A torsion spring is a device used to give support and cushion movement in several types of components. There are two distinct types of torsion spring. The first is not a spring at all, however, it has torsional or spring-like properties and is called a torsion bar. The second one is actually a helical-wound spring, such as the type of spring used in a common mouse trap. The torsion bar is commonly used in automobile chassis, as well as trailer suspensions. The long spring, such as those typically found tightly wound on an overhead garage-door axle, is another type of torsion spring.
While a common coil spring is designed to operate by compressing against a load or stress, the torsion spring is designed to work by twisting against itself while positioned horizontally. This twisting along the axis of the torsion spring causes the coil to wind tighter, thereby providing the power for the spring. As the helix winds tighter, it stores energy in the many small coils that make up the spring. Once released, the spring snaps back to the original wound position.
A torsion spring in the bar form consists of a solid steel bar that is designed to twist without breaking. The bar is attached to a moving component on one end and to a solid component on the other. As the moving component travels through the designed path of motion, the bar twists against itself, providing a spring-like response. On a vehicle, the torsion bar is typically attached to the front control arms, while the other end of the bar is attached to a cross-member. As the control arm moves up and down, the torsion bar twists and provides a softer, cushioned ride to the vehicle.
When used in a garage door application, the torsion spring provides the stored energy to aid in raising the garage door. The spring is wound tightly around the top axle of the door. This is a very dangerous operation with the pent-up energy of the door being enough to seriously injure and even kill a human if it were to break free. The amount of pressure placed upon the torsion spring should be just enough to make raising the garage door effortless to the user. If the garage-door torsion spring is wound so tight that it will attempt to raise the door without assistance, it is too tight and could pose a potential danger to the door, the operator or both if it were to break.