fjærpiston

A fjærpiston, commonly translated as a spring-loaded piston, is a piston assembly in which a compression spring provides a restoring force to return the piston to a predefined position after actuation. The arrangement is used to create a known rest state, preload movement, or fail-safe return in various fluid-power or mechanical systems.

In typical constructions, a cylinder houses a piston and a spring. When external pressure (air or fluid) drives the piston, the spring compresses. When the actuation pressure is removed, the spring expands, pushing the piston back toward its initial position. This can be implemented in single-acting configurations with a spring on one side or in more complex layouts with multiple springs to control travel and force. The piston may also be used to maintain contact with valve seats or to dampen motion at the end of travel.

Variants and related concepts include spring-return (or spring-actuated) cylinders in pneumatic and hydraulic systems, where the spring provides the default position, and bi-directional spring-loaded arrangements used in measurement or sequencing devices. Some designs integrate seals, guides, and end-of-stroke cushions to reduce wear and noise.

Applications span pneumatic actuators and valve operators, where a spring return ensures a safe or known position in the absence of power, as well as simple mechanical dampers, clamps, and test equipment that require a predictable, self-resetting stroke. The choice of spring constant, material, and geometry determines speed, force, and travel range, as well as fatigue life of the assembly.