Abstract:
A sealed solenoid provides an improved actuator for valves and other devices, particular such devices used in extreme environments and/or with corrosive media. For example, the improved solenoid construction can be used to drive a precision flow control valve used in air and space applications, such as to control fuel and oxidizer combustion media in rocket and other thrust components. The solenoid is retained in a solenoid retainer to which is attached a rigid barrier that isolates the solenoid pole piece and coil from the media. A clapper disposed outside the barrier from the solenoid serves as the armature, receiving magnetic flux from the solenoid through the barrier without interference from the barrier. The barrier may be extremely thin and magnetically inert.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional and claims the benefit of U.S. provisional application No. 61/748,419, filed on Jan. 2, 2013, the entire disclosure of which is incorporated by reference as though fully set forth herein. 
    
    
     STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     The present disclosure relates to a sealed solenoid construction, and more particularly, to a sealed solenoid valve in which the solenoid coil and pole piece are protected from the environment. 
     Solenoids are known to be useful for directly actuating valves by applying a current to the solenoid coil to induce a magnetic flux through an armature that causes the armature to move. A direct-drive solenoid valve typically actuates a rod-shaped core armature with a proximal end coupled directly to the valve head. It is also known to use a solenoid to actuate a disc-shaped armature, called a “clapper,” that can be separated from the solenoid by a small gap, such as in a non-energized state of the solenoid. In one configuration, when the solenoid is energized, the magnetic flux crosses the gap and pulls the clapper toward, and often into contact with, the solenoid. The solenoid may provide the opposite actuation (i.e., the clapper is biased into contact with the solenoid until the solenoid is energized and pushes the clapper away). Such a “clapper valve” can be favorable over other solenoid valve constructions because, for the same size solenoid, a greater magnetic flux can be supported by the clapper surface area than by a rod-shaped armature. The greater magnetic flux results in a greater actuation force. Further, a clapper armature does not need to extend into the interior of the solenoid coil, such that a stationary pole piece can be disposed within the coil (creating a solid-core solenoid) to augment the magnetic flux. 
     Solenoids, and in particular solenoid coils and pole pieces, can be manufactured from many different conductive and ferromagnetic materials. In a valve that needs to be very small or lightweight, it may be desirable to, for example, choose a lighter ferromagnetic material for the pole piece than the typically-used iron or soft iron. However, it is known in solenoid-operated valves to immerse the solenoid in the working fluid in order to lubricate or protect the components, to provide a path for fluid flow or armature movement, or to facilitate pressure balancing of the valve. Where the coil and/or pole piece materials are chosen for reduced weight, they may be more susceptible to corrosion by the working fluid. In particular, valves for use in some air and space applications (e.g., rocket engines and thrust boosters) may need to be compact, lightweight, and able to control the flow of corrosive gaseous or liquid media, such as hypergolic propellants like monomethyl-hydrazine (MMH) and oxidizers like nitrogen tetroxide (N2O4). It may be unfavorable to immerse the coil and pole piece(s) in corrosive working media because such a valve design may prevent the selection of materials that provide the necessary functional properties but lesser weight, because such lightweight materials may be more susceptible to corrosion. 
     Solenoid-driven poppet valves can be used in flow control applications where release of a gas from the valve must be controlled accurately. Such valves benefit from being “balanced,” wherein all forces acting on the poppet are substantially equal when the solenoid is non-energized, and only a small force is needed to actuate the valve, even when high pressure media is being controlled by the valve. Typically, the balanced state is closed, with a light gauge spring holding the poppet closed. A balanced poppet valve may be actuated by a solenoid, which magnetic force only has to overcome the biasing force of the spring to actuate the valve. The low force demands less power, which allows the solenoid (i.e., the coil, pole piece(s), and housing therefor) to be smaller and lighter. 
