 |
|
4/2 air valves are normally used where the device to which the compressed air is being supplied is of the double acting type , requiring compressed air to supply and exhaust, alternatively, from each of two air ports on the actuator.
As with other compressed air valves, the first number in the 4/2 air valve indicates the number of ports the valve will have, and the second number indicates the number of positions that the internals of the valve can have when it is actuated.
Port 1 or 'P' will be the port to which the compressed air supply will be plumbed. The port will be a female NPT or female metric threaded hole into which will be installed an appropriately sized fitting . The fitting thread size must match the port in the valve, and the other side of the fitting must correspond to the air line type and size that will be connected to that fitting.
Ports 2 and 4, (possibly marked ‘B’ and ‘D’) will be the female working ports that are plumbed to the two ports in the actuator using the appropriately sized fitting and air lines.
The last port – number 4, or perhaps marked ‘E’, is the exhaust port.
The typical 4/2 valve will have one supply port, two actuator ports and one exhaust port.
If this valve is air-piloted, meaning that the external valve actuator for that valve is an air signal, 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. Usually these ports will be 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.
Since one 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 NC (normally closed) or NO (normally open).
All 4/2 valves have external (on the outside and accessible) valve actuators that will be used to operate or 'shift' the air valve when required. It could be a button, a toggle, a lever or perhaps a solenoid actuator.
A 4/2 valve may have two external actuators, such as the double air-piloted valve referred to above, and shown in this graphic.
 |
Almost all 4/2 valves will have an internal spring actuator, to return the valve to it's "resting state" when the external valve actuator is released or no longer operated.
If the 4/2 valve has two external solenoid 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.
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.
Given that a 4/2 air valve, by design, has only one exhaust port then the two lines from the cylinder will alternately exhaust to that one port and to atmosphere as the valve shifts back and forth. If you use an exhaust flow control, it will 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 cylinder port flow controls.
Please click here to learn how to draw a 4/2 air valve.
What's a 5/2 air valve?
To top
