Fuel delivery system and method of use thereof

A fuel delivery system for a liquid-type fuel cell using diluted fuel, said system comprising:

• a fuel tank containing a concentrated fuel;
• and
• a fuel controller connecting said fuel tank to a reservoir of diluted fuel, which is in contact with an anode and is contained in a chamber, wherein said fuel controller delivers the concentrated fuel to the reservoir of diluted fuel when the fuel concentration of the diluted fuel falls below a predetermined level, and wherein the fuel controller comprises a pressure-operated valve comprising:
• a tubular or valve body having a fuel conduit and an air vent;
• a spring inside the valve body;
• and
• a plunger that is supported by the spring,
• wherein a position of the plunger relative to the valve body is passively determined by a balance between the spring and the pressure inside the chamber,
• wherein the fuel conduit and air vent are blocked by the plunger until the pressure inside the chamber reaches a predetermined value, and
• wherein the spring has a spring constant that allows the plunger to unblock the fuel conduit and the air vent when the pressure inside the chamber reaches the predetermined value.