We are now talking about detented 3/2 air valves.
Detented means it will stay where it's put! Detented valves are useful when an operator needs to actuate a valve and then perform another operation while the detented valve continues to feed compressed air to the application.
These could be air cylinders, air springs, or air diaphragms, anything that is configured to "automatically" let the air back out when the compressed air supply flowing to it is stopped.
For example, a single acting air cylinder may contain a spring that will drive the piston in one direction when the compressed air is shut off, saving energy since compressed air is being used only half the time.
Another device that is normally supplied compressed air through a 3/2 valve is the air spring.
Picture a big rubber tire with a plate covering both sides of the center hole. Into one of the plates is a female port to allow an air supply to be connected. Place this air spring under something, and you have relatively low cost actuator able to supply tremendous loads as compressed air flows into it. When the lifting process is completed, the air flows back out through the exhaust port of the 3/2 valve, and the "tire" deflates. Neat!
In shifting to off, the internal pathways of the valve open the working or power port that is connected to the actuator, and opens the exhaust flow path in the valve, allowing the compressed air in the actuator to flow freely back through the valve to the exhaust port and out to atmosphere.
Some manufacturers don't even manufacture 2/2 valves any more, since the conversion from 3/2 to 2/2 is simple, and this reduces manufacturing costs. This strategy helps reduce inventory too.
Last point on the 3/2 valve. Two of them can be used to operated a double acting air cylinder in the event that a 4/2 air valve isn't in stock when you need it. You simply plumb the cylinder / power port from each valve to one of the two cylinder ports and voila, as each 3/2 is actuated, the cylinder will extend and retract.
Let's have a look at 4/2 valves now. Please click here.