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CHAPTER 1 HYDRAULIC PRINCIPLES

"Operated, moved, or effected by means of water," according to Webster, means that hydraulics is as ancient as water itself. By strict definition, hydraulics has existed ever since the first stream of water eroded the first section of earth. A more modern definition of hydraulics was first realized in the 17th century when it was discovered that a fluid underpressure could be used to transmit power. Hydrostatics, a contemporary definition of the principies of hydraulics, is a very simple terrn based on a discovery by Blaise Pascal (1623-1662). He discovered that if a fluid in a closed container receives a force over any area of that container, the pressure is then transmitted throughout the system undiminished and equal in all direcÍions. From thissimple system (for distribution of power and changes in its direction) an interesting technology has evolved, which is the most versatile means of power transmission known today.
Hydraulics is probably the most unique method to transmit energy to do work. It is more compact than the line of sight methods which are unavoidable in mechanical transmissions. Likewise, hydraulics is considerably moreprecise in controlling energy, and has a broader adjustability range than either electrical or mechanical means. It is the purpose of this chapter to study the laws of physics governing fluids.

our natural resources, namely oil or coa!. In physics the law of conservation states that energy can neither be created nor destroyed, although it can be converted from one forrn to another, with sorne forrnsmore useful to us than others. In a hydraulic system the energy input is called a prime mover. Examples of prime movers are electric motors and internal combustion engines. Prime movers and hydraulic pumps do not create energy, they simply put it in a forrn that can be utilized by a hydraulic system.

WORK

(r

Force

Distance

Example of Work

BASIC PHYSICS OF THE WORLD WELIVEINBefore getting into the specifics of hydraulics it would be helpful for us to understand the objectives we are trying to accomplish through its use. We are not trying to rewrite a Physics I course,but only wish to summarize those elements that a hydraulic system must contend with.

In defining energy we had to use the terrn work. Simply stated, work is done when something is moved. If we lift abook from the table we have done work, however, there are two components which must exist to do work on the book. First of all, if we are to move the book we must exert a force on it in the form of a push or a pull. This force must be equal in magnitude to the weight of the book and opposed in direction. Consequently, a force has the units of pounds (lbs.) and we must know the pounds of forcerequired to do any type oí work. Secondly, if we move the book it must move through sorne distance which can be measured in inches, feet or miles. Thus, we have defined the other unit of work; namely dis· tances represented in inches or fee1.
If enough force in pounds (lbs.) is exerted to move the book through a distance (f1.), then work is done.

ENERGY
One ol the most important topics of today isenergy and conservation thereof. However, most people discuss and debate the use of energy without under~,ti\flding what Ol:w.!;{~'yY~CJ.h.ly is. By simple definition, energy is the ability to do work. Although energy shows itself in the form of mechanical, electrical, sound, light, heat or chemical, its origin is usually from

WORK= FORCE (lbs.) x DISTANCE (ft.) = (ft. - lbs.)

LOAD AS ARESISTIVE FORCE
In hydraulics, the load is the object we want to do work upon. By definition, load is resistance to work. Any force which tends to hinder the movement of an object is resistance. Resistive forces can be frictional, inertial, or forces due to acceleration. Although frictional force s are well understood, inertial force s are somewhat more complicated. [nertia is the tendency of a...