     Ordinary solenoid-driven balanced poppet valves are prone to leakage in high-pressure applications due to the design and materials used. Some such valves exist that overcome the leakage problem at high fluid pressures, and thus may be used in extreme environments and mission-critical applications where the valves must operate rapidly and accurately, exhibit low hysteresis, and provide bubble-tight shut-off. In air and space applications, such valves must further be designed to contribute as little weight as possible to the craft or component in which they are used, and must withstand the extreme conditions of the application, including extremely high fluid pressures (up to 10 kpsi or higher), extreme temperatures and temperature variation (from sub-zero to well above zero), material deformation due to pressure and thermal stresses, and vibrations and stresses due to high speeds of the craft. Existing designs typically either immerse the solenoid in the working media, requiring use of relatively large, heavy corrosion-resistant materials for the solenoid components, or isolate the solenoid and armature from the working media with sealing arrangements that complicate the construction of the valve, particularly when working to meet the stringent operational, weight and form factor requirements of air and space applications. 
     BRIEF SUMMARY 
     The disclosure provides a sealed solenoid construction that allows for the use of lightweight materials in the solenoid coil, pole piece(s), and housing. The sealed solenoid constructions may be used in a lightweight solenoid actuator and a pressure-balanced valve that can be used with corrosive media, is capable of withstanding high vibration and shock loads, and is highly accurate with rapid actuation response, making the valve capable of application in aerospace environments, including supersonic and hypersonic flight. 
     In one aspect, the present disclosure provides a solenoid actuator for a valve having a valve member movable within a housing to control the flow of a working media through an interior of the housing from an inlet port to an outlet port. The actuator may include a wire coil and at least one pole piece made of a magnetically active material, a solenoid retainer configured to couple to the housing and defining an interior space containing the wire coil and the at least one pole piece, a magnetically inert barrier member forming a closed end of the solenoid retainer, and a magnetically active armature separated from the wire coil and the at least one pole piece by the barrier member. The armature may be configured to couple to the valve member to move the valve member when the wire coil is energized and de-energized to control communication between the inlet port and the outlet port. When the solenoid retainer is coupled to the housing, the armature and the barrier member may be in communication with the working media, and the barrier member may seal off the wire coil and the pole piece from the working media. 
     In another aspect, the present disclosure provides a solenoid valve having a housing defining an inlet port, an outlet port, and a valve chamber receiving working media from the inlet port. The solenoid valve further has a valve member movable within the valve chamber to control the flow of the working media from the inlet port to the outlet port. The solenoid member further has a solenoid actuator coupled to the housing and disposed in communication with the valve chamber. The actuator includes a wire coil and at least one pole piece made of a magnetically active material, a solenoid retainer coupled to the housing and defining an interior space containing the wire coil and the pole piece, a magnetically inert barrier member forming a closed end of the solenoid retainer, and a magnetically active armature separated from the wire coil and the at least one pole piece by the barrier member. The armature may be coupled to the valve member to move the valve member when the wire coil is energized and de-energized to control communication between the inlet port and the outlet port. The armature and the barrier member may be in communication with the working media, and the barrier member may seal off the wire coil and the pole piece from the working media. 
     In yet another aspect, the present disclosure provides a clapper solenoid valve having a housing defining an inlet port, an outlet port, a valve chamber receiving working media from the inlet port, and an actuator chamber in communication with the valve chamber. The clapper solenoid valve further has a poppet rod movable within the valve chamber to control the flow of the working media from the inlet port to the outlet port, a solenoid disposed within the actuator chamber and including a wire coil and at least one pole piece made of a magnetizable material, a solenoid retainer having a magnetically inert rigid barrier member and defining an interior space containing the solenoid, a clapper armature made of a magnetizable material and separated from the wire coil and the pole piece by the barrier member, and a spring disposed between the clapper and the solenoid retainer to bias the clapper either toward or away from the wire coil and the pole piece. The clapper and the barrier member may be subjected to the working media during operation of the clapper solenoid valve. The clapper may be coupled to the poppet rod to move the poppet rod in response to the wire coil being energized and de-energized to open and close communication between the inlet port and the outlet port. 
