaust poppet seat engagement member  83 , which contacts an exhaust valve seat  84  in the closed position of exhaust poppet valve  80  (shown in  FIG. 1 ). When exhaust poppet valve  80  is in the closed position, the pressurized fluid  33  flowing from outlet flow passage  34  through outlet port  30  also enters an exhaust/outlet common passage  86 . In the closed position, the exhaust poppet valve  80  is isolated from the exhaust port  32  to prevent the pressurized fluid  33 —from flowing out of exhaust port  32  through an exhaust flow passage  88 . Accordingly, the pressurized fluid  33  in the exhaust/outlet common passage  86  applies a third force F 3  ( FIG. 2B ) on the exhaust poppet valve  80  that generally opposes the second force F 2  that the pressurized fluid  33  in the exhaust valve pressurization chamber  76  applies to the exhaust valve end face  78  of the exhaust poppet valve  80 . The exhaust valve cavity  82  is positioned between and fluidly connects the exhaust/outlet common passage  86  and the exhaust flow passage  88 . 
     The exhaust poppet valve  80  includes an integrally connected, axially extending exhaust valve stem  90 , which is slidingly received in a stem receiving passage  92  of a stem receiving member  94 . The stem receiving member  94  is positioned between a second boundary wall  96  and the first end cap  14 . Similar to the first boundary wall  45 , the pressurized fluid  33  can free-flow through second boundary wall  96  via at least one hole  97 . A size and quantity of the hole(s)  97  controls the speed at which pressure balances across second boundary wall  96 . 
     A dump valve passage  98  is provided at a discharge side of the dump valve  56 , which communicates with the exhaust flow passage  88  via a dump valve exhaust port  100  in the central body portion  22 . The dump valve exhaust port  100  is open to the exhaust flow passage  88  and therefore operates to expel the pressurized fluid  33  in the fill valve discharge passage  64  into the exhaust flow passage  88  when the dump valve  56  is actuated. It is noted that dump valve outlet passage  98  is isolated from the exhaust valve pressurization passage  72 , the fill valve discharge passage  64 , and piston pressurization passage  66  when the dump valve  56  is closed. It is further noted that each of the valve discharge passage  64 , the piston pressurization passage  66 , the exhaust valve pressurization passage  72 , and the dump valve passage  98  are isolated from the pressurized fluid  33  in the outlet flow passage  34  and exhaust/outlet common passage  86  when the fill valve  54  is open. These flow passages therefore allow communication of the filtered, pressurized fluid  33  from the inlet port  28  to be communicated through the fill valve  54  and the dump valve  56  without exposing the fill valve  54  and the dump valve  56  to potentially contaminated fluid lingering around the outlet port  30 . 
     The proportional pressure controller  10  can further include a circuit board  101  positioned inside or outside the controller operator  20 , which is in electrical communication with both the fill and dump valves  54 ,  56 . Signals received at the circuit board  101  for positioning control of either the fill or dump valves  54 ,  56  are received via a wiring harness  102 , which may extend through the controller operator  20  and be sealed using a connecting plug  104 . A control system  106 , which may be external to the controller operator  20 , performs calculation functions and forwards command signals to the circuit board  101 . The circuit board  101  then controls either/both fill and/or dump valves  54 ,  56  to control fluid pressure at the outlet port  30 . Control signals from and to the proportional pressure controller  10  and the control system  106  are communicated using a control signal interface  108 . The control signal interface  108  can be a hard wire (e.g.: wiring harness) connection, a wireless (e.g.: radio frequency or infra-red) connection, or the like. Optionally, the control system  106  may be electrically connected to one or more pressure signaling devices  109   a ,  109   b  via the control signal interface  108 . Although the one or more pressure signaling devices  109   a ,  109   b  may be located at various locations in the proportional pressure controller  10 ,  FIG. 1  illustrates a first pressure signaling device  109   a  that is positioned in the fill valve discharge passage  64  and a second pressure signaling device  109   b  that is position in the outlet flow passage  34 . In operation, the first and second pressure signaling devices  109   a ,  109   b  respectively measure the fluid pressure within the fill valve discharge passage  64  and the outlet flow passage  34  and generate first and second pressure signals that correspond to the measured fluid pressure. The first and second pressure signaling devices  109   a ,  109   b  output the first and second pressure signals to the control system  106 , which controls actuation of the fill valve  54  and the dump valve  56  in response to the first and second pressure signals. 
     It should be appreciated that failing to achieve the desired fluid pressure at the outlet port  30  of the proportional pressure controller  10  can result in rapid opening/closing operation of the fill and dump valves  54 ,  56  and the inlet poppet and exhaust poppet valves  36 ,  80 . This condition, which is known as “motor boating”, occurs as the proportional pressure controller  10  attempts to correct to the desired fluid pressure at the outlet port  30 . Use of the first and second pressure signaling devices  109   a ,  109   b  can provide a differential pressure measurement between the fluid pressure in the fill valve discharge passage  64 , which is sensed by first pressure signaling device  109   a , and the fluid pressure in the outlet flow passage  34 , which is sensed by second pressure signaling device  109   b . Together with fast acting inlet poppet and exhaust poppet valves  35 ,  38  (which respond to pressure differences and do not require a control signal), the proportional pressure controller  10  can help mitigate the chance of motor boating. 
