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Elevator Components
An elevator consists of an enclosed cab within a hoistway, or shat. Depending upon the overall design, the cab is either pushed or pulled vertically through the hoistway. Safety mechanisms, such as emergency brakes, reside underneath the cab for preventing an accidental free fall if the rigging mechanism fails to support the elevator's weight.
Geared Traction Elevators
A geared traction rigging technique pulls the cab through the hoistway with the aid of steel ropes. Above the hoistway space is an AC (alternating current) or DC (direct current) motor. The motor attaches to a set of worm gears. The worm gears transfer the motor's energy to an attached drive sheave, or pulley. The sheave holds and moves the steel ropes that progressively create movement for the cab attached below. The drive sheave has deep grooves for providing traction to the steel ropes, preventing any slipping during elevator movement.
Gearless Traction Elevators
Gearless traction elevators function in the same fashion as the geared traction types, but without the aid of worm gears. The drive sheave attaches directly to the AC or DC motor. The energy transfers directly to the sheave's rigging mechanism for moving the cab as the motor operates.
Counterweight
Both geared and gearless traction elevators use counterweights. The counterweight resides on an individual rail system alongside the cab. The counterweight will move in the opposite direction of the cab's movement. As a result, less motor power is needed for moving the cab within the hoistway. In fact, the counterweight weighs as much as the cab itself, with an additional 40 to 50 percent weight for capacity compensation.
Hydraulic Elevators
Hydraulic elevators use a pushing mechanism for moving the cab. A large piston and cylinder assembly resides at the hoistway's base. Hydraulic oil pressure forces the piston upwards, transferred its vertical motion to the cab above. The piston pushes the cab up and down the hoistway as needed.
Considerations
The choice of rigging technique depends on many factors. Hydraulic systems are mainly used for smaller buildings, between two and seven stories, since a lot of energy is needed to push the piston and cylinder assembly upwards. Geared traction systems work well in buildings between four and 30 stores tall, offering a comfortable ride with less energy needed, as compared to a hydraulic system. Gearless traction systems use even less energy than geared elevators, making them an environmentally friendly rigging technique.