     These and other aspects and advantages of the disclosure will be apparent from the detailed description and drawings. What follows are one or more example embodiments. To assess the full scope of the invention the claims should be looked to, as the example embodiments are not intended as the only embodiments within the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an example valve having a sealed solenoid actuator in accordance with the present disclosure and suitable for use in air and space applications; 
         FIG. 2  is an exploded perspective view of the example embodiment of  FIG. 1 ; 
         FIG. 3  is a sectional view of the example embodiment of  FIG. 1  showing the valve in a closed state; 
         FIG. 4  is a close-up sectional view of area  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a top perspective view of an embodiment of a clapper armature used in the example embodiment of  FIG. 1 ; 
         FIG. 6  is an enlarged sectional view of the valve of  FIG. 3  in a closed state; 
         FIG. 7  is a close-up sectional view of area  7 - 7  of  FIG. 6 ; and 
         FIG. 8  is an enlarged sectional view as in  FIG. 6 , showing the valve in an open state. 
     
    
    
     DETAILED DESCRIPTION 
     A solenoid actuator in accordance with the present disclosure includes a solenoid and an armature, where the solenoid may be structurally isolated from the armature by a rigid barrier member disposed between the solenoid and the armature. The barrier member may be magnetically inert and sufficiently thin so as not to interfere with a magnetic flux between the energized solenoid and the armature. The barrier member may further be flat (i.e., having planar opposing sides), and may be contacted by the armature during operation of the actuator. The armature may, in some embodiments, be a hingeless clapper that moves axially toward and away from the solenoid. The clapper may have recessed areas in its contacting surface that reduce or eliminate this unwanted adherence by reducing the surface area of contact. 
     The barrier member may be attached to or integral with a solenoid retainer that defines an interior space containing all or a portion of the solenoid. The solenoid retainer may interface with a housing of another device, such as a valve, to install the solenoid in the device. Together, the barrier member and solenoid retainer isolate the solenoid from gases and fluids within the device, referred to herein as “working media,” that may contact the barrier member during operative or non-operative periods of the actuator. The barrier member, and further the solenoid retainer, may be resistant to corrosion by the working media. For example, the barrier member and solenoid retainer may be stainless steel, and further may be austenitic stainless steel, to resist corrosion by known vehicle fuels. In this manner, the solenoid actuator may be used in a solenoid valve, wherein the clapper attaches to a valve member, such as a poppet, that operates the valve as the solenoid is energized and de-energized, controlling the flow of the working media through the valve. Because the solenoid is isolated from the working media, the components of the solenoid, which may include a wire coil, a bobbin, and at least one pole piece, may contain materials that are not compatible with the working media (i.e., the selected materials may be corroded, weakened, or otherwise damaged by contact with the working media). The clapper may be immersed in the working media to allow for simplified pressure balancing of the valve as described below; in particular, no additional sealing structures need to be provided to keep the clapper dry and still pressure-balance the valve. 
     In accordance with this disclosure, a lightweight, pressure-balanced, solenoid-operated valve using the above solenoid actuator may be configured to operate in extreme environments associated with travel at very high velocity (e.g., supersonic and hypersonic speeds) and high altitude (e.g., into and beyond Earth&#39;s stratosphere). To this end, a valve in accordance with this disclosure minimizes cost and weight and improves efficiency and dependability over previous solutions. The valve is also suitable for operation at velocities below Mach 1, such as reached in conventional aircraft. Additionally, the valve may be used in any suitable application that requires high speed valve operation, zero or near-zero leakage, low weight, and low power consumption, and which further controls the pressurized flow of corrosive working media that may corrode or degrade a lightweight solenoid. The valve may be a two-way valve, wherein opening the valve allows a high-pressure fluid to pass from an inlet port to an outlet port. Such a two-way valve may have application as a fuel flow control for a hypergolic propellant, and may be used in an attitude thruster or similar propulsion device. The valve may be a three-way valve, wherein opening the valve opens a fluid path between the outlet port and a first port, and closing the valve opens a fluid path between the outlet port and a second port. Such a valve is illustrated in the figures and may be used, for example, as a pilot valve as described below. 