     Still referring to  FIG. 1 , the proportional pressure controller  10  further includes an isolation valve assembly  110 . The isolation valve assembly  110  generally comprises an isolation valve cavity  112  and a isolation valve member  114  that is slidably disposed in the isolation valve cavity  112 . The isolation valve cavity  112  is defined by a cavity wall  116  and has a first end  118  and a second end  120  that is arranged opposite the first end  118 . The isolation valve member  114  is moveable within the isolation valve cavity  112  between an isolation valve closed position ( FIG. 2A ) and a isolation valve open position ( FIG. 2B ). The isolation valve assembly  110  includes a first isolation valve piston  122  and a second isolation valve piston  124 . The first isolation valve piston  122  is positioned along the isolation valve member  114  such that the first isolation valve piston  122  is slidably disposed within the first end  118  of the isolation valve cavity  112 . The second isolation valve piston  124  is positioned along the isolation valve member  114  such that the second isolation valve piston  124  is arranged opposite the first isolation valve piston  122  and is slidably disposed within the second end  120  of the isolation valve cavity  112 . Both the first isolation valve piston  122  and the second isolation valve piston  124  seal against the cavity wall  116  of the isolation valve cavity  112 . The isolation valve assembly  110  also includes one or more isolation valve pressurization chambers  126   a ,  126   b . In  FIG. 1 , one of the isolation valve pressurization chambers  126   a  is open to the first end  118  of the isolation valve cavity  112  while the other isolation valve pressurization chamber  126   b  is open to the second end  120  of the isolation valve cavity  112 . As will be explained in greater detail below, fluid pressure within the isolation valve pressurization chambers  126   a ,  126   b  controls the movement and position of the isolation valve member  114  within and relative to the isolation valve cavity  112 . 
     The isolation valve assembly  110  further comprises a first seat member  128  and a second seat member  130 . The first and second seat members  128 ,  130  are disposed along the cavity wall  116  of the isolation valve cavity  112  and are arranged such that the second seat member  130  is longitudinally spaced from the first seat member  128 . The isolation valve assembly  110  has an intake port  132 , a first discharge port  134 , and a second discharge port  136 . The intake port  132  is open to the isolation valve cavity  112  and receives an incoming flow of the pressurized fluid  33  during operation of the isolation valve assembly  110 . The first discharge port  134  is open to the isolation valve cavity  112  and is positioned longitudinally between the first seat member  128  and the second seat member  130 . The second discharge port  136  is also open to the isolation valve cavity  112 . The intake port  132  and the second discharge port  136  are positioned longitudinally on opposite sides of the first discharge port  134 . In other words, the first discharge port  134  is positioned longitudinally between the intake port  132  and the second discharge port  136 . 
     The isolation valve assembly  110  also includes a first seat engagement member  138  and the second seat engagement member  140 . The first and second seat engagement members  138 ,  140  extend outwardly from the isolation valve member  114  at longitudinally spaced locations. Although other configurations are possible, where the isolation valve cavity  112  is a cylindrical bore (as shown in  FIG. 1 ), the first and second seat engagement members  138 ,  140  extend radially outward from and annularly about the isolation valve member  114 . The first seat engagement member  138  is positioned longitudinally between the first isolation valve piston  122  and the second isolation valve piston  124 . The second seat engagement member  140  is positioned longitudinally between the first seat engagement member  138  and the second isolation valve piston  124 . It should be appreciated that the first and second seat engagement members  138 ,  140  and the first and second isolation valve pistons  122 ,  124  may be integrally formed with the isolation valve member  114  or may be separately formed components that are connected to and carried on the isolation valve member  114 . It should also being appreciated that the isolation valve member  114 , the first and second isolation valve pistons  122 ,  124 , and the first and second seat engagement members  138 ,  140  have transverse cross-sections. Where the isolation valve cavity  112  is a cylindrical bore, the transverse cross-sections of the isolation valve member  114 , the first and second isolation valve pistons  122 ,  124 , and the first and second seat engagement members  138 ,  140  may be circular in shape. Generally speaking, the transverse cross-section of the isolation valve member  114  is smaller than the transverse cross-sections of the first and second isolation valve pistons  122 ,  124  and transverse cross-sections of the first and second seat engagement members  138 ,  140 . The transverse cross-sections of the first and second isolation valve pistons  122 ,  124  may or may not be equal in size to one another and may or may not be equal in size to the transverse cross-sections of the first and second seat engagement members  138 ,  140 . Likewise, the transverse cross-sections of the first and second seat engagement members  138 ,  140  may or may not be equal in size to one another. 
     The proportional pressure controller  10  further includes an actuator  142  for controlling the movement of the isolation valve member  114  between the isolation valve closed position and the isolation valve open position. The actuator  142  may take several forms. In accordance with one exemplary configuration, the actuator  142  includes an actuator valve  144  and an actuator valve passage  146 . The actuator valve  144  is arranged in fluid communication with the isolation valve pressurization chambers  126   a ,  126   b . The actuator valve  144  may also electrically connected to the control system  106  via the control signal interface  108 . Therefore, the control system  106  may also control actuation of the actuator valve  144  in response to the first and second pressure signals that the control system  106  receives from the first and second pressure signaling devices.  109   a ,  109   b . In operation, the actuator valve  144  receives pressurized fluid  33  from the inlet flow passage  58  and selectively pressurizes the isolation valve pressurization chambers  126   a ,  126   b  by selectively supplying the pressurized fluid  33  to the isolation valve pressurization chambers  126   a ,  126   b . The actuator valve passage  146  extends between the actuator valve  144  and the isolation valve pressurization chambers  126   a ,  126   b  and is therefore configured to communicate pressurized fluid  33  from the actuator valve  144  to the isolation valve pressurization chambers  126   a ,  126   b.    
     As will be explained in greater detail below, pressurization of the isolation valve pressurization chambers  126   a ,  126   b  by the actuator valve  144  moves the isolation valve member  114  in the isolation valve cavity  112  between the isolation valve open position and the isolation valve closed position. In the isolation valve closed position, the first seat engagement member  138  that is carried on the isolation valve member  114  contacts the first seat member  128  to fluidly isolate the intake port  132  from the first and second discharge ports  134 ,  136 . In the isolation valve closed position, the second seat engagement member  140  that is carried on the isolation valve member  114  is spaced from the second seat member  130  such that any pressurized fluid  33  at the first discharge port  134  can vent (i.e. be discharged) through the second discharge port  136 . In the isolation valve open position, the first seat engagement member  138  that is carried on the isolation valve member  114  is displaced away from the first seat member  128  to permit fluid flow from the intake port  132 , through the isolation valve cavity  112 , and to the first discharge port  134 . In the isolation valve open position, the second seat engagement member  140  that is carried on the isolation valve member  114  contacts the second seat member  130  fluidly isolate the second discharge port  136  from the first discharge port  134 . 
