Elevators

ELEVATORS are designed to transfer people or materials from one level to another in a vertical direction with safety. Com plete installations comprise the elevator machine with its motive power and controller, platform and enclosure in a hatchway operat ing on guides and with the necessary connecting cables, sheaves and other accessories. There are many types of elevators in use, operated by hand, steam, belt, hydraulic or electric power. Those installed recently (1928) have been almost exclusively of the elec tric type. There is a wide variation in their construction, depend ing upon the motive power, type of building served and the char acter of service to be performed.

The modern elevator dates from a platform hoist made by Henry Waterman in New York, in 185o, this being a very crude affair, operating between two floors. At about the same time George H. Fox and Company of Boston were building the same type of elevator and sending it to other parts of the country. In 1852 Elisha Graves Otis began the manufacture of elevators at Yonkers, N.Y., and in 1854 invented the first safety device to pre vent the falling of the car platform in case the ropes should break.

Early Types.

The first passenger elevator was installed by Otis in 1857 in New York. The distinction of being the first pas senger elevator has been claimed for an elevator installed by Otis Tufts, of Boston, in New York, which was known as the "vertical railway," but this was not installed until 1859. This "vertical railway" had as its principal feature an immense vertical screw, by means of which the car platform was raised and lowered. It was not, however, successful and only two of them were installed. The oscillating cylinder steam engine and the station ary cylinder steam engine which replaced it, were both invented by the Otis organization and remained in use until superseded by the hydraulic type. In 1878, Charles R. Otis invented the safety governor. The first passenger elevator in an office building was of the steam-driven type and was installed in New York in 1869. About this time steam driven belt machines were standard for fac tory elevators.

Hydraulic Elevators.

Early in the '7os, hydraulic machines were introduced and had many advantages over the steam ma chines, principally that of increased speed. This development of the hydraulic elevator began with the direct acting plunger elevator which, however, was soon superseded for all except low rises, by the vertical hydraulic elevator, invented by Cyrus W. Baldwin. This type of elevator was rapidly developed for in creased rises of elevators and improved forms of control. The early machines were operated by a hand rope in the car, but as speeds increased so that this was impossible, there was invented the differential valve and the pilot valve, operated by a lever de vice in the car. In meeting demands for higher buildings and con sequently greater speeds, water pressures were rapidly• increased which, together with further developments in the controlling system of the car, soon made available car speeds of 600 f t. per minute, which at that time was considered marvellous.

Electric Elevators.

In 1887 William Baxter, Jr., designed and installed an electric elevator in Baltimore, which was not successful. In 1889 the first successful electric elevator installa tion was made by Otis Brothers and Company in New York. This elevator remained in service about 35 years. The early electric elevators were of the drum type in which the hoisting cables were wound on the drum which was driven from an electric motor through a worm and gear reduction. These early machines were controlled by hand rope which, however, soon gave way to a lever device somewhat similar to that used with hydraulic ele vators. In a few years this was superseded by what was known as the "magnet control," by means of which the car was stopped and started from a switch in the car itself, which operated electro magnets on a control board.

Shortly after the development of car switch control for electric elevators, there was placed on the market the automatic push button type of control. This type was intended primarily for private residences and apartments and was operated by means of buttons in the car corresponding to the floors served and by buttons at the entrances on each floor. No operator was required and the passenger operated the car by pressing the buttons. This type was limited to slow speeds on account of the difficulty in making level landings under all conditions of loading, and they could only be used where the service was light as only one passenger at a time could be served. Combination door locks and switches were provided to prevent the opening of the hatchway doors until the car was stopped at the landing and to prevent the operation of the elevator if any of the hatchway doors were open.

It was only a few years after its invention that the electric elevator began to take the place of the hydraulic elevator in all except the highest buildings. This was due to its higher efficiency, its easier handling and because much less space was required for machinery. The early electric machines were all of the direct current type and it was not until April 1898, that the Otis organiza tion installed the first alternating current electric elevator, which was mechanically controlled, as electromagnets were not yet adapted for that character of current.