     Looking first to  FIG. 1 , a three-way valve  10  in accordance with an example embodiment of this disclosure is shown. The valve  10  may attach to any suitable pressurized fluid transfer system, such as to a manifold, as described below. The valve  10  may include a valve housing  12  and a solenoid housing  14  that interfaces with the valve housing  12 . The housings  12 ,  14  may be any suitable corrosion-resistant material, such as stainless steel. In some embodiments, the valve housing  12  and the solenoid housing  14  have complementary mating surfaces that engage each other to attach the solenoid housing  14  to the valve housing  12 . In the illustrated embodiment, the housings  12 ,  14  are threaded to matedly attach the proximal end of the solenoid housing  14  to the distal end of the valve housing  12 . As described further below, the solenoid housing  12  houses all or part of a solenoid  30 , and the valve housing  14  includes a plurality of ports  92 ,  94 ,  96  passing through the valve housing  14  into an interior space, referred to herein as a “valve chamber,” defined by the valve housing  14 . In other embodiments, the valve housing  12  and solenoid housing  14  may be integrated as a single housing. 
     Referring to  FIGS. 2 and 3 , one or more o-rings  16  may create a seal between the housings  12 ,  14 . The solenoid housing  14  may be substantially hollow, defining an actuator chamber, and may be open at its distal end to receive a solenoid retainer  18 . A coaxial port  28  may be disposed through the proximal end of the solenoid housing  14 , providing fluid communication between the chambers of the housings  12 ,  14 . Before the solenoid retainer  18  is installed in the solenoid housing  14 , a clapper  20  may be disposed inside the solenoid housing  14  near its proximal end, and a biasing member, such as a clapper spring  22 , may be installed distally from and contacting the clapper  20 . The clapper spring  22  may fit around the proximal end of the solenoid retainer  18  and abut a flange  19  of the solenoid retainer  18  in order to bias the clapper  20  from the solenoid retainer  18  near the outer edge of the clapper  20 . The engagement of the clapper spring  22  with the clapper  20  distally and at the clapper&#39;s  20  outer edge, as opposed to proximally or substantially inside the perimeter of the clapper  20 , stabilizes the clapper  20  when it is both stationary and operating, and further reduces the tendency of the clapper  20  to tilt, skew, or otherwise rotate other than around its own axis when a magnetic flux is flowing through it. 
     The solenoid retainer  18  may be installed over the clapper  20  and clapper spring  22 , and may be matedly attached to the solenoid housing  14  by interoperation of threaded surfaces or other means. One or more o-rings  24  may form a seal between the solenoid retainer  18  and the solenoid housing  14 . The solenoid retainer  18 , clapper  20 , and clapper spring  22  may all be coaxial with the solenoid housing  14 . The solenoid retainer  18 , clapper  20 , and clapper spring  22  may all be in contact with the working media, and therefore may be made of a corrosion resistant material such as stainless steel. In particular, the clapper  20  may be made of a magnetically active, solenoid-quality stainless steel so that the clapper  20  may serve as a magnetized armature of a solenoid. The mass of the clapper  20  may be minimized to reduce the effects of shock and vibration on the sealing aspects of the valve  10 . 