     Various configurations of the proportional pressure controller  10  are possible where either the inlet port  28  or the outlet port  30  in the body  12  of the proportional pressure controller  10  is arranged in fluid communication with either the intake port  132  or the first discharge port  134  of the isolation valve assembly  110 . Moreover, the isolation valve assembly  110  can either be located within (i.e. inside of) or external to (i.e. outside of) the body  12  of the proportional pressure controller  10 . In the example shown in  FIG. 1 , the first discharge port  134  of the isolation valve assembly  110  is arranged in fluid communication with the inlet port  28  in the body  12  of the proportional pressure controller  10 . In addition, the isolation valve assembly  110  is arranged external to the body  12  of the proportional pressure controller  10 . In accordance with this configuration, the isolation valve assembly  110  is used to selectively supply the pressurized fluid  33  to the inlet flow passage  58  in the body  12  of the proportional pressure controller  10  through the inlet port  28 . Other alternative configurations will be discussed in greater detail below. 
     Referring to  FIGS. 2A-2C , operation of the proportional pressure controller  10  of  FIG. 1  is illustrated. In  FIG. 2A , pressurized fluid  33  has been supplied to the intake port  132  of the isolation valve assembly  110 . The isolation valve assembly  110  is isolating the pressurized fluid  33  in the intake port  132  from the inlet port  28  and thus the inlet flow passage  58  of the proportional pressure controller  10 . Accordingly, the fluid pressure at the outlet port  30  of the proportional pressure controller  10  is zero in  FIG. 2A . In  FIG. 2A , the actuator valve  144  has supplied the second isolation valve pressurization chamber  126   b  with pressurized fluid  33 . The pressurized fluid  33  in the second isolation valve pressurization chamber  126   b  applies a fourth force F 4  to the second isolation valve piston  124 , which displaces the isolation valve member  114  to the isolation valve closed position. In the isolation valve closed position, the first seat engagement member  138  contacts the first seat member  128  such that the pressurized fluid  33  in the intake port  132  cannot flow to the first or second discharge ports  134 ,  136 . Meanwhile, in the isolation valve closed position, the second seat engagement member  140  is spaced from the second seat member  130  such that any fluid that is present at the first discharge port  134  (i.e. any fluid in the inlet port  28  and the inlet flow passage  58 ) may be exhausted/expelled through the second discharge port  136 . 
     In  FIG. 2B , the pressurized fluid  33  that has been supplied to the intake port  132  of the isolation valve assembly  110  is allowed to flow through the isolation valve assembly  110 , through the inlet port  28  in the body  12  of the proportional pressure controller  10 , and into the inlet flow passage  58 . In  FIG. 2B , the actuator valve  144  has supplied the first isolation valve pressurization chamber  126   a  with pressurized fluid  33 . The pressurized fluid  33  in the first isolation valve pressurization chamber  126   a  applies a fifth force F 5  to the first isolation valve piston  122 , which displaces the isolation valve member  114  to the isolation valve open position. In the isolation valve open position, the first seat engagement member  138  is spaced from the first seat member  128  such that the pressurized fluid  33  in the intake port  132  can flow to the first discharge port  134 . Meanwhile, in the isolation valve open position, the second seat engagement member  140  contacts the second seat member  130  such that the pressurized fluid  33  that is supplied to the first discharge port  134  by the intake port  132  cannot flow to the second discharge port  136 . 
     As shown in  FIG. 2B , the pressurized fluid  33  in the inlet flow passage  58  also flows into the fluid supply port  60  and the fill inlet passage  62 . The control system  106  sends a signal to open fill valve  54 , with dump valve  56  being retained in a closed position. When fill valve  54  opens, a portion of the pressurized fluid  33  in the inlet port  28  flows through the fill valve  54  and into the fill valve discharge passage  64 . The fluid pressure in the fill valve discharge passage  64  is sensed by the first pressure signaling device  109   a , which according to several embodiments can be a pressure transducer. The pressurized fluid  33  in fill valve discharge passage  64  is directed, in part, through the piston pressurization passage  66  and into the piston pressurization chamber  68 . The pressurized fluid  33  in the piston pressurization chamber  68  applies the first force F 1  to the piston  44 , which causes the piston  44  to slide in the inlet valve opening direction “B”. The piston  44  acts against the inlet valve stem  43  to push the inlet poppet valve  36  away from the inlet valve seat  38 , compressing the biasing member  40 . This opening motion of inlet poppet valve  36  allows the pressurized fluid  33  in the inlet flow passage  58  to flow through the inlet valve cavity  42  and into outlet flow passage  34 , and from there, to the outlet port  30 . The pressurized fluid which exits the outlet port  30  can be directed to a pressure controlled device (not shown) such as a piston operator or similar actuating device. 
     The first boundary wall  45  can also function as a contact surface stopping the sliding motion of the piston  44  in the inlet valve opening direction “B”. A length of time that the inlet poppet valve  36  is open can be used together with the pressure sensed by the first pressure signaling device  109   a  to proportionally control the fluid pressure at the outlet port  30 . Because the first pressure signaling device  109   a  is positioned within the fill valve discharge passage  64 , the first pressure signaling device  109   a  is isolated form potential contaminants that may be present in outlet port  30 . This reduces the possibility of contaminants affecting the pressure signal of first pressure signaling device  109   a . As previously noted, when the pressurized fluid  33  is being discharged through the outlet port  30  and when the fill valve  54  is in the open position, some of the pressurized fluid  33  in the fill valve discharge passage  64  passes through the exhaust valve pressurization passage  72  and into the exhaust valve pressurization chamber  76 . The pressurized fluid  33  in the exhaust valve pressurization chamber  76  applies the second force F 2  to the exhaust valve end face  78  to retain the exhaust poppet valve  80  in the closed position by forcing the exhaust poppet valve  80  in the exhaust valve closing direction “C”. As the pressurized fluid  33  flows through the outlet port  30 , some of the pressurized fluid  33  flows into the exhaust/outlet common passage  86 . The pressurized fluid  33  in the exhaust/outlet common passage  86  applies the third force F 3  to the exhaust poppet valve  80 . The third force F 3  that is applied to the exhaust poppet valve  80  generally opposes the second force F 2 . Accordingly, in  FIG. 2B , the second force F 2  is greater than the third force F 3  such that the exhaust poppet valve  80  remains closed. 
