Content on this page requires a newer version of Adobe Flash Player.

Get Adobe Flash player

Subject: Valves; what do you need to know about compressed air valves?

Valves; what do you need to know about compressed air valves?

Postdate:2014-05-21 15:43:56   Hits:4612

Valves; what do you need to know about compressed air valves?

More specifically - compressed air valves - are discussed on this and the linked pages.

2/2 Air Valves

First, we will talk about a family of fairly simple air valves designated as 2/2 air valves.

The air valve designation 2/2, or perhaps it might be noted as 2/2 NC or 2/2 NO, means the following:

  • the compressed air valve has two working ports – one for air supply in, and another for air supply to the application. Air piloted 2/2 valves may also have a third air port for the pilot signal to shift the valve.
  • it can only be shifted into one of two positions – either it’s opened (something flows through it) or it is closed (nothing flows through it)
  • it is normally open (NO) or normally closed (NC) in its un-actuated, resting state

The first two in the valve designation 2/2 refers to the number of ports that valve has, and the second two refers to the number of positions that valve will have.

In the picture above, the second of the two air ports is directly opposite the port pictured. This is an NC valve, but you normally cannot tell by just looking at it whether it’s NC or NO.

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 “it’s resting state”, not actuated.

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

Here is a whole lot more about 2/2 valves , and I even show you how to draw them for your air circuit drawing

3/2 Air Valves

Next is the 3/2 air valve. As noted earlier, the first number 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, an out and an exhaust port for a total of three ports.

It will have two positions.

At rest, the valve will either be open, with compressed air flowing through, and out the power or working port to the application, or it will be closed. When it is closed, compressed air will be stopped from flowing from the source through the valve, and the working port that let the air flow to the application when this valve was open, will now allow flow to the exhaust port allowing any air that might be in the application downstream of the valve to escape back down the air line, through the valve, to atmosphere.

Here is lots more information on 3/2 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. As the applications using compressed air get more complex, so too will the air valves that control them

For lot's more information on 4/2 compressed air valves, please click 4/2 valves and then click here for tips on how to draw them.

5/2 Air Valves

The 5/2 compressed air valve functions similarly to the 4/2. It will have one compressed air supply port, two working or application ports to supply air to the application, and two exhaust ports through which air will flow to atmosphere alternately from each of the application ports, in turn. Click here for more information on the 5/2 configured air valve and then click here to learn how to draw a 5/2 air valve

5/3 Air Valves

An even more complex air valve is the 5/3. The 5/3 valve will have five ports (2 exhaust ports, 2 working or power ports and 1 supply port), just like the 5/2 valve.

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

Valve Actuators

Regardless of the type of air valve your application demands, all of them will have a valve actuator, or valve actuators. If you have experience with compressed air valves, you’ll be comfortable with the term manual actuator, This simply means that the valve is actuated by an operator (person) that pushes at button, moves a lever, toggles a switch, and so on.

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

Operator Vs 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?

For much more information on compressed air valve actuators, please click here.

Specialty Valves

There are a number of specialty valves available for specific applications such as emergency stop, soft start , check, blocker and so on. Want to know more about them? Check back often. These pages will be added.

For the novice, 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?


  • 2/2 DIRECT OPERRATING VALVE SS304.... 1/4" - 1200 list, 3/8" - 1900 list, 1/2" - 2000 list, 3/4" - 2400 list, 1" - 3000 list, 1 1/4" - 7200 list, 1 1/2" - 7200 list, 2" - 10000 list,

    Read more
  • ACTUATOR WITH 3 PC SS316 BALL VALVE.... 1/2" - 4200 LIST, 3/4" - 6400 LIST, 1" - 7400 LIST, 1 1/4" - 10000 LIST, 1 1/2 " - 11200 LIST, 2" - 15000 LIST,

    Read more