CHAPTER 8
HYDRAULIC SYSTEMS AND EQUIPMENT
INTRODUCTION
the characteristics of liquids. First, a liquid has no
definite shape. It takes the shape of its container. This
Hydraulics (also called fluid power) is the science
characteristic allows liquids to flow freely. When
of transmitting power from one place to another
enough liquid is forced into a system, it fills all the
through the use of liquids. Within the support
lines and chambers open to it. Second, liquids can be
equipment community, this power serves many
only slightly compressed. Third, a liquid has the ability
functions. Hydraulic jacks and several models of
to transmit power.
workstands operate principally by hydraulic power.
INCOMPRESSIBILITY OF LIQUIDS
The lifting and manipulating components of spotting
dollies, forklifts, and weapons loaders are
Fo r a l l p r a c t i c a l p u r p o s e s , f l u i d s a r e
hydraulically operated. The brakes of self-propelled
incompressible. Under extremely high pressure, the
s u p p o r t e q u i p m e n t a r e o p e r a t e d hy d r a u l i c a l l y,
volume of a fluid can be decreased somewhat, though
pneumatically, or by a combination of the two. Test
the decrease is so slight that it is considered to be
stands, which are used to service and test aircraft
negligible except by design engineers.
hydraulic systems, are also hydraulically operated.
The maintenance of these fluid power systems and
Figure 8-1 shows how this characteristic enables a
components is one of the most important
liquid to transmit force. Notice how the liquid
responsibilities of the Aviation Support Equipment
conforms to the shape of its container. In this case the
Technician (AS). As an AS, you should be able to
container consists of two cylinders and the line that
recognize the uses and understand the operating
connects the cylinders. Since liquid is practically
principles of hydraulic components found in support
incompressible, a downward movement of piston 1
equipment.
displaces fluid in cylinder 1. The fluid flows through
the lines to cylinder 2. To make room for the additional
BASIC PRINCIPLES OF HYDRAULICS
fluid in cylinder 2, piston 2 will move upward.
PASCAL'S LAW
LEARNING OBJECTIVES: Recognize the
principles of hydraulic systems. Interpret
Pascal w a s a n o t e d F r e n c h p h y s i c i s t w h o
hydraulic system schematics and diagrams.
discovered that a closed container of fluid could be
used to transfer force from one place to another or to
This course provides a brief overview of support
multiply force by its transmission through a fluid.
equipment hydraulics. You can supplement your study
Pascal's law may be stated as follows:
by taking the correspondence course, Fluid Power,
NAVEDTRA 14105, which deals extensively with
"Pressure applied to an enclosed or confined
hydraulics. For more information on hydraulics, refer
fluid is transmitted equally in all directions
t o t h e Av i a t i o n H y d ra u l i c s M a n u a l , NAVA I R
without loss and acts with equal force on equal
01-1A-17.
surfaces."
Stated another way, pressure applied anywhere on
BASIC CHARACTERISTICS OF LIQUIDS
a confined fluid is transmitted undiminished in every
Hydraulics is the science that deals with liquid
direction. The force thus exerted by the confined fluid
pressure and liquid flow. As applied to support
acts at right angles to every portion of the surface of the
equipment, hydraulics is the action of liquids forced
container, and is equal upon equal areas.
under pressure through tubing and orifices to operate
You should note that Pascal's law applies to
various mechanisms.
fluids--both gas and liquid. It is the principle
As an AS, you need to understand hydraulics. To
underlying Pascal's law that makes possible today's
do this, you must first become familiar with some of
hydraulic systems.
8-1