     Referring to  FIG. 2C , when a desired pressure is reached in the outlet flow passage  34 , as sensed by second pressure signaling device  109   b , the fill valve  54  is directed to close. If the desired pressure is exceeded, the dump valve  56  is directed to open. The dump valve  56  will also be directed to open if a command signal is generated by the control system  106  to lower the fluid pressure in the outlet flow passage  34 . When the fill valve  54  is closed, the pressurized fluid  33  in the fill inlet passage  62  is isolated from the fill valve discharge passage  64 . When the dump valve  56  opens, the exhaust valve pressurization passage  72  vents to the exhaust flow passage  88  via the fill valve discharge passage  64  and the dump valve outlet passage  98 . The residual fluid pressure at the outlet port  30  and the exhaust/outlet common passage  86  therefore exceeds the fluid pressure in the exhaust valve pressurization passage  72 , forcing exhaust poppet valve  80  to translate in the exhaust valve opening direction “D”. In other words, in  FIG. 2C , the second force F 2  that is applied to the exhaust valve end face  78  of the exhaust poppet valve  80  by the pressurized fluid  33  in the exhaust valve pressurization chamber  76  is less than the third force F 3  that is applied to the exhaust poppet valve  80  by the pressurized fluid  33  in the exhaust/outlet common passage  86 . At the same time, the pressurized fluid  33  in the piston pressurization passage  66  vents to the exhaust flow passage  88  via the fill valve discharge passage  64  and the dump valve outlet passage  98 . This reduces the first force F 1  acting on the piston  44  and thus the inlet poppet valve  36  such that the biasing force of biasing member  40  returns the inlet poppet valve  36  in the inlet valve closing direction “A” to seat the inlet poppet valve  36  against the inlet valve seat  38 . The at least one hole  47  provided through the first boundary wall  45  permits fluid pressure equalization across the first boundary wall  45  increasing the sliding speed of the piston  44  when the inlet poppet valve  36  closes. 
     As the exhaust poppet valve  80  moves in the exhaust valve opening direction “D”, the exhaust poppet seat engagement member  83  moves away from the exhaust valve seat  84  allowing the pressurized fluid  33  to flow from the exhaust/outlet common passage  86 , through the exhaust valve cavity  82 , into the exhaust flow passage  88 , and exiting via the exhaust port  32 . When the dump valve  56  receives a signal from the control system  106  to close as the fluid pressure at the fill valve discharge passage  64 , which is sensed by first pressure signaling device  109   a , reaches the desired pressure, the exhaust poppet valve  80  will remain in the open position until the fluid pressure in the exhaust valve pressurization chamber  76  exceeds the fluid pressure in the exhaust/outlet common passage  86 . When this occurs, fluid pressure in the exhaust valve pressurization passage  72  forces the exhaust poppet valve  80  in the exhaust valve closed direction “C” against the exhaust valve seat  84 . 
     If a zero pressure condition at the outlet  30  is desired, the actuator valve  144  of the isolation valve assembly  110  supplies the second isolation valve pressurization chamber  126   b  with pressurized fluid  33 . The pressurized fluid  33  in the second isolation valve pressurization chamber  126   b  applies the fourth force F 4  to the second isolation valve piston  124 , which returns the isolation valve member  114  to the isolation valve closed position. In the isolation valve closed position, the first seat engagement member  138  contacts the first seat member  128  such that the pressurized fluid  33  in the intake port  132  cannot flow to the first or second discharge ports  134 ,  136 . Meanwhile, in the isolation valve closed position, the second seat engagement member  138  is spaced from the second seat member  130  such that any fluid that is present at the first discharge port  134  (i.e. any fluid in the inlet port  28  and the inlet flow passage  58 ) may be exhausted/expelled through the second discharge port  136 . By cutting off flow of the pressurized fluid  33  to the inlet port  28 , the residual pressurized fluid  33  in the outlet flow passage  34 , the exhaust/outlet common passage  86 , the fill valve discharge passage  64 , the piston pressurization passage  66 , the piston pressurization chamber  68 , the exhaust valve pressurization passage  72 , and the exhaust valve pressurization chamber  76  will be exhausted through the exhaust flow passage  88  and the exhaust port  32 . This returns the proportional pressure controller  10  to the condition illustrated in  FIG. 2A . 
     With reference to  FIG. 3 , another proportional pressure controller  10 ′ is shown where the intake port  132 ′ of the isolation valve assembly  110 ′ is arranged in fluid communication with the outlet port  30  in the body  12 . In addition to this change, the entire isolation valve assembly  110 ′ has been flipped vertically (i.e. rotated 180 degrees about an axis running co-axially through the first discharge port  134  shown in  FIG. 1 ). In accordance with this configuration, the intake port  132 ′ of the isolation valve assembly  110 ′ receives the pressurized fluid exiting the outlet flow passage  34  and the exhaust/outlet common passage  86  through the outlet port  30  and the first discharge port  134  supplies the pressurized fluid  33  to the pressure controlled device (not shown). The remaining structure of the proportional pressure controller  10 ′ is substantially the same as that described with reference to the proportional pressure controller  10  of  FIG. 1 . Like in  FIG. 1 , the isolation valve assembly  110 ′ illustrated in  FIG. 3  is external to the body  12  of the proportional pressure controller  10 ′. 
