Posted By KevinD
Hello all,
Please could somebody explain the mechanism by which lifts fail to ground on the power supply failing or fire alarm being activated? Is it through a stored power supply that provides enough power to lower the lift and open the doors or some other means?

Regards,

Kevin

Posted By Dave Merchant
What KevinD was asking about isn't the fire service manual winder, it's an automatic system to relocate the car to the ground floor. They do exist and are far more common in the USA than here, but aren't always a good idea.

Hydraulic lifts (as used for domestic applications) can be made to return slowly to ground simply by leaking pressure back into the header tank under the control of a valve held closed by mains power - important if there's only one person on the premises as it prevents them being trapped.

Rope/cable/crawler lifts are often fitted with an emergency power source (generator or batteries) where the local regulations require it (as in the USA) or where the lift is intended for use as a firefighting access route. The backup power may only permit limited ranges of movement, but normally where the car is designated for firefighter service it's programmed to return to ground during an incident so it's ready for use. It's also common in high-rise buildings in the US to return to ground (first floor in the US) whenever a fire alarm activates so it's obvious to fire marshals that nobody is trapped in a car. Historically it stopped people trying to use the elevator to escape, but these days that's normally the primary escape route anyway if your building's over 20 floors.

The concerns over self-returning cars are of course those of identifying the fire floor - you don't want your lift to automatically take you to the floor that's on fire and open the doors! In the past there have been incidents where a car passing the fire floor stopped because that lobby call button was shorted out, but modern auto-return controllers now ignore any other call signals.

Posted By KevinD
Dear All,

Thank you very much for your replies, these have been very helpful indeed and raised a couple of issues I had not properly considered.

Kind Regards,

Kevin