Abstract:
A magnetically actuated valve system for controlling fluid flow through a first conduit and a second conduit. A first sealing structure associated with the first conduit is moveable in response to a magnetic force to an open position and spring biased toward a closed position. The closed position prevents fluid flow through the first conduit. A second sealing structure associated with the second conduit is moveable in response to a magnetic force in a second direction, substantially opposite to the first direction, to an open position and biased toward a closed position. The closed position prevents fluid flow through the second conduit. A magnetic actuator assembly is constructed and arranged to actuate the first and second sealing assemblies substantially simultaneously by moving the first and second sealing structures in the first and second directions, respectively.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to a magnetically actuated valve system and more specifically to a magnetically actuated valve system in which at least two solenoid valves are actuated by a single electromagnetic actuator. 
     BACKGROUND OF THE INVENTION 
     In typical electromagnetically actuated propellant valves used in bi-propellant systems, a first propellant (fuel) flows through an upstream valve to a downstream valve such that the first propellant will be directed into contact with a second propellant (oxidizer) flowing through a second upstream valve to a second downstream valve within a thruster portion of an engine or the like, whereby the combined propellant will be ignited. The flow of each of the first and second propellants is simultaneously controlled and maintained in the correct proportions by a single magnetic circuit actuating two magnetically linked valves, each housed in a manifold assembly. 
     U.S. Pat. Nos. 3,443,585, 3,472,277 and 4,223,698 disclose various magnetically actuated valve systems wherein a single electromagnetic excitation will actuate each of two valve members, each of which serves its own pressure-fluid flow. In the ′585 patent, a permanent magnet is the common middle element of two separate solenoid-actuated magnetic circuits. Excitation of one solenoid opens both valves; excitation of the other solenoid closes both valves; and the permanent magnet holds the actuated condition of both valves. The ′277 and ′698 patents each disclose an electromagnetic actuating system wherein a single solenoid coil actuates two magnetically linked valves to open condition, against the preload of springs to load valve members in the valve-closing direction. In all cases, construction is highly specialized and complex, leading to unduly expensive products. 
     U.S. Pat. No. 5,450,876 discloses an electromagnetically actuated multiple-valve construction within a single welded housing which contains each of two series-connected valves and a single magnetic circuit for concurrently operating an upstream and a downstream valve. 
     Consequently, there exists a need in the art for a valve system having the functional advantages of the ′876 patent without a welded construction, which adds weight. There also exists a need in the art for a magnetically actuated valve system to provide a pair of magnetically operated valves movable between a power applied and a power removed position by a magnetic solenoid actuator assembly for simultaneously controlling and maintaining first and second propellants in the correct proportions through separate manifold assemblies of a single system. There also exists a need in the art to make a magnetically actuated valve system that is simpler, lighter and more cost effective. 
     BRIEF SUMMARY OF THE INVENTION 
     To meet the described need, one aspect of the invention provides a magnetically actuated valve system. The magnetically actuated valve system comprises a first conduit and a second conduit. A first sealing structure is moveable in response to a magnetic force to an open position and spring biased toward a closed position. The closed position prevents fluid flow through the first conduit. A second sealing structure is moveable in response to a magnetic force in a second direction, substantially opposite to the first direction, to an open position and biased toward a closed position. The closed position prevents fluid flow through the second conduit. A magnetic actuator assembly is constructed and arranged to actuate the first and second sealing assemblies substantially simultaneously by moving the first and second sealing structures in the first and second directions, respectively. 
