.080 17-7 stainless steel torsion spring used in butterfly valves
Torsion springs are helical springs that exert a torque or rotary force and are subject to bending stresses. Torsion springs should always wind up from the free position – never to unwind from the free position. As they wind up, torsion springs reduce in diameter and their length becomes longer. Such springs should be supported over a rod whenever possible. Some spacing should remain between coils to minimize friction which can alter torque and deflection.