An oil-filled deceleration device in the elevator pit that absorbs the kinetic energy of an overrunning car or counterweight.
Full Definition
The elevator hydraulic buffer is a spring-return or self-restoring oil dashpot device installed in the pit to absorb and dissipate the kinetic energy of the car or counterweight in the event of overrun beyond the terminal landing. Unlike spring buffers (which store and release energy), hydraulic buffers dissipate energy as heat through oil flow restriction, providing a controlled, progressive deceleration force. EN 81-20 clause 5.8 requires hydraulic buffers for rated speeds exceeding 1.0 m/s. Buffer stroke is calculated from rated speed: minimum stroke = v²/gn metres. Oil level and viscosity must be checked periodically (typically annually); oil temperature affects dashpot performance. Reduced-stroke buffers are used where pit depth is limited, combined with electronic speed reduction before buffer contact. Each buffer must carry a type approval certificate.