     Other objects, features, and advantages of the present invention will become apparent form the following detailed description, the accompanying drawings, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a cross section of a magnetically actuated valve system taken along the line  1 — 1  of FIG. 3 with the power removed; 
     FIG. 2 is a cross section of the magnetically actuated valve system similar to FIG. 1, but with the power applied; 
     FIG. 3 is a perspective view of the preferred embodiment of the magnetically actuated valve system embodying the principles of the present invention; 
     FIG. 4 is a perspective exploded view of the magnetically actuated valve system shown in FIG. 3; 
     FIG. 5 is an enlarged perspective view of an S-spring of the magnetically actuated valve system shown in FIG. 4; 
     FIG. 6 is an enlarged cross section similar to FIG. 1 showing an upstream fuel valve and an upstream oxidizer valve with the power removed; 
     FIG. 7 is an enlarged cross section similar to FIG. 6 showing the upstream fuel valve and the upstream oxidizer valve, but with the power applied; 
     FIG. 8 is a further enlarged cross section of the magnetically actuated valve system similar to FIG. 6 showing the upstream fuel valve; and 
     FIG. 9 is a further enlarged cross section similar to FIG. 8 showing the downstream fuel valve of the magnetically actuated valve system; 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now more particularly to the drawings, FIGS. 1-9 show a preferred embodiment of a magnetically actuated valve system of the present invention. The magnetically actuated valve system comprises a first conduit, generally indicated at  10  and a second conduit generally indicated at  11  for providing fluid flowpaths for a fuel and an oxidizer, respectively. Fuel conduit  10  is machined or etched into a fuel manifold assembly, generally indicated at  12 , to provide the fuel flowpath and has sealing structures  28 ,  30  disposed therein. Oxidizer conduit  11  is machined or etched into an oxidizer manifold assembly, generally indicated at  14 , to provide the oxidizer flowpath and has sealing structures  36 ,  38  disposed therein. Each manifold assembly  12 ,  14  can be formed in the manner disclosed in copending U.S. patent application Ser. No. 09/257,186, the entire disclosure of which is incorporated herein by reference. 
     Magnetic solenoid actuators  48 ,  50  are disposed within a magnetic actuator assembly housing structure, generally indicated at  16 . Magnetic solenoid actuator  48  is constructed and arranged to exert a magnetic force on sealing structures  28 ,  36  to substantially simultaneously actuate the same in opposite directions relative to one another. Magnetic solenoid actuator  50  is constructed and arranged to exert a magnetic force on sealing structures  30 ,  38  to substantially simultaneously actuate the same in opposite directions relative to one another. 
     As best illustrated in FIGS. 1 and 2, fuel manifold assembly  12  and oxidizer manifold assembly  14  are of identical construction and are similarly described hereinbelow. Fuel manifold assembly  12  includes a pair of valve seats  24 ,  26  machined therein, by standard machining techniques, diffusion bonding or electron beam welding, to define an upstream and a downstream fuel valve, respectively. Valve seats  24 ,  26  are configured and positioned at inlets  91 ,  95  of the upstream and the downstream fuel valves, respectively. Similarly, oxidizer manifold assembly  14  comprises a pair of valve seats  32 ,  34  machined therein, by standard machining techniques, diffusion bonding or electron beam welding, to define an upstream and a downstream oxidizer valve, respectively. It may also be preferable to etch valve seats  24 ,  26  and  32 ,  34  in fuel and oxidizer manifold assemblies  12 ,  14 , respectively, as taught in U.S. patent application Ser. No. 09/257,186, cited earlier herein. Valve seats  32 ,  34  are configured and positioned at each inlet  101 ,  105  of the upstream and downstream oxidizer valves, respectively. 
     As best shown in FIGS. 1-4, magnetic actuator assembly housing structure  16  comprises a pair of circumferentially extending magnetic actuator assembly receiving portions  40  integral with one another. Each circumferentially extending magnetic actuator assembly receiving portion  40  provides a groove  41  for carrying a sealing structure  46 , with each groove  41  positioned on the opposite longitudinal ends of each magnetic actuator assembly receiving portion  40 . As best shown in FIGS. 3 and 4, a pair of generally tubular fastener receiving portions  42  integrally extends from each magnetic actuator assembly receiving portion  40 . Each fastener receiving portion  42  has one threaded fastener receiving orifice  44   a  on one longitudinal end thereof and another threaded fastener receiving orifice (not shown) on the opposite longitudinal end thereof. Magnetic actuator assembly housing structure  16  preferably is made of a low magnetic flux capacity material. It may be preferable to for magnetic actuator housing structure  16  to be made from aluminum or titanium. Housing structure  16  may be cast, forged or machined. 
     As best shown in FIG. 4, the magnetic actuator assembly comprises upstream magnetic solenoid actuator  48  and downstream magnetic solenoid  50 . Upstream magnetic solenoid actuator  48  moves the fuel sealing structure  28  and the oxidizer sealing structure  36  to a power applied, open position. Similarly, downstream magnetic solenoid  50  moves fuel sealing structure  30  and oxidizer sealing structure  38  to a power applied, open position. Magnetic solenoid actuators  48 ,  50  are installed within magnetic actuator assembly receiving portions  40  of magnetic actuator assembly housing structure  16 . Upstream and downstream magnetic solenoid actuators  48 ,  50  comprise solenoid cases  52 , each of which generally surrounds a centrally positioned solenoid core  54 . Each solenoid core  54  extends through a conductive coil  56 , for example of copper, such that each conductive coil  56  is generally surrounded by solenoid case  52  on their radial exterior. It is contemplated that the two magnetic solenoid actuators  48 ,  50  may be operated independently or coupled electrically in series or parallel to normally operate substantially simultaneously, as further described below. 
