What's a 4/2 Compressed Air Valve?
Posted: Tuesday, December 12, 2006
by Bill Wade
http://www.ABOUT-air-compressors.com
Recently, I published articles on this site entitled: What's
a 2/2 or what's a 3/2 compressed air valve? Here, in the next installment in
this series, is information on the 4/2 style.
The first number in the 4/2 air valve, the four, refers to
the number of "working" air ports that are found in the valve body.
That is, the number of ports that supply air to the valve, and channel the
compressed air from the valve to the application. That takes care of three of
the four ports. The fourth port is for exhaust.
The 4/2 valves will have numbers or letters etched, cast or
painted near each of their four "working" air ports. If there are numbers near the ports, the
number 1 would be the supply port to bring the compressed air to that valve.
Port numbers 2 and 4 would be the working ports from which
air would flow to accomplish whatever task that you wanted that valve to do.
The other port, usually adjacent to the supply port, is the
common exhaust port.
A 4/2 air valve is used to power a double acting air driven
device. By double acting, I mean that the device is powered by compressed air
sent to one of two ports on the device and the device reacts by alternatively
moving one way or the other, depending on which air line to it is charged with
compressed air.
A typical example of a double acting air device is the air
cylinder. If air is injected into the port at one end, the piston that is
inside the cylinder is “pushed" to the other end of the cylinder barrel, and
the rod that is attached to the piston moves along with it.
When it’s time to move the cylinder piston and rod in the
opposite direction, air is supplied to the other port on the cylinder, the
piston moves back along with the piston rod, and air exits the other port.
A 4/2 air valve is the valve of choice for a double acting
air cylinder.
When compressed air is brought to the supply port of the 4/2
valve the compressed air will flow through and out of one of the two actuator
ports. The other actuator port will be open, through the valve, to atmosphere.
When the 4/2 valve is shifted, compressed air will flow
through it and out the second actuator port, and the port that was formerly
supplying air to the cylinder, is now opened to exhaust.
A 4/2 compressed air valve will have only one exhaust port.
Each time the valve shifts, one of the two actuator ports on the other side of
the valve are connected internally to this exhaust port.
As the valve shifts back and forth, compressed air is
supplied alternatively to one or the other of the two actuator ports. Since
each of the valve’s actuator ports is connected with an air line to one of the
ports in the air cylinder, as the compressed air flows alternatively to each
actuator port, it too flows through that particular air line to the cylinder,
which move the piston one way or the other inside the cylinder barrel.
Air goes in one end of the cylinder, and the air that was in
the other end, escapes down it’s line, through the valve to exhaust, allowing
the actuator piston to move. If the air couldn’t escape, the cylinder piston
wouldn’t move.
4/2 air valves will usually have an internal spring to
“reset" , or shift, the valve to it’s resting state when it’s external valve
actuator isn’t being operated. An external valve actuator could be a lever, a
push button, a whisker switch, a solenoid, a foot pedal or a host of other
actuators that are used to operate an air valve.
Much more information about compressed air, valves,
actuators, specialty components etc. can be found at my site. If you don’t get
an answer to your question there, please feel free to contact me via my site
contact page.
Bill Wade's experience in compressed air and
other industries spans decades; from field sales positions through to the
corporate presidential office. His sales agency represents a select group of
industrial firms. Mr. Wade writes about all facets of compressed air at http://www.about-air-compressors.com.
I'm a technical writer and editor in the Detroit area and do a lot of automotive stuff. I don't know a lot about your subject, but I like the information you give. There are a number of ways you can improve this article from the POV of structure, target audience, and objective, but I can’t talk about them in the space allowed here. There’s some punctuation and paragraph things also, but they’re minor. If you’d like specifics, email at the address provided, and we’ll talk.
