■ Figure 4. A 12 VDC five port, two
position solenoid valve.
■ Figure 5. A 12 valve pneumatic
manifold with eleven 24 VDC five
port, two position valves installed.
■ Figure 6. The actuator connector
section of the valve manifold. These
are easy to use "press collar" type
connectors making hook up and
experimentation easy. The last two
ports are blocked with plugs as the
manifold only has 11 of the 12 sockets
used.
■ Figure 7. Sideview of the manifold
shows the Exhaust A and B mufflers
in place and the connection point for
air pressure (labeled P).
82
February 2009
air compressor from Sears for about
$125. I figured the compressor might
come in handy as a workbench
accessory, and boy was I right (see
the compressor sidebar)!
Regulator: (Figure 3) Though
most compressors come with a regulator built in to the unit itself, I found
it's handy to be able to tailor the
amount of air delivered to each pneumatic device. Also, in the event that
you have multiple pneumatic devices
being powered by a single air source,
having a regulator at each device
allows you to run your main air lines
at a higher pressure and then adjust
the pressure at each device to the
minimum required to operate a given
actuator.
For example, you could run your
main air line at a pressure high
enough to allow one device on your
system to lift a heavy load, yet still
allow another device on the same
feed line to drop the pressure for a
small cylinder performing more delicate work. It’s a good rule of thumb
to use only as much pressure as is
necessary in order to get a given
device to function. Having regulators
on each device allows you to avoid
having the highest pressure requirements dictate pressure for all devices
on the same air feed.
Solenoid Valve: (Figure 4) In
order to operate a pneumatic actuator, you need to be able to control
where and when the air flows to the
device. A solenoid valve allows you
to use the presence or absence of
power to route air pressure. Typical
industrial solenoid valves use 24 volts
to operate (though 12 volt and 110
VAC solenoid valves are available)
and come in many different configurations. My preferred solenoid valve
is a five port, two way solenoid valve
such as those available from Burden’s
Surplus Center
( www.surpluscenter.com).
This type of valve has a port for
pressure (labeled P) and then has two
ports for a dual-acting cylinder
labeled A and B. When pressure is
applied to the P port, it is sent to the
A port and the B port is routed to the
exhaust port EB. When power is
applied to the solenoid, pressure is
re-routed to the B port while the A
port is then routed to the exhaust EA
port.
A five port, two position valve —
when combined with a dual-acting
cylinder — provides a positive return,
i.e., it doesn't rely on a spring or gravity to return the cylinder to its start
position. It’s also very efficient as it
only uses the amount of air held in
the air cylinder's interior for each activation. Using less air reduces the
compressor requirements and will
also reduce the number of cycles
your compressor will need to run to
keep sufficient air available as the
pneumatic actuator is operated.
Sometimes a group of valves are
placed on a manifold so that you
only need to provide one source for
air pressure to serve multiple pneumatic actuators (Figure 5). From my
contacts through The Robot Group
here in Austin, I was lucky enough to
end up with a couple of these manifolds that were removed from a large
industrial test machine. The manifolds
hold multiple five port, two way
valves with press-fit connectors for
the A and B ports (Figure 6).
In addition, all exhaust ports are
ganged so you only have two exhaust
vents to deal with. Depending on the
pressure, the exhausting air can be
fairly loud. Many systems use air baffles or mufflers in order to reduce the
noise levels (i.e., the hiss of the
exhaust). In the manifold I have, all
the valve exhausts are sent to single
exit points labeled EA (Exhaust A) and
EB (Exhaust B). These ports have
brass mufflers to lower the noise levels produced when the device is in
operation (Figure 7).
The sound pressure levels generated by a device are an important
consideration as long term exposure
to loud sounds can lead to hearing
loss. In some cases, the sound made
by the venting gas could be detrimental to the operation of the finished
device itself. If you're using pneumatics in an animatronic device to sync
jaw motions to a sound track or if
you're using a pneumatically controlled musical instrument of some
type, the hiss of air may detract from
the performance of the unit. In these
