Abstract:
A power generator includes a fuel container adapted to hold a hydrogen containing fuel. A sliding valve is coupled between a fuel cell and a fuel container. A pressure responsive actuator is coupled to the two stage valve and the fuel container.

Description:
BACKGROUND 
     In some fuel cell based power generators, hydrogen is extracted from a fuel in the presence of water and then is introduced into a fuel cell to produce electricity. Power generators based on hydrogen generators and proton exchange membrane (PEM) fuel cells may contain valves to control the rate at which electricity is generated. Such valves may require precision parts and be very expensive to provide adequate seals when closed. There is a need for a valve that can better control the flow of water, hydrogen and/or oxygen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross section representation of a fuel cell based power generator having a slide valve according to an example embodiment. 
         FIG. 2  is a cross section of a portion of the power generator of  FIG. 1  illustrating a slide valve and fuel cell stack according to an example embodiment. 
         FIG. 3  is a cross section of a portion of the power generator illustrating an alternative slide valve and fuel cell stack according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims. 
       FIG. 1  is a cross section representation of a fuel cell based power generator  100  according to an example embodiment. Generator  100  includes a cathode output electrode  110  and an anode output electrode  115 . In one embodiment, the generator may be shaped similar to a commercially available dry cell battery, such that it can be substituted for the dry cell battery. A fuel chamber  120  may contain a hydrogen containing fuel that provides hydrogen to a fuel cell stack  125 , which is shown in expanded form in  FIG. 2 , wherein the numbering is consistent with  FIG. 1 . 
     Fuel cell stack  125  may include a proton exchange membrane (PEM), catalyst layer, gas diffusion layer, micro porous layer. An anode electrode  135  is coupled to the fuel cell stack  125  between the fuel cell stack  125  and the fuel chamber  120 . It is also coupled to the anode output electrode  115 . A cathode electrode  140  is coupled to the other side of the fuel cell stack, and is coupled to the cathode output electrode  110 . It may also be exposed to ambient conditions. 
     Between the fuel cell  125  and the hydrogen chamber  120  is a slide valve. The slide valve includes a fixed plate  145  and a movable plate  150  that are coupled in a sliding relationship in one embodiment. A hydrogen and water vapor permeable particulate filter may also be used between the fuel cell and the fuel or fuel chamber  120 . In one embodiment, the fixed plate  145  is supported in fixed position proximate or adjacent to the fuel chamber  120 , and the movable plate  150  is coupled to a flexible diaphragm  155 , that flexes in response to changes in pressure between the hydrogen pressure in the fuel chamber and ambient pressure. A hole  160  provides the diaphragm access to atmospheric pressure. The diaphragm  155  acts as a pressure responsive actuator that controls the slide valve. Each of the fixed plate  145  and movable plate  150  has openings that prevent flow when in a closed position and allow flow when the openings at least partially line up. 
     In one embodiment the valve responds to a pressure differential between ambient and the inside of the power generator. The fuel cell stack  125  is exposed at a desired pressure differential between hydrogen in the fuel container  120  and ambient. 
     In one embodiment the power generator is cylindrical in shape and the valve plates are concentric cylinders having mating holes. Fixed plate  145  and movable plate  150  correspond to an inner cylinder and an outer cylinder respectively. When a pressure differential exists across the membrane  155  such as when hydrogen pressure is greater than ambient pressure, the membrane  155  deflects and moves the outer cylinder  150  axially relative to the inner cylinder. The movement of the outer cylinder relative to the inner cylinder causes the holes to become misaligned, which closes the valve. 
     In one embodiment, o-rings  165  may be used between the plates or cylinders to provide sealing when the holes are misaligned. In one embodiment, the o-rings  165  are disposed within annular grooves  170  on the inner cylinder or fixed plate  145 . The o-rings  165  seal against the inside of the outer cylinder or movable plate  150  to seal the cylinders when the holes are misaligned, corresponding to the valve being closed. This provides a substantially sealed closed valve position. When substantially sealed, the conductance of the valve is approximately 1% or less than the fully open conductance. 
     In one embodiment, the o-rings  165  may be formed of a compressible material and may reside substantially within the annular grooves  170 . The compressibility of the material may minimize the effects of variations in size of the plates occurring during normal manufacturing. Nitrile, fluoroelastomers, Ethylene-Propylene, Copolymer of tetrafluoroethylene and propylene, FEP, PFA. O-ring cross section can be circular or rectangular. Wear rings or glide rings may also be used. 
     The plates in one embodiment are as thin as possible to maintain high conductance, while maintaining sufficient structural rigidity to move without collapse. Thicker sections on the perimeter of the outer plate running parallel to the direction of movement of the valve may be used to improve structural rigidity while maintaining high conductance. Likewise for the inner plate, where thicker sections may be on the inner diameter. O-rings may also have a small cross section in one embodiment to achieve high conductance, while maintaining a good seal between plates. 
     Other shaped plates may also be used, and may generally conform to the shape of the fuel container and fuel cell. The valve plates may alternatively form a low friction contact fit in one embodiment as illustrated at  300  in  FIG. 3  to enable relative movement or sliding. An o-ring need not be used in this embodiment. A lubricant  310  may be used to reduce stiction between the plates. As illustrated, the lubricant is at least on the outside of the fixed plate  145  and the inside of the moveable plate  150  where the plates contact each other. The outer dimensions, such as diameter of the fixed plate  145  is very close to the dimensions of the inner dimensions of the moveable plate  150  to form the friction fit. 
     Material combinations should have low coefficient of friction, for example stainless steel for the outer electrode and Teflon filled acetal for the inner electrode. Many other combinations that provide similar characteristics may be used. 
     In another embodiment, the outer plate could have a cut in the side, with an inside diameter slightly smaller than the outer diameter of the inner plate, such that the outer plate is expanded slightly when placed over the inner plate, and maintains a sealing force against the inner plate (or o-rings). Additionally, the outer plate could be flexible (rubber) and the inner plate rigid (stailess steel) and as discussed above, the inner diameter of the outer plate could be slightly smaller than the outer diameter of the inner plate, creating a sealing force as the outer plate expands to accommodate the inner plate. 
     The lubricant may also operate as a sealant. In one embodiment, the lubricant may be graphite or silicon or other lubricant compatible with materials used and the electrochemical reactions occurring. Oil or other hydrocarbon lubricants may also be used. 
     The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.