     Isolation caps  58   a,    58   b,    58   c,    58   d  engage opposite longitudinal sides of magnetic solenoid actuators  48 ,  50 , respectively, to retain each magnetic solenoid actuator  48 ,  50  within one of circumferentially extending magnetic actuator assembly receiving portions  40  of magnetic actuator assembly housing structure  16 . Isolation caps  58   a,    58   c  are welded to fuel manifold assembly  12 . Isolation caps  58   b,    58   d  are welded to oxidizer manifold assembly  14 . Isolation caps  58   a,    58   b,    58   c,    58   d  may be made from titanium or any other low flux capacity material capable of exposure to the propellants and suitable for being welded to manifolds  12 ,  14 . 
     Fuel sealing structure  28  includes a fuel armature member  64 , an S-spring  68  and a sealing portion  72 . Fuel sealing structure  30  is disposed downstream from fuel sealing structure  28  and includes a downstream fuel armature member  66  positioned downstream from upstream fuel armature member  64 , an S-spring  70  and a sealing portion  74 . S-springs  68 ,  70  bias sealing structures  28 ,  30  in closed positions to prevent fuel flow through first conduit  10 . Fuel sealing structures  28 ,  30  are enclosed within fuel manifold  12  by isolation caps  58   a,    58   c.    
     Similarly, oxidizer sealing structure  36  includes an oxidizer armature member  76 , an S-spring  80  and a sealing portion  84 . Oxidizer sealing structure  38  is disposed downstream from oxidizer sealing structure  36  and includes a downstream oxidizer armature member  78  positioned downstream from upstream oxidizer armature member  76 , an S-spring  82  and a sealing portion  86 . S-springs  80 ,  82  bias sealing structures  36 ,  38  into closed positions to prevent oxidizer flow through second conduit  11 . Oxidizer sealing structures  36 ,  38  are enclosed within oxidizer manifold  14  by isolation caps  58   b,    58   d.    
     It might be preferable for fuel and oxidizer manifold assemblies  12 ,  14  to include a plurality of diffusion bonded layers of sheet material, for example of titanium, having conduits  10 ,  11  etched therein to provide passageways for fuel and oxidizer respectively in the manner disclosed in copending U.S. patent application Ser. No. 09/257,186. 
     Various fuels and oxidizers could be used within fuel and oxidizer manifold assemblies  12 ,  14 ; however, the preferred fuel used in fuel manifold assembly  12  is monomethylhydrazine (MMH) and the preferred oxidizer used in oxidizer manifold assembly  14  is nitrogen tetroxide (N 2 O 4 ). The fuel may flow through fuel manifold assembly  12  and oxidizer may flow through oxidizer manifold assembly  14  in a liquid or gaseous state. 
     FIG. 5 is an enlarged perspective view showing S-spring  68 , but could be representative of any other S-spring  70 ,  80  or  82 . S-springs  68 ,  70 ,  80  and  82  are preferably flat discs having interior walls  69  defining serpentine slots therein. The interior walls  69  are circumferentially positioned around S-springs  68 ,  70 ,  80  and  82  in interposing relation between an inner section  71  of each S-spring  68 ,  70 ,  80  and  82  and an outer rim  73  of the same S-spring  68 ,  70 ,  80  and  82 . It may be preferable for S-springs  68 ,  70 ,  80  and  82  to be made from ductile, high strength materials with low magnetic flux capacity such as 316L CRES, or 17-4 PH CRES. It is contemplated that disc springs, leaf springs or other spring members may be capable of biasing sealing members  28 ,  30 ,  36 ,  38  against valve seats  24 ,  26 ,  32 ,  34 , respectively. The deflection and preload force of S-springs  68 ,  70 ,  80  and  82  is permanently set by the thickness of spacing shim stack  88   a.  Shim stack  88   a  is used to adjust isolation caps  58   a,    58   c  and  58   b,    58   d  to a position flush with manifold assembly  12 ,  14 , respectively. 
