Active Coils in a Helical Spring
Helical Spring Design Resources – Spring Performance
The active coils are what make a spring a spring. We normally refer to the coils that open in an extension spring, the coils that deflect or close in a compression spring and the coils that twist or wind up/down in a torsion spring as "active".
The active term should really be applied to any portion of a spring that stores and releases energy. In a straight lever, the portion that flexes would be considered active.
It is important to understand what is active and how the active portion of the spring will provide the force you need. It is also very important to realize that in most cases there will be a diameter change as the active portion is deflected or extended. In the case of a compression spring, the active portion will expand as the spring is compressed. The opposite is typical of an extension spring. The action of a clutch spring tightening down on a shaft is typical of the diameter change as a torsion spring winds up.
The number of active coils in a spring is often confusing for those unfamiliar with spring design. Please contact the Newcomb Spring facility nearest you for more information on determining the number of active coils in a spring as well as other considerations of spring design and manufacturing.