     The solenoid retainer  18  may define an interior space that contains all or part of a solenoid  30 . The solenoid  30  may be any suitable solenoid for actuation the clapper  20  as an armature as described below. In some embodiments, the solenoid  30  may be a solid core solenoid having a wire coil  32  wrapped around a bobbin  34  and a magnetically active pole piece  36  that encircles the wire coil  32 , extends over the top (i.e., the distal end) of the wire coil  32 , and then extends through the wire coil  32  via the cylindrical interior of the bobbin  34 . Due to the isolation of the wire coil  32 , bobbin  34 , and pole piece  36  from the corrosive working media in the valve  10  as described below, a wide range of lightweight materials may be used for the components of the solenoid  30  without concern for the deleterious impact of the working media on the materials. 
     As shown in  FIG. 3  and in more detail in  FIG. 4 , the wire coil  32 , bobbin  34 , and pole piece  36  are isolated from the working media of the valve by a precisely machined flat, thin barrier member  40  attached at the proximal end of the solenoid retainer  18  to create a closed end of the solenoid retainer  18  that seals the solenoid  30  (i.e., the wire coil  32 , bobbin  34 , and pole piece  36 ) within the solenoid retainer  18  and isolates the solenoid  30  from the actuator chamber. The barrier member  40  may be entirely magnetically inert so as not to interfere with the magnetic flux of the solenoid  30  and its interaction with the clapper  20 . In some embodiments, the barrier member  40  may be an austenitic stainless steel. Furthermore, the barrier member  40  may have the minimum thickness that is still sufficient to isolate the solenoid  30  from the working media, in a range of about 0.005 to 0.1 inches. The minimum thickness further alleviates interference of the barrier member  40  with the magnetic flux of the solenoid  30 . The barrier member  40  is rigid and unmoving, and may be a metal plate having planar surfaces that provide a uniform contact surface for the clapper  20 . The rigid, stationary, and uniform contact surface allows for precise operation of the clapper  20  and reduces wear on the clapper  20 . The barrier member  40  may be the same material as the solenoid retainer  18 , and may be permanently attached to the solenoid retainer  18  by welding or other means. The barrier member  40  may be supported along all or a portion of its surface that faces the solenoid  30  by one or more components of the solenoid  30 . In some embodiments, the barrier member  40  may contact and be structurally supported by the pole piece  36 . This prevents bowing or other deformation of the very thin barrier member  40 . A magnetically inert filler  50 , such as epoxy, may fill any space between the bobbin  34  and the barrier member  40  to hold the bobbin  34  in place and further support the barrier member  40 . 
     In some embodiments, the clapper  20  may be biased away from the barrier member  40  by the clapper spring  22  when the solenoid  30  is de-energized, leaving a gap  42  of a prescribed dimension that is accounted for in the valve  10  stroke length design. The gap  42  may be significantly wider than the barrier member  40  is thick, such that the barrier member  40  accounts for a small percentage, such as 15%-20%, of the distance between the clapper  20  and the solenoid  30 . That is, the gap  42  may be at least five times the thickness of the barrier member  40 . The gap  42  between the barrier member  40  and the clapper  20  may be present at all times, except at the end of the valve stroke as follows: when the solenoid  30  is energized, it creates a magnetic flux through the pole piece  36  that crosses the barrier member  40  and the gap  42  and pulls the clapper  20  into contact with the barrier member  40  while compressing the clapper spring  22 . In other embodiments, the clapper  20  may be biased against the barrier member  40  when the solenoid  30  is de-energized, and energizing the solenoid  30  pushes the clapper  20  away from the barrier member  40  to create the gap  42  as described above. 
     The clapper  20  has a contact face  44  that is parallel to and may contact or otherwise move into physical abutting relation with the barrier member  40  when the solenoid is energized. However, the contacting surfaces of the barrier member  40  and clapper  20  may be so precisely machined that wringing (also known as the Jo block effect) occurs. That is, the clapper  20  may adhere to the barrier member  40  at the contacting surfaces. When the solenoid  30  is de-energized, at worst the clapper  20  and barrier member  40  may remain adhered together, sticking the valve  10  closed. In a less extreme case, the clapper spring  22  applies sufficient force to the clapper  20  to overcome the Jo block effect and push the clapper  20  to its open position, but the wringing adds several milliseconds or more to the valve  10  operation. 
