Hydraulic System
CNC machining parts The history of hydraulic power is a
long one，dating from man’s prehistoric efforts to harness the energy in the world around him．The only sources readily available were the water and the wind—two free and moving streams.
The
watermill，the first hydraulic
motor，was an early invention· One is pictured on a mosaic
at the Great Palace in Byzantium，dating from the
early fifth century·The mill had
been built by the Romans． But the first record of a watermill goes back
even further, to around 100 BC，and the origins may indeed have been much earlier·The domestication of grain began some 5000 years before and some
enterprising farmer is bound to have become tired of pounding or grinding the
grain by hand．Perhaps， in fact，the inventor was some
farmer’s wife，since she often drew
the heavy jobs·
CNC machining parts Manv mills staved in use until the end
of the 19th century，but they had
been in the process of being replaced by
the Steam engine as a source of power for the previous 150 years．The transmission of the power generated by the waterwheels was by
shafting and crude gears or pulleys．The steam engine for the first time employed an enclosed moving
stream of fluid(steam) under pressure—the
principle to be later employed in hydraulic
power transmission—for transmitting power continuously from the point of
generation to the place where it was
used·
The
transmission of hydrostatic power to a distant point began long before
that,however ．Hero of A1exandria，in the first century AD，built a device in which a fire on the temple altar expanded air in a closed container．The air pressure forced water to travel along a tube
to
the temple doors where，spilling into a
container，it provided the force
through ropes and pulleys to magically
open the doors
Hero also produced a steam engine of sorts．
Its
motion depended on the reaction forces
from jets of steam，as in the
present steam turbine，but it was
little understood and it was no more
than an interesting curiosity·
The
invention of early forms of the hydraulic pump has a similarly early origin·The first pumps were not used to develop hydraulic power，however' but only to transfer water for irrigation or to remove it from mines
Archimedes applied the principle of the screw
to hydraulic machines in the third century BC．
His
screw pumps were used to raise water for irrigation or to the level of
aqueducts·The piston pump，the first mechanical device capable of generating pressure in a
column of liquid，is believed to have
come from Egypt at a similarly early date．Like the screw pump，it was used
only as a means for moving water and not as a means for generating hydraulic
power·
In
more recent years， the role of leadership
in hydraulic power application has been taken over largely by some of the
larger earthmoving and construction equipment manufacturers the total Power
involved is often greater than that required in even the largest aircraft
systems．the concentration of
this power in a few very large loads，as compared to the multitude of smaller loads in an airplane，has spurred the system designer to find new，creative ways to distribute and control the power．This he has succeeded in doing to obtain maximum precision of
control and productivity while minimizing power consumption．
in
modern mobile and industrial applications，the system designer has made full use of the wonderful flexibiIity
and adaptability of hydraulics． It can readily be directed around corners and
past involving joints that virtually defy mechanical power transmission． It can be divided easily to
serve individual loads or recombined to power a high，single一load demand． Electrical and pneumatic power distribution have similar
flexibility，but lack the
compactness
and
certain of the other important characteristics of hydraulics
CNC machining parts A very significant feature of hydraulic
power is its extreme power density． Fig．1 0．1 shows a comparison of a 400 hP(1hp=0·7457kW)hydraulic pumping source with a diesel engine and an
electrical motor of the same power capacity．The contrast is obvious and is one that otters both an opportunity
to the user of hydraulic power and a challenge to the designer
of
hydraulic components.
The
high—power density in a
hydraulic pump or motor creates design challenges beyond those found in many
other products·High loads on rapidly
sliding surfaces，extreme fluid velocities and rapidly recurring pressure
applications on pumping elements(vanes，pistons。 gears) demand careful design attention to
assure long life，complete reliability
and efficient operation·The user,on the
other hand，reaps the benefit of a
family of apparatus that is highly responsive，finely controllable and simple to apply．When the designer understands the user’s needs and the user understands the equipment’s full capabilities，the
maximum potential of hydraulic power can
be achieved．
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