Everything in the safety chain exists to answer one question: if the car starts moving in a way nobody commanded, what stops it? Each device is independent on purpose. Testing them as a group – “the chain is closed, so it must be fine” – is how a real defect survives a maintenance visit.
What sits in the chain
| Device | Operates when | What it does |
|---|---|---|
| Governor | Car speed exceeds the tripping speed | Grips the governor rope, which pulls the safety mechanism |
| Safety gear | Pulled by the governor rope or by a broken suspension member | Wedges or rolls against the guide rails to stop the car |
| Slack rope / slack belt device | Suspension member loses tension | Opens the chain and stops the machine |
| Final limits | Car travels past the normal terminal landing | Cuts the drive and applies the machine brake |
| Buffers | Car or counterweight reaches the pit travel limit | Absorbs the remaining energy; oil buffers have a reset switch |
| Pit stop switch and pit switch | Manually operated / pit access | Removes power from the drive and prevents movement |
| Emergency stop in the car | Manually operated | Opens the chain |
Governor: the numbers that matter
The governor has three speeds, and confusing them invalidates a test:
- Tripping speed – when the governor jaw grips the rope.
- Gripping speed – when the safety gear applies to the rails.
- Electrical trip speed – when the governor switch opens the machine circuit, which must happen before the mechanical trip.
The electrical switch is the one that stops the car in normal overspeed events; the mechanical trip is the last resort. A governor whose switch operates late, or whose jaw is dry and sticky, has lost the layer that actually protects passengers.
Testing without faking a pass
- Isolate and lock out the drive before any work in the pit or on top of the car.
- Check the governor rope for broken wires, correct tension and freedom of movement through the jaw. A rope that drags in the jaw changes the trip speed.
- Verify the governor switch operates at its setting – and that the setting matches the unit’s documentation, not a remembered value from another machine.
- Confirm the safety gear linkage moves freely and the wedges/rollers are not corroded or packed with debris.
- After any safety-gear test, verify the rails are not scored, the gear releases properly, and the car is re-levelled and re-learned where the controller requires it.
- Record what you tested, the method and the result. A test without a record is indistinguishable from no test.
Common findings that should never be left
- Governor rope dry, frayed, or running outside its guide.
- Oil buffer below the marked level, or the buffer switch tied closed.
- Pit switch bypassed “temporarily” to allow inspection.
- Safety gear linkage bent from a previous trip and never straightened.
- Final limit switches adjusted to avoid nuisance trips rather than for correct stopping distance.
Related: system anatomy for how the safety devices fit into the machine room, and routine maintenance program for how these checks are scheduled. Forum threads on specific units are under governor and safety gear.