A hydraulic elevator is an oil circuit with a car attached. Almost every “electrical” symptom on these units traces back to oil condition, oil temperature, or a valve that no longer seals – which is why faults that appear only after a few hours of work are so common.
The circuit, in order of likelihood
| Component | Job | Failure signature |
|---|---|---|
| Oil tank and level | Reservoir and cooling surface | Car runs hot, slows, or sinks; level drops with a leaking jack |
| Pump and coupling | Pressurises the oil | Noise under load, vibration, pressure not reached, coupling wear |
| Motor and starter | Drives the pump | Trips on start, high current, single-phasing symptoms |
| Control valve (up/down) | Sets direction and speed | Car creeps, drops slightly at start, won’t hold, jerky stop |
| Jack and seal | Converts pressure into lift | Oil on the jack, sinking car, oil consumption without visible leak |
| Oil cooler / heater | Keeps viscosity in range | Faults only in hot or cold weather, both directions affected |
| Manual lowering valve | Rescue and levelling | Leaks, or cannot be operated during a rescue |
Three symptoms and what they actually mean
Car sinks slowly when parked
Oil is escaping somewhere. Check the down valve first, then the jack seal, then the piping. A jack leak may show as oil on the jack or as consumption with no visible puddle if it is buried. Sinking is a defect that must be corrected, not monitored: the landing step becomes a trip hazard and the unit can no longer be relied on to hold position.
Rough start or a small drop at start
Almost always the valve: the car settles slightly as pressure transfers. Valve cleaning or replacement – not a change of acceleration setting – is the fix. Adjusting the starter to disguise it makes the stop worse.
Everything is fine until the oil is hot
Viscosity changed, so a marginal valve or a worn pump now leaks internally. The correct diagnostic is to reproduce the condition deliberately: run the unit through a realistic duty cycle, then repeat the measurement. Testing a cold unit and declaring it healthy is the most common maintenance error on hydraulic equipment.
Related: drives and motors, maintenance program, and forum threads on hydraulic units.