     Referring to  FIGS. 4A-4C , operation of the proportional pressure controller  10 ′ of  FIG. 3  is illustrated. In  FIG. 4A , pressurized fluid  33  has been supplied directly to the inlet port  28  and thus the inlet flow passage  58  of the proportional pressure controller  10 ′. The inlet poppet engagement member  46   a  of the inlet poppet valve  36  is held against the inlet valve seat  38  by the biasing member  40 , which acts against the inlet poppet valve  36  in the inlet poppet valve closing direction “A”. In  FIG. 4A , the actuator valve  144 ′ has supplied the second isolation valve pressurization chamber  126   b  with pressurized fluid  33 . The pressurized fluid  33  in the second isolation valve pressurization chamber  126   b  applies the fourth force F 4  to the second isolation valve piston  124 , which displaces the isolation valve member  114  to the isolation valve closed position. In the isolation valve closed position, the first seat engagement member  138  contacts the first seat member  128  such that any of the residual fluid  33  in the outlet port  30  of the body  12  cannot flow from the intake port  132 ′ of the isolation valve assembly  110 ′ to the first or second discharge ports  134 ′,  136 ′. Meanwhile, in the isolation valve closed position, the second seat engagement member  140  is spaced from the second seat member  130  such that any fluid that is present at the first discharge port  134 ′ (i.e. any fluid in the pressure controlled device) may be exhausted/expelled through the second discharge port  136 ′. In this way, a zero pressure condition is provided at the first and second discharge ports  134 ′,  136 ′ of the isolation valve assembly  110 ′. 
     As shown in  FIG. 4B , the pressurized fluid  33  in the inlet flow passage  58  flows into the fluid supply port  60  and the fill inlet passage  62 . The control system  106  sends a signal to open fill valve  54 , with dump valve  56  being retained in a closed position. When fill valve  54  opens, a portion of the pressurized fluid  33  in the inlet port  28  flows through the fill valve  54  and into the fill valve discharge passage  64 . The fluid pressure in fill valve discharge passage  64  is sensed by the first pressure signaling device  109   a . The pressurized fluid  33  in fill valve discharge passage  64  is directed, in part, through the piston pressurization passage  66  and into the piston pressurization chamber  68 . The pressurized fluid  33  in the piston pressurization chamber  68  applies the first force F 1  to the piston  44 , which causes the piston  44  to slide in the inlet valve opening direction “B”. The piston  44  acts against the inlet valve stem  43  to push the inlet poppet valve  36  away from the inlet valve seat  38 , compressing the biasing member  40 . This opening motion of inlet poppet valve  36  allows the pressurized fluid  33  in the inlet flow passage  58  to flow through the inlet valve cavity  42  and into outlet flow passage  34 , and from there, to the outlet port  30 . In addition, some of the pressurized fluid  33  in the fill valve discharge passage  64  passes through the exhaust valve pressurization passage  72  and into the exhaust valve pressurization chamber  76 . The pressurized fluid  33  in the exhaust valve pressurization chamber  76  applies the second force F 2  to the exhaust valve end face  78  to retain the exhaust poppet valve  80  in the closed position by forcing the exhaust poppet valve  80  in the exhaust valve closing direction “C”. As the pressurized fluid  33  flows through the outlet port  30 , some of the pressurized fluid  33  flows into the exhaust/outlet common passage  86 . The pressurized fluid  33  in the exhaust/outlet common passage  86  applies the third force F 3  to the exhaust poppet valve  80 . The third force F 3  that is applied to the exhaust poppet valve  80  generally opposes the second force F 2 . Accordingly, in  FIG. 4B , the second force F 2  is greater than the third force F 3  such that the exhaust poppet valve  80  remains closed. 
     In  FIG. 4B , the actuator valve  144 ′ has supplied the first isolation valve pressurization chamber  126   a  with pressurized fluid  33 . The pressurized fluid  33  in the first isolation valve pressurization chamber  126   a  applies the fifth force F 5  to the first isolation valve piston  122 , which displaces the isolation valve member  114  to the isolation valve open position. In the isolation valve open position, the first seat engagement member  138  is spaced from the first seat member  128  such that the pressurized fluid  33  in the intake port  132 ′ can flow to the first discharge port  134 ′. Meanwhile, in the isolation valve open position, the second seat engagement member  140  contacts the second seat member  130  such that the pressurized fluid  33  that is supplied to the first discharge port  134 ′ by the intake port  132 ′ cannot flow to the second discharge port  136 ′. Accordingly, in the isolation valve open position, the isolation valve assembly  110 ′ permits the pressurized fluid  33  to exit the outlet port  30 , pass through the isolation valve cavity  112 , and flow to the pressure controlled device (not shown) via the first discharge port  134 ′. 
     Referring to  FIG. 4C , when a desired pressure is reached in the outlet flow passage  34 , as sensed by second pressure signaling device  109   b , the fill valve  54  is directed to close. If the desired pressure is exceeded, the dump valve  56  is directed to open. The dump valve  56  will also be directed to open if a command signal is generated by the control system  106  to lower the fluid pressure in the outlet flow passage  34 . When the fill valve  54  is closed, the pressurized fluid  33  in the fill inlet passage  62  is isolated from the fill valve discharge passage  64 . When the dump valve  56  opens, the exhaust valve pressurization passage  72  vents to the exhaust flow passage  88  via the fill valve discharge passage  64  and the dump valve outlet passage  98 . The residual fluid pressure at the outlet port  30  and the exhaust/outlet common passage  86  therefore exceeds the fluid pressure in the exhaust valve pressurization passage  72 , forcing exhaust poppet valve  80  to translate in the exhaust valve opening direction “D”. In other words, in  FIG. 4C , the second force F 2  that is applied to the exhaust valve end face  78  of the exhaust poppet valve  80  by the pressurized fluid  33  in the exhaust valve pressurization chamber  76  is less than the third force F 3  that is applied to the exhaust poppet valve  80  by the pressurized fluid  33  in the exhaust/outlet common passage  86 . At the same time, the pressurized fluid  33  in the piston pressurization passage  66  vents to the exhaust flow passage  88  via the fill valve discharge passage  64  and the dump valve outlet passage  98 . This reduces the first force F 1  acting on the piston  44  and thus the inlet poppet valve  36  such that the biasing force of biasing member  40  returns the inlet poppet valve  36  in the inlet valve closing direction “A” to seat the inlet poppet valve  36  against the inlet valve seat  38 . 
