A power generator comprising: a cylindrical housing; a fuel cell situated in the housing proximate to an outer wall; a fuel chamber situated at about a center of the housing a cathode;an anode; a water permeable membrane situated between the cathode and anode; a valve situated in the housing between the fuel cell and the fuel chamber, the valve adapted to be opened or closed and when closed to effectively provide a barrier between the fuel cell and the fuel chamber to control water vapor from the fuel cell to the fuel chamber; and a pressure sensitive mechanism linked to the valve and adapted to close or open the valve according to a pressure within the housing proximate to the fuel chamber; wherein: the valve is cylindrical and approximately concentrically situated between the fuel chamber and the fuel cell, and the valve comprises a first mesh and a second mesh adjacent to the first mesh, and a first position of the second mesh relative to the first mesh is a closed valve; and a second position of the second mesh relative to the first mesh is an open valve; the pressure sensitive mechanism is adapted to slide the second mesh towards the first position if the pressure within the housing increases, and to slide the second mesh towards the second position if the pressure within the housing decreases; and pressure sensitive mechanism comprises a fluid impervious membrane covering an opening situated between an interior of the housing and an exterior of the housing and a linkage connecting the membrane to the second mesh. a cylindrical housing; a fuel cell situated in the housing proximate to an outer wall; a fuel chamber situated at about a center of the housing a cathode;an anode; a water permeable membrane situated between the cathode and anode; a valve situated in the housing between the fuel cell and the fuel chamber, the valve adapted to be opened or closed and when closed to effectively provide a barrier between the fuel cell and the fuel chamber to control water vapor from the fuel cell to the fuel chamber; and a pressure sensitive mechanism linked to the valve and adapted to close or open the valve according to a pressure within the housing proximate to the fuel chamber; wherein: the valve is cylindrical and approximately concentrically situated between the fuel chamber and the fuel cell, and the valve comprises a first mesh and a second mesh adjacent to the first mesh, and a first position of the second mesh relative to the first mesh is a closed valve; and a second position of the second mesh relative to the first mesh is an open valve; the pressure sensitive mechanism is adapted to slide the second mesh towards the first position if the pressure within the housing increases, and to slide the second mesh towards the second position if the pressure within the housing decreases; and pressure sensitive mechanism comprises a fluid impervious membrane covering an opening situated between an interior of the housing and an exterior of the housing and a linkage connecting the membrane to the second mesh. the valve is cylindrical and approximately concentrically situated between the fuel chamber and the fuel cell, and the valve comprises a first mesh and a second mesh adjacent to the first mesh, and a first position of the second mesh relative to the first mesh is a closed valve; and a second position of the second mesh relative to the first mesh is an open valve; the pressure sensitive mechanism is adapted to slide the second mesh towards the first position if the pressure within the housing increases, and to slide the second mesh towards the second position if the pressure within the housing decreases; and pressure sensitive mechanism comprises a fluid impervious membrane covering an opening situated between an interior of the housing and an exterior of the housing and a linkage connecting the membrane to the second mesh.