     As best shown in FIGS. 1-3 and  6 - 9 , fuel manifold assembly  12  and oxidizer manifold assembly  14  further comprise an inlet  90   a,    90   b,  a main body portion  92   a,    92   b  and a thruster interface port  94   a,    94   b,  respectively. Inlet  90   a,  which is preferably tubular or a thread fitting, extends integrally and is welded to main body portion  92   a.  Likewise, inlet  90   b,  which is preferably tubular or a thread fitting, extends integrally and is welded to main body portion  92   b.  Inlets  90   a,    90   b  are preferably made from titanium, but could be any other suitable low flux capacity material for maintaining fuel and oxidizer in separate flowpaths. Inlets  90   a,    90   b  have an etched disc, diffusion buffed or similar inlet filter  96   a,    96   b  and an inlet plug  97   a,    97   b,  respectively, installed therein. As best shown in FIGS. 1,  2 ,  6  and  7 , inlet plug  97   a  is welded within conduit  10  between inlet  91  and outlet  93  of the upstream fuel valve. Similarly, inlet plug  97   b  is welded within conduit  11  between inlet  101  and outlet  103  of the upstream oxidizer valve. 
     Main body portion  92   a  of fuel manifold assembly  12  has conduit  10  etched or machined therein and main body portion  92   b  of oxidizer manifold assembly  14  has conduit  11  etched or machined therein. 
     Referring back to FIGS. 3 and 4, a pair of circumferentially raised walls  98   a,    98   b  integrally extends from each main body portion  92   a,    92   b  and may have edges spaced from one another, as best shown for the pair of raised walls  98   b  in FIG.  4 . Each pair of raised walls  98   a,    98   b  defines armature receiving spaces, of which only spaces  99   b  are shown in FIG.  4 . Raised walls  98   a,    98   b  could be separate from main body portions  92   a,    92   b,  respectively, and positioned in abutting relation thereto to define armature receiving spaces  99   a,    99   b,  respectively. A pair of fastener receiving openings  100   a,    100   b  integrally extends from opposite sides of main body portions  92   a,    92   b,  respectively. A pair of mounting openings  104   a  and  104   b  passes through main body portions  92   a,    92   b  on opposite sides of respective thruster interface ports  94   a,    94   b  for mounting fuel and oxidizer manifold assemblies  12 ,  14  to the thruster. Thruster interface ports  94   a,    94   b  are disposed on the opposite longitudinal ends of each manifold assembly  12 ,  14  from respective inlets  90   a,    90   b.    
     Upstream and downstream fuel armature members  64 ,  66  and upstream and downstream oxidizer armature members  76 ,  78  are preferably flat discs made from high flux capacity material that is compatible with the propellants such as corrosion resistant steel (CRES), for example of XM-27 CRES, and are resistance welded to S-spring  68 ,  70 , respectively. When inner sections  71  of S-springs  68 ,  70  are joined to upstream and downstream fuel armature members  64 ,  66 , respectively, sealing portions  72 ,  74  are captured therebetween such that sealing portions  72 ,  74  extend through center opening  75  of S-springs  68 ,  70 , respectively. Sealing portions  72 ,  74  may be made from polytetrafluoroethylene (PTFE) or any other suitable material for circumferentially sealing against valve seats  24 ,  26 , respectively, to seal the upstream and downstream fuel valves, respectively. 
     Similarly, upstream and downstream oxidizer armature members  76 ,  78  are made from high flux capacity material that is compatible with the propellants such as corrosion resistant steel (CRES), for example of XM-27 CRES, and are resistance welded to S-spring  80 ,  82 , respectively. When the inner sections  71  of S-springs  80 ,  82  are joined to upstream and downstream oxidizer armature members  76 ,  78 , respectively, sealing portions  84 ,  86  are captured therebetween such that sealing portions  84 ,  86  extend through center opening  75  of S-springs  80 ,  82 . Sealing portions  84 ,  86  may be made from polytetrafluoroethylene (PTFE) or any other suitable material for circumferentially sealing against valve seats  32 ,  34 , respectively to seal the upstream and downstream oxidizer valves, respectively. 
     Upstream and downstream fuel armature members  64 ,  66  are installed within the armature receiving spaces defined by circumferentially raised walls  98   a  extending from fuel manifold assembly  12 . Sealing portions  72 ,  74  contact valve seats  24 ,  26 , respectively, of fuel manifold assembly  12 . As isolation caps  58   a,    58   b  are installed, the outer rim of each S-spring  68 ,  70  is deflected developing a preload on sealing portions  72 ,  74  against valve seats  24 ,  26 , respectively. Isolation caps  58   a,    58   c  are welded to fuel manifold assembly  12  to prevent external leakage of fuel. 
