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A typical overhead garage door consists of several panels hinged together that roll along a system of tracks guided by rollers. The weight of the door is balanced by either a torsion spring system or a pair of extension springs.
Torsion spring lift mechanism
A torsion spring counterbalance system consists of one or two tightly wound up springs on a steel shaft with cable drums at both ends. The entire apparatus mounts on the header wall above the garage door and has three supports: a center bearing plate with a steel or nylon bearing and two end bearing plates at both ends. The springs themselves consist of the steel wire with a stationary cone at one end and a winding cone at the other end. The stationary cone is attached to the center bearing plate. The winding cone consists of holes every 90 degrees for winding the springs and two set screws to secure the springs to the shaft. Steel counterbalance cables run from the roller brackets at the bottom corners of the door to a notch in the cable drums. When the door is raised, the springs unwind and the stored tension lifts the door by turning the shaft, thus turning the cable drums, wrapping the cables around the grooves on the cable drums. When the door is lowered, the cables unwrap from the drums and the springs are rewound to full tension.
Extension spring lift mechanism
An extension spring counterbalance system consists of a pair of stretched springs running parallel to the horizontal tracks. The springs lift the door through a system of pulleys and counterbalance cables running from the bottom corner brackets through the pulleys. When the door is raised, the springs contract, thus lifting the door as the tension is released.
The balance of the door should be checked monthly also. One should be able to raise and lower the door without any resistance and it should smoothly roll along the tracks and should remain stationary at any point of travel. Usually a door that does not pass these tests is out of balance and should be adjusted. It is usually recommended that only a trained door technician with the proper instructions or a mechanically experienced person adjust or replace the springs.
All moving parts of the door should be lubricated monthly also. The door tracks should never be lubricated since the lubricant will only create a sticky surface on the track that can attract more dirt and grime, resulting in a door that is really difficult to operate. The bearings, hinges, and rollers should be lubricated for proper and safe operation. Torsion springs should also be lubricated with a light coat of oil to reduce the friction between the coils and to eliminate any noises and to even increase the life of the springs.
Garage doors with extension springs would normally be installed with a restraint cable running through the center of these springs. This is necessary because the springs weaken from the fatigue and stress exerted on the steel wire from opening and closing the door. If an extension spring breaks, it can seriously injure anyone present in the garage or damage adjacent property. The cable running through the center restrains the spring in the event of a failure.
Most overhead garage doors are equipped with torsion springs which do not need safety restraint cables since the torsion shaft running through the springs restrains the spring if it breaks. Torsion springs are superior to extension springs since they are easier to fine tune and balance the weight of the door more evenly.
The bottom roller brackets located at the bottom corners of the door are always under extreme tension since the counterbalance cables are attached to these brackets. Therefore, one should never attempt to remove or loosen the screws that attach these brackets to the door as serious injury can result. This also applies to other spring hardware such as the setscrews, cable drums, lag screws, center bearing plate, etc.