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5/2 Directional Control Valves Pneumatic Controls

How a 5/2 Directional Control Valve Works

A 5/2 directional valve has five channels and two switch positions. It is particularly suitable for controlling double-action cylinders. The graphic below shows the schematic symbol for such a valve operated on one side by means of an electromagnet with a spring operated return. This type of valve behaves in a monostable fashion since when the power is off the spring returns the valve to its rest position.

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A 5/2 directional valve operated by electromagnets on both sides, as shown by the symbol exhibits bistable behaviour. Each of the solenoids is assigned to one of the two switching states. A short switching pulse is enough to switch the valve to the opposing state.  If the power fails, the valve remains in its current position and no further movement of the machinery takes place. Thus if a piece is clamped for working, it remains so when the power is off.

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The following graphic illustrates how the cylinder and valve interact (the example shows a monostable valve). When the solenoid valve is actuated (a), compressed air (dark blue) from inlet 1 is channeled to outlet 4 where it enters the primary side of the double-acting cylinder. The cylinder thus extends, i.e. the piston moves to the right. The exhaust air (light blue) simultaneously escapes  via the outlets 2 and 3.

If the coil turns off, the return sprng restores the valve to its rest position (b). The compressed air now passes through channels 1 and 2 to the secondary side of the cylinder, causing it to retract, i.e. to move to the left. Exhaust air now escapes through 4 and 5.

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The separation of the exhaust outlets for extension and retraction (3 or 5) makes it possible to regulate the exhaust flows separately using restrictor valves, allowing the cylinder to extend and retract at different speeds. Precise positioning of the cylinder, e.g. stopping it in the middle, cannot be achieved with this method, however.

The following animation once again illustrates the extension and retraction of a cylinder by means of a 5/2 directional control valve.

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