Method for detecting orifice flow phase transition in a pressure-controlled anode

A fuel cell system that determines the phase transition from water to gas through a bleed/drain valve in a water separation device. The fuel cell system includes a fuel cell stack having an anode side and a cathode side. An injector injects hydrogen gas into the anode side of the fuel cell stack. The water separation device receives an anode exhaust gas from the anode side of the fuel cell stack, where the water separation device includes a water holding reservoir. A controller controls the injector and the bleed/drain valve and determines when the bleed/drain valve transitions from draining water to bleeding the anode exhaust gas by comparing the flow rate through the water separation device and the flow rate through the injector.