38 Fluid Power
flow used to transmit energy from the prime mover
throughout the system. As the prime mover turns
the pump or compressor, varying pressure condi-
tions are created within the units that cause fluid
to enter, move through, and then exit into the sys-
tem. One of several different designs may be used
in a fluid power system, Figure 2-7. However, each
design involves an intake area in which a lower-
than-atmospheric pressure is created and an outlet
area in which a higher-than-atmospheric pressure
is generated.
The reservoir is the storage area for oil in a
hydraulic system. The unit may be a simple box-
like container or it may be a cavity in the base of a
machine that serves to store system fluid. A pneu-
matic system uses a receiver to store compressed
air. This unit is usually a cylindrical tank. The res-
ervoir or receiver also plays other important roles
in system operation, such as contributing to sys-
tem temperature control and fluid cleaning.
The other components that complete the basic
power unit are a mechanical coupler and fluid con-
ductors. The mechanical coupler is used to con-
nect and align the power output shaft of the prime
mover and the pump or compressor shaft to assure
smooth transmission of energy between the com-
ponents. A fluid conductor is used to move fluid
from the reservoir to the pump and from the com-
pressor to the receiver.
Actuators
Actuators are the components that convert the
energy in the system fluid to mechanical move-
ment to perform the work for which the system was
designed. Cylinders and motors are the two basic
types of actuators used in fluid power systems.
Cylinders provide linear motion, while motors
provide rotary movement. A variety of specially
designed actuators provide combinations of these
motions for specific applications.
Cylinders
A basic cylinder consists of a cylinder body,
cylinder end caps, piston, piston rod, ports, and
seals, Figure 2-8. A closed chamber is produced
in the cylinder body when the end caps are
attached to the body. The piston rod is attached
Figure 2-6. A typical basic hydraulic system power
unit. (Continental Hydraulics)
Figure 2-7. The internal parts of a vane-type pump.
The vane design is used in both hydraulic pumps
and pneumatic compressors.
(Continental Hydraulics)