     To overcome the Jo block effect between the clapper  20  and the barrier member  40 , the contact face  44  of the clapper  20  may have one or more recessed areas  46  at the contact face  44 . See  FIG. 5 . The recessed areas  46  may be undercuts formed by removing a thin layer of material from the contact face  44 . Undercutting prevents contact of the contact face  44  with the barrier member  40  in the recessed areas  46 , which reduces and may eliminate wringing between the clapper  20  and the barrier member  40 . In the illustrated embodiment, the recessed area  46  is disposed between an inner disc  48  and an outer ring  49  of the contact face  44  that will still contact the barrier member  40  across from the inner and outer portions, respectively, of the pole piece  36  to facilitate the magnetic flux through the clapper  20 . 
     Referring to  FIG. 6 , the clapper  20  may have a valve mount  52  that aligns with the coaxial port  28  at the proximal end of the solenoid housing  14 . The coaxial port  28  may receive an attachment arm  64  of a poppet rod  60 . The attachment arm  64  may have a threaded end that mates with a threaded recess in the valve mount  52  of the clapper  20  to attach the poppet rod  60  to the clapper  20 . The poppet rod  60  may have a cylindrical, substantially hollow poppet body  62  made of a non-corrosive material, such as stainless steel. The mass of the poppet rod  60  may be minimized to reduce the effects of shock and vibration on the sealing aspects of the valve  10 . 
     The poppet body  62  may have opposite-facing sealing edges  66 ,  68  at opposing ends of the poppet body  62 . That is, a distal sealing edge  66  at the distal end of the poppet body  62  may project distally from the poppet body  62  and contact a distal seat  80 , and a proximal sealing edge  68  at the proximal end of the poppet body  62  may project proximally from the poppet body  62  and contact a proximal seat  82 . The poppet body  62  may define an internal flow passage  70  that opens out of the proximal end of the poppet body  62  inside the perimeter of the proximal sealing edge  68 . A channel  72  may be disposed in the poppet body  62  and may extend from the distal end of the poppet body  62 , inside the perimeter of the distal sealing edge  66 , to the flow passage  70 . The flow passage  70  and channel  72  together form a fluid flow path through the length of the poppet body  62 . 
     The distal seat  80  may be disposed in a recess at the proximal end of the solenoid housing  14 , surrounding a bulkhead  54  of the coaxial port  28 . The distal seat  80  may receive a distal o-ring  81  that prevents media leakage past the distal seat  80 . The proximal seat  82  may be disposed in a recess at the proximal end of the valve chamber, between the inner surface of the valve housing  12  and the outlet port bulkhead  90 . The proximal seat  82  may receive a proximal seat o-ring  83  that prevents media leakage past the proximal seat  82 . The seats  80 ,  82  may be annular members and may be made of an at least partially deformable polymer that is compatible with the media used in the valve  10 , and may further be compatible with any media used in associated systems. The polymer may be a plastic, particularly a thermoplastic. The polymer may be a polytetrafluoroethylene (PTFE) material, such as TEFLON by DuPont Co. The PTFE may have a very high purity, up to 100% or “virgin grade.” However, while virgin PTFE has improved chemical and thermal resistance properties over “mechanical grade” PTFE, which may contain additives, virgin PTFE has a tendency to cold-flow. In a critical application where virgin PTFE is preferred, the seats  80 ,  82  may be held in place by the valve  10  components as described herein. The polymer may alternatively be a polychlorotrifluoroethylene (PCTFE) material, which exhibits less creep than PTFE but is also stiffer. The seat  80 ,  82  material should be pliant enough to allow the corresponding sealing edges  66 ,  68  to sink into the seat  80 ,  82  and create the necessary bubble-tight seal. 
