Fig. 242 shows a double pump driven directly, without gears or belt,
from the shaft of an electric motor. The pump crossheads are connected
directly to cranks at each end of the motor shaft. The cranks are set
at right angles and each pump is double acting, or has two plungers
connected by outside rods and with outside packed stuffing-boxes, so
that this portion of the pump is always accessible.
The plungers are 3-1/2 inches diameter and 5-1/2 inches stroke. The
pump and motor are mounted upon a rigid box girder frame: this unit is
self-contained and occupies a relatively small floor space.
_Electric Drive for Fire Pumps._ The importance of instantly operating
fire extinguishing apparatus can scarcely be exaggerated. The largest
conflagrations are but little flames at the beginning, and if caught
at the critical moment they make no record of destruction; for such
service the electric current is the ideal agent. A notable installation
of electric-driven pumps for fire service is in the Marshall Field
store, Chicago, a building occupying an entire city block. The outfit
consists of a Laidlaw-Dunn-Gordon _duplex Underwriter pump connected by
single reduction gearing to a waterproof electric motor_.
[Illustration: FIG. 242.]
The pump cylinders, 8 × 12 inches, have a computed capacity of 700
gallons per minute at 140 pounds water pressure. The pump, besides its
other special features, is claimed to be rust proof throughout so that
it will not get out of ready running condition.
[Illustration: FIG. 243.]