Abstract: The torsion spring is disposed around an axle/shaft and fixed to the axle/shaft at one end, such that the torsion spring rotates with the door drum and fixed to a spring plate as a stationary structure at the other end. The spring plate does not rotate while the torsion spring rotates. The torsional forces created in the spring by the rotation of the door drum provides a variable torque which counteracts the weight of the flexible door. As the flexible door is lowered, the torsional forces developed in the spring pull in the opposite direction of the travel of the flexible door. The amount of tension resulting from the torsional forces generated in the torsion spring determines the performance characteristics of the flexible door.