     The sealing edges  66 ,  68  may each be a knife edge, which is a ring of poppet material that tapers down to a minimum width that allows the knife edge to closely interface with the corresponding seat  80 ,  82  and form a bubble-tight seal. The minimum width of the knife edge may be about 0.002 inches. The depth to which each sealing edge  66 ,  68  sinks into its respective seat  80 ,  82  may depend on the minimum knife edge width and on the seat  80 ,  82  material hardness. As shown in  FIG. 7 , the maximum depth of the sealing edge  66 ,  68  penetration may additionally or alternatively be controlled to a predetermined compression by an adjacent stop surface, such as the proximal stop surface  78  (or a corresponding distal stop surface), that is the external surface of the poppet body  62  inside the associated sealing edge. The sealing edge  66 ,  68  can only compress the seat  80 ,  82  until the stop surface engages a metal surface (e.g., a metal surface  90  contacted by the proximal stop surface  78 ) and can move no further. This limit protects the seats  80 ,  82 , particularly the proximal seat  82 , from becoming over-stressed at high spring loads. This allows higher preloading of the clapper spring  22 , which in turn allows for better sealing capability at high vibration and shock levels. 
     Returning to  FIG. 6 , the valve housing  12  may have a valve chamber in which the poppet rod  60  is centrally disposed. One or more ports may be disposed through the wall of the valve housing  12  into the valve chamber, such as in the illustrated example configuration. An outlet port  92  may be disposed through the proximal end of the valve housing  12 , and may be surrounded by the outlet port bulkhead  90 . A proximal port  94  may be disposed through the valve housing  12  near the proximal end, and a distal port  96  may be disposed through the valve housing  12  near the distal end. In some embodiments, both the proximal port  94  and the distal port  96  may be inlet ports that deliver a working media to the valve under pressure. The same or different working media may be delivered to the valve  10  at the same or different pressures, and the media may fill the voids within the chambers of the housings  12 ,  14  and then be released through the outlet port  92  depending on the position of the poppet rod  60 . In other embodiments, and as described further below, the proximal port  94  may be an inlet port delivering a highly pressurized working media to the valve  10 , and the distal port  96  may be a vent that relieves the pressure in the valve depending on the position of the poppet rod  60 . 
     One or more rod guides  100 ,  110  may be disposed in the valve chamber. The rod guides  100 ,  110  will be in contact with the working media and therefore may be an anti-corrosive material, such as stainless steel. The rod guides  100 ,  110  may be precisely machined to abut both the inner surface of the valve housing  12  and the outer surface of the poppet body  62  of the poppet rod  60 , in order to secure the poppet rod  60  coaxially with the clapper  20 . The rod guides  100 ,  110  may further define media chambers  102 ,  112  in communication with the ports  94 ,  96  and adjacent to the sealing edges  66 ,  68  of the poppet rod  60 . The rod guides  100 ,  110  may further abut the seats  80 ,  82  to hold the seats  80 ,  82  in place. Finally, the rod guides  100 ,  110  may support a dynamic seal  98  with the poppet rod  60 . The dynamic seal  98  may prevent leakage of media between the ports  94 ,  96  and may stabilize the moving components of the valve  10  (i.e., the poppet rod  60  and clapper  20 ) while the valve  10  is subjected to vibration. Furthermore, the dynamic seal  98 , together with the seals formed by the sealing edges  66 ,  68  and the seats  80 ,  82 , may provide pressure balancing of the poppet rod  60  by all having essentially identical effective surface areas. Thus, the poppet rod  60  is entirely pressure balanced throughout the entire stroke and is essentially unaffected by pressure in any of the fluid paths. The pressure balancing allows for significant reductions in the size of the valve  10 , as well as significantly increases the efficiency of the valve  10 . 
