2-2 Air Valves

2-2-Air-Valves; this page is about what are they and how can they used in a compressed air circuit or for simple air operations. Let's identify what a 2-2-air-valves is, first.

If a compressed air valve is identified as a 2-2 air valve, or perhaps it is written as 2/2 air valve, these numbers indicate the following about that particular air valve:

1) t has two ports (an in and an out air line fitting port)
2) it can be shifted into two positions
3) it is in a normally open (NO) or normally closed (NC) configuration in its un-actuated, resting state

What does resting state for an air valve mean?

Air Valves At Rest

When an air valve is not being actuated by an electric or manual or internal operator, or when someone isn't pushing the button or moving the valve's lever, it is normally referred to as being "at rest".

If the "at rest" position results in the air valve being closed (compressed air is not flowing from the in to the out port) then this valve is deemed to be an NC valve - one that is normally closed.

If, at the "at rest" position compressed air flows from the in port through the valve to the out port, then this valve is deemed to be an NO or a normally open valve.

For most applications the NC form of an air valve is selected, as most folks would want a compressed air valve that is shut, that is, not flowing air through itself, when the valve is at rest.

Actuating A Valve

An air valve is actuated when that valve's external actuator is being operated by someone or something.

This could be an operator pushing a button or lever, a moving object depressing a toggle or whisker switch, or electricity operating a solenoid actuator on that air valve.

I differentiate between the actuator (the device that is used to actuate the valve) and the operator (who is a person that actuates the valve).

Others may not use these same terms of differentiation, so when you are talking to colleagues about compressed air, do make sure you understand their frame of reference and make sure you are talking about the same thing.

Uses for 2-2 air valves are varied. Here are a few that you may come in contact with.

Blow Gun

The 2/2 NC air valve that folks use often is the air gun or blow gun.

The blow gun contains (or is itself) a 2/2 NC compressed air valve.

When the external actuator (the trigger or button) is actuated by an operator, air will flow from the supply side out the nozzle to do work.

When the actuator is released, the internal actuator (the spring inside the gun) moves the internal seals back into place to stop the air flow.

The blow guns working port is the opening in the blow gun barrel. The barrel is open to atmosphere. That means that when the actuator is released, supply air stops flowing through the valve, and the compressed air that is in the gun and barrel of the blowgun continues to vent to atmosphere until all pressure is gone.

This is a typical type of application for 2-2-air-valves. The air that is flowing through the 2/2 valve vents to atmosphere, not into some sort of closed container, where the air could be trapped when the valve is shut off.

Blow Off / Cleaning Applications for 2-2 Air Valves

Other applications for the 2/2 air valve include quality control, cleaning, blow off, cooling, drying...etc.

2/2 air valves are commonly used in any application where the compressed air flows through the valve to atmosphere and not into something else be it a vessel or cylinder.

For example, in one quality control application, product may be moving down a conveyor system. When the product moves through a quality checkpoint, a sensor (perhaps a weigh scale or some sort of color scanner) determines if that product meets the quality set points. If it does not, a signal is sent to a PLC which in turn sends a signal to an actuator on a 2/2 air valve. The 2-2-air valve shifts to passing air, and compressed air flows through the valve to a nozzle and blows the defective part from the conveyor. All this takes place in a split second.

Some other 2-2 Valve Applications

In another application for a 2/2 valve, parts may be exiting a manufacturing operation of some sort. If debris is noted by the quality checking sensors - then, a signal is generated that actuates the 2/2 valve allowing it to blow air through the air knife onto the part to remove debris from that part.

Typically, the 2-2 valve that could be used in the quality control or cleaning operations as noted above is a solenoid actuated valve. In the graphic just above is a small 2/2 air valve with a solenoid operator and a DIN electrical connection.

2-2 Air Valves as Cooling Devices

When compressed air is flowed through certain types of devices, the flowing compressed air generates a cooling effect.

These venturi compressed-air-driven appliances are used to provide simplistic cooling to control cabinets where the application cannot use other forms of cooling such as fans or refrigeration.

When a 2-2 air valve is used for cooling an electrical cabinet, when the temperature inside the cabinet reaches a specific set point, a signal is generated which, in turn, opens the 2/2 air valve. Compressed air flows to and through the cabinet cooler, and lowers the temperature in the cabinet to an acceptable level. When the low temperature set point is reached the air valve shifts to a closed position until the high set point is again reached and the cycle repeats.

2-2 Air Valves Driving Air Motors

2/2 air valves are used to drive air motors.

As an example, an air motor may be powering a fixture to turn tops onto bottles. When a bottle reaches a set spot in the assembly line, a signal is generated. The PLC fires the 2/2 valve which powers the air motor, and possibly also triggers an air cylinder to lower the motor and cap, and then the air motor turns the cap onto the bottle.

A compressed air regulator could be used to modulate air motor force, allowing the air motor to stall out before it over torques the cap.

Or a simple timer may be used, which would allow the air to drive the air motor for just the time it takes to install the cap, and then shuts off the signal to the valve, the 2-2 valve would close, and the air motor would stop.

Air Driven Pumps

Compressed air driven pumps are another frequent user of 2/2 valves.

Picture a submersible air pump in a tank. A float switch signals when the tank level reaches a set point, a signal is sent to the PLC and then to the 2/2 valve. The pump starts and runs until the level in the tank reaches a low set point, at which point, the PLC is signalled again, and the valve is de-energized, allowing the pump to stop. The cycle repeats as the level in the tank reaches the start set point again.

2-2 Air Valve Issues!

Do you see a potential problem with using the 2/2 air valve in certain applications?

No 2/2 air valve can be used to supply air to any device that is a closed vessel. If a 2-2 valve is plumbed to a closed vessel or cylinder, once the 2/2 air valve is shut off, compressed air in the air line from the valve to the vessel or cylinder, and any compressed air in the vessel itself - are both now at full line pressure. That air is trapped! Compressed air cannot get back out if it is a 2-2 air valve that is used to supply air to that application.

As a result, 2/2 air valves are normally only used when the application leads to atmosphere. Then, when the valve is shut off, downstream air can bleed to atmosphere.

Valve Sizes

2/2 air valves are available in a variety of port sizes - in some cases as small as 4 MM or 10-32.

Of course, as the need for more air flow for the application is determined, larger ported 2/2 valves are selected. Economies of manufacturing come into play when considering manufacturing larger 2 - 2 air valves.

Larger air valves used for a 2/2 applications may have 3/2 or even 4/2 body styles. Since there are fewer (relatively speaking) applications for larger 2-2 air valves, it is more economical to make larger valve bodies multi-ported and to then plug unused ports to make a 2 - 2 valve, than it is to purchase tooling to manufacture many different, lower volume, body styles.

Installation / Application 2-2 Air Valves

2/2 valves can be plumbed individually in line as needed. 2/2 air valves can be stacked or manifolded together with other models offering sub-based type installations, this allowing quick removal of the valve without touching the air lines.

Drawing The 2/2 Air Valve

And no, I have not forgotten. I promised to, and here's where you learn how to draw the schematic for a 2/2 air valve.

2-2 Air Valves Forum

To allow us to share information about the 2/2 air valve with others who might be interested, I have set up an 2-2 air valve forum here. This forum opens in a new window or tab, and is where you can share your experiences or questions about the 2-2 Air Valve.