COMPONENTS OF HYDRAULIC
foreign particles, and separate air from the fluid. The
size and the design of a hydraulic reservoir depend
upon the hydraulic system. For example, the reservoir
LEARNING OBJECTIVES: Identify the
for an automatic transmission also serves as a housing
components of hydraulic systems.
for the assembly. In most hydraulic brake systems, the
reservoir and master cylinder, although two separate
Since fluids are capable of transmitting force and
units, are physically contained in one housing. In
at the same time flow easily, the force applied to the
common hydraulic jacks and workstands, the reservoir
fluid at one point is transmitted to any point the fluid
serves as a housing for the pump and other
reaches. Hydraulic systems are assemblies of units
components. However, in most hydraulic systems, the
capable of doing this. They contain a unit for
reservoir is a separate component. Figure 8-5 is a
generating force (pumps), suitable tubing and hoses
typical reservoir. The housing is normally constructed
for containing and transmitting the fluid under
of heavy gauge metal and welded at the seams.
pressure, and units in which the energy in the fluid is
The functionality of the hydraulic system
converted to mechanical work (cylinders and fluid
determines the size of the reservoir; however, the shape
motors). In addition, all operative systems contain
may sometimes be designed to fit into some convenient
valves and restrictors to control and direct the flow of
location in the equipment. Inspection plates are
fluid and limit the maximum pressure in the system.
generally installed on the top of the reservoir to provide
Although the system illustrated in figure 8-1
easy access for cleaning. A plug or valve is located at
demonstrates the fundamental principles of fluid
the lowest point in the bottom of the reservoir to
power, several additional components are required for
provide a means for draining.
a complete, workable, fluid power system. For
A hy d r a u l i c r e s e r vo i r r e q u i r e s a m e a n s o f
example, the basic hydraulic system requires a
equalizing the air pressure in the top of the reservoir
reservoir, a pump, a control or selector valve, an
and the surrounding atmospheric pressure. This is
actuator, and tubing or flexible hose to connect these
accomplished by incorporating an air breather in the
components. Most fluid power systems contain one or
more additional components, such as pressure-relief
top of the reservoir. The breather may be a separate unit
(safety) valves, filters, accumulators, and pressure
as in figure 8-5, or it may be part of the filler cap. The
breather normally includes an air filter. The filler neck
usually contains a strainer filter.
Maintenance of fluid power systems includes
troubleshooting to locate and determine the causes of
A space is provided above the required fluid level
malfunctions. To locate the causes of malfunctions,
in a reservoir to allow for thermal expansion of the
you must understand how the system operates. And to
fluid. This space also allows fluid to foam and air to
understand system operation, you must know the
purge from the fluid.
functions and the interrelationships among the
Some method must be provided to check the fluid
components that make up the system.
level in the reservoir. Some reservoirs are provided
Fluid Power, NAVEDTRA 14105, contains
with a sight gauge as shown in figure 8-5, or a
information concerning the purpose and operation of
mechanical gauge on the side of the reservoir. In
fluid power components in general. Since the material
others, the filler neck is recessed into the top of the
in the following text covers representative components
reservoir. With the reservoir filled to the bottom of the
used in the fluid power systems of support equipment,
filler neck, the required air space is provided.
this information is intended to supplement, rather than
There are two main ports in the reservoir. One
repeat, the information given in Fluid Power.
serves as an outlet to supply fluid to the pump, and the
Therefore, you should study the applicable chapter of
other serves as an inlet for return fluid from the system.
Fluid Power in conjunction with the following text.
In some systems, the supply line is connected directly
to the pump, and one line serves as a return line with
subsystem return lines connected to it at appropriate
places. Some systems are provided with manifolds in
Each fluid power system requires a source of fluid
the supply and return lines. A manifold is a fluid
supply. The reservoir, sometimes referred to as a tank,
conductor that provides multiple connection ports. The
serves as a source of fluid supply in a hydraulic system.
In addition, the reservoir serves to dissipate heat, trap
reservoir shown in figure 8-6 has a selector valve. It is a