UKHeliBob:
Start with everything turned off.
Go round loop() until the button becomes pressed then turn on the gas and the welder
Keep going round loop() until the button becomes released
When that happens turn off the welder, save the value of millis() as the start time and set a boolean to true.
Keep going round loop() and if the boolean is true test whether the current time minus the start time is greater than the post flow period. If not then keep going, otherwise turn off the gas and set the boolean to false.Look at the StateChangeDetection example in the IDE to see how to detect when a pin becomes a certain state.
THIS is where I get confused. Won't the millis get updated each time through the program? How do you capture it only once?