The rope-geared hydraulic elevator, which was eventually to become known
as the "standard of the industry," is generally thought to have evolved
directly from an invention of the English engineer Sir William Armstrong
(1810-1900) of ordnance fame. In 1846 he developed a water-powered crane,
utilizing the hydraulic head available from a reservoir on a hill 200 feet
above.
The system was not basically different from the simple hydraulic press so
well known at the time. Water, admitted to a horizontal cylinder,
displaced a piston and rod to which a sheave was attached. Around the
sheave passed a loop of chain, one end of which was fixed, the other
running over guide sheaves and terminating at the crane arm with a lifting
hook. As the piston was pressed into the cylinder, the free end of the
chain was drawn up at triple the piston speed, raising the load. The
effect was simply that of a 3-to-1 tackle, with the effort and load
elements reversed. Simple valves controlled admission and exhaust of the
water. (See fig. 11.)
[Illustration: Figure 11.--Armstrong's hydraulic crane. The main cylinder
was inclined, permitting gravity to assist in overhauling the hook. The
small cylinder rotated the crane. (From John H. Jallings, _Elevators_,
Chicago, 1916, p. 82.)]
The success of this system initiated a sizable industry in England, and
the hydraulic crane, with many modifications, was in common use there for
many years. Such cranes were introduced in the United States in about 1867
but never became popular; they did, however, have a profound influence on
the elevator art, forming the basis of the third generic type to achieve
widespread use in this country.
The ease of translation from the Armstrong crane to an elevator system
could hardly have been more evident, only two alterations of consequence
being necessary in the passage. A guided platform or car was substituted
for the hook; and the control valves were connected to a stationary
endless rope that was accessible to an operator on the car.
The rope-geared hydraulic system (fig. 13) appeared in mature form in
about 1876. However, before it had become the "standard elevator" through
a process of refinement, another system was introduced which merits notice
if for no other reason than that its popularity for some years seems
remarkable in view of its preposterously unsafe design. Patented by Cyrus
W. Baldwin of Boston in January 1870, this system was termed the
Hydro-Atmospheric Elevator, but more commonly known as the water-balance
elevator (fig. 12). It employed water not under pressure but simply as
mass under the influence of gravity. The elevator car's supporting cables
ran over sheaves at the top of the shaft to a large iron bucket, which
traveled in a closed tube or well adjacent to and the same length as the
shaft. To raise the car, the operator caused a valve to open, filling the
bucket with water from a roof tank. When the weight of water was
sufficient to overbalance the loaded car, the bucket descended, raising
the car. On its ascent the car was stopped at intermediate floors by a
strong brake that gripped the guides. Upon reaching the top, the operator
was able to open a valve in the bucket, now at the bottom of its travel,
and discharge its contents into a basement tank, to be pumped back to the
roof. No longer counterbalanced, the car could descend, its speed
controlled solely by the brake.
The great popularity of this novel system apparently was due to its smooth
operation, high speed, simplicity, and economy of operation. Managed by a
skillful operator, it was capable of speeds far greater than other
systems could then achieve--up to a frightening 1,800 feet per minute.[6]
[Illustration: Figure 12.--Final development of the Baldwin-Hale water
balance elevator, 1873. The brake, kept applied by powerful springs, was
released only by steady pressure on a lever. There were two additional
controls--the continuous rope that opened the cistern valve to fill the
bucket, and a second lever to open the valve of the bucket to empty it.
(From _United States Railroad and Mining Register_, Apr. 12, 1873, vol.
17, p. 3.)]
In addition to the element of potential danger from careless operation or
failure of the brake, the Baldwin system was extremely expensive to
install as a result of the second shaft, which of course was required to
be more or less watertight.
Much of the water-balance elevator's development and refinement was done
by William E. Hale of Chicago, who also made most of the installations.
The system has, therefore, come to bear his name more commonly than
Baldwin's.
The popularity of the water-balance system waned after only a few years,
being eclipsed by more rational systems. Hale eventually abandoned it and
became the western agent for Otis--by this time prominent in the
field--and subsequently was influential in development of the hydraulic
elevator.