     Similarly, upstream and downstream oxidizer armature members  76 ,  78  are installed within armature receiving spaces  99   b  defined by circumferentially raised walls  98   b  extending from oxidizer manifold assembly  14 . Sealing portions  84 ,  86  contact valve seats  32 ,  34 , respectively, of oxidizer manifold assembly  12 . As isolation caps  58   a,    58   b  are installed, the outer rim of each S-spring  80 ,  82  is deflected developing a preload on sealing portions  84 ,  86  against valve seats  32 ,  34 , respectively. Isolation caps  58   b,    58   d  are welded to oxidizer manifold assembly  14  to prevent external leakage of oxidizer. FIG. 4 illustrates the alignment of fastener receiving openings  100   a  of fuel manifold assembly  12  with threaded fastener receiving orifices  44   a  of fastener receiving portions  42 . Similarly, fastener receiving openings  100   b  of oxidizer manifold assembly  14  align with the threaded fastener receiving orifices (not shown) on the opposite longitudinal end of fastener receiving portions  42 . A plurality of fasteners  106   a  and  106   b  are in the form of tie wired cap screws and have one threaded end thereof. Fasteners  106   a  extend through fastener receiving openings  100   a  and into threaded fastener receiving orifices  44   a  to fixedly secure fuel manifold assembly  12  to magnetic actuator assembly housing  16 . 
     Fasteners  106   b  extend through fastener receiving openings  100   b  and into the threaded fastener receiving orifices (not shown) on the opposite ends as threaded fastener receiving orifices  44   a  to fixedly secure oxidizer manifold assembly  14  and magnetic actuator assembly housing  16  together. It should be noted that in FIGS. 1-9, oxidizer manifold assembly  14  could be shown mounted above magnetic actuator assembly housing structure  16  and fuel manifold assembly  12  could be shown mounted below magnetic actuator assembly housing structure  16 . 
     After titanium fuel and oxidizer manifold assemblies  12 ,  14  are attached to magnetic actuator assembly housing  16 , magnetic solenoid actuators  48 ,  50  are protected from the ambient environment. Sealing structures  46 , preferably in the form of O-rings, are disposed between manifold assemblies  12 ,  14  and magnetic actuator assembly housing structure  16  within each groove  41  to environmentally seal the enclosure, as best shown in FIGS. 1 and 2. It may be preferable for the O-rings to be made from silicone. 
     OPERATION 
     The integrity of each seal may be tested by energizing only one of magnetic solenoid actuators  48 ,  50  at a time. With one actuator energized and fluids under pressure supplied to both inlets  90   a  and  90   b,  the integrity of the seals controlled by the other actuator will be tested. In normal operation, both actuators are energized in unison. 
     Referring to FIGS. 1,  2  and  6 - 9 , the operation of the magnetically actuated valve system will be fully described below. The operation of fuel manifold assembly  12  will be described as fuel flows from inlet  90   a  through upstream fuel valve  28  and downstream fuel valve  30  to thruster interface port  94   a  within fuel manifold assembly  12 . Fuel inlet filter  96   a  protects the upstream and downstream fuel valves from impurities or harmful agents that could deter operation of the upstream and downstream fuel valves. The passing fuel flows through fuel inlet filter  96   a  before reaching inlet  91  for the upstream fuel valve. The upstream fuel valve controls the fuel flow to inlet  95  for the downstream fuel valve, which in turn controls fuel flow to thruster interface port  94   a.    
     Fuel enters fuel manifold assembly  12  through fuel inlet  90   a  where inlet plug  97   a  directs its flow through fuel filter  96   a  and into the inlet for the fuel upstream valve. Fuel flows into the fuel upstream valve through inlet  91 , which is in the form of an opening in fuel manifold assembly  12 . Conduit  10  in the main body portion  92   a  of fuel manifold assembly  12  connects outlet  93  of the upstream fuel valve to inlet  95  of the downstream fuel valve. The downstream fuel valve discharges into the thruster through thruster interface port  94   a.  The thruster may be included within a spacecraft engine, or any other suitable engine in which two fluids are delivered to combustion chambers. 
     Before power is applied to coils  56  of upstream and downstream actuators  48 ,  50 , S-springs  68 ,  70  firmly preload sealing portions  72  and  74  against valve seats  24 ,  26 , respectively. As described above, the preload is sufficient to close and seal the upstream and downstream fuel valves against leakage and to prevent liftoff under worst-case vibration loading. 
