Governor Trip Speed After a Contract-Speed Increase
A 500 fpm, 2,500 lb passenger traction elevator is due for its annual test. The car governor nameplate reads 600 fpm. A calibrated tachometer shows the governor tripping at 590 fpm while the car runs at 505 fpm. The building owner wants to increase the contract speed to 600 fpm by changing the machine sheave. The governor is 12 years old and its spring adjustment seal is intact. The mechanic proposes to adjust the governor spring so it trips at 690 fpm after the sheave change, arguing that 690 fpm is 115% of 600 fpm. The car has oil buffers. The inspector wants the governor and buffer test plan before approving the speed change.
1. Is the current 590 fpm trip speed acceptable for a 500 fpm car? Show the range.
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For a 500 fpm car, the general car-governor trip range is 115% to 140% of rated speed: 575 to 700 fpm. The measured 590 fpm is about 118% of 500 fpm, so it is within the range, assuming the tachometer is calibrated, the car speed is actually 505 fpm, and the test method matches the adopted code.
The measured car speed of 505 fpm is about 1% above rated, which is normally acceptable for test purposes, but confirm the contract speed and machine data. Do not adjust the governor just because 590 fpm sounds low. The relevant question is whether the trip speed is within the code range and whether the governor is listed and sealed for the application.
2. If the car speed is raised to 600 fpm, can the existing governor simply be adjusted to 690 fpm?
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Not automatically. At 600 fpm, 115% is 690 fpm and 140% is 840 fpm, so 690 fpm is the minimum acceptable trip point, not a comfortable target. The existing governor is nameplated 600 fpm and has been running at a 590 fpm trip. Before adjusting it to 690 fpm, verify that the governor is listed and rated for 600 fpm car speed, that the spring and flyweight range can achieve 690 fpm, and that the governor rope and safety linkage are rated for the higher speed.
If the governor cannot be re-rated or adjusted within its listed range, replace it with a governor rated for 600 fpm. Adjusting a sealed spring beyond its designed range is not acceptable. After the change, test the trip speed with a calibrated tachometer and verify the car safety engages and stops the car within the code distance.
3. What tests should be performed after the speed increase?
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Perform an acceptance test for the altered speed, including governor trip speed, car safety engagement, and stopping distance. Test the oil buffers with the car and counterweight at the required impact speed, verify oil level and return, and confirm the buffer stroke and deceleration. Check the brake for sufficient torque at the new speed and load, and perform a full-load test if the rated load or speed change requires it.
Also verify terminal stopping, normal and final limits, emergency braking, and leveling at 600 fpm. The governor and safety tests must be witnessed and documented. If the car safety stopping distance is excessive or the buffer impact is too severe, the speed increase cannot be approved until the mechanical components are corrected.