About Air Valves

If you are looking for information on compressed air valves - this and other pages on this site provide a broad range of information about them. And before we start discussing air valves, if you are seeking information about Unloader Valves, this valve page on this site explains them in detail.

also, compressed air leaking from an unloader valve may actually be a symptom of a leaking compressor tank check valve (information page on this site). This link will be useful if that is the information you are looking for.

Now, back to compressed air valves.

2/2 Air Valves

A fairly simple air valve might be designated as a 2/2 air valve, or perhaps a 2/2 air valve. That designation might be followed by the letters N-O.

This is what those designations mean.

  • this compressed air valve has two working ports - one for air supply in, and another for air supply out to the application. An air piloted 2/2 valve might also have a third air port for the pilot signal to enter and shift the air valve.
  • it can only be shifted into one of two positions - either it is opened, compressed air flows through it, or it is closed, no air flows through it
  • it is normally open (NO) or normally closed (NC) air valve in its un-actuated, resting state

air valve

The first -2- in an air valve is designated as a 2/2, refers to the number of ports that valve has. The second -2- refers to the number of positions that valve will have.

In the picture above, the second of the two air ports is hidden. It is directly opposite the port shown.

I know that this is an NC valve, since I took the photo. You normally cannot tell by just looking at an air valve whether it is an NC or NO configured valve.

NC Air Valves

Normally Closed (NC) means that when the valve is not being actuated, compressed air will not pass through it. If the solenoid in the valve shown above is not getting an electrical signal, then the valve is in its resting state. It is not being actuated.

NO Air Valves

Normally Open (NO) means, that when the valve is not being actuated, air will pass through it.

There are some circumstances where an air circuit designer might want air to be flowing through a specific valve when the circuit is turned off, and in those circumstances, might specify a 2-2 N.O. air valve.

Here is a whole lot more about 2/2 valves.

Here is how to draw them 2/2 air valves if you are working on designing an air circuit.

3/2 Air Valves

Next valve I will talk about is the 3/2 air valve.

As noted earlier, the first number in the valve designation is the number of working ports that the valve has, and the second number indicates the number of positions that the valve has.

A 3/2 air valve will have an in port, an out port (to the application) and an exhaust port, a total of three ports.

The second number in the a 3/2 valve designation is a two, so this valve will have two positions it can be shifted into.

At rest, the 3/2 air valve will either be open, with compressed air flowing through it and out the power or working port to the application, or it will be closed. When it is closed, compressed air will be stopped a the valve supply or in port, and the working port that let the air flow to the application when this valve was open, will now allow that same air to flow through the air valve to the exhaust port and out to atmosphere.

Here is lots more information on 3/2 air valves and their uses or, visit this page that shows you how to draw a 3/2 air valve.

4/2 Air Valves

Next in the series is the 4/2 air valve. More complex air valves are required for more complex air-using appliances, and the 4-2 air valve is one of these.

The 4/2 valve will have four working ports, and it will have two positions into which it can be shifted when actuated.

The four ports will be:

  • one supply port that brings compressed air from the compressor to the air valve
  • two ports that can be plumbed from the valve to two separate applications, or to one air cylinder
  • and one exhaust port which will allow air to travel back through the valve to atmosphere alternately from one of the working (application) ports or the other

Here is lots more information on 4/2 compressed air valves and and here is how to draw them.

5/2 Air Valves

The 5/2 compressed air valve functions similarly to the 4/2.

The 5-2 air valve will have:

  • one compressed air supply port
  • two working or application ports to supply air to the application
  • two exhaust ports through which air will flow to atmosphere alternately from each of the application ports
Click here for more information on the 5/2 air valve and then learn how to draw a 5/2 air valve.

5/3 Air Valves

The 5-3 is an even more complex air valve.

The 5/3 valve will have five ports...

  • 2 exhaust ports
  • 2 working or power ports
  • 1 air supply port
..just like the 5/2 valve.

3 Positions

Rather than the two positions that most valves have however, the 5/3 valve will have three operating positions.

The center positions are;

  • pressure center
  • center exhaust
  • center blocked

Lots more information here on the 5/2 and 5/3 configured valves and their applications, and here to see how to draw 5/3 and 4/3 air valves .

Valve Actuators

Regardless of the type of air valve your application needs, every single valve will have some sort of a valve actuator, or in some cases, valve actuators.

If you have experience with compressed air valves, you will be comfortable with the term manual actuator. This simply means that the valve is actuated by an operator (person) that pushes a button, moves a lever, toggles a switch, to make the air valve shift.

For complex air circuits that demand multiple and sequential operation of devices, the valve of choice will typically be solenoid operated.

Valve Operator Versus Actuator

Please note that I define an operator as a person that actuates a valve, and an actuator (sometimes noted as external actuator) as the device on the valve that actually shifts it.

This is my personal definition, and you may find that other people have different terms for the same thing. Make sure when you are talking to folks about valves that you understand their terms, will you?

Here is much more information on compressed air valve actuators.

Specialty Valves

There are a number of specialty valves available for specific applications such as emergency stop valves, soft start valves, check valves, blocker valves and so on.

For the novice, for the newcomer to the world of pneumatic fluid power, many of the terms used and products discussed will be confusing. I will clarify as much as possible, and continue to provide a huge amount of information on this site about those terms and products.

Got a question about air valves? Here is the forum on this site.