     When power is applied to coil  56  of upstream magnetic solenoid actuator  48 , a magnetic flux is generated in a magnetic circuit consisting of core  54 , case  52 , and upstream fuel armature member  64 . The magnetic flux in the air gap between each upstream fuel armature member  64 , case  52  and core  54  exerts an attractive force on upstream fuel armature member  64 . This attractive force overcomes the preload of S-spring  68  causing upstream fuel armature member  64  to be drawn up against isolation cap  58   a  lifting sealing member  72  off valve seat  24 . With sealing member  72  lifted off valve seat  24 , fuel is allowed to flow across valve seat  24  to the inlet for the downstream fuel valve. Upstream armature member  64  is held in the power applied, open position as long as power is applied to coil  56  of magnetic solenoid actuator  48 . 
     When power is applied to coil  56  of downstream actuator  50 , a magnetic flux is generated in a magnetic circuit consisting of core  54 , case  52 , and downstream fuel armature member  66 . The magnetic flux in the air gap between downstream fuel armature member  66 , case  52  and core  54  exerts an attractive force on downstream fuel armature member  66 . This attractive force overcomes the preload of S-spring  70  causing downstream fuel armature member  66  to be drawn up against the isolation cap  58   c  lifting sealing member  74  off valve seat  26 . With sealing member  74  off valve seat  26 , fuel is allowed to flow across valve seat  26  and through thruster interface port  94   a  into a thruster combustion portion of an engine, for example a spacecraft engine. Downstream armature member  66  is held in the power applied, open position as long as power is applied to coil  56  of magnetic solenoid actuator  50 . 
     When the power is removed from coils  56  of upstream and downstream magnetic solenoid actuators  48 ,  50 , the magnetic fields collapse, thus reducing the magnetic attracting force on upstream and downstream fuel armature members  64 ,  66  to virtually zero. Without magnetic force to oppose them, S-springs  68 ,  70  drive upstream and downstream fuel armature members  64 ,  66  and the sealing portions  72  and  74 , respectively, to the power removed, closed position and reapply the preload. 
     Because the operation and nature of oxidizer manifold assembly  14  is basically the same as for fuel manifold assembly  12 , it is therefore unnecessary to repeat details. Fuel and oxidizer simultaneously flow into and through conduits  10 ,  11  of fuel and oxidizer manifold assemblies  12 ,  14 , respectively, so that both fuel and oxidizer will be maintained in correct proportions therein and directed into the thruster portion of an engine whereby the fuel will be ignited. 
     Alternatively, a permanent magnet (not shown) could be inserted into each core  54  so that upstream and downstream actuators  48 ,  50  would be the same in construction and operation. Only the operation of upstream actuator  48  will be described below. 
     A first short electrical pulse is applied to coil  56  of upstream actuator  48  to generate a magnetic flux in a magnetic circuit consisting of case  52 , core  54  and upstream fuel armature member  64 . The magnetic flux in the air gap between each upstream fuel armature  64 , case  52  and core  54  exerts a larger attractive force on upstream fuel armature  64  than that of the permanent magnet. This attractive force overcomes the preload of S-spring  68  causing upstream fuel armature  64  to be drawn up against isolation cap  58   a  lifting seat member  72  off valve seat  24 . With sealing member  72  lifted off valve seat  24 , fuel is allowed to flow across valve seat  24  to the inlet for the downstream fuel valve. The permanent magnet positioned axially within core  54  holds upstream armature member  64  in the power applied, open position. 
     To reduce the magnetic attractive force on upstream armature member  64 , a second short electrical pulse having a reverse polarity of the first pulse is applied to coil  56  to create a magnetic flux polarity opposite of the permanent magnet. Reversed polarity of the electromagnet is preferably achieved by using a reversed polarity electric pulse or by providing a second coil along the same axis as coil  54  but with an opposite winding direction. Then, S-spring  68  would drive upstream fuel armature member  64  and sealing portion  72 , respectively, to the power removed, closed position and reapply the preload. The air gap between each upstream fuel armature member  64 , case  52  and core  54 , permanent magnet strength and spring constant of S-spring  68  are selected so that the permanent magnet is insufficiently powerful to exert an attractive force able to overcome the preload of S-spring  68  when in the closed position. 
     While the principles of the invention have been made clear in the illustrative embodiments set forth above, it will be apparent to those skilled in the art that various modifications may be made to the structure, arrangement, proportion, elements, materials, and components used in the practice of the invention. 
     It will thus be seen that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing preferred specific embodiments have been shown and described for the purpose of illustrating the functional and structural principles of this invention and are subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.