     As the exhaust poppet valve  80  moves in the exhaust valve opening direction “D”, the exhaust poppet seat engagement member  83  moves away from the exhaust valve seat  84  allowing the pressurized fluid  33  to flow from the exhaust/outlet common passage  86 , through the exhaust valve cavity  82 , into the exhaust flow passage  88 , and exiting via the exhaust port  32 . When the dump valve  56  receives a signal from the control system  106  to close as the fluid pressure at the fill valve discharge passage  64 , which is sensed by first pressure signaling device  109   a , reaches the desired pressure, the exhaust poppet valve  80  will remain in the open position until the fluid pressure in the exhaust valve pressurization chamber  76  exceeds the fluid pressure in the exhaust/outlet common passage  86 . When this occurs, fluid pressure in the exhaust valve pressurization passage  72  forces the exhaust poppet valve  80  in the exhaust valve closed direction “C” against the exhaust valve seat  84 . 
     If a zero pressure condition at the first discharge port  134 ′ is desired (i.e. the pressure supplied to the pressure controlled device), the actuator valve  144 ′ of the isolation valve assembly  110 ′ supplies the second isolation valve pressurization chamber  126   b  with pressurized fluid  33 . The pressurized fluid  33  in the second isolation valve pressurization chamber  126   b  applies the fourth force F 4  to the second isolation valve piston  124 , which returns the isolation valve member  114  to the isolation valve closed position. In the isolation valve closed position, the first seat engagement member  138  contacts the first seat member  128  such that the pressurized fluid  33  in the intake port  132 ′ cannot flow to the first or second discharge ports  134 ′,  136 ′. Meanwhile, in the isolation valve closed position, the second seat engagement member  138  is spaced from the second seat member  130  such that any fluid that is present at the first discharge port  134 ′ (i.e. any fluid in the pressure controlled device) may be exhausted/expelled through the second discharge port  136 ′. By isolating the first discharge port  134 ′ from the outlet port  30  and the residual pressurized fluid  33  in the outlet flow passage  34 , the isolation valve assembly  110 ′ creates a zero pressure condition at the first discharge port  134 ′, which is connected in fluid communication with the pressure controlled device (not shown). 
     With reference to  FIG. 5  another proportional pressure controller  10 ″ is shown where the intake port  132 ″ of the isolation valve assembly  110  is arranged in fluid communication with and directly adjacent to the outlet port  30 ″ in the body  12 ″. In addition to this change, the isolation valve assembly  110 ″ has been arranged within the body  12 ″ creating a more compact proportional pressure controller  10 ″. In accordance with this configuration, the intake port  132 ″ of the isolation valve assembly  110 ″ receives the pressurized fluid  33  exiting the outlet flow passage  34  and the exhaust/outlet common passage  86  through the outlet port  30 ″. The actuator valve  144 ″ of the actuator  142 ″ has also been moved from a position external to the body  12 ″ to a position that is within the body  12 ″ and the controller operator  20  of the proportional pressure controller  10 ″. The actuator valve  144 ″ is disposed in fluid communication with the fill inlet passage  62  and only one isolation valve pressure chamber  126  in this configuration by way of the actuator valve passage  146 ″. The isolation valve pressure chamber  126  is open to the second end  120  of the isolation valve cavity  112 ″. The other isolation valve pressure chamber at the first end  118  of the isolation valve cavity  112 ″ has been replaced by a isolation valve biasing member  148 . By way of example and without limitation, the isolation valve biasing member  148  may be a coil spring. To prevent a vacuum from forming in the first end  118  of the isolation valve cavity  112 ″, the isolation valve member  114 ″ may optionality include a vent passageway  150  that extends through the isolation valve member  114 ″ such that the first end  118  of the isolation valve cavity  112 ″ remains in constant fluid communication with the second discharge port  136 ″. 
     Although the isolation valve cavity  112 ″ may be defined by the central body portion  22 ″ of the proportional pressure controller  10 ″, in  FIG. 5 , the isolation valve cavity  112 ″ is defined by an isolation valve cartridge  152 , which is received in the central body portion  22 ″ of the proportional pressure controller  10 ″. The first and second seat members  128 ″,  130 ″ may be integral with the isolation valve cartridge  152  or may be separately formed components. As shown in  FIG. 5 , where the first and second seat members  128 ″,  130 ″ are separately formed components, the first and second seat members  128 ″,  130 ″ may have seals that seal against the isolation valve cartridge  152 . Similarly, the first and second isolation valve pistons  122 ,  124  may seal against the isolation valve cartridge  152  or may seal against first and second isolation valve end caps  154 ,  156 . As shown in  FIG. 5 , where the first and second isolation valve pistons  122 ,  124  seal against the first and second isolation valve end caps  154 ,  156 , the first isolation valve end cap  154  is positioned in the first end  118  of the isolation valve cavity  112 ″ between the isolation valve cartridge  152  and the first isolation valve piston  122  while the second isolation valve end cap  156  is positioned in the second end  120  of the isolation valve cavity  112 ″ between the isolation valve cartridge  152  and the second isolation valve piston  124 . The first and second isolation valve end caps  154 ,  156  may also have seals that seal the first and second isolation valve end caps  154 ,  156  to the isolation valve cartridge  152 . The shape of the exhaust flow passage  88 ″ in  FIG. 5  has been modified such that the exhaust port  32 ″ now exits through the first end cap  14 ″ of the proportional pressure controller  10 ″. Finally, the second end cap  16 ″ of the proportional pressure controller  10 ″ has been modified to include an accumulator cavity  158  that is disposed in fluid communication with the piston pressurization chamber  68 . As such, the accumulator cavity  158  receives pressurized fluid  33  from the piston pressurization chamber  68  when the fill valve  54  is open. The remaining structure of the proportional pressure controller  10 ″ is substantially the same as that described with reference to the proportional pressure controller  10 ′ of  FIG. 3 . 
