4-2 Air Valves
4/2 air valves are typically used for double acting type air cylinder / actuators.
A double acting type of air actuator, like a DA cylinder, requires compressed air to both supply and exhaust, alternatively, from each of two air ports on the actuator.
What The Numbers Mean
The first number in the 4/2 air valve indicates the number of ports the valve will have. So, a 4/2 air valve will have 4 ports.The second number 2 means that the valve spool or poppet or other air control mechanism inside that valve will have only two positions. So, a 4/2 air valve will be able to control the flow of air inside it in two positions only.
Port 1 or port P will be the port to which the compressed air supply from the air compressor will be plumbed. This port will normally be a female NPT or female metric threaded hole into which will be installed an appropriately sized air fitting . The fitting thread size must match the port in the valve, and the other side of the fitting must correspond to the type and size of air line that will be connected to that fitting.
Ports 2 and 4, (possibly marked 'B' and 'D') will be the female threaded working or power ports, that are plumbed to the two ports in the actuator using the appropriately sized fitting and air lines.The last, or 4th port, - number 4, or perhaps marked 'E', is the exhaust port.
The typical 4/2 valve will have then, one supply port, two actuator ports and one exhaust port.
If this 4/2 air valve is air-piloted, meaning that the external valve actuator is compressed air, then there will be an air port on one or both ends of the valve depending on whether it is single or double air piloted type of valve. These "control air ports" are usually smaller than the working ports unless the working ports themselves are 10-32 or 3 or 4 MM in size. Then the control air ports might be the same size. If they are marked it will likely be with two digit numbers, perhaps as 12 or 14.
Not NO / NC
Since a single 4/2 valve is supplying air to one of two ports on the actuator, while at the same time exhausting air from the other port, they are not normally considered to be an NC (normally closed) or NO (normally open) air valve.External Valve Actuators
All 4/2 valves have external (on the outside and accessible) valve actuators that will be used to operate or 'shift' the air valve internal flow paths when required. The 4/2 valve actuator could be a button, a toggle, a lever, a solenoid actuator or other types of valve actuators.A 4/2 valve may have two external actuators, such as the double air-piloted valve shown in this graphic.
Almost all 4/2 valves will have some sort of an internal spring actuator, to return the valve to its "resting state" when the external valve actuator is released or no longer being operated.
If the 4/2 valve has two external valve actuators though, it normally would not have an internal spring actuator. Without the internal spring, the valve spool or poppet will stay in the position dictated by the last valve actuator used.
The friction between seals and valve body inside the valve will, in effect, detent (stays in the last position set) a 4/2 double solenoid valve. Therefore, a circuit designer will know what position the valve will be in should either the compressed air supply or electrical signal fail. Knowing that a double solenoid valve, without an internal spring, won't move by itself allows the designer to design safety into the circuit.
Creative Plugging
Can you plug one of the two cylinder ports in a 4/2 valve to make it a 3/2? Of course; and, since compressed air is always flowing through the valve to one of the two cylinder ports, then depending on which of the two ports you plug, you can make the resulting 3/2 valve either NC or NO.Exhaust Flow Control
Given that a 4/2 air valve, by design, has only one exhaust port then the two lines from the cylinder will alternately exhaust through that one port to atmosphere as the valve shifts back and forth. You can use an exhaust flow control, to control both the extend and retract of the cylinder equally in both directions.In order to have the cylinder rod extend at one speed, and retract at another, it would be necessary to install in line or in cylinder port flow controls.
Please click here to learn how to draw a 4/2 air valve.
What's a 5/2 air valve? Click here to find out.
