Rhythmic Thump and Uneven Rope Tension on a Geared Traction Elevator
A TSSA-certified mechanic is assigned to an eight-stop geared traction passenger elevator: 2,500 lb capacity, 350 fpm, four 5/8-inch suspension ropes, counterweight balanced at 45% of rated load. Tenants report a rhythmic thump that occurs at the same point in the travel, plus a high-pitched 'singing' near the machine room. The car rides quietly at low speed but vibrates at contract speed. Inspection finds one rope with several broken wires near the equalizer hitch, a worn rope-groove profile on the traction sheave, and a counterweight guide shoe with visible clearance. Rope tension, measured by deflection, varies by about 20% between ropes. The building owner wants the mechanic to 'just tighten the ropes and replace the one bad rope' so the elevator can stay in service for a weekend event.
1. How should the mechanic separate rope, sheave, and counterweight-guide causes of the vibration, and what measurements or observations would confirm each?
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Treat the symptoms as clues and test one variable at a time. The thump at the same point in travel is position-dependent, so first run the car slowly and mark the exact point. If the thump occurs once per rope revolution, it points to a rope defect (broken wires, a nick, or a tight strand) or a sheave flat or groove defect. If it occurs at a rail joint or at the counterweight position, inspect the guide shoes and rail alignment. The 'singing' is often rope vibration against the sheave or a misaligned equalizer. Measure rope tension by deflection with a spring scale at the same point on each rope, inspect all ropes along their length, check sheave groove profile with a template, and check guide shoe clearance. A 20% tension variation is enough to overload individual ropes. Record all readings and compare them with the manufacturer's criteria. Do not adjust blindly; the measurements determine whether the fix is tensioning, rope replacement, sheave work, or guide adjustment.
2. Evaluate the owner's proposal to replace one rope and tighten the rest. What are the technical and code reasons for or against?
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Reject the proposal as written. Suspension ropes on a traction elevator are a set: they share load and must stretch together. Installing one new rope alongside three old ropes means the new rope carries a disproportionate share, the old ropes go slack or the new one overloads, and the sheave and equalizer wear unevenly. 'Tightening' ropes to hide a 20% imbalance is not a repair; it can overload the sheave and bearings and mask a broken-wire condition. The rope with broken wires near the equalizer must be evaluated against the retirement criteria in the adopted CSA B44 and the rope manufacturer's data (broken-wire count in a lay, diameter loss, corrosion, distortion). If one rope has reached retirement, the normal judgment is to replace the set and equalize tension with a gauge, not by feel. The worn sheave groove profile must also be corrected or the sheave replaced, because a worn groove changes rope pitch diameter and accelerates wear. The car should stay out of service until the set is replaced and tensioned.
3. What should be done before the elevator is returned to service, and what must be recorded?
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Before return to service: replace the rope set if any rope meets retirement, regroove or replace the sheave if groove wear exceeds the template, correct the counterweight guide shoe clearance, re-tension all ropes evenly, and run the car through the full travel at contract speed to confirm the thump is gone. Check that rope guards and hitch attachments are secure, and that counterweight runby and clearances are unchanged. A short low-speed and full-speed test with a load is warranted. Record rope diameters, broken-wire counts, tension readings, sheave measurements, guide clearances, and the work order. Give the owner a written explanation that the 'one rope' shortcut was refused for load-sharing reasons. If the car cannot be repaired before the event, keep it out of service and arrange passenger alternatives.