     In accordance with one configuration illustrated in  FIG. 5 , the dump valve passage  98  may extend between the discharge side of the dump valve  56  and the exhaust flow passage  88 ″. In this configuration, the dump valve exhaust port  100  opens directly into the exhaust flow passage  88 ″. When the dump valve  56  is opened, fluid flows through the dump valve passage  98  and is expelled from the dump valve exhaust port  100  into the exhaust flow passage  88 ″. In an alternative configuration, the proportional pressure controller  10 ″ includes a dump valve passage  98 ′ in the body  12 ″ that extends between the dump valve  56  and a dump valve exhaust port  100 ′ that opens to an outer surface  12   a  of the body  12 ″. When the dump valve  56  is opened, fluid flows through the dump valve passage  98 ′ and is expelled from the body  12 ″ via the dump valve exhaust port  100 ′, which is a standalone port disposed along the outer surface  12   a  of the body  12 ″. In another alternative configuration, the proportional pressure controller  10 ″ includes a dump valve passage  98 ″ in the body  12 ″ that extends between the dump valve  56  and the second discharge port  136 ″ of the isolation valve assembly  110 ″. In this configuration, the dump valve exhaust port  100 ″ opens directly into the second discharge port  136 ″. When the dump valve  56  is opened, fluid flows through the dump valve passage  98 ″ and is expelled from the dump valve exhaust port  100 ″ into one of the second discharge port  136 ″. 
     Referring to  FIGS. 6A-6C , operation of the proportional pressure controller  10 ″ of  FIG. 5  is illustrated. In  FIG. 6A , pressurized fluid  33  has been supplied directly to the inlet port  28  and thus the inlet flow passage  58  of the proportional pressure controller  10 ″. The inlet poppet engagement member  46   a  of the inlet poppet valve  36  is held against the inlet valve seat  38  by the biasing member  40 , which acts against the inlet poppet valve  36  in the inlet poppet valve closing direction “A”. As shown in  FIG. 6A , the isolation valve member  114 ″ is biased to the isolation valve closed position. More particularly, the isolation valve biasing member  148  applies the fourth force F 4  to the first isolation valve piston  122 , which pushes the isolation valve member  114 ″ towards the isolation valve closed position. In the isolation valve closed position, the first seat engagement member  138  contacts the first seat member  128 ″ such that any of the residual fluid  33  in the outlet port  30 ″ of the body  12 ″ cannot flow from the intake port  132 ″ of the isolation valve assembly  110 ″ to the first or second discharge ports  134 ″,  136 ″. Meanwhile, in the isolation valve closed position, the second seat engagement member  140  is spaced from the second seat member  130 ″ such that any fluid that is present at the first discharge port  134 ″ (i.e. any fluid in the pressure controlled device) may be exhausted/expelled through the second discharge port  136 ″. In this way, a zero pressure condition is provided at the first and second discharge ports  134 ″,  136 ″ of the isolation valve assembly  110 ″. 
     As shown in  FIG. 6B , the pressurized fluid  33  in the inlet flow passage  58  flows into the fluid supply port  60  and the fill inlet passage  62 . The control system  106  sends a signal to open fill valve  54 , with dump valve  56  being retained in a closed position. When fill valve  54  opens, a portion of the pressurized fluid  33  in the inlet port  28  flows through the fill valve  54  and into the fill valve discharge passage  64 . The fluid pressure in fill valve discharge passage  64  is sensed by the first pressure signaling device  109   a . The pressurized fluid  33  in fill valve discharge passage  64  is directed, in part, through the piston pressurization passage  66  and into the piston pressurization chamber  68 . The pressurized fluid  33  in the piston pressurization chamber  68  applies the first force F 1  to the piston  44 , which causes the piston  44  to slide in the inlet valve opening direction “B”. The piston  44  acts against the inlet valve stem  43  to push the inlet poppet valve  36  away from the inlet valve seat  38 , compressing the biasing member  40 . This opening motion of inlet poppet valve  36  allows the pressurized fluid  33  in the inlet flow passage  58  to flow through the inlet valve cavity  42  and into outlet flow passage  34 , and from there, to the outlet port  30 . In addition, some of the pressurized fluid  33  in the fill valve discharge passage  64  passes through the exhaust valve pressurization passage  72  and into the exhaust valve pressurization chamber  76 . The pressurized fluid  33  in the exhaust valve pressurization chamber  76  applies the second force F 2  to the exhaust valve end face  78  to retain the exhaust poppet valve  80  in its closed position by forcing the exhaust poppet valve  80  in the exhaust valve closing direction “C”. As the pressurized fluid  33  flows through the outlet port  30 ″, some of the pressurized fluid  33  flows into the exhaust/outlet common passage  86 . The pressurized fluid  33  in the exhaust/outlet common passage  86  applies the third force F 3  to the exhaust poppet valve  80 . The third force F 3  that is applied to the exhaust poppet valve  80  generally opposes the second force F 2 . Accordingly, in  FIG. 6B , the second force F 2  is greater than the third force F 3  such that the exhaust poppet valve  80  remains closed. 
     In  FIG. 6B , the actuator valve  144 ″ has supplied the isolation valve pressurization chamber  126  with pressurized fluid  33 . The pressurized fluid  33  in the first isolation valve pressurization chamber  126  applies a fifth force F 5  to the second isolation valve piston  124 , which displaces the isolation valve member  114 ″ to the isolation valve open position, compressing the isolation valve biasing member  148 . In the isolation valve open position, the first seat engagement member  138  is spaced from the first seat member  128 ″ such that the pressurized fluid  33  in the intake port  132 ″ can flow to the first discharge port  134 ″. Meanwhile, in the isolation valve open position, the second seat engagement member  140  contacts the second seat member  130 ″ such that the pressurized fluid  33  that is supplied to the first discharge port  134 ″ by the intake port  132 ″ cannot flow to the second discharge port  136 ″. Accordingly, in the isolation valve open position, the isolation valve assembly  110 ″ permits the pressurized fluid  33  to exit the outlet port  30 ″, pass through the isolation valve cavity  112 ″, and flow to the pressure controlled device (not shown) via the first discharge port  134 ″. 
