CHAPTER 3 HYDRAULIC AND PNEUMATIC SYSTEMS

INTRODUCTION

Learning Objective: Explain the operating principles of hydraulic and pneumatic systems.

Identify the components, component functions, and maintenance procedures of hydraulic and pneumatic systems. In automotive and construction equipment, the terms hydraulic and pneumatic describe a method of transmitting power from one place to another through the use of a liquid or a gas. Certain physical laws or principles apply to all liquids and gases. You should be familiar with the following terms, as they are associated with hydraulic and pneumatic systems.

HYDRAULICS

is a branch of science that deals with the study and use of liquids as related to the mechanical aspects of physics.

PNEUMATICS

is a branch of science that deals with the study and use of air and other gases as related to the mechanical aspects of physics.

The chapter covers the basic principles associated with hydraulics and pneumatics, followed by coverage of various system components. The purpose of this information is to give you an analytical understanding of the interrelationships of principles and the components in an operating system.

HYDRAULIC SYSTEMS

Learning Objective: Identify operational characteristics, component functions, and maintenance procedures of a hydraulic system.

The extensive use of hydraulics to transmit power is due to the fact that a properly constructed hydraulic system possesses a number of favorable characteristics. These are as follows:

Eliminates the need for complicated systems using gears, cams, and levers.

Motion can be transmitted without the slack inherent in the use of solid machine parts.

The fluids used are not subject to breakage as are mechanical parts.

Hydraulic system mechanisms are not subjected to great wear.

If the system is well-adapted to the work it is required to perform and not misused, it can provide smooth, flexible, uniform action without vibration and is unaffected by variation of load. Hydraulic systems can provide widely variable motions in both rotary and straight-line transmission of power. The need for control by hand can be minimized. In addition, they are economical to operate.

BASIC PRINCIPLES OF HYDRAULICS

The basic principles of hydraulics are few and simple and are as follows:

Liquids have no shape of their own.

Liquids will NOT compress.

Liquids transmit applied pressure in all directions.

Liquids provide great increase in work force.

Pressure and Force The terms force and pressure are used extensively in the study of fluid power. It is essential that we distinguish between these terms. Force means a total push or pull. It is push or pull exerted against the total area of a particular surface and is expressed in pounds or grams. Pressure means the amount of push or pull (force) applied to each unit area of the surface and is expressed in pounds per square inch (lb/in² ) or grams per square centimeter (gm/cm² ). Pressure may be exerted in one direction, in several directions, or in all directions.

Computing Force, Pressure, and Area A formula is used in computing force, pressure, and area in hydraulic systems. In this formula, P refers to pressure, F indicates force, and A represents area.

Force equals pressure times area. Thus, the formula is written F = P x A

Pressure equals force divided by area. By rearranging the above formula, this state may be condensed into the following: P = F divided by A.