_HYDRAULIC APPARATUS FOR TRANSMITTING POWER._
Although a system but recently developed, the employment of
hydraulic machinery for transmitting and applying power has reached
an extended application to a variety of purposes, and gives promise
of a still more extensive use in future. Considered as a means of
transmitting regularly a constant amount of power, water apparatus
is more expensive and inferior in many respects to belts or shafts,
and its use must be traced to some special principle involved which
adapts hydraulic apparatus to the performance of certain duties.
This principle will be found to consist in storing up power in
such a manner that it may be used with great force at intervals;
and secondly, in the facilities afforded for multiplying force
by such simple mechanism as pumps. An engine of ten-horse-power,
connected with machinery by hydraulic apparatus, may provide for a
force equal to one hundred horse-power for one-tenth part of the
time, the power being stored up by accumulators in the interval;
or in other words, the motive power acting continuously can be
accumulated and applied at intervals as it may be required for
raising weights, operating punches, compressive forging, or other
work of an intermittent character. Hydraulic machinery employed
for such purposes is more simple and inexpensive than gearing and
shafts, especially in the application of a great force acting for
a considerable distance, and where a cylinder and piston represent
a degree of strength which could not be attained with twice the
amount of detail, if gearing, screws, levers, or other devices were
employed instead.
Motion or power may be varied to almost any degree by the ratio
between the pistons of pumps and the pistons which give off the
power, the same general arrangement of machinery answering in all
cases; whereas, with gearing the quantity of machinery has to be
increased as the motive power and the applied power may vary in
time and force. This as said recommends hydraulic apparatus where a
great force is required at intervals, and it is in such cases that
it was first employed, and is yet for the most part used.
In the use of hydraulic apparatus for transmitting and applying
power, there is, however, this difficulty to be contended with:
water is inelastic, and for the performance of irregular duty,
there is a loss of power equal to the difference between the duty
that a piston may perform and what it does perform; that is, the
amount of water, and consequently the amount of power given off,
is as the movement and volume of the water, instead of as the work
done. The application of hydraulic machinery to the lifting and
handling of weights will be further noticed in another place.
(1.) Under what conditions is hydraulic apparatus a suitable
means for transmitting power?--(2.) To what class of operations
is hydraulic apparatus mostly applied?--(3.) Why is not water
as suitable a medium as air or steam in transmitting power for
general purposes?