Chapter 2 Fluid Power Systems 35
■ Control valves.
■ Fluid conditioning.
Each component group has primary tasks to per-
form that relate to one of the five system functions.
However, each group also performs secondary tasks
relating to one or more of the other functions.
Power Unit
The power unit group of components deals pri-
marily with the energy-conversion function of the
system. The unit consists of a prime mover, pump,
and reservoir. The prime mover is the source of
energy for the system. The energy produced by
the prime mover turns the pump, which produces
fluid flow that transmits energy through the sys-
tem. The reservoir serves as a storage unit for
system fluid. It also performs fluid maintenance
functions.
Actuators
The actuators group of components performs
the work done by the system. These components
convert the energy in the system fluid to linear or
rotary motion. The basic actuators are cylinders
for linear motion and motors for rotary motion. A
variety of cylinder and motor designs are used to
produce the specific motion needed to complete
the work required of the system.
Conductors
Fluid distribution is the primary function of
the conductors group of components. Pipes, hoses,
and tubes serve as the conductors that confine and
carry system fluid between the pump and other
system components. Conductors perform such
tasks as the intake of fluid for the pump, distribu-
tion of fluid to and from control valves and actua-
tors, transmission of sensing and control pressures,
and the draining of liquids that have accumulated
in components.
Control Valves
Three different types of valves are required to
perform the fluid control function in a fluid power
system. The valves in the control valves group are:
■ Directional control valves.
■ Pressure control valves.
■ Flow control valves.
Directional control valves provide control over
fluid flow direction in sections of a system to
start, stop, and change the direction of actuator
movement. Pressure control valves are used to
limit the maximum pressure of the system or in
a section of the system. Flow control valves pro-
vide control over fluid flow rate in a section of
a system to control the rate of movement of an
actuator.
A
B
CONTROL
VALVES
FLUID
CONDITIONING
POWER
UNIT
ACTUATORS
FLUID
CONDITIONING
CONTROL
VALVES
FLUID
CONDITIONING
POWER
UNIT
ACTUATORS
CO
ND
UC
T
O
R
C
O
N
D
U
CTOR
C
ONDUCTOR
T T
CONDUCTOCTOR
R
CONDU
C
O
N
D
U
C
T
O
R
C
O
N
D
U
C
T
O
R
C
O
N
D
U
C
T
O
R
CONDUCTOR
C
O
N
D
U
C
TO
R
ATMOSPHERIC
RETURN
ATMOSPHERIC
PICKUP
Figure 2-2. The structure of fl uid power systems.
A—Hydraulic system. B—Pneumatic system.