Gilpin observer., 1899-01-26
USE OF COMPRESSED AIR.
Many Avenues open to Its Application Il

I,ooo years, lls hrst practical applica-
ton was made by Prof Colladon of
Geneva. in transmitting power for op-
Grating machine drills in the construc-
ton of the Mont Gents tunnel. In this
country the first application of any
note was in the large plant used in the
construction of the Hoosac tunnel.
Since this time the applications of
compressed air have steadily increased.
until at the present time the list com
priseS over 300 various uses
AT first efforts We're mainly directed
toward the production of airmachinery
which would work under the most ad-
verse circumstances, but during the
Hst few years the larger manufactur-
ing companies have devoted consider
able attention to the development of
machines which would combine with
simplicity and certainty of operation IL
reasonable amount of efficiency.
The widest application of compressed
air is found in mining. 1t may be used
to run the drills, furnish power to the
hoisting machinery. to the pumps, to
tcal cutting machinery, to locomotives
used to handle the product of the
larger coal mines. and to motors used
to run mills. or for the varied uses to
which power may be applied in min
ing camp.
Depending on the machinery en-
ployed and the method of handling the
air, compressed-air plant may be an
economical or Il costly method of sup
plying power. For short distances up
to one or two miles energy may be
transmitted in a well-designed plant
by compressed air with but little loss
and at IL reasonable expense.
With the high price of coal which
prevails in most mining camps. it
would undoubtedly pay. in Il plant of
fair size, to put in tirst-class moderr
compreSsors. When any attempt at
economy in compression is made the
air cylinders should be thoroughly
jacketed with water, and for the higher
pressures the air should be compressed
in two or three stages. depending on
the pressure, and then passed through
an inter-cooler in going from the low
pressure cylinder to the high-pressure
cylinder. The inter-cooler should be
so constructed that the air in passing
through it is reduced to at least as low
q temperature as it had on entering the
compressor.
The value of these cooling arrange
mentS is readily understood when one
remembers that the work required to
compress one pound of air to any given
prtssure adibatically-that' is without
Gfoling it in any way-is about 1.3
Zines as much us if the same air had
been compressed to the same pressure
isothermally-that is, ut Il constant
temperature.
A rather peculiar fact in this connec-
tion may be noted here: That for the
most economical compression all the
work of compression. that is, all the
l. tt,. nj &c
= isted in heating the jacket water.
EI'his comes from the fact that one
pound of air at any given temperature
contains the same amount of intrinsic
energy. no matter what its pressure.
All the compressor does, then, is to put
the air in n state where this energy is
available.
In any mechanical compressor there
are at least the following direct
sources of loss:
First-The friction of the compressor.
This may vary from > per cent. in some
of the best types in perfect condition
to 20 per cent in the ordinary compress
sor in fair order. and may reach 30 to
81 per cent. in Il poor compressor III
bad order.
Second-The loss due to heating the
air by compressing it. The amount of
this loss varies with the type of com
Dressor and with the final pressure
reached.
Air pipes should be liberal in size,
without sharp bends. and, above all,
must not leak. The amount of air dis
charged even from II small leak is sur
prising. For Il pipe having Il number
of small leaks such that the aggregate
area is one-tenth of one square inch the
IN Six nntrn1s
minute at 100 pounds pressure. This
would amount to net loss of seven to
eigHt horsepower or II loss ut the
cHnpressor of not far from ten horse
fower. This. with coal mt So per ton.
would cost. for coal only, about $500
per year If the compressor Is running
twenty-four hours per day.
The actual friction loss in pipes is
not so great as II Is ordinarily sup
\Dosed to he. This is due to the fact
Nat ms the pressure diminishes the
volume increases. so that the product
of the pressure and the volume re-
mains constant. The actual per cent.
of loss is only from one-third to one
half the loss of pressure in per cent. of
the total pressure.
The most extensive Use Of COM
pressed air in mines, and the one use
where IL has at present no rival, Is III
the operation of percussion drills.
These drills use air in Il most efficient
way. requiring from twelve to twenty
horse power at the compressor to OPP
orate each drill Here economy of
power counts but little compared with
certainty of operation. simplicity and
ability to stand abuse. Compressed
air Is also extensively employed In fur
niSItinfr Dnprntp diamond
prospecting drills. and for most mines,
for this purpose, has no real rival other
than electricity.
one of the uses to which compressed
air is put, and which more than any
thing else has given II its universal