According to two major manufacturer's layouts, the overhead reactions (loads in the down direction)for basement-machine elevators are about double that of conventional overhead machines, for the same speed and capacity.

Can someone explain this?

-- Ted McG (amcgregor@rooneyirving.ca), September 21, 2000

Answers

Know how a block & tackle works? Count the rope groups. Add up the forces. When the machine is in the basement there are 4 vertical ropes instead of the usual 2 with an overhead machine. Each rope is tensioned to the weight of the car or counterweight. Each deflection pulley/sheave at the top is being pulled downward by the forces on a pair of ropes, and there are 2 deflection sheaves. So the total downward force on the building structure is approx 4 times the weight of the car.

An interesting sidelight is that the traction machine is being pulled UP by ~2X the weight of the car. So make sure it is bolted down tight.

DonV

-- Don Vollrath (dvollrath@magnetek.com), September 22, 2000.