Patent ID: 7073524

Claim:
A fail-safe apparatus for controlling fluid flow through a series arrangement of first and second valves, wherein the fail-safe apparatus is operable at any of a plurality of switching cycles, wherein each of the plurality of switching cycles defines successive on and off states each having a given duration, wherein the duration of the successive on and off states defines one of a plurality of duty cycles, the fail-safe apparatus comprising: a first solenoid coil for controlling operation of the first valve between an unactuated state and an actuated state; a second solenoid coil for controlling operation of the second valve between an unactuated state and an actuated state; a switch operable to couple during the on state of any of the plurality of duty cycles an input voltage across the first solenoid coil to cause a first current to flow therein; and an energy-transfer device coupling the first solenoid coil with the second solenoid coil, the energy-transfer device operable to store energy therein, wherein: (i) during the on state of at least one of the plurality of duty cycles, a potential established in the energy-transfer device in combination with the input voltage causes a second current to flow in the second solenoid coil, (ii) during the off state of any of the plurality of duty cycles, the potential established in the energy-transfer device affects a decay rate of any first and second current flowing through their respective first and second solenoid coils, and (iii) when the first and second currents exceed respective first and second thresholds, the first and second solenoid coils cause their respective valves to operate in the actuated state.