The rope-geared system of hydraulic elevator operation was so basically
simple that by 1880 it had been embraced by virtually all manufacturers.
However, for years most builders continued to maintain a line of steam and
belt driven machines for freight service. Inspired by the rapid increase
of taller and taller buildings, there was a concentrated effort,
heightened by severe competition, to refine the basic system.
[Illustration: Figure 13.--Vertical cylinder, rope-geared hydraulic
elevator with 2:1 gear ratio and rope control (about 1880). For higher
rises and speeds, ratios of up to 10:1 were used, and the endless rope was
replaced by a lever. (Courtesy of Otis Elevator Company.)]
By the late 1880's a vast number of improvements in detail had appeared,
and this form of elevator was considered to be almost without defect. It
was safe. Absence of a drum enabled the car to be carried by a number of
cables rather than by one or two, and rendered overtravel impossible. It
was fast. Control devices had received probably the most attention by
engineers and were as perfect and sensitive as was possible with
mechanical means. Cars with lever control could be run at the high speeds
required for high buildings, yet they could be stopped with a smoothness
and precision unattainable earlier with systems in which the valves were
controlled by an endless rope, worked by the operator. It was almost
completely silent, and when the cylinder was placed vertically in a well
near the shaft, practically no valuable floor space was occupied. But most
important, the length of rise was unlimited because no drum was used. As
greater rises were required, the multiplication of the ropes and sheaves
was simply increased, raising the piston-car travel ratio and permitting
the cylinder to remain of manageable length. The ratio was often as high
as 10 or 12 to 1, the car moving 10 or 12 feet to the piston's 1.
In addition to its principal advantages, the hydraulic elevator could be
operated directly from municipal water mains in the many cities where
there was sufficient pressure, thus eliminating a large investment in
tanks, pumps and boilers (fig. 14).
By far the greatest development in this specialized branch of mechanical
engineering occurred in the United States. The comparative position of
American practice, which will be demonstrated farther on, is indicated by
the fact that Otis Brothers and other large elevator concerns in the
United States were able to establish offices in many of the major cities
of Europe and compete very successfully with local firms in spite of the
higher costs due to shipment. This also demonstrates the extent of error
in the oft-heard statement that the skyscraper was the direct result of
the elevator's invention. There is no question that continued elevator
improvement was an essential factor in the rapid increase of building
heights. However, consideration of the situation in European cities, where
buildings of over 10 stories were (and still are) rare in spite of the
availability of similar elevator techniques, points to the fundamental
matter of tradition. The European city simply did not develop with the
lack of judicial restraint which characterized metropolitan growth in the
United States. The American tendency to confine mercantile activity to the
smallest possible area resulted in excessive land values, which drove
buildings skyward. The elevator followed, or, at most, kept pace with,
the development of higher buildings.
[Illustration: Figure 14.--In the various hydraulic systems, a pump was
required if pressure from water mains was insufficient to operate the
elevator directly. There was either a gravity tank on the roof or a
pressure tank in the basement. (From Thomas E. Brown, Jr., "The American
Passenger Elevator," _Engineering Magazine_ (New York), June 1893, vol. 5,
p. 340.)]
European elevator development--notwithstanding the number of American
rope-geared hydraulic machines sold in Europe in the 10 years or so
preceding the Paris fair of 1889--was confined mainly to variations on the
direct plunger type, which was first used in English factories in the
1830's. The plunger elevator (fig. 16), an even closer derivative of the
hydraulic press than Armstrong's crane, was nothing more than a platform
on the upper end of a vertical plunger that rose from a cylinder as water
was forced in.
There were two reasons for this European practice. The first and most
apparent was the rarity of tall buildings. The drilling of a well to
receive the cylinder was thus a matter of little difficulty. This well had
to be equivalent in depth to the elevator rise. The second reason was an
innate European distrust of cable-hung elevator systems in any form, an
attitude that will be discussed more fully farther on.