Most residential overhead doors use garage door torsion springs. There is typically one spring operating a single door. One interesting fact to note is that this hardware component does most of the work during the opening and closing. The share of work done by the opener is significantly smaller.
The torsion spring has long tubular shape. It is made from steel and has a coil design. It is loaded with force corresponding to the weight of the door. It is set over a steel shaft fixed above the garage door. More specifically, the shaft goes through the center of the spring. Usually, the spring is positioned in the middle, but it may also be set on one of the sides. The first setting is the most common. In this case, there is one drum fixed on each side of the shaft. There is a metal cable connected to each drum and to the bottom of the door. Together the spring, shaft, drums and cables form the lifting system.
When the door is in closed position, the spring counterbalances its weight. When you press the button on the remote to open the door, the electric operator engages the movement while the spring unwinds and releases the power stored in it by applying torque to the shaft. The released power is used for opening the door, so when the door closes, the spring winds. This way, it gets loaded again.
Each overhead door requires a specific spring. It has to have a particular length, diameter and wire size. Lift is a unique measure specific for garage door torsion springs. It shows the amount of door weight that the piece of hardware can lift. Each component has its own cycle life as well. It shows how many cycles a spring can complete before it breaks.