Oil Buffer: Hydraulic Energy Dissipation, 115% Speed Stroke, Deceleration Limits, 90s Return Switch and EN 81-50 Type Test

Oil buffers (hydraulic buffers, energy-dissipation buffers) are required by EN 81-20 Cl. 10.4 for all elevators with rated speeds exceeding 1 m/s. Construction: a cylinder filled with hydraulic oil and a plunger (ram). On car or counterweight impact, the plunger compresses and forces oil through calibrated orifices or an annular gap, converting kinetic energy into heat. Key technical requirements: (1) Buffer stroke sufficient to absorb full kinetic energy of car at rated load at 115% of rated speed; (2) Average deceleration ≤1g; peak deceleration ≤2.5g; (3) Plunger must return to fully extended position within 90 seconds of load removal — verified by a buffer return switch (direct-opening safety contact in the safety circuit); (4) Oil level indicator (sight glass) required for maintenance; (5) Type-tested per EN 81-50 with certified stroke and energy rating; (6) Minimum clearance from car structural member: ≥150 mm; maximum clearance ≤400 mm (EN 81-20 pit dimensions). Two buffers are always installed: one under the car sling and one under the counterweight sling. Buffer stroke is calculated per EN 81-50 based on rated speed and rated load. For speeds ≤1 m/s, spring buffers are permitted as an alternative.

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