     The proximal rod guide  100  may abut the proximal seat  82  along the portion of the proximal seat&#39;s  82  proximal surface that is outside of the ring where the proximal sealing edge  68  contacts the proximal seat  82 . The proximal rod guide  100  may extend from the proximal seat  82 , across the proximal port  94 , distally to the distal port  96 . A guide o-ring  101  may prevent media leakage between the proximal rod guide  100  and the valve housing  12 . A proximal media chamber  102  may be disposed within the proximal rod guide  100  near its proximal end. Specifically, the proximal media chamber  102  may extend from the proximal port  94  through the proximal end of the proximal rod guide  100 , leaving a substantially cylindrical space that is in fluid communication with the outlet port  92  and receives the proximal end of the poppet rod  60 . A seal recess  104  disposed in the distal end of the proximal rod guide  100  may retain the dynamic seal  98  between the proximal rod guide  100  and the poppet rod  60 . The dynamic seal  98  may be any suitable dynamic sealing mechanism, such as an o-ring supported by additional seat material. 
     The distal rod guide  110  may abut the distal seat  80  along the portion of the distal seat&#39;s  80  distal surface that is outside of the ring where the distal sealing edge  66  contacts the distal seat  80 . The distal rod guide  110  may contact an inner surface of the solenoid housing  14 , and may extend from the distal seat  80 , proximally across the distal port  96  and into abutment with the proximal rod guide  100 . A neck  114  of the distal rod guide  110  may extend into the seal recess  104  of the proximal rod guide  100  and abut the dynamic seal  98 . A distal media chamber  112  may be disposed within the distal rod guide  110 , extending from the distal port  96  through the distal end of the distal rod guide  110 , leaving a substantially cylindrical space that is in fluid communication with the coaxial port  28  and receives the distal end of the poppet rod  60 . 
     When the solenoid  30  is de-energized, the poppet rod  60  thus is normally closed against the proximal seat  82  and open away from the distal seat  80  due to the clapper spring  22  pressing “down” (i.e., in the proximal direction) on the clapper  20  and the attached poppet rod  60 . See  FIG. 6 . In this “closed” position, the proximal media chamber  102  is sealed off from the outlet port  92  by the proximal sealing edge&#39;s  68  penetration into the proximal seat  82 , and the distal media chamber  112  is open across the distal sealing edge  66 . With respect to the flow path of pressurized media in the valve  10 , in this “normally closed” position, the media delivered through the proximal port  94  pressurizes the proximal media chamber  102  around the proximal sealing edge  68 , while the outlet port  92  is open to vent through the distal port  96 . Thus, any pressure in the valve  10  is relieved. If the valve  10  is a pilot valve for a device attached to the outlet port  92 , the pressure relief may actuate that device. 
     When the solenoid  30  is energized, the magnetic flux overcomes the biasing force of the clapper spring  22  and the clapper  20  is pulled into contact or near-contact with the barrier member  40 , in turn pulling “up” (i.e., in the distal direction) the poppet rod  60  to seal the distal sealing edge  66  against the distal seat  80  and open the proximal sealing edge  68  away from the proximal seal  82 . See  FIG. 8 . In this “open” position, the distal media chamber  112  is sealed off from the outlet port  92  by the distal sealing edge&#39;s  66  penetration into the distal seat  80 , and the proximal media chamber  102  is open across the proximal sealing edge  68 . With respect to the flow path of pressurized media in the valve  10 , in this “open” position, the pressurized media delivered through the proximal port  94  may travel into the proximal media chamber  102 , across the proximal sealing edge  68 , and up through the poppet rod  60  into the distal housing  12 , pressurizing the valve  10  before traveling out of the outlet port  92 . De-energizing the solenoid  30  causes the clapper  20  to drop out to the normally closed position without adhering to the barrier member  40 . 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, 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 description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. Explicitly referenced embodiments herein were chosen and described in order to best explain the principles of the disclosure and their practical application, and to enable others of ordinary skill in the art to understand the disclosure and recognize many alternatives, modifications, and variations on the described example(s). Accordingly, various embodiments and implementations other than those explicitly described are within the scope of the following claims.