I was born to drive relays and
solenoids, and I’m always looking
for unique ways to make them click
and move. This month, I have some
new “air traffic control” devices,
drivers, and circuits to show you.
By the time you read the final
sentence of this discussion, you’ll
not only have a couple of relay/
solenoid/LED driver circuits in your
pocket, you’ll be able to read and
interpret standard pneumatic
symbols, as well.
FIGURE 1. This is a simplified hydraulic system.
What I would like for you to take away from this illustration
is the component naming convention, which is the basis
that is used to describe today’s pneumatic systems.
42 SERVO 11.2009
By Fred Eady
I feel that I may be preaching to the choir in that most
of you that are experienced robot heads already know and
use the physics employed by simple pneumatic systems.
Well, you’re all here and I’m gonna preach the sermon I
prepared, anyway. So, please turn your hymnals to Figure 1.
The hydraulic components that make up Figure 1 have
a direct correlation with the pneumatic components we’re
about to discuss. If you put a dictionary to work on the
words hydraulic and pneumatic, you’ll find that pressure,
liquid, and hydraulic go together while compressed and air
are the key words in the pneumatic definition. You’ll also
discover that hydraulic systems are in general more robust
than pneumatic systems. In either instance, valves are used
to control the flow rate, direction, and pressure in hydraulic
and pneumatic systems. Hydraulic systems are normally
high pressure concoctions that use liquids such as water
and oil to perform the work. Compressed air is the energy
transfer medium of choice in a pneumatic system.
In that we have an open tank depicted in Figure 1, this
is most likely a hydraulic circuit. Yes, circuit. That’s what the
folks that work with hydraulics and pneumatics call the
collection of components you see in Figure 1. The hydraulic
fluid is drawn from the tank by the pump — which is also
acting as a compression device — and directed to the input
of the control valve. Note that the input of the control valve
is designated with the letter P, which fills in for the word
PUMP. The fluid entering at the P input is currently being
directed to the control valve’s A port. Hydraulic fluid from
the control valve’s A port applies pressure to the actuator
plunger, forcing an exhaust of hydraulic fluid into the
control valve’s B port which routes the exhausted hydraulic
fluid back to the source tank via the bottom control valve T
port. Ports A and B of the control valve are I/O ports while
the T ports are exhaust ports. The T, in this case, stands for
TANK. Note that there is an exhaust port for each I/O port.