     Referring to  FIG. 6C , when a desired pressure is reached in the outlet flow passage  34 , as sensed by second pressure signaling device  109   b , the fill valve  54  is directed to close. If the desired pressure is exceeded, the dump valve  56  is directed to open. The dump valve  56  will also be directed to open if a command signal is generated by the control system  106  to lower the fluid pressure in the outlet flow passage  34 . When the fill valve  54  is closed, the pressurized fluid  33  in the fill inlet passage  62  is isolated from the fill valve discharge passage  64 . When the dump valve  56  opens, the exhaust valve pressurization passage  72  vents to the exhaust flow passage  88 ″ via the fill valve discharge passage  64  and the dump valve outlet passage  98 . The residual fluid pressure at the outlet port  30 ″ and the exhaust/outlet common passage  86  therefore exceeds the fluid pressure in the exhaust valve pressurization passage  72 , forcing exhaust poppet valve  80  to translate in the exhaust valve opening direction “D”. In other words, in  FIG. 6C , the second force F 2  that is applied to the exhaust valve end face  78  of the exhaust poppet valve  80  by the pressurized fluid  33  in the exhaust valve pressurization chamber  76  is less than the third force F 3  that is applied to the exhaust poppet valve  80  by the pressurized fluid  33  in the exhaust/outlet common passage  86 . At the same time, the pressurized fluid  33  in the piston pressurization passage  66  vents to the exhaust flow passage  88 ″ via the fill valve discharge passage  64  and the dump valve outlet passage  98 . This reduces the first force F 1  acting on the piston  44  and thus the inlet poppet valve  36  such that the biasing force of biasing member  40  returns the inlet poppet valve  36  in the inlet valve closing direction “A” to seat the inlet poppet valve  36  against the inlet valve seat  38 . 
     As the exhaust poppet valve  80  moves in the exhaust valve opening direction “D”, the exhaust poppet seat engagement member  83  moves away from the exhaust valve seat  84  allowing the pressurized fluid  33  to flow from the exhaust/outlet common passage  86 , through the exhaust valve cavity  82 , into the exhaust flow passage  88 ″, and exiting via the exhaust port  32 ″. When the dump valve  56  receives a signal from the control system  106  to close as the fluid pressure at the fill valve discharge passage  64  reaches the desired pressure, the exhaust poppet valve  80  will remain in the open position until the fluid pressure in the exhaust valve pressurization chamber  76  exceeds the fluid pressure in the exhaust/outlet common passage  86 . When this occurs, fluid pressure in the exhaust valve pressurization passage  72  forces the exhaust poppet valve  80  in the exhaust valve closed direction “C” against the exhaust valve seat  84 . 
     If a zero pressure condition at the first discharge port  134 ″ is desired (i.e. the pressure supplied to the pressure controlled device), the actuator valve  144 ″ of the isolation valve assembly  110 ″ releases the pressurized fluid  33  from the isolation valve pressurization chamber  126 . This relieves the first force F 5  that the pressurized fluid  33  in the isolation valve pressurization chamber  126  was applying to the second isolation valve piston  124 . As such, the fourth force F 4 , which the isolation valve biasing member  148  applies to the first isolation valve piston  122 , returns the isolation valve member  114  to the isolation valve closed position. In the isolation valve closed position, the first seat engagement member  138  contacts the first seat member  128 ″ such that the pressurized fluid  33  in the intake port  132 ″ cannot flow to the first or second discharge ports  134 ″,  136 ″. Meanwhile, in the isolation valve closed position, the second seat engagement member  138  is spaced from the second seat member  130 ″ such that any fluid that is present at the first discharge port  134 ″ (i.e. any fluid in the pressure controlled device) may be exhausted/expelled through the second discharge port  136 ″. By isolating the first discharge port  134 ″ from the outlet port  30 ″ and therefore the residual pressurized fluid  33  in the outlet flow passage  34 , the isolation valve assembly  110 ″ creates a zero pressure condition at the first discharge port  134 ″, which is connected in fluid communication with the pressure controlled device (not shown). 
     The configurations shown in the Figures are not intended to be limiting. For example, although the inlet poppet valve  36  and the exhaust valve poppet valve  80  are shown in an opposed configuration, these poppet valves can be arranged in any configuration at the discretion of the manufacturer. Alternate configurations can provide the poppet valves in a side-by-side parallel disposition. The poppet valves can also be oriented such that both poppet valves seat in a same axial direction and unseat in the same opposed axial direction. The configurations shown in the Figures are therefore exemplary of some and not all of the possible configurations available. Similarly, further embodiments of the proportional pressure controller may include different types of valves for the fill valve  54 , the dump valve  56 , and the actuator valve  144 . For example, one or more of the fill valve  54 , the dump valve  56 , and the actuator valve  144  can be hydraulically operated, solenoid operated, or air operated valves, which can provide different operating characteristics. 
     Proportional pressure controllers of the present disclosure offer several advantages. By eliminating solenoid actuators associated with the main flow valves of the controller and replacing the valves with poppet valves, small and lower energy consumption pilot valves in the form of fill and dump valves are used to provide pressure actuation to open or close the poppet valves. This reduces the cost and operating power required for the proportional pressure controller. The use of passageways created in the body of the proportional pressure controller to transfer pressurized fluid to actuate the poppet valves (which are isolated from the main poppet valve flow paths) prevents potentially contaminated fluid at the outlet of the proportional pressure controller from back-flowing into the pilot valves, which could inhibit their operation. One of the passageways can be used to simultaneously provide pressure to open one of the poppet valves while holding the second poppet valve in a closed position. By positioning a pressure sensing device in one of the isolated passageways, the pressure sensing device is also isolated from contaminants to improve the accuracy of the device&#39;s pressure signal. In addition, the proportional pressure controllers of the present disclosure operate to create a zero pressure condition at either the outlet port in the body of the proportional pressure controller or at the first discharge port of the isolation valve assembly. Beneficially, either the outlet port in the body of the proportional pressure controller or the first discharge port of the isolation valve assembly is configured to supply the pressurized fluid to a pressure controlled device, which may require the zero pressure condition during at least part of its operation. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.