Your hydraulic elevator parks at a floor, sits for a while with nobody using it, and then you notice the car has quietly settled a few inches below the landing. Or you hear it relevel itself with a short run when someone finally steps on. That is drift, and it almost always means oil is escaping somewhere it should not.
Audience: property manager / facility manager. Last reviewed: 2026-08-04 · Editorial review · Confidence: high.
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What is happening
A hydraulic elevator holds the car up with oil pressure under a piston (the jack or cylinder). When the car is parked, a valve holds that oil in place. If oil slowly bleeds past a seal - in the valve or the jack - the car sinks. When it drops out of the level zone, the controller runs the pump briefly to bring it back up. That repeated re-leveling is the symptom you notice.
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Most likely causes
- Internal control-valve leak. The most common cause. Seals inside the control valve wear and let oil bleed back to the tank. This is a valve repair or replacement - meaningful, but not a major job.
- Jack packing / seal leak. The seal where the piston enters the cylinder head weeps oil. You may see oil in the pit or around the jack. This is a larger repair.
- Cylinder leak. The cylinder itself is leaking, often underground on an older single-bottom jack. This is the expensive scenario and can carry environmental concerns.
Less common causes
- A leaking or failed check valve.
- A line or fitting leak between the power unit and the jack.
- Temperature effects: oil viscosity changes can slightly exaggerate apparent drift in a cold machine room.
What you can safely observe
Note how far the car settles and how long it takes, whether it happens at every floor or one, and whether there is visible oil in the pit or around the power unit. Take a photo of any oil. That is the whole of what you should do.
Safety. Do not enter the pit, open the power unit, or touch the valve or any hydraulic line - these are pressurized and are qualified-mechanic tasks. If the car is stopping noticeably out of level with the floor, treat it as a trip hazard and get it looked at promptly; if it is drifting far, take it out of service and call your contractor.
Urgency & safety level
Medium, rising to high if the mislevel at the door is large or the car drifts out of the door zone. Small, self-correcting drift is a nuisance and a wear signal; large drift is a trip-and-fall and entrapment risk.
When repeated drift means it is time to modernize
If the fix is the valve, repair it and move on. If the leak is in the jack packing or the cylinder - especially a buried single-bottom cylinder on an older unit - you are looking at a major, disruptive job, and it is often the moment to weigh a fuller modernization (a new cylinder, valve, and controller together) rather than a cylinder alone. Ask for the diagnosis in writing before you decide.
Questions to ask your contractor
- Is the leak in the control valve, the jack packing, or the cylinder itself? How did you confirm which?
- Is my jack a single-bottom or double-bottom cylinder, and how old is it?
- If it is the valve, what does a valve repair cost versus what you have quoted?
- Is there any oil in the pit, and if so, is there an environmental disposal concern?
Related
- Equipment: Hydraulic power unit and valve reference
- Also see: Why does my elevator level unevenly?
- Decision: Repair vs. modernize
- Hub: Problems & symptoms
Recommended next step
Got a cylinder-replacement quote and not sure it is justified? Run the proposal through our free scanner - it flags premature "you need a new cylinder" claims and lock-in language before you accept.
Get a realistic cost range based on your elevator type, building, and location.
Frequently Asked Questions
Is a drifting hydraulic elevator dangerous?
It can be. A small amount of settling triggers the anti-creep system to relevel, which is a nuisance. But if the car drifts far enough that the floor and the cab no longer line up, you get a trip hazard at the sill and, in the worst case, the car can move out of the door zone. Persistent drift should be looked at promptly by a qualified mechanic.
Does drifting mean I need a new cylinder?
Not necessarily. Drift is most often an internal control-valve leak, which is a far smaller repair than the jack. It only means a cylinder job if the leak is in the jack packing or the cylinder itself. Insist the contractor identify which one it is before you accept a cylinder-replacement quote, because the cost difference is large.