FIGURE 9. I found this valve very interesting. A single
off-on-off pulse applied to the A or B pilot valve
solenoid is enough to switch the flow to that port.
PHOTO 1. This is an SMC SY3000 series manifold. The
majority of the valve assemblies are 5/2 SY3240-5L0ZD
units. The longer valve assembly is a 5/3 SY3440-5L0ZD.
All of the valves are internally piloted.
valve as an amplifier. The pilot valve uses a tap off of the
main compressed air supply to drive a small internal air
cylinder with enough force to move a larger directional
valve mechanism. When the pilot solenoid is deenergized,
the pilot valve is disabled and the spring regains control of
determining the valve’s position.
Now that you are privy to what’s behind pneumatic
symbols and understand how piloted directional control
valves work, let’s put that schooling to practical use. We’re
going to analyze a commercial pneumatic manifold assembly
and design some hardware and firmware to drive it.
A Six-Position SMC
Believe it or not, you already know quite a bit about
the compressed air manifold you see in Photo 1. The gray
subassemblies on the valve assemblies marked with 24 VDC
are the pilot valves. The pilot valve assemblies also house
the power connectors that provide voltage for the internal
pilot valve solenoids of each valve. The pilot valve solenoids
draw around 20 mA each. The orange controls associated
with each pilot valve assembly are overrides that allow the
user to activate the pilot valves manually. Five of the six
directional control valves are identical types with a separate
pilot valve solenoid assembly for ports A and B. There are
no internal return springs in these five valves. So, activating
the pilot valve for port A will direct flow from P to A and
exhaust port B to EB. Activating the pilot valve for port B
will direct flow from P to B and exhaust port A to EA. As
long as sufficient pressure is present, the valve will assume
and keep its last selected position. Activating both the
A and B pilot valves simultaneously is a NO-NO as
unpredictable results will be your reward. The five like
valves you see in Photo 1 are called 5/2 pneumatic return
valves. I’ve drawn one up in Figure 9.
The longer valve differs from the other valves in that it
is self-centering with spring returns on both the A and B
valve ports. This valve will only assume the desired position
when the associated port solenoid is activated. Otherwise,
the center position of Figure 10 is the default.
The A, B, P, and R ports we’ve been jawing about can be
seen in Photo 2. Note that each valve has two associated I/O
ports (A and B). The bottom row of ports are the A ports.
Remember the P and R ports? Well, the P and R ports are
accessed via the larger port interfaces to the right that
don’t directly associate with a valve assembly. The R
exhaust port is on the bottom. Each individual valve has
access to the common P and R air busses that flow through
FIGURE 10. This is Figure 2 with an electromechanical
means of shifting the flow.
PHOTO 2. This is the compressed air business end of the
manifold. A word to the wise: Don’t test with long pieces of
free-hanging tubing and pressures above 20 PSI. The tubing will
whip you silly before you can grab it and get it under control.
SERVO 11.2009 45