Chapter 2 Fluid Power Systems 49
Accurate control of actuator speed in a pneu-
matic system is difficult because of the compress-
ibility of air. To provide the best control in a basic
system, the flow control valve is placed in the
return line between the actuator and the direc-
tional control valve. Adjusting the flow control
valve changes the size of an orifice in the valve.
The larger the orifice, the higher the airflow and
the higher the actuator speed. Reducing the orifice
size reduces actuator speed.
During actuator operation, air is routed
through the flow control valve before it is returned
to the directional control valve, where it is then
exhausted to the atmosphere. This placement of
the flow control creates pressure on both sides
of the actuator piston, which produces a more-
uniform actuator speed. During actuator retrac-
tion, system airflow must pass through the flow
control valve before entering the actuator. Flow
through the valve orifice is reversed, but the size
of the orifice still controls the airflow rate, slow-
ing the retraction speed of the actuator. A one-way
check valve allowing free flow of air around the
restrictive orifice is often used to allow the actua-
tor to be retracted at maximum speed.
This system illustrates the structure and oper-
ation of a typical pneumatic system. The size, com-
plexity and arrangement of the components varies
from system to system, but the basic system func-
tions remain the same.
Chapter Test
Answer the following questions. Write your answers on
a separate sheet of paper.
1. Fluid power systems are made up of ______
containing parts designed to perform specific
tasks.
2. The tasks of fluid power system component
groups can be classified under one of five
functions. List these five functions.
3. The fluid control function of a fluid power
system controls system pressure and fluid
flow ______ and ______ .
4. The number and appearance of components
in a fluid power system is influenced by the
type of ______ , application, and ______ .
5. The basic actuators used in fluid power
systems are ______ and ______ .
6. Fluids are distributed throughout a fluid
power system by components referred
to as ______ .
7. Shifting a(n) ______ control valve creates a
new fluid flow path in the system, which
controls actuator movement.
8. The basic pressure control valve in a hydraulic
system is a(n) ______ valve that does not
______ until a desired system operating pres-
sure is reached.
9. The maximum pressure in a basic pneumatic
system is set by a(n) ______ that remains
______ until the desired pressure is reached.
10. Flow control valves control the volume of flow
by varying the size of a(n) ______ through
which system fluid flows.
11. Fluid power system filters may be located in
one or more of three typical locations. List
these three locations.
12. Removal of water droplets from pneumatic
system is the responsibility of the ______ .
13. During retraction of a cylinder, free flow
around a flow control valve is provided by a
one-way ______ .
14. In the pneumatic fluid power system, after
the pressurized system air has completed its
work, it is exhausted to the ______ .
15. In a pneumatic system, a preset maximum
system pressure is established by a(n) ______
electrical switch, which controls the operation
of the compressor.