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LAWN AND GARDEN EQUIPMENT HYDRAULICS
INTRODUCTION
The desire to have more useful work performed by the machinery used to
care for our outdoor spaces has led to the application of hydraulic
principles to accomplish these tasks. The most basic description of
hydraulics is that it is the science of transmitting force or motion
through a fluid. A fluid can be described as any liquid or gas.
A child blowing a pinwheel, or a stream of water flowing over a mill wheel
are simple examples of the hydraulic science called hydrodynamics. The
energy is transmitted by the impact of moving fluid against an object that
is able to respond. This science is however, too inefficient for our
use.
The hydraulic science we are concerned with is called hydrostatics, and
deals with the ability to transmit force or motion through a fluid that is
confined. Because liquids are practically incompressable, they are the
choice fluid. Gasses can be compressed in volume, so are therefore
unacceptable for our application.
Flexibility is the most distinct advantage in the use of liquid to
transmit power. It can change shape, divide into parts, reunite as a
whole, and fit exactly the container it is in. The liquid usually used in
hydrostatics is oil, which provides the high lubricating qualities
required for the components in the system.
HYDRAULIC PRINCIPLES
In the mid sixteenth century a French mathematician named Pascal described
the basic law of hydrostatics. It says ‘Pressure in a confined fluid is
transmitted undiminished in every direction, acts with equal force on
equal areas, and acts at right angles to container walls”. In a
cylinder containing oil, a close fitting piston can be used to apply
pressure to the oil to illustrate Pascal’s law. (Fig. 1)
As we study the basic principle, we can see that a second
piston exposed to the oil will react to the forces applied by the first
piston (Fig. 2). A transfer of energy takes place because a quantity of
liquid is subject to pressure. The flexibility of fluid can be noted also
as it fills the confines of the cylinders regardless of their shape.
Click for a closer view
The piston applying force to the oil is, in
effect, a pump. The piston that can actuate as a result of the pressure
upon its surface can be described as a motor. The quantity of oil
positively displaced by the pump must be accepted by the motor (assuming
no other path of less resistance exists). This piston to piston
energy transfer is the basis for the operation of the hydrostatic
transmission.
Click for a closer view
[Source: Simplicity publication, Hydraulic Systems Training
Information, #840172, Principles and Operation of Tractor Hydraulic Systems]
