Answer
Hysteresis in wave springs refers to the difference in load at a given height between the compression and extension cycles. This is primarily caused by inter-turn friction in multi-turn springs and friction between the spring and the housing/shaft. In precision control valves, hysteresis results in 'stiction' and dead-band errors, where the valve position does not accurately reflect the actuator pressure. To minimize hysteresis, engineers specify dry-film lubricants (e.g., $MoS_2$ or PTFE) or electropolishing to reduce the coefficient of friction. Furthermore, using a single-turn wave spring or a nested spring with fewer turns can reduce the contact area, thereby lowering the cumulative frictional force and providing a more linear, predictable response curve.
