Elevator types and their differences
Elevators are devices
that move people and goods vertically within a dedicated shaft that connects
the floors of a building. They became commonplace in the 1850s as steel and
iron structural frames allowed taller construction; however it was Elisha
Otis's safety mechanism that prevented the car from falling that made elevators
popular. In almost all modern multi-floor buildings, elevators are required to
provide universal access.
There are three main
types of elevators commonly used: traction with a machine room,
machine-room-less traction, and hydraulic; however, there are variations on
each type.
Hydraulic
Elevators
Hydraulic elevators are supported by a
piston at the bottom of the elevator that pushes the elevator up as an electric
motor forces oil or another hydraulic fluid into the piston. The elevator descends as a valve releases the
fluid from the piston. They are used for low-rise applications of 2-8 stories
and travel at a maximum speed of 200 feet per minute. The machine room for
hydraulic elevators is located at the lowest level adjacent to the elevator
shaft.
Conventional Hydraulic Elevators have a
sheave that extends below the floor of the elevator pit, which accepts the
retracting piston as the elevator descends.
Some configurations have a telescoping piston that collapses and
requires a shallower hole below the pit.
Max travel distance is approximately 60 feet.
Hole-less Hydraulic Elevators have a piston
on either side of the cab. In this
configuration, the telescoping pistons are fixed at the base of the pit and do
not require a sheave or hole below the pit.
Telescoping pistons allow up to 50 feet of travel distance. Non-telescoping pistons only allow about 20
feet of travel distance.
Roped Hydraulic Elevators use a combination
of ropes and a piston to move the elevator.
Maximum travel distance is about 60 feet.
Hydraulic elevators have a low initial cost
and their ongoing maintenance costs are lower compared to the other elevator
types. However, hydraulic elevators use more energy than other types of
elevators because the electric motor works against gravity as it forces
hydraulic fluid into the piston. A major drawback of hydraulic elevators is
that the hydraulic fluid can sometimes leak, which can cause a serious environmental
hazard. The environmental risk and high energy use are two main reasons that
hydraulic elevators are not being installed as often as in the past.
Geared and
Gearless Traction Elevators with Machine Room
Traction elevators are lifted by ropes,
which pass over a wheel attached to an electric motor above the elevator
shaft. They are used for mid and
high-rise applications and have much higher travel speeds than hydraulic
elevators. A counter weight makes the
elevators more efficient by offsetting the weight of the car and occupants so
that the motor doesn't have to move as much weight.
Geared Traction Elevators have a gearbox
that is attached to the motor, which drives the wheel that moves the
ropes. Geared traction elevators are
capable of travel speeds up to 500 feet per minute. The maximum travel distance
for a geared traction elevator is around 250 feet.
Gear-less Traction Elevators have the wheel
attached directly to the motor.
Gear-less traction elevators are capable of speeds up to 2,000 feet per
minute and they have a maximum travel distance of around 2,000 feet so they are
the only choice for high-rise applications.
Geared traction elevators are middle of the
road in terms of initial cost, ongoing maintenance costs, and energy consumption.
Gear-less traction elevators have a high initial cost, medium ongoing
maintenance costs, and use energy a bit more efficiently than geared traction
elevators.
It is important that traction elevator
ropes and sheaves are checked for wear on a regular basis. As they wear, the
traction between the sheave and the cables is reduced and slippage becomes more
regular, which reduces the efficiency and can become dangerous if left
unchecked.
Traction elevators have height restrictions
that are governed by the length and weight of the cables or ropes. New
materials that are stronger and lighter, such as carbon fiber, will allow
traction elevators to achieve new heights.
Machine-Room-Less
(MRL) Elevators
Machine-Room-Less Elevators are traction
elevators that do not have a dedicated machine room above the elevator
shaft. The machine sits in the override
space and is accessed from the top of the elevator cab when maintenance or
repairs are required. The control boxes are located in a control room that is
adjacent to the elevator shaft on the highest landing and within around 150
feet of the machine.
Machine-room-less elevators have a maximum
travel distance of up to 250 feet and can travel at speeds up to 500
feet-per-minute. MRL elevators are comparable to geared traction elevators in
terms of initial and maintenance costs, but they have relatively low energy
consumption compared to geared elevators.
Machine-room-less elevators are becoming
the most popular choice for mid-rise buildings where the travel distance is up
to 250 feet. They are energy efficient, require less space, and their operation
and reliability are on par with gear-less traction elevators.
The main reason that MRL elevators have
been adopted so slowly in the United States is because the building codes had
provisions that didn't allow the motor to be within the hoistway. This is
slowly being changed, but it is worth consulting with the local authorities
before specifying an MRL elevator.
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BRAUN ELEVATOR CO., LTD (ZHEJIANG, CHINA)
Contact:mingxia.hu@braun-elevator.net
NO.899, YUNXIU NORTH ROAD, DEQING COUNTY, ZHEJIANG PROVINCE, CHINA
TEL: 0086-572-8363972 FAX: 0086-572-8363992
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