i STEAM COAL - Clpdigital.org

machines of moderate capacities, and to show the
relation of these two types of compressor plants
to each other as regards complete installation
costs and operating expenses, the accompanying
diagrams were prepared.
As shown in plates I. and II. the free air capacity
of the two types of compressors is compared
with installation costs and operating expenses for
sizes from 1,500 to 11,000 cubic feet per minute.
The installation costs are close approximations to
actual costs and would meet general conditions
under which such plants are installed in different
parts of the country. The difference in first cost
THE COAL TRADE BULLETIN. 31
made up in two years. At 5,01)0 cubic feet capacity
the difference is made up in one year with
coal at 75 cents per ton. Beyond this point there
is absolutely no question about the economy of the
Corliss type of compressor for the difference in
installation costs is a decreasing one and at 9.500
cubic feet capacity the installation cost of the
Corliss plant is less than that of the straight-line
compressor plant.
The straight-line plants tabulated here have
been favored in many respects for both types of
plants are considered as placed under one roof,
whereas the average straight-line plant of four to
TDtrrcnENcrs IN IHSTRLL/'TION COSTS RNJI ANNUML OPSHHTING £xpf«jfi Or SmnitiHT LINE HN-Q
Cnoss CoMPOuNii COFILISS Rm T^LHNTZ.
TC.WOlBTfl. ^NSSw.LTa
PLRTE M.
fyy.nfrlletl B,
renter ,,...
Cutlet X • ~0,J/.ree.c. ,. tn.tallat,.* Cat* oj Jttaijtlt Lit,. ••>« Carina Cre.s C.mF..r.et riant.. CC»r..,» Ct in o»li u^ To ?£J0 c.ft Caj.ae,Ty)
Diff.r.ne. In Opeeattna Erp.n.ta. Coal at JS f*' rem. Curve H * bee, hea Cot... £. ' ioao hr,
- ' Coal, .t loo per In, ' 2%' oooo ' I — iooa -
- • C.al at ta. per Tor,. ' C'booo ' G '3ooo •
' * - • C.al at o.. y' Ton " £J-t,aoo • ' H'Cooo •
DTrcRCLNCCS IN /NSTftLLrlTION COSTS ~ Utrrti Fy C NCCS llN RlVN OPZFttirtNC £>\PCNSt2 6
and operating expenses between the two types is
shown in plate III.
The operating expenses are based on 6,000 hours
work per year and the price of coal is taken at
75 cents, $1.00, $2.00 and $3.00 per ton. The last
two costs are intended for mines other than coal
mines. The conditions assumed in these calculations
are such as obtain in general practice and
are as shown in table on the preceding page.
From a study of the results it is apparent that
the Corliss compressor has a legitimate field in
the coal mine, for even wth capacities as low as
2,500 cubic feet, the difference in installation is
six machines has at least three to four buildings
and separate engineers and firemen.
Aside from its economic advantages, the Corliss
compressor possesses mechanical advantages over
the other type that recommend it. It has a
higher mechanical efficiency, or less friction, its
volumetric efficiency is higher, the inlet air is
cooler, the lubrication is better, the maximum
strains are lower and resistance is more uniform
and its life is longer. The regulation is automatic
and is effected through the governor on the
cut-off mechanism of the valve gear.
It is generally possible to place the power plant