A method of opening a mine door leaf installed in a mine passageway having a high pressure zone and a low pressure zone. The method includes the steps of operating a variable-throw crank mechanism in a first configuration having a first crank length to apply a first force to the mine door leaf to move at a first speed, operating the variable-throw crank mechanism in a second configuration having a second crank length less than the first crank length to apply a second force greater than the first force to the mine door leaf to move at a second speed slower than the first speed, and using a resistance pressure associated with the high and low pressure zones in the mine passageway to convert the variable-throw crank mechanism from the first configuration to the second configuration.