In

1899 the plunger type of elevator was developed for high rise, high speeds. The claim of safety put forth was that the eleva tor could not fall. There were, however, many inherent disad vantages and this type of elevator for high rises had a very brief period of popularity. The electric elevator of the worm geared type, as then developed, had two disadvantages which prevented its ready adoption for the then highest type of building. Elevator travel was limited because the hoisting ropes were wound on the drum, the face of which necessarily projected in the hatchway, and the face of the drum was limited by the space available in the width of the hatch. The result was that the vertical hydraulic elevators continued in use for high speed service.

1:1 Gearless Traction Elevator.

In 19o4 the Otis Elevator Company installed in Chicago, the first gearless traction electric elevator apparatus, which was of the direct drive type, known as the 1:1 elevator. This elevator machine consisted of a slow speed motor with the driving sheave mounted directly on the armature shaft and with an electric brake on the same shaft. The hoisting ropes attached to the car ran directly to the driving sheave on the machine and around that and a secondary sheave, and directly to the counterweight. This direct drive, without any intermediate gear reduction, and with the slow speed motor, per mitted car speeds of 55o to 600 feet. This type of machine was placed over the hatchway and so saved a great deal of valuable space in the basement. They developed very high efficiency and were easily operated at high speed. This machine was perfected rapidly and within a few years had come into general use for all high speed service.

Where it is desired to use a gearless traction machine for very heavy duties at slower speeds, it is possible to utilize the gearless machine with rope gearing of 2 by means of sheaves on the top of the counterweight and on the steel frame of the elevator car. By 1916 an improvement on the worm gear drum type machine was made which consisted of the use of a driving sheave instead of a drum and which became known as the single wrap traction geared elevator. This improvement provided the geared type of elevator with greater safety, as it gave it the inherent advantage of the traction type of drive in that if the car or counterweight should bottom in the hatchway the other member would not be drawn into the overhead work, as had happened with the drum type machine.

Micro-drive or Self-levelling Elevator.

With this type, the elevator platform is automatically levelled exactly with the floor landing at each stop, irrespective of the operator. This elim inates "inching" at the floors, with consequent saving of time. It also saves power consumption and wear on the machinery.

Automatic Operation.

In 1924 an important advance was made in elevator operation by the invention of the Otis automatic signal control. The entire operation is automatic and controlled by the pressing of buttons in the car by an attendant, or on the floors of the building by the waiting passengers. Upon being given the signal to start, the attendant releases the doors, which close automatically. The elevator then starts automatically and runs to the first floor for which a button has been pressed, where the car stops automatically and the doors open automatically. After the passenger has alighted the attendant releases the doors and the cycle of operation is repeated at each floor for which a button has been pressed. In the meantime waiting passengers press buttons at the floors, indicating the direction in which they wish to travel. Each call is automatically registered on the first elevator travelling in the proper direction, which then automatically stops at that floor, without even the foreknowledge of the attendant. This type of control is supplied with micro-drive, which enables these ele vators to be operated at speeds up to 900 or i,000 ft. per minute, and as much higher as may be required by buildings of the future. These high speeds are made possible by the automatic levelling, as cars travelling at such speed could not be satisfactorily handled by manual operation of an operator, with car switch control.

A form of control which has become very popular in the United States in recent years and which is known by various names such as unit multi-voltage, variable voltage, etc., was patented many years ago by Ward Leonard and has been used extensively outside of the elevator industry wherever considerable variation of speed and smooth retardation and acceleration were desired. In the elevator industry it consists of an individual generator driven by direct or alternating motor-supplying current to the elevator motor. A further development of the automatic signal control is the collective automatic control and the department store control. The collective automatic control is an outgrowth of the ordinary automatic push button elevator used for private residences and small apartment houses as previously described. With the collec tive type of control, combined with micro-drive, speeds of 450 ft. per minute may be attained with perfect stopping, and the control is so arranged that the elevator will stop at each floor for which a button has been pressed in the direction in which the car is travel ling. These improvements make it possible to use this type of elevator without an operator in larger apartments and small hotels.

The department store type of control is designed for buildings of that character, or other service where stops are usually made at each floor in both directions. With this system there are no floor buttons required, nor is the attendant required to press any buttons in the car. Upon the releasing of the doors at the first floor, which close automatically, the car then starts automatically and runs to the next floor, where it stops automatically and the doors are opened automatically, this cycle being repeated at each floor. It is possible, however, by the movement of a switch in the car to have the elevator travel past any floors without stopping. There are variations of both collective control and department store con trol to suit individual requirements of certain buildings.

