A coil-spring mechanical device installed in the elevator pit beneath the car and counterweight that stores and returns kinetic energy upon over-travel contact, providing a cushioned stop. Permitted only for elevator rated speeds up to 1 m/s.
Full Definition
Spring buffers (energy-storage buffers) use a compressed metal coil spring on a base plate to absorb the impact of the car sling or counterweight sling during over-travel events. EN 81-20 Cl. 10.4 permits spring buffers only for rated speeds ≤1 m/s; above this speed, oil (hydraulic) buffers are mandatory. The spring compresses under impact force, decelerating the car. Unlike an oil buffer, the spring then re-extends, pushing the car or counterweight back — so the buffer both decelerates and re-accelerates. Average deceleration must not exceed 1g per EN 81-50. The spring stroke is calculated per EN 81-50 based on kinetic energy at rated speed and load. Testing: type-tested per EN 81-50; verified at commissioning by checking stroke and spring condition. A buffer return switch is not required for spring buffers (the spring returns immediately without a time delay, unlike oil buffers). Spring buffers do not require oil level maintenance. Advantages: simpler construction, no moving fluid parts, lower cost. Disadvantages: harsher deceleration profile than oil buffer; rebound effect; not suitable for high-speed elevators. Spring buffers are also sometimes called polyurethane buffers if the spring element is replaced by a polyurethane foam block (used for very low speed applications). Note: spring buffers must be fully extended before the elevator can operate (if a return switch is fitted); in practice, for low-speed elevators this is usually not fitted.
