I am pleased to offer this course of study for the theory and
practice of modern fluid power -- hydraulics and pneumatics. These lessons are generic in the
sense that there is no particular bias for any specific application.
The level of presentation is suitable for 4-year apprenticeship
Study Topics for
This short lesson that introduces fluid power as
hydraulics and pneumatics.
The study of liquids is divided into two main parts: liquids
at rest (hydrostatics) and liquids in motion (hydraulics). The
effects of liquids at rest can often be expressed by simple
formulas. The effects of liquids in motion, on the other hand,
are more difficult to express due to frictional and other
factors whose actions cannot be expressed by simple mathematics.
This lesson is devoted to hydraulic fluids. Included in it
are sections on the properties and characteristics desired of
hydraulic fluids; types of hydraulic fluids; hazards and safety
precautions for working with, handling, and disposing of
hydraulic liquids; types and control of contamination; and
The purpose of a hydraulic pump is to supply a flow of fluid
to a hydraulic system. The pump does not create system
pressure, since pressure can be created only by a resistance
to the flow. As the pump provides flow, it transmits a force to
the fluid. As the fluid flow encounters resistance, this force
is changed into a pressure.
Fluid power is a term that describes the generation, control,
and application of smooth, effective power of pumped or
compressed fluids (either liquids or gases) to provide force and
motion to mechanisms. This force and motion may be in the form
of pushing, pulling, rotating, regulating, or driving. Fluid
power includes hydraulics and pneumatics, which involve liquids
and gases, respectively.
It is all but impossible to design a practical fluid power
system without some means of controlling the volume and pressure
of the fluid and directing the flow of fluid to the operating
units. This is accomplished by the incorporation of different
types of valves. A valve is defined as any device by which the
flow of fluid may be started, stopped, or regulated by a movable
part that opens or obstructs passage. As applied in fluid power
systems, valves are used for controlling the flow, the pressure,
and the direction of the fluid flow. Valves must be accurate in
the control of fluid flow and pressure and the sequence of
This lesson deals primarily with the different types of
materials used in the construction of seals. You will also learn
about the different shapes and designs of seals and their
application as gaskets and/or packings in fluid power systems.
Finally you will find sections concerning the functions of
wipers and scrapers in fluid power systems and the selection,
storage, and handling of sealing devices.
For safe and efficient operation, fluid power systems are
designed to operate at a specific pressure and/or temperature,
or within a pressure and/or temperature range. Most fluid power
systems are provided with pressure gauges and thermometers for
measuring and indicating the pressure and/or the temperature in
the system. Additionally, various temperature and pressure
switches are used to warn of an adverse pressure or temperature
condition. Some switches will even shut the system off when an
adverse condition occurs. These devices will be discussed in
Fluid power systems must have a sufficient and continuous
supply of uncontaminated fluid to operate efficiently. This
lesson covers hydraulic reservoirs, various types of strainers
and filters, and accumulators installed in fluid power systems.
One of the outstanding features of fluid power systems is
that force, generated by the power supply, controlled and
directed by suitable valving, and transported by lines, can be
converted with ease to almost any kind of mechanical motion
desired at the very place it is needed. Either linear (straight
line) or rotary motion can be obtained by using a suitable
actuating device. This lesson describes various types of
actuating cylinders and their applications, different types of
fluid motors, and turbines used in fluid power systems.
The word pneumatics is a derivative of the Greek word
pneuma, which means air, wind, or breath. It can be defined
as that branch of engineering science that pertains to gaseous
pressure and flow. As used in this series of lessons, pneumatics
is the portion of fluid power in which compressed air, or other
gas, is used to transmit and control power to actuating
mechanisms. This series of lessons discuss the basic principles
of pneumatics--the characteristics of gases comapred with the
characteristics of liquids.