Compressed Air Power Plant At The St. Louis Exposition
The central compressed air power plant at the St. Louis Exposition will
contain two main compressing units; one cross-compound, two-stage, Cincinnati-gear
compressor, having 13 and 24-1nch steam cylinders, 22 and 14-inch air cylinders
and 24-inch stroke, with a displacement at 125 r. p.m. o{ 1300 cubic feet
per minute, and one cross-compound, two-stage, Meyer-gear compressor having
12 and 2o-inch steam cylinders and 11-inch air cylinders and 18-inch stroke,
with a displace-ment at 100 r. p.m. of 530 cubic feet per minute. The first
machine is to supply the general compressed air requirements of the exposition,
while the second is to supply the transportation exhibits. The larger machine
is of special interest as being the first compressor of its type publicly
exhibited, although a number of similar machines have been and are being
installed in private plants. A 15oo-ft. machine is at the present time being
placed in the Jersey City power house of the Central Railroad of New Jersey.
The general construction of one of these machines is shown in Figs. 1 and
2. The frames, as will be noted, are of massive construction, with a long
bearing on the foundation, while the steam and air cylinders, joined in
the direct line of thrust by heavy cast-iron housings, are also supported
by bed-plates under their entire length, the weight of each side being thus
taken on two large bearing surfaces extending to the ends of the machine,
avoiding the objectionable features of over-hung cylinders, and giving the
compressor great stability. The general construction is characteristic of
the best grade of engine work, and comprises removable quarter-boxes and
main bearings, steel forged connecting rods, with wedge take-up, specially
large crank and wrist pins and caststeel cross-heads with adjustable babbitted
slippers, top and bottom, working in bored guides.
The reciprocating motion is of the simplest possible character, this sirnplicity
in construction permitting low reciprocating' weights without sacrifice
of strength. These features' allow satisfactory balancing, and in connection
with the long bearing on the foundations insure an especially easy-running
machine. The steam valve-gear is of our four-valve type. Steam distribution
is effected by means of short, double-potted, slide valves, working at either
end of the steam chest on a valve face as close as possible to the cylinder
bore, the port volume being restricted as far as the large valve area will
allow. The exhaust valves are of the Corliss rotary type and are placed
at the bottom of the cylinder.
This construction has been followed in order to produce a valve gear having
the essential advantages of a Cotlisa, namely, separate passages for the
steam and the exhaust with corresponding reduction in cylinder condensation,
together with short straight ports and small clearance. On the other hand,
the complicated Corliss releasing gear, which is necessarily prejudicial
to even moderate speeds, has been eliminated, the action being positive
throughout.
