Loaded Stop Below Floor After Brake Work
A 1,600 kg geared traction passenger elevator with 2:1 roping serves eight stops in a medical office building. The brake coil was replaced two weeks ago. Since then, when the car travels up to the top landing with 10 to 12 passengers, it stops 20 to 30 mm below floor level. An empty car levels within 5 mm at the same landing, and down travel is normal. The brake picks up with a sharp clunk, there are no controller faults, and the car does not roll back after stopping. A feeler gauge shows 0.20 mm air gap on the left brake shoe and 0.55 mm on the right; the manufacturer's range is 0.20 to 0.40 mm. The drum is dry and free of oil. The maintenance supervisor proposes increasing the leveling speed to hide the stop. You have a load test weight set and a brake torque test procedure available.
1. What is the most likely cause, and what additional checks would confirm it?
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The most likely cause is uneven brake application after the coil replacement, not a leveling-speed problem. The right-side air gap is 0.55 mm, above the 0.20 to 0.40 mm range, while the left side is at the minimum. That asymmetry means one shoe contacts the drum before the other. Under a loaded up run the machine has more stored energy and the brake must absorb more torque; an uneven or delayed application can produce a sharp grab and stop the car short of the floor. The clunk supports a mechanical seating or binding issue rather than a purely electrical fault.
Confirm by checking the air gap at several points around each shoe, not just one. Verify that the armature moves freely and squarely on its guides, that the guides are clean and lubricated as specified, that the springs are matched and seated, and that the drum has no runout or glazing. Check the brake switch timing and the controller's stopping sequence. Then repeat a loaded up run at the top landing and compare the stopping position with the brake set. If the gap can be brought into range and the loaded stop returns to within tolerance, the brake was the cause.
2. What is the correct repair, and why is raising the leveling speed unacceptable?
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Correct the brake first. Clean and lubricate the armature guides per the manufacturer, free any binding, seat the armature squarely, set both shoes to the specified air gap, and verify spring condition and drum condition. Replace components that are worn or damaged rather than compensating with adjustments. After reassembly, perform a brake torque or holding test using the load set and the approved procedure, then run loaded and empty tests in both directions at all floors. Record the gaps, test results, and final leveling readings.
Raising the leveling speed is unacceptable because it treats the symptom while leaving a degraded safety device in service. The brake is the primary means of stopping and holding the car; an uneven gap can increase stopping distance, cause unpredictable deceleration, accelerate lining wear, and reduce holding margin during an emergency stop or power loss. It may also mask a binding armature that could worsen. Changing the leveling speed can alter stopping distances and door-zone behavior and may move the car outside the intended landing accuracy. The correct judgment is to restore the brake to its designed condition, not to tune around it.
3. What acceptance evidence should be recorded before the car is returned to normal service?
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Record enough evidence to show the brake and leveling performance are back to design, not merely that the complaint stopped. Include: measured air gaps on both shoes at multiple points; armature free movement and guide condition; spring and drum inspection results; brake torque or holding-test values against the manufacturer's criteria; loaded and empty stopping positions at every landing in both directions; the load used and the direction of travel; any controller adjustments and why they were made; and the final test date and signatures. Note that the original complaint was load- and direction-specific, so the acceptance run must reproduce that condition: a loaded up run to the top landing. If the car still stops outside tolerance under load, the job is not complete even if empty-car leveling looks normal.