In an emergency situation such a fire inside rail or road tunnels, or even underground passenger platforms, electric motor operated dampers in the ventilation system can act to clear smoke from the structure as well as to suppress spreading of the fire. Most electric actuators that operate these dampers are required to be "failsafe". They are equipped with mechanical springs that open (or close) the damper upon sudden loss of power. These electric spring return actuators automating dampers ...This story is related to the following:Mechanical Power TransmissionSearch for suppliers of: Electric Failsafe Spring Return Actuators