5-3 Air Valves

5/3 or 4/3 air valves, like their "cousins", the 5/2 or 4/2 air valves are used to power double acting air actuators.

These are directional-control valves. The 5/3 design, and for that matter, the 4/3 body style air valves, allows them to supply compressed air to one port of a double acting air cylinder while simultaneously allowing air to exhaust from the other port on the same air cylinder.

By shifting the internal flow paths of the valve, the 5/3 and 4/3 air valve sends compressed air alternatively to each of the two actuator ports and exhaust from the other, thus allowing the double acting air cylinder to function.

5/3 Valve Numbers

The first number in a valve designation will identify the number of working ports that the valve has. Therefore, the 5/3 or 4/3 air valve will have either five or four working ports respectively.

The 5/3 valve body ports are; one supply, two air cylinder and two exhaust ports.

The 4/3 valve body ports are: one supply port, two air cylinder ports, and one exhaust port.

The second digit in the valve designation indicates how many positions that valve can have. The 5/3 or 4/3 will have three positions.

Three Position Valves

The "extra" position inside a 5/3 or 4/3 air valve means that the internal spool can be shifted to a center position. The typical spool movement is end to end inside the valve. With a three position valve, the spool shifts from end, across middle, and to the other end, and in this body style, the spool can be positioned to stop in the middle location.

Each of the three spool positions is selected to accomplish a desired result in the action of the air cylinder.

Since valves with three position spools are more expensive than their two position counterparts, the selection of a three position valve will be deliberate. The circuit designer will have a particular scenario in mind for the action of the air cylinder when the valve that controls it is shifted, and that circuit will require the selection of a specific three position valve to accomplish the goal.

A 5/3 or 4/3 valve will normally have two internal spring actuators that, when the valve is not being operated by an external valve actuator, shifts that valve spool to the center position automatically. It is normally when the 5/3 or 4/3 valve is "at rest" that the third of the three positions comes into play.

Three Positions - Three Results

In that third, or center position, there are three things that can happen to the air flow through that particular valve.

Blocked Center

In this position all the valve ports are blocked. Air cannot flow through the valve to either actuator port as the supply path to those ports is closed. Air also cannot flow from either actuator port to either exhaust port as those flow paths too are blocked. Supply, actuator and exhaust ports are all closed.



In this position, since air cannot travel through the valve to the air cylinder or from the cylinder back through the valve, then when the valve shifts into "Blocked Center", the air cylinder will freeze. That is the intent of the circuit designer when selecting a "Blocked Center" 5/3 or 4/3 valve. When this valve is "at rest", they want the cylinder to be frozen. Air cannot get in or out of the cylinder, and it stops dead.

Open Center

When the 5/3 or 4/3 air valve is shifted into its center position in an "Open Center" three position style valve, the supply line to the valve is blocked, and both cylinder ports are open through the valve to exhaust.

With this spool selection, the circuit designer has decided that when the valve is "at rest", it will be necessary to move the cylinder rod (and of course the end of rod tooling) by hand, or perhaps another operation will move the rod and tooling, and since there is no air on either side of the piston inside the cylinder, this can happen relatively easily, this is facilitated.

Pressure Center

In the "Pressure Center" position, air will flow from the supply to both air actuator ports, and the exhaust port(s) are blocked.

In this scenario the air circuit designer wants to have air to both sides of the air actuator when this valve is at rest.

The air actuator might be a rodded air cylinder, but it also might be a rodless type .

By exerting pressure on both sides of the piston inside a rodless ( band, magnetically couples or cable type) cylinder, the end of rod tooling can be held in one location. As an added advantage, if there are small leaks in the lines or through the seals of the rodless cylinder, a pressure center valve means that the air pressure will be maintained inside the cylinder regardless of small leaks.

Not all valve manufacturing companies offer three position valves, and those that do, not all of them offer all three of the possible valve spool configurations.

Because of the various spool configurations, drawing a 5/3 or 4/3 is a bit of a challenge. Here is how to draw the 5/3 air valve.