garage doors springs
A standard torsion spring has a stationary cone which secures the spring to the spring anchor bracket. Since this bracket is secured to the wall, the stationary cone, as its name suggests, does not move. The other end of the torsion spring has a winding cone. This winding cone is used when installing, adjusting, and uninstalling the springs. When installing the torsion spring, the coils of the spring are wound up to create a lot of torque.
The torque transfers from the shaft to the cable drum, pulling the cable and the bottom of the garage door upward.
This torque is then applied to the shaft, the metal tube that goes through the torsion spring. The ends of the shaft are held up by the end bearing plates. Resting against the race of the bearings are the cable drums. The cable wraps tightly around the cable drum, and the cable goes down to the bottom of the garage door, securing to the bottom bracket.
Since these cables hold the weight of the garage door, the torque from the torsion springs does not dangerously spin the shaft until the spring is loose. Instead, the garage door weight slightly exceeds the lift produced by the torsion spring(s). (The lift is the amount of weight that each spring can raise off the ground.) As a result, a properly operating garage door with the right springs should not seem to weigh nearly as much as the garage door itself. When this principle holds true through the duration of the door's travel, the door is balanced.
With the help of the torsion springs, you should be able to operate the garage door manually without much trouble. Likewise, it does not take too much work from the garage door opener to lift the garage door. As the door opens (either manually or with the opener), the torque on the shaft keeps the cable tight on the cable drum. As a result, the cable winds up on the cable drum, allowing the torsion springs to unwind.
As the torsion spring unwinds, it loses some of its torque. Therefore, it also loses the amount of lift that it can produce. Vertical lift and high liftgarage doors deal with this problem in a slightly different way, and you can read about .How Vertical Lift and * High Lift Garage Doors Work Standard lift garage doors are almost universally used in residential garages, and are in the majority in commercial and industrial settings.
It all comes down to the cable drums. Standard lift cable drums have a flat portion for the cable, with one or two grooves that are a little higher. (These higher grooves are addressed in the link above.) As the garage door opens, the rollers slide along the track. The door transitions from the vertical track to the horizontal track.
When the top section is supported by the horizontal track, each spring does not need to support as much weight. Since the springs have unwound a little by this point, the amount of weight supported by the horizontal tracks roughly equals the lift that was lost from the decrease in torque in the torsion springs.
When the garage door is fully open, there is still about 3/4 to 1 turn still applied to each torsion spring. Since the bottom roller on the garage door typically rests on the curved portion of the track, the door will want to fall down. The extra torque in the torsion springs, though minimal in comparison to the torque when the garage door is closed, keeps the door open.