Page:Collier's New Encyclopedia v. 03.djvu/577

LEFT ELEVATOR 603 ELEVATOR per cent, of the installations of the pres- ent time, are of two types, namely, those with winding di-ums and those with traction sheaves. The former type are designed with drums spirally grooved on which the cables wind and unwind in DRIVtNG 5HCAVC lOLrff SHE/tVC JOLCR SH£/jy£ Cou/^TSf? W£/GHr O/l Bl/fr£R OiL Bomn GEARLESS TRACTION ELEVATOR raising and lowering the elevator. Ele- vators of the traction type are provided with straight grooved sheaves over which the cables pass, the friction be- tween the sheave and the cables being utilized for raising and lowering the elevator. Figure 1 shows in diagram the usual arrangement of car, counter- balance cables, etc., for an electric drum machine, while Figure 2 shows a similar arrangement for the traction type electric elevator. The worm-geared drum machine was almost universally used until the advent of the high-speed gearless traction machine which was desig^ned to eliminate the excessive drum sizes required for tall buildings. The worm-geared traction machine has now been developed to cover the field of the worm-geared drum type machine. The elevator machinery may be located either at the base of the hatchway or over the top of the hatchway, the latter location being preferable as it simpli- fies the arrangement. There are three principal types of hy- draulic elevators: the vertical, the hori- zontal and the plunger type. Both the vertical and the horizontal types consist of a cylinder with piston rods connected to traveling sheaves, around which pass the cables which are attached to the car. By introducing water into the cylinder under pressure, the piston is caused to move and the car raised. To lower the car, the water is allowed to discharge from the cylinder, the weight of the car being sufficient to overcome the friction of the water through the valves, pipes, etc. The plunger elevator consists of a tube sunk in the ground a distance equal to the rise of the elevator and a plunger attached to the bottom of the car work- ing in this tube through a stuffing box. Movement of the car is accomplished by water under pressure entering the cylin- der, causing the plunger and the car to rise. To lower the car the water is allowed to discharge from the cylinder. Except in special cases, very few hydraulic elevators are being installed at the present time, the cost of installa- tion and also the cost of operation being much higher than for the electric type of elevator. The steam type of elevator consists of a steam engine as the motive power, geared to a winding drum around which the cables to the car pass. This type of elevator is practically obsolete at the present time. The belt elevator is usually driven from a line shaft and is only used for slow speeds. The hand power elevator is used only when the service is infrequent and the expense of installing a power-driven elevator is not warranted. It is oper-