40 Fluid Power
Conductors
Conductors confine the system fluid as it is
distributed throughout the system. Pipes, tubes,
and hoses are the three general types of conduc-
tors used in fluid power systems. Special mani-
folds consisting of multiple passageways are used
in systems where space and weight are important
factors. The type of conductor used depends on
the type of fluid, system pressure, required com-
ponent movement, and the environment in which
the system operates. This group of components
also includes a variety of fittings and adapters to
allow easy assembly while assuring a system free
from leaks.
Pipes are rigid conductors commonly used in
stationary fluid power installations. Piping is lower
in cost than most other conductors with compa-
rable specifications. The pipe designed for use in
fluid power systems is made from mild steel. It is
manufactured as seamless.
Tubes are similar to pipes, but are considered
to be semirigid. Tubing for use as a conductor in
fluid power installations is made from thin steel.
Tubing is lightweight, easy to install, has a good
appearance, and develops few leaks during system
operation, Figure 2-11.
Hoses are flexible conductors made from lay-
ers of materials. They contain system fluid while
withstanding system pressure and allowing easy
movement of system components. Hose construc-
tion includes an inner tube to contain the fluid, a
middle section of braided fabric or wire to with-
stand pressure, and an outer layer of material for
protection from dirt and abrasion, Figure 2-12.
Fittings and adapters are needed to assemble
conductors and other system components. Fittings
are considered the parts needed to assemble simi-
lar conductors, while adapters are required when
connecting different types of conductors or when
attaching conductors to system components.
Control Valves
Control valves are the components that make
it possible to establish the direction of movement
and the maximum force and speed of a system
actuator. These characteristics are achieved by
controlling fluid flow direction, pressure, and
flow rate in the system. Many different designs of
valves are available to achieve these characteris-
tics. These designs range from simple, basic valves
to extremely complex devices. However, each of
these designs can be placed under a basic classi-
fication of directional control, pressure control, or
flow control.
Figure 2-11. Tubing is used in both hydraulic and
pneumatic systems for transfer of pressurized
fl uids. Here, both tubing and hoses are used to
allow required machine member movement.
Outer layer
Inner
tube
Braided
reinforcement
material
Figure 2-12. Hydraulic hose is made using multiple
layers of synthetic rubber, braided fabric, and wire
to provide a fl exible high pressure conductor.