efficiency of drainage machinery
is very largely a question of method of power application. The
actual pump can be built to almost the same efficiency for any
power application, and with the exception of the limited field
of bailing with tanks, mechanical drainage is a matter of pumps.
All pumps must be set below their load, barring a few possible
feet of suction lift, and they are therefore perforce underground,
and in consequence all power must be transmitted from the surface.
Transmission itself means loss of power varying from 10 to 60%,
depending upon the medium used. It is therefore the choice of
transmission medium that largely governs the mechanical efficiency.

SYSTEMS OF DRAINAGE.--The ideal pumping system for metal mines
would be one which could be built in units and could be expanded
or contracted unit by unit with the fluctuation in volume; which
could also be easily moved to meet the differences of lifts; and
in which each independent unit could be of the highest mechanical
efficiency and would require but little space for erection. Such
an ideal is unobtainable among any of the appliances with which
the writer is familiar.

The wide variations in the origin of power, in the form of transmission,
and in the method of final application, and the many combinations
of these factors, meet the demands for flexibility, efficiency,
capital cost, and reliability in various degrees depending upon
the environment of the mine. Power nowadays is generated primarily
with steam, water, and gas. These origins admit the transmission of
power to the pumps by direct steam, compressed air, electricity,
rods, or hydraulic columns.

DIRECT STEAM-PUMPS.--Direct steam has the disadvantage of radiated
heat in the workings, of loss by the radiation, and, worse still,
of the impracticability of placing and operating a highly efficient
steam-engine underground. It is all but impossible to derive benefit
from the vacuum, as any form of surface condenser here is impossible,
and there can be no return of the hot soft water to the boilers.

Steam-pumps fall into two classes, rotary and direct-acting; the former
have the great advantage of permitting the use of steam expansively
and affording some field for effective use of condensation, but
they are more costly, require much room, and are not fool-proof.
The direct-acting pumps have all the advantage of compactness and
the disadvantage of being the most inefficient of pumping machin