Method of opening a mine door leaf

A method of opening a mine door leaf installed in a mine passageway, said passageway having a first pressure zone on a first side of said door leaf and a second pressure zone on a second side of said door leaf, the first pressure zone having a pressure that is higher than a pressure of the second pressure zone, the method comprising:

• 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 the mine door leaf 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 the mine door leaf at a second speed slower than the first speed, and
• using a resistance pressure associated with the first and second pressure zones in the mine passageway to convert the variable-throw crank mechanism from the first configuration to the second configuration.