Hydraulic Elevator Settling and Slow Down Travel
You are the EDM-B mechanic called to a 22-year-old, two-stop hydraulic elevator in a three-storey office building. The car serves P1 and the ground floor, travel 4.2 m, rated 1,150 kg, single-bottom jack, 180 mm plunger. The building operator reports that after the car stops at P1 it settles about 150 mm over 10 minutes, and the down trip is noticeably slower than usual. The machine room is at 30°C; the tank sight glass shows oil at the minimum mark. There is a light film of oil at the jack head and a faint hiss near the power unit when the car is at rest. The car has not been recalled. You have a pressure gauge, a stopwatch, and the maintenance records, which show the last oil change was 4 years ago and the last category 1 test was 11 months ago. The owner wants the car back in service before noon because a tenant move is scheduled.
1. What three checks would you perform first, and what would each result tell you?
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First, check the oil level and oil temperature against the manufacturer’s limits. Oil at the minimum mark and a 30°C machine room can cause pump cavitation, slow down travel, and overheating; low oil also means the leak must be found rather than simply topped up. Second, perform a static leak test: run the car to the top landing, stop it, mark the plunger and watch the pressure gauge and plunger for at least 10 minutes. A falling gauge with plunger movement points to internal leakage past the lowering valve, check valve, or jack packing; oil at the jack head supports a packing problem. Third, inspect the lowering valve, check valve, and relief valve for contamination or misadjustment. A partially leaking valve can explain the drift, while a misadjusted relief valve can explain slow speed. Record all readings and compare them with the maintenance record; the 4-year oil change interval and minimum oil level suggest the system has not been maintained to the manufacturer’s schedule.
2. The owner asks you to return the car to service and just top up the oil. What do you do and why?
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I would not return the car to service. A hydraulic elevator that settles 150 mm after stopping is showing a loss of hydraulic support, and the source could be a leaking valve, a failed jack packing, or a damaged cylinder. Topping up the oil would hide the low-level symptom without correcting the cause, and the slow down travel may be cavitation from air entering the system. The car should be tagged out, the owner notified in writing, and the unit kept out of service until the leak is located, repaired, and the system is re-tested. The scheduled tenant move is an operational concern, not a reason to operate an unsafe device. Before return to service I would verify the repair with a static pressure test, check the relief valve setting, confirm oil level and temperature, and perform the applicable Category 1 tests. If the jack is a single-bottom cylinder, I would also confirm that the required means to prevent uncontrolled descent is present and functioning.