The morning news. [volume] (Savannah, Ga.) 1887-1900, 1899-07-09

street and the North river, nominally for
the American Air Power Company. but
really for the Metropolitan Traction Com
pany, which is about TO run some OF its
crosstown cars with air.
When power is stored for future use by
COMPRISING air it is usual to put the lat
ter into storage tanks at a higher pressure
than that al which it is used. The higher
the pressure the more work is ODtaina bic
from a given volume. Accordingly. when
any wholesale JOB, like running a heavy
street car for several miles, is about to be
performed, it is desirable to employ much
greater pressure, at least for storage pur-
poses, than in any of the other common
applications of compressed air The gas
enters the cylinder of the motor at a
pressure of $50 pounds to the inch, per-
haps, having first passed through re
ducing valve" But the huge TASKS or
bottles that are placed under the car to
carry the compressed air are charged
at the station at a pressure of 2C0O
pounds to the inch or more. The COM
pTessor that charges these TASKS and the
stationary storage tanks at the power
house, then, must be capable of squeezing
the air down to about 200 or $500 pounds
10 the inch.
The plant just installed in West Twenty
fourth street is exceptional in being the
hrst combination ever made of an engine
of lOO0-horse power with a compressor
that develops $500 pounds 10 the inch
The engine, built by the Alls people Of
AIiwaukee is of The vertical cross-com-
pound type. The compressor, made by
the acknowledgement company divides
its work into four stages. At the first
it brings the pressure up to forty pounds.
at the second $50 pounds, at the third 10
$40 pounds, and at the last to 1900 The
hight OF the double machine is sixty feet
An air compressor is an exact counter
part Of a steam engine. In the latter,
vspor, already under high pressure, pushes
a piston along and develops power there
by. In compressor, power from another
source pushes the piston, and thus
squeezes up air from o low 70 high pres
sure. Just as the expansion Of The steam
is often divided into three or four stages.
so the compression of air is usually ef-
fected by degrees instead of all at once.
This compressor has four cylinders The
biggest has a diameter of 46 inches, and
carries on the first part Of the work The
next has diameter Of "a inches. the third
one is IA inches across, and the fourth ONLY
o. But the pistonS in them all have
strokes of the same length-sixty inches.
Here is another point of comparison be-
tween the engine and the compressor. Ex-
pansion chills any vapor and compression
heats it. The steam that enters the cylin-
ders of an engine grows cooler and cooler
as Il drives the piston before it, The air
in a compressor grows hotter and hotter
as the piston drives il into corner. If
single-stage compressor is used TO carry
the pressure up 10 100 pounds TO the inch
ordinary atmospheric air would be heated
to 500 or perhaps $50 degrees Fahrenheit.
This would be bad for machinery. 1t is
customary, therefore, 10 divide the work
into two or more Stages, and send the hot
air into APPARATUS for cooling Il after each
compression BY going up to only forty
pounds at the outset. the temperature is
kept down to the vicinity Of 300 or $50 de
grees. The four-stage compressor is pro
Vided with four coolers, one for each CYL
inder, so that the air enters the storage
tanks at something like ordinary temper
atures.
The steel bottles in which the air is
stored are intended TO sustain q pressure
Of only 200 or 300 pounds ordinarily. but
to insure safety they are tested up to
1000 pounds 70 the inch before being put
into service. In the power station about
800 of these bottles are to be used These
are connected with each other and with
the charging tube for the cars by means
OF PIPES and valves. The method Of al
taching the feed pipe to car for charg-
ing Is similar to that by which the breech
plug is fastened into a gun. ii is pro-
vided with an interrupted screw" and
only quarter of a turn is necessary TO
fasten and unfasten IL.