Theatre Design & Technology - Spring 1976 - 16

or off the lifts entirely.
The stage lifts can be combined to form a double-or
triple-size platform, with two or three lifts operating in
tandem, all in the same plane. They can also be joined at
different levels so adjacent platforms form a step or
steps. Step height can be adjusted in one-foot increments, up to approximately seven feet of vertical separation between adjacent platforms. The upper deck of one
stage lift can be joined with the lower deck of the other.
When adjacent platforms are operated as a unit, they are
mechanically joined together by coupling bars which
prevent any relative vertical motion between them.
Coupling bars are on the long side of the stage lift
and in line with the upright section. One bar is located
at each end of each side of the platform adjacent to
another. Bars are designed with steel guide rollers to support the coupling load, the rollers spaced so that the
bars will just fit between when extended. The rollers
allow a slight vertical play during coupling, and some
relative horizontal movement between stage lifts while
coupled, without squeal from the metal-to-metal contact
of the connection.
The first step in coupling two or three lifts in a configuration is to bring the stage lifts to their proper relative
position and place them on the lock bars. Each lift is
brought slightly above its desired location, the lock bars
extended, and the lift then lowered until the bars are
resting on shelves.
Each corner of the lift actually has two lock bars,
straddling the guide shoe in a compact arrangement that
·fits the limited space in the pit. The bars transmit a load
through the same vertical line to the building. When the
lifts are on lock bars, the coupling bars can be extended
to physically couple two adjacent lifts. Electrical signals
from the control system open the motor-operated ball
valves that connect the hydraulic systems. The rams
raise the coupled lifts, the lock bars retract, and the lifts
operate as a single unit. Coupling and lock bars are part of
a single hydraulic system on each stage lift, an arrangement resulting in a more efficient, quieter hydraulic
power unit.
Elevators are the safest means of transportation, a
record achieved with the aid of restrictions the elevator
manufacturer has imposed on the public for its own
well being. Elevator cars have long been completely
enclosed so that passengers cannot fall out. Nor can
people get on or off until the car is level with the landing
and no longer moving. Well-lighted cars minimize tripping
hazards. A closed-in stage lift, however, is out of the
question; performers need free access to and from the
stage, from either side, front or rear, special effects and
precision dance routines often call for a moving stage and
low-level lighting, all contributing to hazardous conditions.
One redeeming circumstance, however, aids safety' on
stage lifts-performers are aware of the hazards involved
and can be expected to guard against them. Special provisions guard against the possibility of a performer being
caught between passing stage lifts. Should that happen,

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A hydraulic system operates locking bars which secure
platforms to the building structure as weI! as bars which
couple the platforms together when necessary.

astragal-tape switches under the platform and under
the adjacent open floors that the lift passes will cut
off power from the lift. For rapid, safe removal, the stage
lifts can then be operated by power from the machineroom control station. Electrical interlocks in the circuitry automatically prevent movement in the wrong
direction.
Creepage correction as usually incorporated in hydraulic elevators would allow the stage lift to sink approximately one inch, compared with three inches the ANSI
A 17.1 Code permits. Instead of the usual creepage correction, continual releveling, adjustable from 0.1 to 0.9
inch, accurately holds the stage lifts at desired levels and
reduces tripping hazards to a minimum.
When the lifts are below stage level, the
covered by three motor-driven carts, with
horizontal dimensions as the lift platforms.
carts are not in use they are stored under the
downstage and the other two upstage.

opening is
the same
When the
stage, one

The single-deck lift is constructed similarly to the
double deckers. Since any two or all three lifts must be
operable as a single unit, ram diameters were kept the
same to maintain identical speed settings. To minimize
coupling bar loads, the total weight of the single-deck
is almost as great as that of each double-deck unit.
Variations in rise account for differences in pit depths
between the single and double-deck lifts. The single-deck
lift has a deeper pit, allowing the use of two guideshoes
per guide rail, thus reducing the loads on the rope equalization system. The support steel was extended upward
to accommodate this arrangement.
Welded casings to accommodate the cylinders, rams
and equal izer struts, were by far the largest Otis has

THEATRE DESIGN AND TECHNOLOGY

USITT

Table of Contents for the Digital Edition of Theatre Design & Technology - Spring 1976