A form of automatic operation for freight elevators in large groups is known as the operatorless control, used with a number of elevators in one or more banks. With this system there is one central operator for each group who receives by telephone all calls from any floor where an elevator is required. He has before him an indicator board which shows him the position of all elevators at all times and whether they are in use or not. By means of but tons on his desk, which automatically control all of the elevators, he then dispatches the nearest available elevator to the floor where it is needed. This effects a great saving in time and elimi nates the possibility of waiting for an elevator that is in use.

Safety Devices.

The first essential of an elevator installation is the inclusion of all necessary safety devices to accomplish this purpose and prevent accident or injury. The early builders, with very crude machines, did not require any devices other than that of one over the platform to prevent its falling in case the ropes should break. As the machines developed in character, capacities and speed, various other devices were put into operation to take care of increased hazards until at the present time the elec tric elevator of the reputable manufacturers has a number of safety devices which cover practically every condition which might occur.

In addition to the safety device under the car connected with the automatic speed governor, there is also, on high speed instal lations, a switch on the governor which cuts off current to the motor and applies the brake if the car should attain excessive speed. Automatic stopping and final limit switches are provided to slow down and stop the car at the terminal landings in case the operator should fail to throw the car switch, or in case an automatically controlled machine should run beyond its normal stopping point. Buffers are provided in the pit to bring the car to a gradual stop if other safety devices should fail. On high speed installations, these long stroke oil buffers are so arranged that if the car lands upon them they are gradually compressed and checked by oil circulating through graduated openings. Featured in the traction type of plant, in which, where neither the car nor the counter-weight can be pulled into the overhead work if the other should be checked in its descent, buffers mean that another possibility of accident is eliminated.

All automatic types of elevators used without a regular oper ator have the interlocking door locks and contacts as heretofore described. In many American cities the regulations now require that all passenger elevators shall have a gate or door on the plat form, with a switch so connected that the car cannot be operated while this gate is open. This prevents any possibility of passengers in the car coming in contact with the side of the hatchway while the elevator is running.

Signals.

The early annunciator in the car to notify the oper ator of calls has given place on the high speed elevators to flash light signal systems of several types. When service is not continu ous the flash light annunciator is used ; this being automatically reset when the call is answered. In continuous service, as in office buildings where the elevators are kept running continuously, the signal system on car switch controlled elevators is such that the pressing of a button by a waiting passenger on any floor signals the first car in the desired direction by flashing a light when the car is approximately two floors away, thus notifying the operator of the call. This light is extinguished when the car passes the floor. There is also provided with this system an "up" and "down" signal lan tern in front of each elevator at each floor to notify the passenger as to which elevator will service his call. On signal control eleva tors the pressing of a button on any floor registers the.call on the elevator controllers. Signal lanterns are provided on each floor.

Influence of Elevators on Buildings.

Before the advent of the elevator it was not feasible to construct buildings more than a few storeys in height. The early elevators permitted of a few addi tional storeys. As the speed and reliability of elevators increased this improvement was reflected in the taller buildings which sprang up in the larger cities. With the coming of the steel skeleton build ing structure builders saw the possibilities of increased returns from their property, especially in the more congested districts where land values are high, and turned to the elevator as the means of making it possible to rent such buildings advantageously.

The development and application of gearless electric elevators which removed the height limitation of building as far as the ele vator is concerned, was immediately reflected in the 41 storey Singer building in New York. Since 1924, coincident with the development of the still higher speeds of the signal control ele vator, there has been a tremendous increase in the number of high buildings erected in the larger cities throughout the United States. The present maximum car speed of 90o f t. per minute has already been exceeded in estimates for still higher speeds in buildings which might require it. It would thus appear that no matter to what extent the builders may aspire in the height of their build ings, elevator manufacturers will be able to meet their require ments.

In office buildings the character of elevator service is frequently the most important feature in the success of the building. Eleva tors in a building are divided into those for local service, approxi mately from the 1st to the i oth floor ; then express elevators serv ing the roth to loth floors; another group making no stops to the loth, and serving from there to the 3oth and so on. In this way the offices on the upper floors become practically as easy of access as those on the lower floors and are frequently more desirable on account of the better light and ventilation and freedom from street dust and noise. (J. H. VAN A.)